TWI857005B - Method of producing an electrical component - Google Patents

Abstract

Methods for fabricating electrically conductive vias are disclosed. In particular, a solution of electrically conductive particles are driven into a hole that extends through a glass substrate. The solution is evacuated, and the packing density of the particles in the hole can be increased. One or more subsequent steps of driving the particles into the hole can be performed. The particles can be driven into a first end of the hole during a first step of driving the particles into the hole, and can be driven into a second end of the hole during a second step of driving the particles into the hole. The particles can subsequently be substantially non-densification sintered.

Description

Method for manufacturing electrical components [Cross-reference to related applications]

This application claims the benefit of priority to U.S. Patent Application Serial No. 62/799,690 filed on January 31, 2019, U.S. Patent Application Serial No. 62/799,712 filed on January 31, 2019, U.S. Patent Application Serial No. 62/799,641 filed on January 31, 2019, and U.S. Patent Application Serial No. 62/799,679 filed on January 31, 2019, each of which is hereby incorporated by reference in its entirety as if fully set forth herein.

This application also claims the benefit of priority to U.S. Provisional Patent Application Serial No. PCT/US2019/024891 filed on March 29, 2019, which is hereby incorporated by reference in its entirety as if fully set forth herein.

The present invention relates to a method for manufacturing an electrical component.

2.5-D and 3-D packaging, previously known as multichip modules (MCMs), are a novel implementation of a well-established concept. A thin glass, silicon, or other dielectric substrate material is created with a plurality of holes or vias and metalized in a manner that creates an electrical path. The integrated circuit packaging industry refers to these interconnected substrates as interposers. The holes created in the interposer are typically very small, for example, 5μm to 100μm in diameter and 50μm to 500μm deep. The number of holes can be in the hundreds or even thousands per square centimeter. After the processing required to create these holes, the next step is to metalize the holes to provide a conductive path from one circuit plane or substrate to another.

The current state-of-the-art process method, called "copper plating," used to metallize the interposer through blind vias is very expensive and lacks manufacturing scalability. The metallization method involves a combination of physical vapor deposition (PVD) or sputter deposition to form a seed layer, followed by electroplating of copper. The sputtering or PVD methods and the very complex copper plating operations are very expensive in terms of material and operating costs, and require highly trained technicians to operate the process. The equipment required to run these processes is extremely expensive and difficult to scale up to high-volume manufacturing. Depending on the hole diameter and aspect ratio, the copper plating process can take from 1 to 8 hours per substrate. The electroplating process requires each substrate to be plated in a separate operating unit with complex analysis and distribution control and precise electric field distribution across the substrate.

Electroplated copper deposits that extend beyond the substrate surface are referred to in the art as "overburden". In order to level the electroplated copper deposits or flush with the substrate surface, a secondary process using chemical mechanical polishing (CMP) is required. The maintenance and operation of the CMP process requires highly skilled technicians to monitor and control to achieve consistent results. Copper is a relatively soft metal, and mechanical removal of excess copper is limited by the loading of the soft copper into the polishing material.

The second method of depositing copper or other conductive materials into vias in interposer substrates is to utilize metal inks. Metal inks are typically formulated with metal powder dispersed in a binder resin or other polymer to facilitate hole filling, and a capping agent to prevent oxidation of the metal powder. After the holes are filled with the metal ink and resin or capping agent, all organic materials must be volatilized and removed from the metal powder to achieve reasonable conductivity. The temperatures required to volatilize these organic compounds can reach 400°C to 800°C. The carbon ash left behind after the volatilization of the organic compounds can negatively impact optimal conductivity and leave a significant possibility of discontinuous filling of the hole. The possibility of discontinuities or electrically open areas in the filled hole or via is unacceptable.

Most of these processes operate only within very limited hole length/width ratios and have difficulty making narrow or ultra-wide holes in a consistent manner.

In one aspect, a method for producing an electrical component is provided. The method may include the step of introducing at least one suspension into a hole extending from a first surface of a glass substrate through the glass substrate to a second surface of the glass substrate, wherein the at least one suspension includes first and second bimodal particles, wherein the first and second bimodal particles include different metals, and the melting point of the second bimodal metal is lower than the melting point of the first bimodal metal. The method may further include the step of draining the liquid medium from the hole so that the second bimodal particles are disposed in a gap defined by the first bimodal particles. The method may further include the step of sintering the first and second bimodal particles in the hole, thereby defining a conductive matrix having a first end and a second end opposite to each other in a transverse direction, wherein the conductive matrix defines a conductive path from the first end to the second end.

20: Substrate

21: Intermediate layer

22: First surface

23: First opening

24: Second surface

25: Second opening

26: Holes

27: Hole array

28:Through hole

30: Blind/buried vias

34: Conductive vias

35: Conductive filling

36:Through-hole

37: Conductive redistribution layer

39:Buried vias

40: Methods

41: Air

42: Steps

44: Steps

46: Filling and removal steps

50: Stacking step/pressing step

52: Sintering step

53: Hard pressing steps/filling and stacking sequence

54: Sealing step

56: Steps

60: Suspension liquid

60a: First suspension

60b: Second suspension

62: Particles

62a: The first particle

62b: Second particle

63: First or initial accumulation of powder

64: Fluid medium

65: First filling

66: First double peak gap/first triple peak gap

67: Powder accumulation/filling

68:Dispersion

69: The gap between the third and third peaks

70: Single peak distribution

72: Bimodal distribution

73: Three-peak distribution

74: The first bimodal granules/the first trimodal granules

75: Second double peak gap/Second triple peak gap

76: Second bimodal particles/second trimodal particles

77: Highly stacked powder

78: The third bimodal granules/the third trimodal granules

79: Pile up powder

81: Powder accumulation

82: Fluid pressure filling device

84: Vacuum filling device

85: Suspended vacuum device

86:Framework

87:Framework body

90: Vacuum chamber

91:Export

92: Open end

94:Sealing pad

95: Plug

96: convex frame

97: Inner surface

98: Sealing components

99: External surface

100: Filter media

102: First interface

103: Great

104: Second interface

106: Exclude area

108: Supporting components

110: Alignment area

112:Affected areas

114: Drain pipe

116:Block

118: Shell

119a: First stacking plate

119b: Second stacking plate

120: Outer layer

120a: First outer layer

120b: Second outer layer

121: Molten material

122: Inner layer

122a: First inner layer

122b: Second inner layer

124:Inner space

126: Closed body

130: Stacking main body filling

132: Final accumulation of powder

134: Final filling

136: Air gap

140:Hard press

142: First and second pressing surfaces

144: Rod

145: Neck

146: Outer end/outer protrusion

148: First and second pressed components

149: Grain boundary

150: Centrifuge/Centrifugal force

152: wheel hub

154: Arm

156: Jidou

157: Support surface/inner surface

158: Far wall

159: Geometry Center

160: Supporting components

161: End cover

162: Powder accumulation

164: Oven

166: Great

170: Groove

200: Electrostatic filling device

202: Weakened area

204: Conductive layer

205: Second charge

206: Non-Reactive Mask

209: Shaking component

500: Exemplary components

D1: First distance

D2: Second distance

When read in conjunction with the accompanying drawings, the aforementioned invention and the following exemplary embodiments of the present application will be better understood. For the purpose of illustrating the locking structure of the present application, exemplary embodiments are shown in the drawings. However, it should be understood that the present application is not limited to the precise configurations and means shown. In the drawings: [FIG. 1A] is a perspective view of a substrate having a plurality of hole arrays, each hole array defining a plurality of holes; [FIG. 1B] is a schematic side elevation view of a portion of the substrate shown in FIG. 1A, showing through holes (through holes) hole) and blind hole; [FIG. 2A] is a schematic side elevation view similar to FIG. 1, but showing a hole including a conductive fill to define a conductive via and a conductive redistribution layer above the via; [FIG. 2B] is a SEM micrograph of one of the vias shown in FIG. 2A; [FIG. 3] is a diagram illustrating a method for conductively filling the hole shown in FIG. 1B to produce the conductive via shown in FIG. [FIG. 4A] is a perspective view of a suspension of conductive particles in a liquid medium; [FIG. 4B] is a perspective view of the suspension after stirring; [FIG. 4C] is a perspective view of a second suspension; [FIG. 5] is a schematic cross-sectional view of a vacuum filling device configured to drive the suspension into the holes of the substrate; [FIG. 6A] is a schematic side elevation view of a portion of the substrate shown in FIG. 1B, which is shown after a first filling operation using the vacuum filling device shown in FIG. 5 to produce a first conductive fill in one of the holes; [FIG. 6B] is a schematic side elevation view of a portion of the substrate shown in FIG. 6A after a pressing operation to increase the filling density of the first conductive fill; [FIG. 7A] is a schematic view of the particles of the suspension shown in FIG. 4A to FIG. 4B, which shows a substantially single [FIG. 7B] is a schematic cross-sectional view of the particles of the suspension shown in FIG. 4A to FIG. 4B, which shows a bimodal distribution including small particles and large particles according to an alternative specific example; [FIG. 7C] is a schematic cross-sectional view of the particles of the suspension shown in FIG. 4A to FIG. 4B, which shows a trimodal distribution including small particles, large particles and medium-sized particles; [FIG. 8A] is a schematic cross-sectional view of the particles set in the housing FIG. 8B is a schematic cross-sectional view of a substrate disposed in the housing shown in FIG. 8A, the housing being configured to compress the particles after a filling operation and removal of the liquid medium; FIG. 8C is a schematic cross-sectional view of a substrate disposed in the housing shown in FIG. 8B, but showing the housing under pressure during a pressing operation to compact the particles. [FIG. 9A] is a schematic side elevation view of a portion of the substrate shown in FIG. 6A, which is shown after a subsequent filling operation using the vacuum filling apparatus shown in FIG. 5; [FIG. 9B] is a schematic side elevation view of a portion of the substrate shown in FIG. 9A, which is shown after pressing followed by filling and adding a third filling operation using the vacuum filling apparatus shown in FIG. 5; [FIG. 9C] is a schematic side elevation view of a portion of the substrate shown in FIG. 9A, which is shown after the second and third filling operations; [FIG. 10] is a schematic cross-sectional view of a hanging vacuum filling apparatus similar to FIG. 5, but configured to hang the substrate; [FIG. 11] is a schematic side cross-sectional view of the substrate shown in FIG. 9C, which is shown filled by the vacuum filling apparatus; [FIG. 12A] is a schematic cross-sectional view of the substrate shown in FIG. 11; [FIG. 12B] is an enlarged schematic side elevation view of the substrate shown in FIG. 12A, which is shown after pressing the small particles; [FIG. 12C] is an enlarged schematic side elevation view of the substrate shown in FIG. 12A, which shows the filled holes according to one embodiment; [FIG. 13A to FIG. 13C] show a method for delivering a suspension to the holes of a substrate during a filling operation in one embodiment, thereby; [FIG. 13A] shows a substrate in an initial angular orientation; [FIG. 13B] shows a substrate in a first angular orientation, which is different from the initial angular orientation; [FIG. 13C] shows a substrate in a second angular orientation, which is opposite to the first angular orientation. [FIG. 13D] shows a method of delivering a suspension to a hole of a substrate during a filling operation in another embodiment; [FIG. 14] is a schematic side elevation view of a method step of sintering a substrate; [FIG. 15A] is a schematic side view of adjacent particles in a hole after pressing and before sintering; [FIG. 15B] is a schematic side view of adjacent particles in a hole after sintering; [FIG. 16 [FIG. 16A] is a schematic side view of the substrate shown in FIG. 14 (but after sintering), which shows the surface finishing operation; [FIG. 16B] is a schematic side view of the substrate shown in FIG. 16A, which shows the airtight sealing after the surface finishing operation; [FIG. 17] is a schematic view of the substrate in FIG. 16A, which shows the conductive redistribution layer applied to the substrate according to an embodiment; [FIG. 18A] is a schematic view of the substrate of FIG. 16A, which shows the grooves formed in its outer surface; [FIG. 18B] is a schematic view of the substrate of FIG. 18A, which shows the conductive redistribution layer applied to the substrate in the groove 170; [FIG. 19A] is a schematic top plan view of a centrifuge for filling holes according to an alternative embodiment, which shows a plurality of rotatable buckets; [FIG. 19B] is a schematic side view of the substrate shown in FIG. 1A [FIG. 19C] is a schematic side view of the bucket shown in FIG. 19B, showing the bucket oriented during rotation of the centrifuge; [FIG. 19D] is a schematic side view of the bucket shown in FIG. 19C, showing the conductive particles after being forced into the pores of the substrate by the centrifugal force; [FIG. 19E] is a schematic side view of the bucket shown in FIG. 19D [FIG. 20A] is a schematic diagram of a substrate showing a weakened area after ablation; [FIG. 20B] is a schematic diagram of the substrate shown in FIG. 20A, but showing a conductive layer applied to the inner surface of the substrate; [FIG. 20C] is a schematic diagram of the substrate shown in FIG. 20B, but showing the weakened area removed to reveal the hole, and including the application of 20D] is a schematic diagram of the substrate shown in FIG. 20C, but showing conductive particles being driven into the holes; [FIG. 20E] is a schematic diagram of the substrate shown in FIG. 20C, but showing conductive particles accumulated in the holes and extending along the entire length of the holes; [FIG. 20F] is a schematic diagram of the substrate shown in FIG. 20E, but showing the conductive layer removed in one embodiment; [FIG. 20 [0G] is a schematic diagram similar to FIG. 20D, but showing application of electrostatic force to a suspension to fill the holes of a substrate according to another embodiment; [FIG. 21A] is a schematic diagram of application of hard pressing to an overfilled substrate according to another embodiment; [FIG. 21B] is a schematic diagram of a substrate after the hard pressing operation; [FIG. 22] is a schematic diagram of a component assembly configured to be mounted to an interposer of the type described herein.

One or more different disclosures may be described in this application. In addition, many alternative embodiments may be described for one or more disclosures described herein; it should be understood that such alternative embodiments are presented for illustrative purposes only and do not in any way limit the disclosure contained herein or the scope of the application patents proposed herein. One or more disclosures may be broadly applicable to many embodiments, as may be apparent from the disclosures. Generally, the embodiments will be described in sufficient detail to enable one or more disclosures to be implemented by a person having ordinary knowledge in the art to which the invention belongs, and it should be understood that other embodiments may be utilized and that structural, logical, software, electrical and other changes may be made without departing from the scope of the specific disclosure. Therefore, a person of ordinary skill in the art to which the present invention pertains will recognize that one or more disclosures may be implemented with various modifications and alterations. Specific features of one or more disclosures described herein may be described with reference to one or more specific embodiments or drawings forming part of the present disclosure, and wherein one or more specific embodiments of the disclosure are shown by way of illustration. However, it should be understood that such features are not limited to use in reference to the one or more specific embodiments or drawings in which they are described. The present disclosure is neither a literal description of all specific embodiments of one or more disclosures nor an enumeration of features of one or more disclosures that must be present in all specific embodiments.

The description of a specific example with several elements that communicate with each other does not mean that such elements are required. On the contrary, various optional components may be described to illustrate various possible specific examples of one or more disclosures and to more fully illustrate one or more aspects of the disclosure. Similarly, although process steps, method steps, algorithms, etc. may be described in sequence, such processes, methods, and algorithms may generally be configured to operate in an alternating order (unless otherwise specified). In other words, any order or sequence that may be described in this patent application does not itself represent a requirement to perform the steps in that order. The steps of the process may be performed in any practical order. In addition, although some steps are described or implied to occur non-simultaneously, the steps may still be performed simultaneously (for example, because one step is described after another step). Furthermore, some steps shown in the method or in the method steps may be omitted. Furthermore, the description of the process in the figure does not mean that the process shown does not include other variations and modifications to the process, does not mean that the process shown or any of its steps is necessary for one or more of the present disclosures, and does not mean that the process shown is preferred. Furthermore, for each specific example, the steps are generally described only once, but this does not mean that the steps must occur once or that the steps may only occur once each time the process, method or algorithm is performed or executed. Some steps may be omitted in some specific examples or some events, or some steps may be performed more than once in a given specific example or event. Furthermore, in some specific examples, some steps may be removed. Furthermore, other steps may be added as needed.

For clarity, the techniques and mechanisms described or referenced herein will sometimes be described in singular form. However, it should be understood that unless otherwise stated, a particular embodiment may include multiple repetitions of the technique or multiple instantiations of the mechanism. The process description or block in the figure should be understood to represent a module, segment, or portion of code that includes one or more executable instructions for implementing a specific logical function or step in the process. As understood by a person of ordinary skill in the art to which the present invention belongs, depending on the functions involved, alternative implementations are included within the scope of the specific embodiments of the present disclosure, where, for example, the functions may not be performed in the order shown or discussed, including substantially simultaneous or reverse order.

Referring first to FIGS. 1A to 1B , substrate 20 defines opposing outer surfaces including a first surface 22 and a second surface 24 opposing the first surface. Substrate 20 further includes a plurality of holes 26. Holes 26 extend from first surface 22 along a central axis to second surface 24. For example, hole 26 may extend from first surface 22 along a central axis to second surface 24. Substrate 20 may be cut into wafers having a diameter of 150 mm, 200 mm, or 300 mm, but it is recognized that substrate 20 may define any suitable diameter or other maximum dimension as desired. Therefore, unless otherwise specified, the term "diameter" may be used interchangeably with the term "maximum cross-sectional dimension" to indicate that the reference structure need not be circular.

The holes 26 may have any suitable diameter as desired. For example, the holes 26 may have a diameter with other cross-sectional dimensions in the range of 10 μm to 25 μm. The holes 26 may have a depth along their respective center axes in the range of 100 μm to 500 μm. These dimensions are given by way of example, and it should be understood that other dimensions may be considered. The aspect ratio between the hole diameter and the hole depth is not limited to this process. In addition, a plurality of different hole diameters may be placed in the same substrate. The shape of the holes 26 may be conical, cylindrical, hourglass-shaped, or may define any suitable shape along its length. The holes 26 may be arranged in one or more hole arrays as desired. Thus, substrate 20 may define one or more arrays 27 that are spaced apart from one another at any suitable distance suitable for cutting the glass and separating arrays 27 into separate elements of substrate 20. While glass substrates may be particularly suitable for certain end applications, it should be understood that the substrate may be a glass substrate, a silicon substrate, a ceramic substrate, or any organic substrate or any other suitable alternative material as desired. In one embodiment, when substrate 20 is a glass substrate, the glass may be substantially lead-free, including lead-free. In other embodiments, the glass may include lead.

As used herein, the term "substantially lead-free", its derivatives and phrases of similar meaning may mean that the amount of lead complies with the Restriction of Hazardous Substances Directive (RoHS) specifications. In one embodiment, the term "lead-free", "lead-free", and their derivatives may mean that the amount of lead is less than 0.1% by weight, including 0% by weight. Alternatively or more, the term "lead-free", its derivatives and phrases of similar meaning may mean that the amount of lead is less than 0.1% by volume. In another embodiment, the term "lead-free", its derivatives and phrases of similar meaning may mean that the amount of lead is less than 100 parts per million (ppm).

At least one or more of the holes 26 may be configured as a through hole 28 that extends through the substrate 20 from the first surface 22 to the second surface 24. Thus, the first surface 22 defines a first opening 23 of the through hole 28, and the second surface 24 defines a second opening 25 of the through hole 28. Unless otherwise stated, the through hole 28 defines a first end at the first opening 23 and a second end at the second opening 25. Thus, both the first and second ends of the through hole 28 open to the outer periphery of the substrate 20. The through hole 28 may be straight and linear from the first opening 23 to the second opening 25. Alternatively, one or more portions of the through hole 28 may be angled, curved, or define any suitable alternative non-straight shape.

Alternatively or more, at least one or more of the holes 26 may be configured as blind holes 30, which may extend from one of the first surface 22 and the second surface 24 toward the other of the first surface 22 and the second surface 24. In addition, the blind hole may terminate at a location spaced apart from the other of the first surface 22 and the second surface 24. Thus, the blind hole 30 opens to a surface of the substrate 20 at a first end and is closed by the interior of the substrate 20 at a second end opposite to the first end. It is further explained that the first end of the blind hole 30 extends to one of the first opening 23 and the second opening 25 at the first surface 22 and the second surface 24, respectively, and the second end of the blind hole 30 is disposed between the first surface 22 and the second surface 24. However, it is recognized that the second end of the blind hole 30 may terminate at another hole 26 and thus may be in fluid communication with both the first opening 23 and the second opening 25. Furthermore, the blind hole 30 may be linear or may have one or more segments that are angled relative to each other. One or more segments may include lateral elements. The substrate 20 may include a sacrificial hole that extends from the blind hole 30 to an outer surface of the substrate 20. For example, when the blind hole 30 opens to the first surface 22 of the substrate 20 directly or through another hole, the sacrificial hole may extend from the closed end of the blind hole 30 to the second surface 24.

Referring next to FIGS. 2A-2B , according to one embodiment, one or more or up to all of the holes 26 may contain a conductive material, thereby defining a conductive via 34. In one embodiment, the conductive material may include a conductive fill 35 disposed in each of the one or more or up to all of the holes 26. The hole array 27 including the conductive material as shown in FIGS. 2A-2B may thus define a via array. In this regard, it will be understood that the substrate 20 having the conductive via 34 may be referred to as an electrical component.

In particular, the through hole 28 containing the conductive fill can be said to define a through via 36. The buried via 30 containing the conductive fill 35 can be said to define a buried via 39. Therefore, the term "via" and its derivatives as used herein may refer to one or both of the through via 36 and the buried via 39. The conductive fill 35 may extend continuously from the first end of the via 34 to the second end of the via 34. Therefore, the conductive fill 35 may define a conductive path along the via 34 along a direction extending between the first end of the via and the second end of the via. For example, a conductive path may be defined from the first end of the via 34 to the second end of the via 34. In this regard, it is understood that when the via 34 is a through via 36, the first end and the second end of the via 34 may be defined by the first opening 23 and the second opening 25. As will be understood from the following, in some embodiments, fill 35 may include only conductive material and air 41. Air 41 may include one or both of ambient air and an inert gas, alone or in combination with hydrogen. Ambient air includes oxygen, nitrogen, and other gases of the Earth's atmosphere. In one embodiment, air 41 may be part or pure argon, alone or in combination with ambient air. Alternatively or more preferably, air 41 may be part or pure nitrogen, alone or in combination with ambient air.

Additionally, in some embodiments, at least 50% by volume of the vias may include only fill 35. For example, in some embodiments, 50% by volume to 100% by volume of the vias may include only fill 35. In particular, in some embodiments, 75% by volume to 100% by volume of the vias may include only fill 35. For example, 90% by volume to 100% by volume of the vias may include only fill 35. In particular, 95% by volume to 100% by volume of the vias may include only fill 35.

The substrate 20 may include at least one or more conductive redistribution layers 37. The redistribution layer may be applied to one or both of the first surface 22 and the second surface 24. The redistribution layer 37 extends over at least one conductive via 34 and is thus electrically connected to the conductive fill 35. In one embodiment, the substrate 20 may be configured as a conductive interlayer configured to form an electrical connection at each of the first surface 22 and the second surface 24 at electrical contacts that are electrically connected to each other by the conductive vias.

The conductive fill 35 may be defined by any suitable highly conductive conductive material as desired, thereby producing a conductive via 34. As will be described in more detail below, the conductive material may be defined by sintered particles of a conductive material. In one example, the conductive material may be a metal. For example, the conductive material may be copper, gold, silver, or any suitable alternative metal, or alloys thereof, or other combinations thereof. Alternatively, the conductive material may be a non-metal, such as a conductive polymer. The conductive material may further include any suitable metal or conductive polymer coated on any suitable different metal or non-metal particles, which may be conductive or non-conductive. Therefore, in some embodiments, the conductive via 34 may be referred to as a metallized via 34. Similarly, the substrate 20 may be referred to as a metallized substrate. As will be understood from the following, the conductive via 34 can be suitable for conducting both direct current (DC) and radio frequency (RF) current. The conductive fill 35 extends in the via 34 from the first end of the via to the second end of the via, so that the conductive material defines a conductive path from the first end to the second end. Therefore, when the via 34 is a through via 36, the conductive fill 35 can define a conductive path from the first surface 22 to the second surface 24 of the substrate 20.

Referring next to FIG. 3 , a method 40 for conductively filling a hole 26 with a conductive fill 35 is provided to produce a conductive via 34 . The method begins at step 40 , whereby a substrate 20 and a suspension 60 of at least one particle suspended in a liquid medium are obtained. Then, in step 44 , the at least one suspension may be stirred as needed to disperse the particles in the liquid medium.

Next, in step 46, the hole 26 may be filled with one or both of the particles of the at least one suspension 60 and the liquid medium. The filling step may be performed by forcing the suspension into the hole 26 by one or two pressures, wherein the pressure may be positive or negative pressure, centrifugal force, or electrostatic force. In step 50, the particles are compacted. The filling step 46 and the stacking step 50 define a filling and stacking sequence 53, which may be repeated as many times as necessary until the hole 26 has a desired volume of particles 62. However, as will be described in more detail below, the stacking step 50 may be omitted in some embodiments. In one embodiment, the desired volume of particles 62 may extend from the first end of the hole 26 to the second end of the hole 26. When the hole 26 is a through hole, the particles 62 may extend to one or both of the first surface 22 and the second surface 24 of the substrate 20. In some embodiments, the hole 26 may be overfilled with particles 62 so that the particles 62 may extend beyond one or both of the first surface 22 and the first surface 24.

In step 52, the particles are sintered. In the sintering step, the particles 62 may be subjected to hard pressing so that the particles 62 are stacked together and substantially planarized along each of the first surface 22 and the second surface 24 of the substrate 20, respectively. In step 54, the vias may be sealed and, for example, surface processed. In some embodiments, step 54 may be omitted. Thus, the method may proceed from step 52 to step 56. As will be understood below, the particles 62 may form an airtight seal with themselves and with the substrate 20. The combination of the sintered particles 62 and air may define a conductive fill. Finally, in step 56, at least one or more redistribution layers are applied to one or both of the first surface 22 and the second surface 24 of the substrate 20. The steps of method 40 will now be described in more detail.

Now referring to FIG. 1A to FIG. 4A, the method begins with step 42, whereby a substrate 20 is obtained, and a suspension of at least one conductive particle 62 is disposed in a liquid medium 64. Step 42 may include manufacturing a substrate 20 having holes 26 as shown in FIG. 1, or obtaining a substrate 20 having holes 26. Further, step 42 may include suspending particles in a liquid medium, or obtaining a suspension 60.

As described above, the conductive particles 62 can be defined by any suitable conductive material as desired. For example, the conductive material can be a metal, such as copper, silver, gold. Alternatively, the conductive material can be a combination of more than one metal. For example, one metal can be coated on another metal. Alternatively or more preferably, the conductive material can be a conductive polymer. In one embodiment, the metal can be coated with a conductive polymer. Alternatively, the conductive polymer can be coated with one of the metals. It should be understood that one or more conductive metals and conductive polymers can be coated with any suitable metal as desired. In one example, the conductive particles 62 can be silver particles. Alternatively, the conductive particles 62 can be configured to include copper particles coated with silver. Alternatively, the conductive particles 62 may be configured as uncoated copper particles.

In this regard, it is recognized that silver is a highly conductive metal. In addition, silver is a highly ductile metal, which can be used during sintering. In particular, the inventors of this case have found that the process of sintering silver does not cause the glass substrate with the vias filled with silver particles to crack. Without wishing to be bound by theory, it is believed that the ductility of the silver particles allows the substrate 20 to expand and contract during sintering and thereafter without damaging the structural integrity of the substrate 20. At the same time, silver exhibits sufficient strength characteristics. In addition, copper is a substantially non-porous metal, thereby enhancing the conductivity of the resulting conductive fill 35 in the via 34.

Alternatively, as described above, the particles 62 can be copper particles. Although it is recognized that copper is susceptible to oxidation, it is recognized that during the method steps described herein, the formation of an oxide layer formed on the copper particles can be minimized or can be removed from the copper particles. For example, as described in more detail below, when the liquid medium 64 is evacuated from the pores 26 under vacuum or centrifugal force, it is recognized that at least a certain amount of copper oxide produced from oxidation of the copper particles 62 can be removed from the pores 26. In addition, sintering the copper particles 62 as described herein can remove at least a certain amount of copper oxide, and substantially remove all of the copper oxide produced by oxidation of the copper particles 62 in the pores 26 during the sintering step. Therefore, it may be desirable to sinter the copper in step 52 under reducing conditions for the cupric oxide.

Additionally, at least one antioxidant may be applied to the particles 62, particularly when the particles 62 are copper. In some embodiments, the at least one antioxidant may prevent or reduce oxidation of the copper particles 62. Alternatively or more preferably, the at least one antioxidant may reduce oxidation that forms on the copper particles. The antioxidant may be applied to the particles 62 prior to placing the particles 62 in the liquid medium 64.

For example, the antioxidant may be configured as an antioxidant coating that coats the particles 62 to define a barrier that blocks exposure of the particles 62 to oxygen in the ambient air and thereby prevents or reduces oxidation of the copper particles 62. For example, the antioxidant coating may be configured as an anti-agglomeration coating of the type described below. In other embodiments, at least one antioxidant may include a getter material that has a higher affinity for, for example, oxygen in the air than copper has for, for example, oxygen in the air. The step of sintering the particles 62 may be performed while the getter material is present in the particles 62 to reduce oxidation of the copper present during sintering of the particles 62. In some examples, the getter material may be copper or titanium or other refractory material. Without wishing to be bound by theory or a particular formulation, at least one antioxidant may include an antioxidant coating such as a neoalkoxy titanate, which may be applied to the copper particles to prevent or reduce oxidation of the copper particles 62. An example of a neoalkoxy titanate is LICA 38 (trade name), available from Kenrich Petrochemicals, Inc. (doing business in Bayonne, NJ).

As shown in FIG. 7A , when the particles 62 are stacked, it may be desirable that they are substantially spherical, with the particles 62 in the pores 26 defining respective gaps 66 therebetween (see, e.g., FIG. 7A ), which gaps may combine to define at least one liquid flow path for draining the liquid medium from the pores 26, thereby leaving the particles 62 in the pores 26. Thus, the term “substantially spherical” recognizes that the particles 62 may not be perfectly spherical, but may approximate a spherical shape to the extent that the resulting gaps 66 define a reliable flow path. Thus, the particles 62 may define any shape that defines the gaps 66 described herein. Thus, the particles 62 may be at least partially or fully curved, or, more particularly, may include straight edges. Additionally, it should be understood that when voids 26 are at least partially or completely filled with particles 62, fill 35 may include pores defined by gaps 66. It should be understood that the gaps may define internal pores of the conductive material in voids 26. In some embodiments, substantially all of the pores of conductive fill 35 may be defined by gaps. Unless otherwise specified, the words "substantially", "approximately", their derivatives and phrases of similar meaning as used herein may mean within 10% of the stated value or shape.

In addition, as described in more detail below, it may be desirable that the conductive particles 62 may be crystallite controlled so that the particles 62 may be sintered without significant densification. While it is desirable that the silver or copper be as pure as possible and therefore free of organic material, it is recognized that processes that produce substantially spherical silver or copper particles that are crystallite controlled may produce particles with trace amounts of organic material. Therefore, "substantially pure" as used with respect to the material of the particles 62 may mean greater than 90% pure material by weight. In one embodiment, the particles 62 may be greater than 95% pure material by weight. For example, the particles 62 may be greater than 98% pure material by weight. That is, the particles 62 may not contain more than 2% organic impurities by weight. For example, the particles 62 may be approximately 98.3% pure material by weight. Unless otherwise specified, in one embodiment, substantially pure particles 62 may mean 10% or less organic material by weight, such as less than 5% organic material by weight, and in one embodiment, less than 2% organic material by weight. For example, the particles 62 may have approximately 1.7% organic material by weight. In one embodiment, the solid particles 62 have a porosity of no greater than approximately 5% by volume.

Thus, while the conductive material may include a small amount of organic material as described above, it can be said that the resulting via 34 may include only the conductive material and air. It can further be said that the resulting via 34 may consist essentially of the conductive material and air. As described above, in some examples, the conductive material may be a metal such as silver or copper, although other materials are contemplated as described herein. Alternatively, the silver or copper may be mixed with a conductive polymer to provide greater conduction in the air gap. In addition, the particles 62 may be substantially non-porous, and the resulting sintered matrix 51 provides a highly conductive path from the first end of the via to the second end of the via. In one embodiment, the via may conduct DC current and radio frequency (RF) current at a desired rate.

For example, the conductive via 34 may conduct RF current along its entire length with an insertion loss of no more than about -0.15 decibels (dB) at an operating frequency of about 20 gigahertz (GHz). For example, in some embodiments, the insertion loss may be no more than about -1 dB at an operating frequency of about 20 GHz. For example, in some embodiments, the insertion loss may be no more than about -0.5 dB at an operating frequency of about 20 GHz. For example, in some embodiments, the insertion loss may be no more than about -0.3 dB at an operating frequency of about 20 GHz. For example, in some embodiments, the insertion loss may be no more than about -0.1 dB at an operating frequency of about 20 GHz. The term "no more than" is used in this context to mean "no less than" the stated decibel.

The liquid medium may be any suitable liquid medium as needed to suspend the conductive particles 62. In one example, the liquid medium 64 may be an alcohol. In particular, the alcohol may be one of isopropyl alcohol, ethanol, and methanol. In this regard, it is recognized that metals such as silver and copper may have a zeta potential or electrical surface charge. Therefore, the metal particles may thus agglomerate with each other. In addition, the particles may interact with a substrate that may be electrostatically charged (for example, when the substrate is a glass substrate), and may interact with each other. The alcohol may be slightly polar, and therefore may be configured to neutralize the zeta potential of the particles 62.

The size of the particles 62 may be adjusted as desired. It will be appreciated that it may be desirable to have the size of the particles 62 large enough so that the gaps 66 define a reliable liquid flow path to drain the liquid from the holes 26 of the substrate 20 while leaving the conductive material in the holes 26. However, it may be desirable to have the size of the particles 62 small enough so that the resulting vias 34 contain an appropriate volume of the conductive material of the particles to define a reliable electrical path from the first end of the via to the second end of the via. In one embodiment, the particles 62 may have an average particle size in a range of about 1 micron to about 10 microns, such as about 2 microns to about 10 microns. In one embodiment, the average particle size of the particles 62 may be in a range of about 2 microns to about 4 microns. In another embodiment, the average particle size of particles 62 may be in the range of about 2.5 microns to about 3.5 microns.

However, it is recognized that after the liquid medium 64 is emptied, auxiliary conductive material can be added to the particles 62 in the gap 66 as a partial conductive fill. In particular, it is contemplated that the auxiliary conductive material is added before sintering. Alternatively or more preferably, it is contemplated that the auxiliary conductive material is added to the hole after sintering. The reliable electrical path can be configured to reliably conduct one or both of DC current and RF current. In one embodiment, the particles 62 of the suspension 60 can have an average particle size in the range of about 1 micron to about 10 microns. In one embodiment, the average particle size of the particles 62 can be in the range of about 2 microns to about 4 microns. In another embodiment, the average particle size of the particles 62 can be in the range of about 2.5 microns to about 3.5 microns.

In one embodiment, the conductive fill 35 may include molten particles of different sizes. In one embodiment, the particles may be melted during the sintering operation. For example, at least one suspension 60 may include a first suspension 60a and a second suspension 60b. As shown in Figure 4B, the first suspension 60a may contain a plurality of first particles 62a suspended in a liquid medium 64. As shown in Figure 4C, the second suspension 60b may contain a plurality of second particles 62b suspended in a liquid medium 64. The first particles 62a may include any suitable conductive material described herein. Similarly, the second particles 62b may include any suitable conductive material described herein. In one embodiment, the first particles 62a and the second particles 62b may be defined by materials that may be the same. In another embodiment, the first particle 62a and the second particle 62b may be defined by materials that may be different from each other. As will be understood below, in some embodiments, the conductive fill may include a bulk fill of the first particle 62a and a final fill of the second particle 62b that extends from the bulk fill to the first end and the second end of the via.

When the material of the first particle 62a and the second material 62b are the same material, the material can be a single homogeneous material from the first end of the hole 26 to the second end of the hole 26. When the hole 26 is a through hole, it can be said that the material can be a single homogeneous material from the first surface 22 of the substrate 20 to the second surface 24 of the substrate 20. When the material is a metal, it can be said that the metal is a single uniform metal from the first surface to the second surface. Alternatively, the respective materials of the first particle 62 and the second particle 62b can be different materials. In addition, the liquid medium 64a of the first suspension 60a and the second suspension 60b can be any suitable liquid medium as described herein. The liquid medium 64 of the first suspension 60a and the liquid medium of the second suspension 60b can be the same liquid medium or different liquid mediums.

In one embodiment, the first particles 62a may have a first average particle size ranging from about 1 micron to about 10 microns, such as about 1.2 microns. In one embodiment, the average particle size of the particles 62 may range from about 2 microns to about 4 microns. In another embodiment, the average particle size of the particles 62 may range from about 2.5 microns to about 3.5 microns.

The average particle size of the second particle 62b may be smaller than the average particle size of the first particle 62a. Therefore, it can be said that the first particle 62a has a first average particle size, the second particle 62b has a second average particle size, and the first average particle size is larger than the first average particle size. In one embodiment, the first average particle size may range from about 1.5 times to about 120 times the first average particle size, unless otherwise specified. In one embodiment, the first average particle size may range from about 5 times to about 20 times the second average particle size. For example, the first average particle size may range from about 10 times to about 15 times the second average particle size.

In one embodiment, and without limitation unless otherwise specified, the second average particle size may be in a range of about 0.01 microns to about 1 micron. For example, the second average particle size may be in a range of about 0.05 microns to about 0.9 microns. In particular, the second average particle size may be in a range of about 0.15 microns to about 0.75 microns. In particular, the second average particle size may be in a range of about 0.15 microns to about 0.5 microns. In one embodiment, the second average particle size may be in a range of about 0.15 microns to about 0.3 microns. For example, the second average particle size may be about 0.22 microns.

Unless otherwise specified, the "particles 62" and their "materials" mentioned herein are intended to apply to each of the first particles 62a and the second particles 62b. Similarly, unless otherwise specified, the "liquid medium" mentioned herein is intended to apply to the liquid medium of each of the first suspension 60a and the second suspension 60b. Similarly, unless otherwise specified, the "suspension 60" mentioned herein is intended to apply to each of the first suspension 60a and the second suspension 60b.

The viscosity of one or both of the first suspension 60a and the second suspension 60b may be less than the viscosity of conventional slurries that have been used in attempts to metallize vias in glass substrates. The viscosity of one or both of the first suspension 60a and the second suspension 60b may be in a range of about 1 centipoise (cP) to about 1,000 cP. For example, the viscosity may be in a range of about 1.5 cP to about 50 cP. In another embodiment, the range may be about 1.8 cP to about 15 cP. For example, the range may be between about 1.9 cP to about 5 cP.

The first suspension 60a may have a solid concentration of the first particles 62a in the range of about 0.1% to about 20% by weight. In one embodiment, the solid concentration may be in the range of about 1% to about 15%. For example, the range may be about 1% to about 10%. In one embodiment, the solid concentration may be about 5%. In another embodiment, the solid concentration may be about 10%. Alternatively, the first suspension 60a may have any suitable alternative solid concentration as desired. The second suspension 60b may have a solid concentration of the second particles 62b in the range of about 0.1% to about 10% by weight. In one embodiment, the range may be about 1% to about 5%. For example, the range may be about 1% to about 4%. In one embodiment, the second suspension 60b may have a solid concentration of about 2%. In another embodiment, the solid concentration may be about 10%. Alternatively, the second suspension 60b may have any suitable alternative solid concentration as desired. In this regard, it should be understood that any concentration of solid particles greater than zero will allow the respective liquid medium to cause the particles to flow into the holes 26.

As described above, it is recognized that at least one anti-agglomeration agent may be applied to the particles 62 to reduce or prevent the particles 62 from agglomerating in the pores 26. Alternatively or more particularly, at least one anti-agglomeration agent may reduce agglomeration of particles that has already occurred. Reducing agglomeration may result in a higher concentration of particles 62 in the pores 26, which may be filled into the pores 26 at a faster rate. In one embodiment, at least one anti-agglomeration agent may be configured as an anti-agglomeration coating that coats the particles 62, thereby reducing or preventing the particles 62 from agglomerating with each other. The coating may be applied to the particles 62 prior to placing the particles 62 in the liquid medium 64. In one non-limiting example, the anti-agglomeration coating may be oleic acid or stearic acid. During the step of sintering the particles 62, the oleic acid and stearic acid may combust and form a gas that is vented from the holes 26. Although a trace amount of residual material may remain after sintering, it is believed that the amount of residual material is insufficient to significantly affect the electrical performance of the vias 34. Therefore, as shown in FIG. 2B, when an anti-agglomeration agent is added to one or both of the suspensions 60a and 60b, it can still be said that the vias 34a include only substantially conductive material and air. It can further be said that the vias 34 are substantially composed of conductive material and air. As described above, in one example, the anti-agglomeration coating can be oleic acid. In other examples, the anti-agglomeration coating can be capric acid. During the step of sintering the particles 62, the capric acid may combust and form a gas that is evacuated from the holes 26. Prior to placing the particles 62 in the liquid medium 64, an anti-agglomeration coating may be applied to the particles 62. The anti-agglomeration coating may be configured to prevent the particles 62 from agglomerating. In addition, as described above, the anti-agglomeration coating may further define an anti-oxidation coating that prevents or reduces exposure of the particles 62 to oxygen, thereby preventing or reducing oxidation of the particles 62.

Alternatively or more preferably, an anti-agglomeration agent may be applied to the particles to reverse the agglomeration of the particles 62 that has occurred. In one embodiment, the anti-agglomeration agent may include sound waves, which are applied to the particles 62 during the sonication step described herein. That is, the sound waves may cause at least some of the particles 62 that have aggregated in the liquid medium 64 to separate or de-agglomerate. The anti-agglomeration coating applied to the particles 62 may help the sonic waves de-agglomerate the powder.

Referring to FIG. 7A , particles 62 may define a unimodal distribution 70. Unless otherwise specified herein, and without limitation, in a unimodal distribution 70, particles 62a may be within a range of plus or minus 100% of the average particle size. For example, the range may be within plus or minus 50% of the average particle size.

In one embodiment, and not intended to be limiting unless otherwise specified in the claims, the first particles 62a may define a unimodal distribution 70, which may have an average particle size in the range of about 1 micron to about 10 microns, such as about 1.2 microns. Unless otherwise specified, the words "approximately" and "substantially" used herein with respect to size and shape may be interpreted as within 10% of the stated value or shape. In one embodiment, the average particle size of the first particles 62a may be in the range of about 2 microns to about 4 microns. In another embodiment, the average particle size of the particles 62 may be in the range of about 2.5 microns to about 3.5 microns.

Additionally, unless otherwise specified in the claims, the second particles 62b may define a unimodal distribution 70 having an average particle size that is smaller than the average particle size of the first particles 62a. Thus, the first particles 62a may be said to have a first average particle size, the second particles 62b may have a second average particle size, and the first average particle size may be greater than the first average particle size. In one embodiment, and without limitation, unless otherwise specified, the first average particle size may be in a range of about 1.5 times to about 120 times the second average particle size. In one embodiment, the first average particle size may be in a range of about 5 times to about 20 times the second average particle size. For example, the first average particle size may be in a range of about 10 times to about 15 times the second average particle size.

Referring now to FIG. 7B , first particles 62a of first suspension 60a may alternatively define a bimodal distribution 72. The bimodal distribution 72 of first particles 62a may have a packing density of conductive particles in vias 34 that is greater than that of a unimodal distribution. Packing density may be defined as the density of particles in vias 34. Thus, it is contemplated that in some embodiments, vias 34 produced by a bimodal distribution may have greater conductivity than vias 34 produced by a unimodal distribution.

The first particles 62a can include a plurality of first bimodal particles 74 and a plurality of second bimodal particles 76. The first bimodal particles 74 can have a first bimodal average particle size as described above with respect to the first particles 62a of the unimodal distribution. Thus, the first bimodal particles 74 can define interstices 66 as described above. The second bimodal particles 76 can have a second bimodal average particle size that is smaller than the first bimodal average particle size of the first bimodal particles 74. As shown, the second bimodal particles 76 can be sized to fit within respective interstices 66 defined by the first bimodal particles 74. In some embodiments, it may be desirable to maximize the size of the second bimodal particles 76 so that they can fit within respective interstices 66 without enlarging the interstices 66. However, it is understood that the second bimodal particles 76 can enlarge the gap 66 while increasing the density of the first particles relative to the unimodal distribution. Regardless, it can be said that the first bimodal particles 74 and the second bimodal particles 76 can combine to define a second bimodal gap 75 that is smaller than the gap 66, which can be referred to as the first bimodal gap. In addition, the second bimodal gap 75 can be disposed within the interior of the first bimodal gap 66.

Unless otherwise indicated, and without limitation, the first bimodal particle size and the second bimodal average particle size may define a ratio in a range of about 4:1 to about 10:1. For example, the ratio may be about 7:1. It is contemplated that the size of the gap 66 containing the bimodal particles 74 remains large enough so that the bimodal gap 66 combines to define a liquid flow path to drain the liquid medium 64 from the hole 26 of the substrate 20, while being small enough so that the resulting via 34 contains an appropriate volume of particulate conductive material to define a reliable electrical path. It should be understood that the second particles 62b of the second suspension 60b may also define a bimodal distribution if desired. In particular, one or both of the first particles 62a and the second particles 62b may include a bimodal distribution. The amount of the second bimodal particles 76 may range from about 5 volume % of the pore to about 20 volume % of the pore. For example, the amount may be about 10 volume % of the pore. It is understood that including the second bimodal may reduce the viscosity of the suspension during the filling step 46 and may result in a higher green density of the fill and a more diffuse pore structure of the resulting metallized via.

It is understood that the bimodal distribution can achieve a higher bulk density than a single main body fill before sintering. Therefore, the resulting conductive fill can have a higher density. The second bimodal particles 76 can be a different metal than the metal of the first bimodal particles 74. The second bimodal particles can be any suitable metal. In one example, the second bimodal particles 76 can have a smaller melting point than the first bimodal particles. In one embodiment, the second bimodal particles 76 can include indium. In another embodiment, the second bimodal particles 76 can include tin. The bimodal particles 76 can form an intermetallic or alloy with the first bimodal particles 74 for transient liquid phase sintering. Additionally, transient liquid phase sintering can result in templated/shape retainer pore configurations remaining from the second bimodal particles 76. The resulting pore structure and associated porosity can be tunable to obtain desired RF and DC conductivity for the resulting vias. In particular, the pore structure can be at least partially tunable based on the volume of the second bimodal particles 76 and the average particle size of the second bimodal particles 76. Alternatively, if desired, one or both of the volume and average particle size of the second bimodal particles 76 can be controlled to eliminate continuous porosity from the first end to the second end. Additionally, the transient liquid phase can result in less organic contamination, better adhesion of the fill to the via wall, and more controlled via geometry.

It is further appreciated that the alloy can be temperature stable during the future RDL step. In particular, the sintering step causes the second bimodal particles 76 to melt and liquefy in the first bimodal particles 74, which produces an alloy having a melting point greater than the temperature at which the RDL layer is applied.

In one embodiment, when the stacking step is performed, the bimodal particles 60a can be overfilled into the holes. In addition, the compressibility of the bimodal particles 60a can be lower than that of the unimodal filling. Therefore, it is conceivable that the coating can be applied to the ends of the vias and the outer surface of the substrate. In addition, the redistribution layer can be applied without coating.

It is recognized that the bimodal particles 60a can be filled to the extent outside the outer surface of the substrate. In particular, the sacrificial layer can be applied to the outer surface having holes aligned with the holes of the plate. Therefore, the sacrificial layer extends along a length that effectively increases the length of the hole. Therefore, the holes of the substrate can be filled, and the holes of the sacrificial layer can be at least partially or completely filled. The sacrificial layer can be removed before or after the filling is compressed. It is envisioned that after the sintering step, the compressed fill can be substantially coplanar with the outer surface of the substrate. Therefore, the redistributed layer can be applied to the sintered fill 35 alone or in combination with the coating layer without applying the final fill. Or as described in more detail below, if necessary, the final fill can be applied.

Alternatively, a conductive layer may be applied to one or both outer surfaces of the substrate prior to filling the hole. The conductive layer may further extend along the inner wall of the hole. For example, the conductive layer may extend along one or both outer regions of the inner wall. In one example, the conductive layer may be titanium. It is contemplated that the fill 35 may bond to the conductive layer during the sintering step to form a hermetic seal.

Referring now to FIG. 7C , the first particles 62a of the first suspension 60a may alternatively define a trimodal distribution 73. The trimodal distribution of the first particles 62a may have a packing density of conductive particles in the vias 34 that is greater than that of the bimodal distribution, and therefore also greater than that of the unimodal distribution. Therefore, it is contemplated that in some embodiments, the vias 34 produced by the trimodal distribution may have a greater conductivity than the vias 34 produced by each of the bimodal distribution and the unimodal distribution.

The first particle 62a may include a plurality of first bimodal particles 74 defining a first trimodal particle as described above, a plurality of second bimodal particles 76 defining a second trimodal particle as described above, and a plurality of third trimodal particles 78. The first trimodal particle 74 may have a first trimodal average particle size as described above relative to the first particle 62a of the unimodal distribution. Thus, the first trimodal particle 74 may define a gap 66 as described above. The gap 66 of the trimodal distribution 73 may be referred to as a first trimodal gap. The second trimodal particle 76 may have a second trimodal average particle size that is smaller than the first bimodal average particle size of the first trimodal particle 74 relative to the first bimodal particle and the second bimodal particle as described above. Therefore, the size of the second trimodal particles 76 can be set to be accommodated in the first trimodal gap 66, thereby defining the second trimodal gap 75 as described above.

In addition, the third trimodal particles 78 can be deposited in the pores 26 so as to be disposed in the second trimodal interstices 75. As shown, the third trimodal particles 78 can be configured to be accommodated in each of the second trimodal interstices 75 defined by the first trimodal particles 74 and the second trimodal particles 76. In some embodiments, it may be desirable to maximize the size of the third trimodal particles 78 so that they can be accommodated in each of the second trimodal interstices 75 without enlarging the interstices 75. However, it is understood that the third bimodal particles 78 can enlarge the second trimodal interstices 75 while increasing the density of the first particles 62a relative to the bimodal distribution. Regardless, it can be said that the first, second and third bimodal particles 76 and 78 can be combined to define a third trimodal gap 69 that is smaller than the second trimodal gap 75.

The third trimodal particle 78 may have a third trimodal average particle size that is smaller than the second trimodal average particle size. Unless otherwise specified, the second trimodal average particle size and the third trimodal average particle size may be defined in a ratio ranging from about 4:1 to about 10:1. For example, the ratio may be about 7:1. It should be understood that if desired, the second particle 62b of the second suspension 60b may also define a trimodal distribution. It should be understood that if desired, the second particle 62b of the second suspension 60b may also define a trimodal distribution. Therefore, one or both of the first particle 62a and the second particle 62b may define a trimodal distribution. Or if desired, the trimodal distribution may exist in a single suspension.

As described below, when the second particle 62b defines a bimodal or trimodal distribution, and the second particle 62b defines a final fill, the bimodal or trimodal distribution can produce an airtight seal at one or both of the first end and the second end of the conductive fill 35.

In one embodiment, the third trimodal particles 78 can be made of any suitable conductive material. For example, the third trimodal particles 78 can be the same material as the first trimodal particles 74. Thus, in one embodiment, the third trimodal particles 78 can be made of silver. During the sintering step, the second trimodal particles 76 can transport the third trimodal particles 78 during the transient liquid phase.

Referring again to FIGS. 1A through 4C , it is generally contemplated that fill 35 may have a porosity between about 10 volume % and about 60 volume %. For example, the porosity may be between about 20 volume % and about 50 volume %. The porosity may depend on several factors, including particle size, the nature of the distribution (e.g., unimodal, bimodal, or trimodal), and any conductive additives that may be added to the conductive material prior to or after sintering. In other embodiments, it is recognized that particles 62 may be provided as a tetramodal distribution. In still other embodiments, it is recognized that particles 62 may be provided as a pentamodal distribution.

It is recognized that the hole 26 may contain a main fill and a final fill. The main fill may occupy a first portion of the hole 26 or via, and the final fill may occupy a second portion of the hole 26 or via that is different from the first portion. For example, the main fill may occupy the interior of the hole 26 or via, and the final fill may occupy a relatively outer area of the hole 26 or via. Therefore, the final fill may extend from the main fill to each opposite end of the hole 26 or via. For example, when the hole or via is a through hole or a through-hole, the final fill may extend from the main fill to each of the first surface 22 and the second surface 24 of the substrate 20. Therefore, it can be said that the conductive fill 35 may include one or both of the main fill or the final fill. In one embodiment, the main fill may be defined by the first particle 62a. In one embodiment, the final fill may be defined by the second particle 62b. Alternatively, both the bulk fill and the final fill may be defined by the first particle 62a as desired. In this regard, it is recognized that the method 40 may include multiple steps of bulk filling the holes. One or more bulk filling steps may be performed using a first particle 62a of one of a unimodal distribution, a bimodal distribution, and a trimodal distribution, and one or more other bulk filling steps may be performed using another different first particle of the unimodal distribution, the bimodal distribution, and the trimodal distribution. Alternatively, all bulk filling steps may be performed using the same first particle of the unimodal distribution, the bimodal distribution, and the trimodal distribution.

The bulk fill may occupy a length of the hole 26 or via that is in a range of about 50% to about 100% of the total length of the hole 26 or via. For example, the bulk fill may occupy a length of the hole 26 or via that is in a range of about 80% to about 100% of the total length of the hole 26 or via. In particular, the bulk fill may occupy a length of the hole that is in a range of about 90% to about 99% of the total length of the hole 26 or via. In one embodiment, the bulk fill may occupy a length of the hole or via that is in a range of about 94% to about 99% of the total length of the hole 26 or via 34. In one particular embodiment, the main fill may occupy a length of the hole or via that ranges from about 96% to about 98% of the total length of the hole 26 or via. The final fill may extend from the main fill to the first end of the hole 26 or via. Furthermore, the final fill may extend from the main fill to the second end of the hole 26 or via. Furthermore, in one embodiment, the portion of the hole referred to herein as occupied by the final fill is not occupied by the main fill. In one particular embodiment, the final fill may occupy a length ranging from about 1% to about 4% of the total length of the via 34 at each of the first and second ends of the via 34.

The inventors of the present invention recognize that conductive particles 62 may tend to settle in liquid medium 64 (especially if stored for a long time), as shown in FIG. 4A. Therefore, in step 44, and as shown in FIG. 4B to FIG. 4C, the suspension 60 may be stirred to disperse the particles 62 in the liquid medium 64. For example, in one embodiment, the suspension may be sonicated to disperse the particles 62 in the liquid medium 64. Therefore, it is understood that the liquid medium 64 is configured to maintain the particles 62 as a dispersion 68. Therefore, it should be understood that the liquid medium can be any liquid suitable for maintaining the particles 62 to facilitate filling the holes 26 of the substrate with the particles 62 according to at least one method described herein.

Next, in step 46, the holes 26 may be filled with at least one suspension 60. Next, it will be understood that in step 46, the holes 26 may be filled with at least one suspension 60. It will be understood from the following that, as shown in Figures 5 and 10, the suspension 60 and therefore the particles 62 may be urged to flow into the holes 26 under the action of a force defined by a pressure differential across the substrate 20. The pressure differential may be defined by an air pressure differential. For example, the air pressure differential may be defined by a vacuum suction. Thus, a vacuum device may be used to urge the particles 62 to flow into the holes 26 under the action of a vacuum pressure. Alternatively, the air pressure differential may be defined by a positive air pressure. Alternatively or more preferably, the force urging the particles 62 to flow into the holes 26 may be a centrifugal force, such as using a centrifuge as described below with respect to Figures 19A to 19E. Alternatively or more, the force that causes the particles 62 to flow into the holes 26 may be electrostatic force, as described below with reference to FIGS. 21A to 21F. In the following, for example, a vacuum device as shown in FIGS. 5 and 10 may be used to cause the particles 62 to flow into the holes 26 under the action of air pressure. Alternatively or more, for example, a centrifuge as shown in FIG. 19A may be used to cause the particles 62 to flow into the holes 26 under the action of centrifugal force. Alternatively or more, the particles 62 may be caused to flow into the holes 26 under the action of electrostatic force as shown in FIGS. 20A to 20F.

Now, referring to FIG. 5 to FIG. 6B , the step 46 of filling the hole 26 under air pressure in one embodiment will be described. In particular, the fluid pressure filling device 82 is configured to apply a pressure difference on the entire suspension 60 to force the suspension 60 to flow into the hole 26. For example, the fluid pressure filling device 82 may be configured as an air pressure filling device, which is configured to apply an air pressure difference on the entire suspension 60 to force the suspension 60 to flow into the hole 26. In one embodiment, the air pressure filling device 82 may be configured as a vacuum filling device 84, which is configured to apply vacuum pressure to the suspension 60 to generate an air pressure difference. In another embodiment, the vacuum filling device 82 can be adjusted to apply forced air to the suspension 60 under positive pressure to generate an air pressure differential. It is recognized that the suspension will be caused to flow in the direction from higher pressure to lower pressure.

As shown in FIG. 5 , the vacuum filling device 84 may include a frame 86 that defines an interior cavity 88 that at least partially defines a vacuum chamber 90. The frame 86 includes a frame body 87 that defines an open end 92 to the interior cavity 88. At least a portion of the substrate 20, and in particular the holes 26, is in fluid communication with the vacuum chamber 90. In addition, the substrate 20 is sealed to the frame 86 so that the vacuum pressure generated is applied to the substrate 20, and therefore to the holes 26, without any significant air being drawn into the interior cavity from the interface between the substrate 20 and the frame 86. In one embodiment, the vacuum filling device 84 may include a sealing pad 94 that seals the substrate 20 to the frame 86 relative to the gas flow at the interface between the substrate 20 and the frame 86. For example, the sealing pad 94 may extend across the interface between the substrate 20 and the frame 86. The sealing pad 94 can be made of any suitable material as needed. For example, the sealing pad 94 can be made of rubber. In one example, the sealing pad 94 can be vulcanized silicone. In particular, the sealing pad 94 can be room-temperature vulcanizing silicone (RTV silicone).

The frame 86 may include a frame body 87 and a shelf 96 attached to the frame body 87 to directly or indirectly support at least a portion of the substrate 20. The shelf 96 may close a portion of the open end 92. For example, the shelf 96 may close the outer perimeter of the open end 92. The vacuum filling device 84 may include a sealing member 98 that seals the shelf 96 to the frame body 87. Thus, the shelf 96 may be separated from the frame body 87. When the vacuum chamber 90 is at a negative pressure, the sealing member 98 may define a non-porous interface with respect to the air flow between the shelf 96 and the frame body 87. It should be understood that the shelf 96 may be integrally formed with the frame body 87. The frame body 87 may define an outlet 91 that is configured to be connected to a vacuum source to induce a negative pressure in the vacuum chamber 90. When the vacuum chamber 90 is at a negative pressure, both the frame body 87 and the ledge 96 may be substantially imperforate with respect to airflow therethrough.

The vacuum filling device 84 can further include a filter medium 100 between at least a portion of the substrate and the vacuum chamber 90. For example, the filter medium 100 can be aligned with the opening for receiving the suspension 60. The filter medium 100 can be porous with respect to air and the liquid medium 64, but non-porous with respect to the particles 62. Therefore, both air and the liquid medium 64 can pass through the filter medium, while the particles 62 are retained in the pores 26. The sealing pad 94 can further seal the substrate 20 to the filter medium 100 with respect to the air flow at the interface between the substrate 20 and the filter medium 100. Thus, the first interface 102 between the substrate 20 and the filter medium 100 is sealed with respect to the airflow therebetween, and the second interface 104 between the filter medium 100 and the frame 86 is sealed with respect to the airflow therebetween. It should be understood that the same sealing pad 94 can seal each of the first interface 102 and the second interface 104. Alternatively, a first sealing pad can seal the first interface 102, and a second sealing pad separated from the first sealing pad can seal the second interface 104. Thus, it can be said that at least one sealing pad seals the first interface 102 and the second interface 104.

The filter medium 100 may be made of any suitable material as desired that is suitable for allowing the liquid medium 64 and air to pass therethrough while preventing the particles 62 from passing therethrough. A non-limiting list of potential materials for the filter medium includes glass microfiber, cellulose, mixed cellulose esters (MCE), cellulose acetate, cellulose nitrate, polytetrafluoroethylene (PTFE), polyamide, polyimide-imide, polyether sulfone, polyvinylidene fluoride, polyacrylonitrile, polyvinylidene fluoride, phenol-formaldehyde, VVPP, VVLP, HVLP, and many types of filters commercially sold by companies such as Millipore, Membrane Solutions, Whatman, and Ahlstrom under trade names such as Durapore, ExpressPlus, Isopure, etc.

Because the first interface 102 and the second interface 104 are sealed, substantially all or all of the vacuum pressure in the vacuum chamber 90 can be applied to the hole 26 of the substrate 20. It should be understood that the sealing pad 94 prevents gas flow through the substrate 20 at the exclusion area 106 of the substrate 20, wherein the exclusion area 106 is covered by the sealing pad 94. Therefore, it may be desirable to produce a substrate 20 without openings at the exclusion area 106. In one embodiment, the exclusion area 106 can be disposed at the outer periphery of the substrate 20, however it should be understood that any position of the substrate 20 covered by at least one sealing pad can define the exclusion area 106.

The vacuum filling device 84 may further include a support member 108 configured to directly or indirectly support at least a portion of the substrate 20. In particular, the support member 108 may be aligned with the hole 26 of the substrate 20, and the hole 26 will receive the suspension 60 under the induced pressure difference. The support member 108 may be supported by the frame 86 so as to span at least a portion of the open end 92 to the entire open end 92. In particular, the support member 108 may be supported by the protrusion 96. In addition, because the filter medium 100 is aligned with the hole 26, the filter medium 100 is similarly aligned with the support member 108. In one embodiment, the filter medium 100 may be disposed between the substrate 20 and the support member 108. In particular, the filter medium 100 can be placed on the support member 108, and the substrate 20 can be placed on the filter medium 100.

Each of the substrate 20, the filter medium 100, and the support member 108 defines an inner surface 97 facing the vacuum chamber 90, and defines an outer surface 99 opposite to the inner surface 97. The outer surface 99 of the substrate 20 may be defined by one of the first surface 22 and the second surface 24. The inner surface 97 of the substrate 20 may be defined by the other of the first surface 22 and the second surface 24. At least a portion of the inner surface of the support member 108 may be open to the vacuum chamber 90. At least a portion of the inner surface of the filter medium 100 may rest on at least a portion of the outer surface of the support member 108. At least a portion of the inner surface 97 of the substrate 20 may rest on at least a portion of the outer surface of the support member 100. The sealing pad 94 may rest on the outer surface 99 of the substrate at the exclusion area 106. Thus, each hole 26 receiving the suspension 60 can be aligned with each of the filter medium 100 and the support member 108 relative to the length of the hole 26, which is consistent with the direction of the hole 26 defining the air pressure difference.

The support member 108 may be made of any suitable material that is porous relative to both air and the filter medium 100. In particular, the porosity of the support member 108 is greater than the porosity of the filter medium 100. Therefore, both air and the filter medium can pass through the support member 108. In a non-limiting embodiment, the support member 108 may be defined by fritted glass (also known as glass frit). Therefore, the support member 108 may be a rigid support member.

During operation, a certain amount of suspension 60 is applied to the outer surface 99 of the substrate 20 so that the suspension covers at least a portion of the outer surface 99. For example, the suspension 60 can be coated on the outer surface 99. During the main filling operation, the suspension 60 can be defined by the first suspension 60a. As will be understood from the following, during the final filling operation, the suspension can be defined by the second suspension 60b, however it should be understood that particles of other sizes may be sufficient for the final filling. For example, the first suspension 60a can be used for the final filling.

In particular, the suspension 60 is applied to the filling area of the substrate 20. The filling area of the substrate 20 can be defined by the hole 26 aligned with the filter medium and the support member 108. Therefore, the suspension 60 can cover the hole 26 to be filled. For example, the suspension 60 can extend above the hole 26 and through the hole 26. Alternatively or more preferably, as described in more detail below, the suspension 60 can be induced to flow through the hole 26 along the outer surface 99 of the substrate 20. It is understood that unless otherwise specified, the term "filling" used herein with respect to the suspension 60 includes at least partial filling or complete filling.

The filling step 46 may include the step of applying the suspension 60 to the outer surface 99 of the substrate 20. The vacuum source may be activated to apply a negative pressure to the vacuum chamber 90. It should be understood that the vacuum source may be activated before applying the suspension 60 to the substrate 20, during applying the suspension 60 to the substrate 20, or after applying the suspension 60 to the substrate 20.

Referring now also to FIG. 6A , the negative pressure causes the suspension 60 to flow from the outer surface 99 of the substrate 20 into the respective holes 26 opening to the outer surface 99 of the substrate. As described above, the filter medium 100 extends through the inner surface 97 of the substrate 20 through the holes 26. Because the filter medium 100 and the support member 108 are porous to air, the negative pressure in the vacuum chamber 90 generates a pressure differential between the holes 26, which can be configured to draw a certain amount of the suspension 60 into the negative pressure of the holes 26. Therefore, under the action of the pressure differential, both the liquid medium and the particles 62 suspended in the liquid medium 64 flow into the holes 26. Because the filter medium 100 is porous relative to the liquid medium 64 but non-porous relative to the particles 62, the pressure difference causes the liquid medium 64 to flow through the filter medium 100. Because the particles 62 cannot flow through the filter medium 100, the particles 62 remain in the pores 26. Therefore, when the liquid medium 64 flows through the pores 26, the particles 62 will accumulate in the pores 26. In addition, because the filter medium 100 can be flat against the inner surface 97 of the substrate 20, the particles 62 can accumulate on the filter medium 100 and thus can be substantially flush with the inner surface 97 of the substrate 20. In addition, when all filling steps are completed, the particles 62 can extend outward relative to the outer surface 99 of the substrate 20. Alternatively, the particles may be substantially flush with the outer surface 99. Alternatively, the particles 62 extending from the outer surface 99 may be removed from the outer surface, for example, by driving a drive rod across the outer surface 99 of the substrate 20 to remove the particles 62 extending from the outer surface 99.

As described above, the holes 26 can be through holes, so that one or both of the negative pressure and the flow of the liquid medium 64 (from the outer surface 99 of the substrate 20 to the inner surface 97 of the substrate 20) cause the particles 62 to pile up against each other, thereby defining one or more gaps of the type described above with respect to Figures 7A to 7C (depending on the particle size distribution properties). In particular, a vacuum force applied to the inner surface 97 of the substrate 20 can draw the suspension from the outer surface into the holes 26. Alternatively, a positive air pressure applied to the outer surface 99 can cause the suspension to flow into the holes 26 toward the inner surface 97. The air and liquid medium of the suspension can be evacuated from the through holes 26. Alternatively, if the holes 26 are blind holes of the type described above, the sacrificial layer can extend from the blind hole to the outer surface of the substrate 20 to form a through hole. Thus, the conductive particles 62 may be forced into the blind and sacrificial holes under one or more or up to all of the pressure differentials, centrifugal forces, and electrostatic forces. To prevent the sacrificial layer from acting as a conductive via, the sacrificial hole may be capped with an electrically insulating cap adjacent to the second surface 24. Thus, the redistributed layer will not be electrically connected to the metal in the sacrificial hole. As described herein, the electrically insulating cap may seal the sacrificial layer to provide airtightness to the sacrificial hole. Alternatively or more, at least some or up to all of the metal may be removed from the sacrificial hole. For example, the laser may ablate the metal in the sacrificial hole without removing the metal from the blind hole. Alternatively or more preferably, the sacrificial hole may be etched to remove the metal in the sacrificial hole without removing the metal from the blind hole. Alternatively or more preferably, the redistribution layer may avoid contact with the metal in the sacrificial hole, for example at the second surface 24.

It is recognized that the particles 62 may not actually be as highly packed as the particles 62 shown in FIGS. 7A to 7C . Therefore, the size of the resulting gaps may be larger than the size shown in FIGS. 7A to 7C , which allows the liquid medium 64 to flow through the particles 62 at a greater flow rate. As further described above, the gaps between the packed particles 62 can define a flow path that allows the liquid medium 64 to flow through the holes 26 and to empty the holes through the filter medium 100. Therefore, the liquid medium 64 that has entered the holes 26 is also removed from the holes 26. As the suspension 60 continues to flow into the holes 26, the particles 62 accumulate in the holes 26 until the filling step 46 is completed.

In addition, because the support member 108 is porous relative to the liquid medium 64, the liquid medium 64 can be sucked into the vacuum chamber 90 under the action of vacuum pressure. Depending on the speed of the required filling process, the vacuum pressure can be any pressure below atmospheric pressure. In a non-limiting embodiment, the negative pressure can be a pressure ranging from any pressure below atmospheric pressure to up to about 120KPa, such as about 80KPa.

The frame 86 may define a drain 114 that extends through the frame body 87 and is in fluid communication with the vacuum chamber 90. Thus, the drain 114 may provide an outlet for the liquid medium 64 to flow out of the vacuum chamber 90 (as evacuated liquid medium 64). The evacuated liquid medium 64 may be discarded. Alternatively, the evacuated liquid medium 64 may be reused. In one embodiment, a quantity of particles 62 may be fed into a quantity of evacuated liquid medium 64 to produce a suspension 60 for use in a subsequent substrate 20 filling operation, or for a different substrate 20 filling operation. In one embodiment, the evacuated liquid medium 64 may be circulated as a stream through a hopper that dries the particles 62. The hopper can release a certain amount of dry particles into the flow to produce a suspension 60.

While it is understood that the filter medium 100 may be non-porous with respect to the particles 62 as described above, it is recognized that the filter medium 100 may be porous with respect to a certain amount of particles 62 (less than all of the particles 62 that enter the pores 26). Regardless of whether the filter medium 100 is non-porous with respect to all or some of the particles 62, particles 62 that do not pass through the filter medium 100 may accumulate in the pores 26 in the manner described above.

6A, it is recognized that the pressure differential causes the aligned portion of the suspension 60 (disposed on the outer surface 99 at the alignment area 110) to align the suspension with the respective holes 26. Therefore, the suspension 60 at the alignment area 110 can be forced into the respective holes 26 under the action of the pressure differential. In addition, the pressure differential causes the deflected portion of the suspension 60 to flow into the respective holes 26, which is disposed on the outer surface 99 of the substrate 20 at the affected area 112. The affected area 112 can have a circular shape on the outer surface 99 of the substrate 20, or can have any suitable alternative shape as desired. The offset portion of the suspension disposed in the affected area 112 is laterally offset from the respective hole 26 along a transverse direction perpendicular to the length of the hole 26. The affected area is located sufficiently close to the respective hole 26 so as to be drawn into the hole 26 under the force from the pressure differential. It is found that the affected area 112 is substantially spherical. However, it is contemplated that the affected area 112 may be alternatively shaped depending on a number of factors, including the dispersion gradient of the particles 62 in the liquid medium. It is recognized that the suspension 60 disposed on the outer surface 99 of the substrate 20 may be agitated during the filling step 46 to maintain the dispersion of the particles 62 in the liquid medium 64. For example, the substrate 20 may be vibrated, shaken, or otherwise moved to agitate the suspension 60 and move the suspension to the respective holes 26 or to the affected area 112, thereby forcing the suspension to enter the respective holes 26.

Depending on the volume of the suspension 60 applied to the outer surface 99 of the substrate 20, the volume of the aligned portion of the suspension 60 and the offset portion of the suspension 60 may be sufficient to fill the holes 26. Thus, in one embodiment, the filling step 46 may be completed when substantially all of the holes 26 are filled with particles 62. Alternatively, it is recognized that in some embodiments, the volume of the aligned portion of the suspension 60 and the offset portion of the suspension 60 may not be sufficient to fill the holes 26 in one filling operation. In this case, the vacuum pressure is unable to draw additional amounts of the suspension 60 into the holes 26 and leaves a volume of particles 62 in the holes 26 (less than a volume of particles 62 sufficient to fill substantially all of the holes 26 from the first end of the holes to the second end of the holes). Therefore, it should be understood that step 46 of filling the holes 26 may include partially filling the holes 26 and filling substantially all of the holes 26.

Once the liquid medium 64 is sucked into the hole 26 from the alignment area 110 and the affected area 112 under the vacuum pressure, and no other liquid medium 64 is sucked into the hole 26 under the pressure differential, the pressure differential will continue to be applied to the hole 26 to suck air through the hole 26. The sucked air forces the liquid medium 64 in the hole to empty the hole 26 through the flow path defined by the gap. Because the conductive material is at least substantially non-porous, the liquid medium 64 does not enter the conductive material. On the contrary, the liquid medium 64 empties the hole 26 under the pressure differential. Therefore, the pressure differential applied during the filling step causes the accumulated particles 62 in the hole to be at least substantially dry or completely dry relative to the liquid medium 64.

It is understood that once the liquid medium 26 has left the pores 26, the resulting stacked conductive particles 62 can contact each other to define a first or initial stacked powder 63 of a first fill 65. The first or initial stacked powder 63 can be configured as a main fill as described herein. It should be recognized that when the liquid medium 64 has emptied the pores, the surface charge of the particles 62 is no longer neutralized by the liquid medium 64. Therefore, the particles 62 can agglomerate with each other so that the particles 62 in the pores 26 define a certain volume of stacked particles.

In one embodiment, the filling step 46 may include the step of causing additional suspension 60 to enter one or both of the alignment region 110 and the affected region 112. The additional suspension 60 may increase the volume of particles 62 accumulated in the holes 26. For example, the additional suspension 60 may cause the holes 26 to be substantially completely filled with particles 62. Alternatively, the additional suspension 60 may increase the volume of particles 62 in the holes to a volume that is less than the volume of particles 62 sufficient to substantially fill the holes, but greater than the volume of particles 62 that would accumulate in the holes 26 without the causing step.

For example, referring now to FIG. 6A and FIG. 13A to FIG. 13C , the causing step may include the step of rocking the substrate 20 so as to angle the substrate 20 back and forth in one or more angular planes. In particular, the causing step may include the step of rocking the fluid pressure filling device 82 including the substrate 20 back and forth. The rocking step may cause the suspension 60 on the outer surface 99 of the substrate 20 to flow over the outer surface 99. As a result, a certain amount of the suspension may flow into one or both of the alignment area 110 and the affected area 112 of the hole 26. When the substrate 20 is continuously rocked, the additional amount of the suspension 60 may replace the certain amount of the suspension that flows into the hole 26 from one or both of the alignment area 110 and the affected area 112. The rocking member 209 may be activated to apply the rocking step. It is recognized that the substrate 20 may be rocked manually or by activating the rocking member. Alternatively, the vacuum filling device 84 may define a rocking platform that directly or indirectly supports the substrate 20 and is configured to automatically rock the substrate 20. It is understood that the fluid pressure filling device 82 may include a dam 116 that captures the suspension 60 and prevents the suspension 60 from flowing out of the substrate 20 when the substrate 20 is rocked. In one embodiment, the dam 116 may be defined by at least one sealing pad 94. For example, the at least one sealing pad 94 may be defined by at least one sealing pad 94 that seals the first interface 102, as described above with reference to FIG. 5. The baffle 116 may extend to a height sufficiently high relative to the substrate 20 to prevent the suspension from overflowing during the step of shaking the substrate 20.

Alternatively, referring now to FIG. 13D , the causing step may include the step of causing the suspension 60 to fill the holes 26 laterally. Specifically, the suspension 60 may be applied to the outer surface 99 of the substrate 20 at a position laterally spaced apart from the holes 26. The substrate 20 may then be tilted so that the suspension 60 flows over the outer surface 99 and sequentially flows through the holes 26. When the suspension 60 flows through the first holes 26, a certain volume of the suspension 60 may flow into the first holes 26. Then, the suspension 60 flows through the second holes 26 adjacent to the first holes 26 so that a certain amount of the suspension 60 flows into the second holes 26. Thus, the tilting of the substrate 20 may cause the suspension 60 to flow sequentially through the holes 26. The suspension may flow into the holes 26 under the action of gravity. In this regard, when the substrate 20 is shaken as described above with reference to FIGS. 13A to 13C , the suspension may flow into the hole 26 under the action of gravity. Alternatively, tilting the substrate 20 may allow the suspension to enter the affected area where the suspension may be sucked into the hole. For example, when the suspension 60 flows through a given hole 26, the hole may be filled with the suspension 60 under the force applied to the suspension (the pressure difference caused in the above manner). In addition, as described above, after completing the causing steps of FIGS. 13A to 13D , vacuum pressure is continuously applied to the hole 26 to suck air into the hole 26, thereby at least substantially drying the hole 26.

As shown in FIG. 3 , once the liquid medium has been removed from the holes 26 during the step of filling the holes 26, the density of the particles 62 drawn into the holes 26 prior to the subsequent filling step 46 may be increased in the stacking step 50. In one embodiment, referring now to FIGS. 8A-8B , the substrate 20 may be placed in the housing 118. The housing 118 includes a first stacking plate 119a and a second stacking plate 119b spaced apart from the first stacking plate 119a, thereby defining an interior space 124 sized and configured to receive the substrate 20.

In particular, the first laminate plate 119a may include a first outer layer plate 120a and a first inner layer 122a. The second laminate plate 119b may include a second outer layer plate 120b and a second inner layer 122b. The first inner layer 122a and the second inner layer 122b face each other and thus face the substrate 20 when the substrate 20 is disposed in the inner space. It will be understood from the following that the first inner layer 122a and the second inner layer 122b may be referred to as a first stacking member and a second stacking member, respectively, which are configured to apply pressure to the dry initial stacking powder 63 to further stack the dry initial stacking powder 63 into a highly stacked powder 77, the particles 62 of which are more pressed together after the filling step and the removal step 46 and before the filling step 50 than when the particles 62 are stacked particles. In particular, the first inner layer 122a and the second inner layer 122b may have sufficient flexibility to extend into the respective holes 26 to stack the particles 62. In this regard, the outer shell 118 may be referred to as a soft stacking outer shell. Similarly, stacking step 50 may be referred to as a soft stacking step. It will be appreciated that the density of particles 62 in pores 26 after stacking step 50 may be greater than the density after filling step 46 and before stacking step 50. In this regard, stacking step 50 may also be referred to as a densification step.

The inner space 124 is sized and configured to receive the substrate 20 after the step of removing the liquid medium 64 from the hole 26. Therefore, the inner layer 122 faces the respective opposite surfaces of the substrate 20. The outer layer 120 is non-porous and flexible relative to air and can surround the inner layer 122. Therefore, when the first laminate 119a and the second laminate 119b are fused to each other so that the inner space 124 is completely closed to define the enclosure 126, air cannot enter the enclosure 126.

In one embodiment, respective portions of the first and second laminated plates 119a, 119b may be sealed to each other to partially define the enclosure 126. Then, before forming the enclosure 126, the substrate 20 may be placed in the interior space 124 so that the interior surface 97 faces one of the first and second inner layers 122a, 122b, and the exterior surface 99 faces the other of the first and second inner layers 122a, 122b. Then, a vacuum is applied to the interior space 124 of the enclosure 126 to remove air from the interior space 124, and the first and second laminated plates 119a, 119b may be sealed to each other (e.g., heat sealed) to define the enclosure 126 under vacuum. When the housing 118 is placed under vacuum, the inner layers 122a and 122b can lie flat on the inner surface 97 and the outer surface 99 of the substrate 20 and can extend above the hole 26. In addition, the first inner layer 122a and the second inner layer 122b can abut against any overfill particles 62 that extend outward relative to one or both of the surfaces 97 and 99.

Therefore, referring now to FIG. 8C , the shell 118 may be placed in a press 128 configured to apply sufficient external pressure to the shell 118 so that the shell 118 densifies the particles 62 of the initial fill powder 63. For example, the press 128 may be an isostatic press that applies isostatic pressure to the stacking plates. Therefore, the stacking step 50 may be referred to as an isostatic press stacking step. Isostatic pressure may be applied to the outer layer plate 120a and the outer layer plate 122a, which in turn applies isostatic pressure to the inner layer 122a and the inner layer 122b. The isostatic pressure may range from about 5,000 pounds per square inch (PSI) to about 60,000 PSI. For example, the isostatic pressing may be in the range of about 20,000 PSI to about 50,000 PSI. In one embodiment, the isostatic pressing may be in the range of about 25,000 PSI to about 40,000 PSI.

The pressure of the isostatic press applied to the outer shell 118 can drive the inner layers 122a and 122b into the opposite ends of the hole 26 under the action of the isostatic pressure, thereby further stacking the particles of the initial stacking powder 63 obtained during the filling step 46 into the highly stacked powder 77, whose particles 62 are more densely stacked than the stacked particles 62. Therefore, it can be said that the pressure densifies the particles 62 in the hole 26. In particular, the isostatic pressure drives the inner layers 122a and the inner layers 122b to densify the stacked powder 63. It should be understood that when the initial accumulation powder is further accumulated into a highly accumulated powder, the distance occupied by the particles of the highly accumulated powder along the length of the hole 26 is reduced relative to the distance occupied by the particles of the initial accumulation powder. In other words, the particles can be compressed longitudinally in the hole.

The isostatic press may be applied at room temperature. In this regard, the isostatic press may be referred to as a cold isostatic press (CIP). Alternatively, the isostatic press may be configured as a warm isostatic press (WIP), which may be configured to apply isostatic pressure at a temperature in the range of about 120°C to about 250°C and for a sufficient period of time to deform and further densify the particles 62.

Without wishing to be bound by theory, it is believed that the inner layers 122a and 122b can densify the outer ends of the initial accumulation powder 63 relative to the middle portion of the initial accumulation powder 63 extending between the outer ends. In addition, referring also to FIG. 6B , the inner layers 122a and 122b can drive the initial accumulation powder 63 of the first filling step 46 to move in the hole 26 toward the center of the hole 26. Therefore, as shown in FIG. 6B , the initial accumulation powder 63 can be driven to substantially the center of the hole 26 relative to the total length of the hole 26. The subsequent pressing step of the subsequent filling can drive the resulting subsequent accumulation powder 79 against the powder (also referred to as the previous powder) that was drawn into the hole 26 during the previous filling step 46. If desired, the previous powder may be defined by one or both of the first filling step 46 and the first pressing step 50. Alternatively, if desired, the previous powder may be defined by one or both of the subsequent filling step 46 and the subsequent pressing step 50.

In one embodiment, when the inner layer 122a and the inner layer 122b extend into opposite ends of the hole 26, substantially equal amounts of pressure may be applied to each end of the hole 26. Thus, the initial accumulation powder 63 disposed off-center relative to the length of the hole 26 may contact one of the respective inner layers 122a and 122b, be driven toward the center of the hole 26, and be compressed between the inner layers 122a and 122b. The initial accumulation powder is then compressed on the previously compressed highly accumulated powder. Therefore, one of the inner layers 122a and 122b contacts the outer end of the previously compressed highly accumulated powder, and the other of the inner layers 122a and 122b contacts the outer end of the subsequent initially accumulated powder, thereby highly accumulating the subsequent initially accumulated powder into highly accumulated powder. When the initially accumulated powder is longitudinally accumulated from the inner layers 122a and 122b, it should be understood that the initially accumulated powder can expand radially when it is accumulated into highly accumulated powder, thereby pressing each particle 62 against the inner wall of the substrate 20 defining the hole 26.

The inner layer 122a and the inner layer 122b can be made of any suitable material as needed. In one embodiment, the inner layer 122a and the inner layer 122b can be made of a viscoelastic material and thus configured to enter the hole 26 to compress the particles 62 disposed in the hole 26. For example, the inner layer 122a and the inner layer 122b can evenly and consistently distribute the isostatic pressure on the substrate so that the inner layer 122a and the inner layer 122b conform to the outer surface of the substrate 20 and extend into the hole 26. Therefore, the inner layer 122a and the inner layer 122b can mechanically stack the initial stacking powder 63 into a highly stacked powder. Therefore, it is desirable that the inner layer 122a and the inner layer 122 are made of a material that does not adhere to the particles 62, so that when the isostatic pressing is removed, the inner layer 122a and the inner layer 122b can be removed from the hole 26 without pulling the particles 62 out of the hole 26. In one embodiment, the inner layer 122a and the inner layer 122b can be made of Mylar. In another embodiment, the inner layer 122a and the inner layer 122b can be made of Teflon. The outer layer plates 120a and the outer layer plates 120b can be made of any suitable non-porous material. For example, the outer layer plates 120a and the outer layer plates 120b can be made of a flexible metal such as aluminum.

In one embodiment, if desired, outer sheet 120a and outer sheet 120b may include molten material 121 (such as Mylar) coated on their respective inner surfaces. Molten material 121 may melt itself to produce vacuum enclosure 126. Inner layer 122a and inner layer 122b may be separated from outer sheet 120a and outer sheet 120b and placed between the outer sheet and substrate 20. Alternatively, inner layer 122a and inner layer 122b may be lined with outer sheet 120a and outer sheet 120b as desired.

Therefore, it will be appreciated that the vacuum in the enclosure 126 is sufficient to cause the inner layer 122a and the inner layer 122b to lie flat on the inner surface 97 and the outer surface 99, either alone or in combination with overfilling. Therefore, it will be appreciated that any suitable means may be contemplated for causing the inner layer 122a and the inner layer 122b to lie flat on the inner and outer surfaces 97 and 99, either alone or in combination with overfilling, prior to uniformly and consistently applying isostatic pressure directly or indirectly through the outer layer to the inner layer 122a and the inner layer 122b, as described herein. Therefore, the inner layer may be referred to as a stacking member, which may be configured to be driven into the hole 26 of the substrate 20, thereby highly stacking the initial stacking powder 63 into a highly stacked powder disposed therein.

Referring now to FIGS. 3 and 6B , once the isostatic pressing is removed from the stacked member, the step of increasing the stacking density 50 is completed. Once the step of increasing the stacking density is completed, the first filling and stacking sequence is also completed. However, it is understood that in certain embodiments, the stacking step 50 may be omitted. Instead, as described in more detail below, the step of hard pressing the substrate 20 to stack the particles 62 may be performed in step 53. In yet other embodiments, both steps 50 and 53 may be performed during method 40. Furthermore, it should be understood that the step of isostatically pressing the particles 62 may be performed in a plurality of embodiments between a plurality of consecutive iterations of filling the voids.

6B-7C , it is recognized that in some embodiments, after the first filling step 46 and optionally after the first stacking step 50, the particles 62 may define a bulk fill that extends along only a portion of the hole 26. In other embodiments, the bulk fill may extend along substantially all of the hole 26. When the bulk fill extends along only a portion of the hole, the particles 62 may occupy a length of the hole 26 that is less than the entire length of the hole 26, thereby defining a longitudinal distance measured from the bulk fill to each of the first surface 22 and the second surface 24 of the substrate 20. If each distance is greater than a predetermined distance, a subsequent sequence 55 is implemented to fill the hole 26 with additional bulk fill until the predetermined distance is reached. If each distance is less than or equal to the predetermined distance, the final filling can be introduced into the hole 26 from the first end and the second end of the hole 26, respectively. The distance can be measured after the filling step 46 is performed. Alternatively, the distance can be measured after the stacking step 50 is performed.

Alternatively, it is recognized that in some embodiments, after the first stacking step 50, the bulk fill particles 62 may extend from the first end of the hole 26 to the second end of the hole. Thus, the bulk fill may extend from the first surface 22 of the substrate 20 to the second surface 24 of the substrate 20. For example, the bulk fill may extend from the hole 26 beyond one or both of the first surface 22 and the second surface 24 of the substrate 20. Thus, a single filling step 46 may fill the hole 26 such that the conductive particles 62 extend continuously through the hole and may extend from the hole beyond each of the first surface 22 and the second surface 24 of the substrate 20. As will be understood below, the particles 62 may then be compacted within the hole 26 and against one or both of the first surface 22 and the second surface 24 during the hard pressing step 53 (described in more detail below).

In one embodiment, the predetermined distance may be in the range of about 1 micron to about 30 microns. In one embodiment, the range may be about 1 micron to about 20 microns. For example, the range may be about 1 micron to about 10 microns. For example, the range may be about 2 microns to about 6 microns. In one embodiment, the predetermined distance may be in the range of about 0.5% of the total length of the hole 26 to about 25% of the total length of the hole 26. For example, the range may be about 0.5% of the total length of the hole 26 to about 20% of the total length of the hole 26. For example, the range may be about 0.5% of the total length of the hole 26 to about 15% of the total length of the hole 26. For example, the range may be about 0.5% of the total length of the hole 26 to about 10% of the total length of the hole 26. For example, the range may be about 0.5% of the total length of the hole 26 to about 5% of the total length of the hole 26. For example, the range may be about 1% of the total length of the hole 26 to about 4% of the total length of the hole 26.

When the distance reaches a predetermined size or size range, a final sequence 53 of at least one filling and pressing step may be implemented. Therefore, as shown in FIG. 9B , the particles 62 that enter the hole 26 during the final filling step 46 of the final sequence 53 may be referred to as the final filling. The final filling is intended to occupy a portion of the hole 26 that extends from the main filling to the first end and the second end of the hole 26. When the hole 26 is a through hole, the final filling is intended to extend from the main filling to each of the first surface 22 and the second surface 24 of the substrate 20. The particles 62 of the main filling may be defined by the first particles 62a that are configured and intended to extend along the length of most of the hole 26. The final fill particles 62 may be defined by the second particles 62b, but it is understood that particles of other sizes may be considered for the final fill. Thus, in one embodiment, the hole 26 may be filled with both a main fill and a final fill.

As shown in FIG9A, when each distance is greater than the predetermined distance, the subsequent filling step 46 is performed in the above-described manner, thereby producing the initial accumulation powder 63 from the subsequent filling 67 of the subsequent filling step 46. The subsequent filling step 46 may be a main filling step. As shown in FIG9B, if the subsequent pressing step 50 is performed, the highly accumulated powder 77 may be produced from the subsequent filling 67. After the first filling step and optionally the first accumulation step 50, the highly accumulated powder may be further accumulated. Therefore, as shown in FIG9A, the subsequent filling step begins with step 46 as described above with reference to the first filling step, thereby performing the subsequent filling step 46 in the above-described manner with respect to the first filling step. In particular, the inner surface 97 of the substrate 20 is placed against the filter medium 100 in the manner described above.

9A , the highly packed powder 77 of the first fill 65 may provide a plug 95 that allows air and liquid medium 64 to pass through but does not allow the first particles 62a to pass through. In particular, when the particles 62 in the holes 26 define the unimodal distribution 70 described above, the particles 62 define gaps 66. Alternatively, when the particles 65 of the first fill 65 define a bimodal distribution 72, the particles 62 may define a first bimodal gap 66 and a second bimodal gap 75, respectively, as described above. Alternatively, when the particles 65 of the first fill 65 define a trimodal distribution 73, the particles may define a first trimodal gap 66, a second trimodal gap 75, and a third trimodal gap 69, respectively, as described above. It is recognized that in some embodiments, the size of the gaps of the first fill 65 may be smaller than the size of the first particles 62a. Thus, it can be said that the plug 95 defines an inner filter layer in the void 26 that is non-porous relative to the first particle 62a. The plug 95 can be defined by the highly packed powder 77, or can be defined by the first particle 62a that is sucked into the void 26 during the first filling step 46. The gaps of the inner filter layer are large enough to be porous relative to the fluid and air. Therefore, it can be expected that the inner filter layer defined by the first particle 62 can prevent the particle 62 that flows into the void in the subsequent filling step 46 from passing through the filter medium 100 located below the substrate 20 from the void 26. However, it is still desirable to include the filter medium 100 as a barrier to protect the support member 108 (see FIG. 5 ) from dispersed particles that may still be able to flow through the holes 26 . In some embodiments, the filter medium 100 of the subsequent filling step may be coarser than the filter medium 100 of the first filling step.

Referring now to FIG. 9A , it should be understood that during the first subsequent filling step, the inner surface 97 of the substrate may be defined by the same surface of the first surface 22 and one of the second surfaces 24 that defined the inner surface 97 during the immediately preceding filling step (which may be the first filling step as shown or a subsequent filling step). Similarly, the outer surface 99 may be defined by the same surface of the first surface 22 and one of the second surfaces 24 that defined the outer surface 99 during the immediately preceding filling step. Alternatively, the substrate 20 may be flipped relative to the immediately preceding filling step so that the inner surface 97 is defined by the other of the first surface 22 and the second surface 24. Similarly, the substrate 20 may be flipped relative to the immediately preceding filling step so that the outer surface 99 is defined by the other of the first surface 22 and the second surface 24.

Therefore, during the first subsequent filling step, the vacuum pressure may cause the suspension 60 to flow into the same end of one of the first and second ends of the hole 26 as in the immediately preceding filling step. Alternatively, the substrate 20 may be flipped so that the vacuum pressure causes the suspension 60 to flow into the opposite end of one of the first and second ends of the hole 26.

9, the first subsequent filling step 46 may be performed so that the subsequent accumulation powder 79 of the subsequent filling 67 of the first subsequent filling step 46 overfills the hole 26. That is, the particles 62 of the subsequent accumulation powder 79 extend beyond the hole 26, passing through each of the first surface 22 and the second surface 24. However, it is recognized that if the subsequent accumulation step 50 is performed, the subsequent accumulation powder 79 is accumulated into a subsequent highly accumulated powder. Thus, after subsequent filling step 46 but before subsequent stacking step 50, the distance along the length of the void occupied by the subsequent stacking powder is reduced relative to the distance occupied by particles 62 of the subsequent stacking powder 79. That is, if implemented, particles 62 may be longitudinally compressed during the subsequent stacking step. Therefore, even if the particles 62 are overfilled (meaning that they extend beyond one or both of the first surface 22 and the second surface 24) before stacking, it is recognized that the subsequent height of the stacked powder defined by the subsequent filling 67 after the subsequent stacking step 50 can be recessed relative to the respective outer surfaces of the substrate 20 (as shown in FIG. 9B), thereby defining the above distance.

If desired, as shown in FIG9A, once the first subsequent filling step 46 has been performed at one end of the hole 26 to define the subsequent accumulation powder 79, the subsequent accumulation powder 67 can be accumulated into a highly accumulated powder 77 (as shown in FIG9B) in a subsequent step 50. Thus, the conductive material can include regions of highly accumulated powder 77 that are spaced apart from each other along the hole and along the resulting conductive via. Alternatively, the accumulation step 50 can be omitted so that the particles 62 that extend to at least one end of the hole 26 (and possibly through) can remain as subsequent accumulation powder 79 without being highly accumulated. Next, as shown in FIG9B , the substrate may be flipped relative to FIG9A , and a second or opposite subsequent filling step 46 may be performed at the opposite end of the hole 26, thereby defining a second or opposite subsequent accumulation powder 81 that extends to (and possibly past) the opposite end of the hole 26. Then, if necessary, an opposite subsequent accumulation step 50 may be performed to accumulate the opposite subsequent accumulation powder 81 into a highly accumulated powder 77 as desired. Thus, the first or initial accumulation powder 63 of the first filling 65 may be disposed between the subsequent accumulation powder 79 and the opposite subsequent accumulation powder 81. If desired, any one or more or up to all of the first or initial stacking powder 63, the subsequent stacking powder 79, and the opposite subsequent stacking powder 81 may define a highly stacked powder 77. As shown in FIG. 9C, the particles 62 of the first fill 65 and the subsequent fill 67 may be combined to define a stacked main fill 130.

Referring now to FIG. 9C and FIG. 12A , when the distance is within the predetermined distance, a final filling step 46 may be performed at each end of the hole 26. The final filling step 46 may use the second suspension 60b as desired. Thus, the particles 62b of the second suspension 60b may be referred to as the final filling. Alternatively, the first suspension 60a may be used for the final filling step 46. Thus, although the final filling step is described below in conjunction with the second suspension 60b, the description may equally apply to the first suspension 60a. The final filling step 46 may be performed after the first filling step 46 or after one or more subsequent filling steps 46. Alternatively, if the first filling step 46 causes the particles 62 to extend beyond the first surface 22 and the second surface 24 of the substrate 20 and the stacking step 50 is omitted, the final filling step 46 can be omitted.

The suspension 60 used during the final filling step may be defined by the second suspension 60b or by any suitable alternative suspension as desired to produce the final stockpile powder 132. During the first final filling step 46, the final suspension 60 may be filled at one end of the hole 26. During the second or opposite final filling step 46, the second or opposite suspension 60 may be filled at the opposite end of the hole 26. The first final suspension 60 may be defined by the second suspension 60b, or may be defined by the first suspension 60a as described above. The first final suspension 60 may be overfilled, thereby extending the hole 26 beyond the outer surface 99 of the substrate 20, which may be defined by the first outer surface 22 or the second outer surface 24. Next, if desired, a first final accumulation step 50 may be applied to the first final suspension 60 to accumulate the final accumulation powder 132 into a highly accumulated powder 77 of a final fill 134 (as shown in FIG. 12B ). In this regard, it is understood that the highly accumulated powder 77 of the final fill 134 may be overfilled relative to the hole 26.

The substrate 20 may then be flipped over and a second or opposite final filling step may fill the opposite end of the hole with a second final suspension, thereby producing an opposite final accumulation of powder at the opposite end of the hole 26. The second final suspension may be accumulated in step 50 to produce a highly accumulated powder as shown in FIG. 12B as a final fill 134 that is substantially flat and/or substantially flush with the first surface 22 and the second surface 24. It is recognized that the term "substantially" in "flat and flush with the first surface 22 and the second surface 24" herein may vary slightly from perfectly flat and perfectly flush, however, for the purposes of future patterning and subsequent use, it will be understood by those of ordinary skill in the art to be flush. Alternatively, as described above, the stacking step 50 may be omitted. Alternatively, if the first final filling is not stacked in the stacking step 50, the stacking step 50 may be performed after the second or opposite final filling step 46, thereby producing a highly stacked powder from the final stacked powders of both the first and second final stacking steps 46. After the final filling step 46, the opposite highly stacked powder 77 of the final filling may also be overfilled relative to the hole 26.

It is recognized that the deposited main fill 130 and the deposited final fill 134 may combine to define the fill 35 of the via 34, whether deposited in step 50 or not. Thus, the fill 35 may be said to be defined by the conductive material.

It is recognized that the density of particles 62 in pores 26 of highly packed powder 77 of first fill 65 is greater than the density of particles 62 in pores of initial packed powder 63. It is recognized that the density of particles 62 in pores 26 of highly packed powder 77 of first fill (if applicable) is greater than the density of particles 62 in pores of initial packed powder 63 of first fill 65. It is further recognized that the density of particles 62 in pores 26 of highly packed powder 77 of subsequent fill 67 (if applicable) is greater than the density of particles 63 in pores of subsequent packed powder 63. Similarly, it is recognized that the density of particles 62 in holes 26 of highly packed powder 77 of final fill 134, if applicable, is greater than the density of particles 62 in holes of final packed powder 132. It is further recognized that the density of particles 62 in holes 26 of highly packed powder 77 of subsequent fill 67 is greater than the density of particles 63 in holes of subsequent packed powder 63. Similarly, it is recognized that the density of particles 62 in holes 26 of highly packed powder 77 of final fill 134 is greater than the density of particles 62 in holes of final packed powder 132.

Now referring to FIG. 10 , it is recognized that the subsequent filling step 46 can be implemented by performing subsequent filling on one side of the hole with particles 62, flipping the substrate 20, and performing subsequent filling on the opposite side of the hole with particles in step 50 without stacking particles after the first subsequent filling step 46. Then, the stacking step 50 (if implemented) can simultaneously stack the first and second subsequent filling particles 62 at both ends of the hole 26.

In this regard, the vacuum device 84 may define a suspended vacuum device 85. In particular, the suspended vacuum device may be constructed as the vacuum device 84 described above with respect to FIG. 5. However, the sealing pad 94 of the suspended vacuum device 85 may extend beyond the interface between the protrusion 96 and the support member 108. The sealing pad 94 may be spaced apart from the outer surface of the support member 108. Therefore, the substrate 20 may be placed on the outer surface of the sealing pad 94. Therefore, the alignment area of the substrate 20 defining the hole 26 may be suspended on the support member 108. Therefore, an air gap 136 may be defined between the substrate 20 and the support member 108. In particular, the substrate 20 and the support member 108 may be spaced apart from each other along the same direction as the elongation direction of the hole 26.

The gap 136 may be sufficient to accommodate the overfill of powder particles 62 that may be produced during the final filling step 46, such that the overfill facing the support structure 108 does not contact the support structure 108. As described above, when the liquid medium 64 has emptied the holes, the remaining particles 62 may be referred to as dry packing powder. In addition, because the surface charge of the particles 62 is no longer neutralized by the liquid medium 64, the particles 62 may agglomerate with each other. Therefore, the agglomerated particles will not fall out of the holes 26 and enter the gap 136 before they are accumulated into a highly packed powder. If desired, the filter medium 100 may be positioned above the support member 108 to protect the support member 108 from dispersed particles 62 that escape through the holes 26 during the filling step 46. The filter medium 100 may extend across the support member 108 and into the interface between the sealing pad 94 and the support member 108 as desired.

Referring to FIG. 11 , during operation, at least one sealing pad seals a first interface 102 between substrate 20 and support member 108, or seals a first interface 102 between substrate 20 and filter medium, relative to airflow therebetween. At least one sealing pad may further seal a second interface between support member 108 and boss 96 relative to airflow therebetween. Sealing pad 94 may support the outer periphery of substrate 20 at the exclusion zone as described above. In addition, a portion of sealing pad 94 or other auxiliary support member may extend between support member 108 and substrate 20 to support a middle region of substrate 20 that may be subject to increased force from the application of negative pressure.

The suspension 60 is applied to the outer surface 99 of the substrate 20 until the respective ends of the holes 26 are filled with particles as described above. The liquid medium 64 is drained from the holes 26 in the manner described above. The substrate is then turned over so that the former inner surface 97 now defines the outer surface 99, and the suspension is again applied to the outer surface 99, and the respective holes are filled with particles. If the subsequent filling process is a main filling process, the first and opposite subsequent accumulation powders can be filled without performing the stacking step 50 between the step of filling the first subsequent accumulation powder and the step of filling the opposite subsequent accumulation powder. The substrate 20 can then be stacked in the manner described above in step 50, if necessary. The stacking step 50 can stack the first subsequent stacking powder and the opposite subsequent stacking powder into respective high stacking powders. Alternatively, the stacking step 50 of the subsequent filling process can be omitted. Alternatively, if the subsequent filling process is the final filling process, the first and opposite final stacking powders 132 can be filled without performing the stacking step 50 between the step of filling the first final stacking powder and the step of filling the opposite final powder. After the final filling step 46, the substrate 20 can be stacked in the above-mentioned manner in step 50, which stacks the first final stacking powder and the opposite final stacking powder into respective high stacking powders 77 (as shown in FIG. 12A).

Thus, it is recognized that the suspended vacuum device 85 may be used to fill the holes 26 with the first and second or opposite subsequent accumulation powders prior to the accumulation of the particles 62 in step 50. If the accumulation step 50 is performed, both the first and opposite subsequent accumulation powders may be accumulated into a highly accumulated powder during step 50 at the same time. Alternatively, as described above, the accumulation step 50 may be omitted. Alternatively or moreover, it is contemplated that the suspended vacuum device 85 may be used to fill the holes 26 with the first and opposite final accumulation powders prior to the final accumulation step 50. The final accumulation step 50 may accumulate both the first and opposite final accumulation powders into a highly accumulated powder at the same time. Alternatively, as described above, the final stacking step 50 may be omitted.

For example, referring to FIG. 12C , the stacking step 50 may be omitted after the final filling step 46 is completed. When the stacking step 50 is omitted in the method 40 , the particles 62 in the pores 26 may extend from the first surface 22 to the second surface 24. In some embodiments, after completing one or more filling steps 46 , the particles 62 may extend beyond the first surface 22 and the second surface 24. In addition, after completing one or more filling steps and when the sintering step 52 is to be performed (see FIG. 3 ), the particles 62 may be free of areas of highly stacked powder 77 in the pores 26 .

Referring now to FIG. 19A , although the filling step 46 is described in the above embodiment as inducing air pressure to drive the suspension 60 into the hole, it is recognized that the filling step 46 may be implemented according to other embodiments. For example, the centrifuge 150 may provide a force to drive or draw the suspension into the hole 26. In one embodiment, the hole 26 may be a through hole of the type described above. Therefore, the force that causes the particles 62 to flow into the hole 26 may be a centrifugal force. The centrifuge 150 may include a rotating wheel hub 152, at least one bucket 156 (such as a plurality of buckets 156), and an arm 154 extending between the wheel hub 152 and the bucket 156.

As shown in FIG. 19B , the substrate 20 may be placed in the bucket 156 such that the substrate 20 is supported by the distal wall 158 of the bucket 156. Thus, the inner surface 97 of the substrate 20 faces the distal wall 158 of the bucket 156, and the outer surface 99 of the substrate 20 faces away from the distal wall 158. The inner surface 97 may be defined by one of the first surface 22 and the second surface 24. The outer surface 99 may be defined by the other of the first surface 22 and the second surface 24. The inner surface 97 may be placed against a corresponding support surface 157 of the distal wall 158 within the bucket 156. The support surface 157 of the bucket 156 may be flat and made of a suitable material that enables the substrate 20 to be subsequently removed from the inner surface 157 without pulling out particles disposed in the holes. Alternatively, an auxiliary support member 160 may be placed in the bucket 156 between the substrate 20 and the inner surface 157. The support member 160 may define a support surface such that the inner surface 97 of the substrate 20 is placed against the support surface. The support member 160 may be made of any suitable material, such as glass, which may be coated as needed to prevent the support member 160 from adhering to particles of the substrate 20. The inner surface 157 or support member 160 may seal the inner surface 97 of the substrate 20 to prevent particles 62 from being emptied from the hole 26 at the interface between the inner surface 97 of the substrate 20 and the support surface. In some embodiments, it is recognized that the hole may be a blind hole as opposed to a through hole. Thus, the centrifuge 150 can cause particles to flow into the blind holes through the open ends of the blind holes, thereby filling the blind holes relative to the through holes in the manner described herein.

As shown in FIG. 19B , the suspension 60 may then be applied to the outer surface of the substrate 20 in the bucket 156 such that the suspension covers at least a portion of the outer surface 99. As described above, the suspension 60 may be sonicated or otherwise agitated to disperse the particles 62 in the liquid medium before the suspension is applied to the substrate 20 in the bucket 156.

The bucket 156 can be positioned in a first orientation so that the inner surface 157 can be positioned substantially horizontally so that the suspension 60 does not slide off the outer surface of the substrate or pour out of the bucket. Referring next to FIG. 19C , the bucket 156 can be pivotally attached to the arm 154. Thus, as the bucket 156 rotates about the hub 152, the bucket 156 can pivot from a first orientation to a second orientation so that the inner surface 157 can be positioned substantially vertically, or substantially perpendicular to the first orientation. The centrifuge 150 can rotate the bucket 156 about the hub 152 at any suitable speed as desired. For example, the centrifuge 150 can rotate at any suitable speed to apply any suitable G-force as desired to drive the particles 62 into the holes 26. For example, the G-force may be between about 100G and about 15,000G. In one embodiment, the G-force may be about 6,000G.

As shown in FIG. 19D , it is recognized that the specific gravity of the particles 62 is significantly higher than that of the liquid medium 64. Therefore, the centrifugal force applied to the suspension 60 causes the particles 62 to displace the liquid medium 64 from the holes and flow into the holes 26. The particles 62 in the holes 26 are piled up on each other under the centrifugal force, thereby generating a piled powder 162. However, because the liquid medium 64 remains between the gaps between the particles of the piled powder 162, the piled powder 162 can be called a wet piled powder. After the centrifugal operation is completed, a certain volume of the residual liquid medium 64 may remain on the outer surface 99 of the substrate 20. As shown in FIG. 19D , the solid content of the suspension 60 may be greater than the solid volume of the filled holes 26, so that the residual liquid medium 64 may include a certain amount of particles 62. However, after the filling operation, the concentration of particles 62 in the residual liquid medium 64 outside the substrate 20 is less than the particle concentration of the suspension 60 before the centrifuge 150 is operated. Alternatively, the particle content of the suspension 60 may be calculated to fill the holes 26 during the centrifugation operation so that substantially no particles 62 remain in the residual liquid medium 64. Once the holes 26 are filled with the accumulated powder 162, the centrifugation operation is terminated and the residual liquid medium may be dried or otherwise removed from the substrate 20.

The liquid medium 64 disposed in the holes 26 may then be removed. For example, the substrate 20 may then be placed in any suitable warm environment to evaporate the liquid medium. Alternatively or more preferably, air may be forced through the holes 26 to remove the liquid medium from the holes 26. It should be appreciated that in one embodiment, when the filling process is performed with a centrifuge 150, the filling process 46 may be brushless. That is, the method 40 may omit any brushing or other steps that introduce any structure along the outer surface of the substrate 20, thereby forcing the removal of excess conductive material from the outer surface 99 of the substrate 20 after the filling step 46. Alternatively or more preferably, referring to FIG. 9E , a scraper step may be performed to remove residual liquid medium 64 from outer surface 99 of substrate 20 before or after liquid medium 64 is removed from holes 26. For example, any suitable rod 103 may be driven across outer surface 99 of substrate 20 to remove residual liquid 64 containing particles 62. Rod 103 may be made of any material that will not pull conductive particles from holes 26 as desired. For example, a Teflon rod may be particularly suitable. Alternatively, if the residual liquid medium 64 is free of particles 62, the remaining liquid medium 64 may be removed in the manner described above without using rod 103.

After the filling step 46 is performed by a centrifuge, the stacking step 50 may be performed. In one embodiment, the stacking step 50 may be performed after the residual liquid medium 64 and the particles 62 are removed from the outer surface 99 of the substrate 20. In particular, the substrate 20 may be placed in the housing 118, and air may be removed from the housing 118 as described above with reference to Figures 8A to 8B, and the substrate 20 may be pressed in the press 128 as described above with reference to Figure 8C. The stacking step 50 may further stack the particles 62 in the pores 26, thereby producing a bulk fill of the dry highly stacked powder as described above.

Alternatively, the stacking step 50 may be performed without first removing the residual liquid medium and particles 62 from the outer surface 99. Without wishing to be bound by theory, it is believed that if the residual liquid medium 64 and particles 62 are not first removed, then when the substrate 20 is removed from the enclosure after the stacking step 50 is completed, most or substantially all of the residual liquid medium 64 and particles 62 may be removed from the substrate by adhering to the inner layers 122a and 122b. Alternatively, as described above, the stacking step 50 may be omitted after the filling step 46 is performed by a centrifuge.

In one embodiment, after the filling step 46 is performed by a centrifuge, it is recognized that the resulting bulk filling of particles 62 may extend along the entire length of the hole 26 from the first end of the hole to the second end of the hole 26. In addition, the particles 62 may extend beyond one or both of the first surface 22 and the second surface 24 of the substrate 20. For example, before the filling step 46 is performed under the action of a centrifugal force, one or both of the inner surface 97 and the surface of the support member 160 facing the inner surface 97 may be pre-coated with the suspension 60, thereby producing an overfill at the inner surface 97. Alternatively, before the filling step 46 is performed under the action of a centrifugal force, a stand-off member may be disposed between the support member 160 and the inner surface 97. The support member may define a gap between the inner surface 97 and the support member 160. Therefore, the particles may be pushed to a position between the inner surface 97 and the support member 160 under the action of the centrifugal force. Therefore, the single filling step 46 may fill the hole 26 so that the conductive particles 62 extend continuously through the hole and may extend beyond each of the first surface 22 and the second surface 24 of the substrate 20.

Alternatively or more preferably, substrate 20 may be flipped so that previously inner surface 97 is now outer surface 99, and previously outer surface 99 is now inner surface 97. Then, filling step 46 under centrifugal force may be repeated as a subsequent filling step under centrifugal force. Thus, where centrifugal force 150 pushes particles from first surface 22 into hole 26 during the first filling step, the centrifugal force may now push particles from second surface 24 into hole 26 under centrifugal force during the subsequent filling step.

After completing one or more filling steps 46 under the action of centrifugal force, the particles 62 can then be compacted within the hole 26 and abut against one or both of the first surface 22 and the second surface 24 during the hard pressing step 53 (described in more detail below).

If the accumulation step 50 is performed, the resulting highly accumulated powder may occupy the length of the hole 26 (which is less than the entire length of the hole), thereby defining the longitudinal distance measured from the main fill to each of the first surface 22 and the second surface 24 of the substrate 26 as described above. If the distance is greater than the predetermined distance as described above, one or more of the vacuum device 84, the suspended vacuum device 85, and the centrifuge may be used as needed to describe at least one of the above-described types of subsequent main fill steps 46. It should be understood that filling the hole with the first and opposite subsequent accumulation powders using one or both of the vacuum device 84 and the centrifuge 150 includes filling the first subsequent accumulation powder in step 46. Next, another subsequent sequence 55 includes filling the opposite subsequent accumulation powder in step 46. Alternatively, as described above, a suspended vacuum device 85 can be used to fill the first and opposite powders in sequence. The accumulation step 50 can be implemented after one or more or up to all accumulation steps 46 as needed. Alternatively, the accumulation step 50 can be omitted. Once each distance is equal to or less than the predetermined distance, a final filling step 46 of the type described above is implemented.

Now referring to FIG. 20A to FIG. 20F , the filling step 46 can be performed by applying an electrostatic force to the particles 62, and the electrostatic force drives the particles 62 to flow into the holes 26. In particular, the electrostatic filling device 200 is configured to apply an electrostatic force to the suspension 60 to drive the suspension 60 to flow into the holes 26.

As shown in FIG. 20A , a region of substrate 20 may be etched (e.g., laser etched) to define a weakened region 202 that may be removed in a subsequent step to define a hole. As shown in FIG. 20B , a conductive layer 204 may be applied to the inner surface 97 of substrate 20. For example, layer 204 may be a metal layer. In one embodiment, the metal layer may be sputter plated onto the inner surface 97 of substrate 20. Next, as shown in FIG. 20C , a non-reactive mask 206 may be applied to conductive layer 204. For example, non-reactive mask 206 may be a photoresist or other suitable material. Next, the etched region may be etched to produce hole 26. In this regard, while the holes are shown as conically tapered, it should be understood that all holes 26 and resulting vias 34 herein may be shaped in any manner as desired. For example, hole 26 may be substantially cylindrical. Alternatively, hole 26 may be conical. For example, hole 26 may taper inwardly from outer surface 99 to inner surface 97. Alternatively, hole 26 may taper outwardly from outer surface 99 to inner surface 97. Hole 26 may define any suitable alternative shape as desired. It should be further understood that substrate 20 as described in all embodiments herein may be fabricated according to any suitable available method, including laser ablation and subsequent etching to form hole 26.

As shown in FIG. 20D , the suspension 60 may be applied to the outer surface 99 of the substrate 20, thereby covering at least a portion of the outer surface 99 as described above. The layer 204 may have a charge opposite to the charge of the particles 62. For example, the charge of the particles 62 may be defined by the above-described Zeta potential. The layer 204 may have a surface charge. Alternatively, the layer 204 may be electrically connected to an electrode that applies a charge to the layer 204. In one embodiment, the layer 204 may define a negative charge and the particles 62 may have a positive charge. The liquid medium 64 may be any suitable liquid that does not neutralize the electrical surface charge of the particles 62 relative to the attractive force of the oppositely charged layer 204 outside the suspension 60. Alternatively, the particles 62 may be disposed in a slurry. Alternatively or more particularly, a charge may be applied to particles having a charge opposite to that of layer 204.

During operation, layer 204 can electrostatically attract particles 62 to flow into pores 26 and can displace liquid medium 64 disposed in pores 26. Thus, particles 62 can define a wet-deposited powder of the type described above. The pores 26 can then be dried. It is recognized that in one embodiment, the force associated with the charge can fill the entire length of the pores 26 (as shown in Figure 20E). The charge can further cause particles 62 to accumulate within pores 26. In another embodiment, particles 62 can be deposited in the manner described above with respect to depositing step 50. Of course, as described above, depositing step 50 can be omitted. It should be understood that, regardless of whether the filling step is performed under the action of a pressure difference, centrifugal force, or electrostatic force, the particles 62 disposed in the hole 26, including one or both of the first particles 62a and the second particles 62b, may contact the inner surface of the substrate 20 extending from the first surface 22 to the second surface 22, so that after the filling step, the hole 26 is at least partially defined.

If stacking step 50 is performed, it should be understood that only one of inner layer 122a and inner layer 122b (see FIGS. 8A-8B ) enters hole 26 at outer surface 99 of substrate 20. The other of inner layer 122a and inner layer 122 may abut layer 204. Alternatively, layer 204 may be removed and the other of inner layer 122a and inner layer 122b may enter hole 26 at inner surface 97. Once stacking step 50 is completed, or if stacking step 50 is omitted, a final filling step may be performed alone or in combination with one or more subsequent filling steps. If performed, one or more subsequent filling steps and the final filling step may be performed in the manner described herein. It should be understood that layer 204 may define a redistribution layer (RDL) for sputtering, as will be described in more detail below. Alternatively, layer 204 may be removed, as shown in FIG. 20F. It is recognized that this method is intended for use with a large number of holes commonly found on substrate 20. Layer 204 may cover a plurality or all of holes 26, thereby drawing particles 62 into each hole 26 in the manner described herein.

As shown in FIG. 20G , a second charge 205 may be adjacent to the outer surface 99, which is the same charge as the particle 62. Thus, the second charge 205 may exert a force that drives the particle 62 along the outer surface 99. As described above, the particle 62 may be in suspension. Alternatively, the particle 62 may be dry. For example, the second charge may be a positive charge that repels the suspension 60 away from the second charge. The second charge may be applied at a location outside the array of holes 26 so that the second charge drives the suspension 60 to flow through the outer surface 99 and into the holes 26 in the manner described above.

In another embodiment, layer 204 may be provided as a sacrificial oxide layer, and the carrier layer may be disposed over the oxide layer. The redistribution layer may be applied to the outer surface 99 of the substrate 20, and the oxide may then be etched so that the redistribution layer may be applied to the inner surface 99 of the substrate 20.

Thus, it is recognized that particles 62 may be pushed into the holes by air pressure differentials, centrifugal forces, electrostatic forces, or a combination thereof. Additionally, it is recognized that one or more main fill operations may be performed. In some embodiments, a final fill step may be performed after one or more main fill operations. The average size of the particles during the final fill operation is less than the average size of the particles during the main fill operation. In one embodiment, the fill step may include filling the holes at a first side of the substrate 20 defining the first surface 22, flipping the substrate, and filling the holes at an opposite second side of the substrate defining the second surface 24. Alternatively, it is recognized that the first step of filling the substrate may include introducing a final fill into the holes on the first side of the substrate according to any of the fill steps described herein, such that the final fill accumulates at the second side of the substrate. Thus, the final fill may extend from the second surface of the substrate into the hole. Alternatively or more preferably, the first final fill may extend from the hole to the second surface in the manner described above, thereby defining the button after the hard pressing step. Next, the main fill may be introduced into the hole at the first side of the substrate according to any of the filling steps described herein, such that the main fill extends from the first final fill toward the first surface. Finally, the second final fill may be introduced into the hole at the first side of the substrate according to any of the filling steps described herein, such that the second final fill extends from the main fill toward the first surface of the substrate. Alternatively or more preferably, the first final fill may extend from the hole to the second surface in the manner described above, thereby defining the button after the hard pressing step.

Referring again to FIG. 3 , once the filling step or step 46 is completed to fill the holes 26 alone or in combination with one or more stacking steps 50, the particles 62 may be sintered in a sintering step 52. It is understood that the particles 62 may be dried prior to the sintering step 52. In particular, referring now to FIG. 14 , the substrate may be placed in an oven 164 for a period of time at a temperature sufficient to sinter the particles 62 and at a suitable pressure. For example, the pressure in the oven 164 may be atmospheric pressure. Alternatively, the oven 164 may define a vacuum. The oven may further include any suitable gas environment as desired. In one embodiment, the sintering process is substantially a non-densifying sintering process. It is recognized that densification during sintering may cause portions of adjacent particles 62 to flow toward each other, thereby causing the resulting conductive fill 35 to shrink.

Referring now to FIGS. 15A-15B , it is recognized that deformation of the particles 62 may occur during the substantially non-densification sintering step 52. However, the deformation is relatively minimized compared to the densification sintering. For example, FIG. 15A shows substantially non-densification, where a plurality of adjacent particles 62 contact each other and define respective geometric centers 159 that are separated from each other by a first distance D1. As shown in FIG. 15B , after the substantially non-densification sintering step, the geometric centers 159 of two adjacent particles 62 define a second distance D2 between their respective geometric centers. In one embodiment, the difference between the second distance D2 and the first distance D1 is no more than about 30% of the first distance. For example, the difference is no more than about 20% of the first distance. For example, the difference is no more than about 15% of the first distance. In another embodiment, the difference is no more than about 10% of the first distance. For example, in a particular embodiment, the difference is no more than about 5% of the first distance. In a particular embodiment, the first distance D1 may be substantially equal to the second distance D2.

It is recognized that sintering includes an initial stage, whereby a neck 145 extending between adjacent sintered grains is formed, thereby defining grain boundaries 149 at respective interfaces between adjacent sintered grains 62. It should be understood that the grains 62 can define a so-called "bulk nanostructure" powder. Each grain 62 can include an array of stacked nanograins. In one embodiment, each grain 62 can include at least one thousand or as many as one million nanograins. However, for example, when the average size of the grains is 0.22 microns, it is expected that the grains 62 can each include less than one thousand nanograins. During the initial stage of sintering, the nanograins that make up the grains 62 can expand or grow. When this occurs, the pores inside the particles 62 can move to the outer surface of the particles 62 and be removed. In the second or intermediate stage of sintering, the gaps 66 between adjacent particles 62 can shrink during the densification of the particles 62. However, the densification of the particles 62 can be adjusted by determining the average grain size in the original synthesized particles 62 of the suspension 60 described above. The densification of the particles 62 can be further adjusted by determining the bimodal distribution of the particles 62. For example, as described above with reference to Figures 7A to 7C, the particles 62 can, for example, define a unimodal distribution, a bimodal distribution, and a trimodal distribution. It is understood that the modal distribution of particles 62 does not affect the grain growth behavior of the nanocrystals within each particle 62. Quite the contrary, the multimodal distribution may affect the densification behavior of particle-particle interactions during sintering, such as necking.

It has been found that during the first stage of densification, smaller sized nanocrystals produce larger nanocrystal growth. It has been found that larger nanocrystal growth in the first stage of densification results in smaller densification of particles 62 during the second or intermediate stage of densification. In addition, a larger initial density of conductive particles 62 in the voids 26 prior to sintering may also produce smaller densified particles 62 during the second or intermediate stage of densification. It is recognized that the initial density of the trimodal distribution is greater than the initial density of the bimodal distribution. In addition, the initial density of the bimodal distribution is greater than the initial density of the unimodal distribution. Therefore, the initial density of the trimodal distribution of particles is greater than that of the unimodal distribution.

Therefore, to reduce densification during the second or intermediate stages of sintering, it may be desirable to reduce the size of the nanocrystallites forming the particles 62. Additionally, to reduce densification during the second or intermediate stages of sintering, it may be desirable to provide particles with a bimodal or trimodal distribution. However, it is recognized that particles may be sintered substantially non-densified in a unimodal distribution.

Without wishing to be bound by theory, it is believed that reducing the size of the nanocrystals alone or in combination with providing a bimodal particle or trimodal particle distribution can reduce the transition point of the total densification that can be achieved between the intermediate stage of sintering and the final stage of sintering. Unless otherwise stated, the ability of the particles 62 to densify during the intermediate stage of sintering can be reduced, so that the resulting sintered particles 62 are substantially non-densified. During the final stage of sintering, in addition to the growth achieved during the initial sintering stage, the nanocrystals can further grow, which can be a precursor to the closure of the pores within the particles 62. After sintering is complete, the end result is a connected metal network fill within the via that can extend from the first surface 22 to the second surface 24 without changing the coplanarity of the metallized via and the surrounding substrate 20 (see FIG. 2A ). In addition, the connected metal network fill can contact the substrate 20 at one or more or up to all locations of the via, at the first surface and at the second surface 24. The connected metal network fill can extend from the via to one or both of the first surface 22 and the second surface 24 of the substrate 20.

Thus, it should be understood that the method of regulating the densification of particles 62 during step 52 may include the step 46 of filling the pores with a bulk nanostructured conductive powder having particles, each particle comprising a stacked array of nanoparticles. The method may further include the step 52 of sintering the particles in the pores for a period of time and within a temperature range. The method may further include the step of determining at least one of the average grain size and the modal distribution prior to the filling step to determine the amount of densification during the sintering step. As described above, the filling step may include filling the pores with a suspension of particles in a liquid medium and draining the liquid medium from the pores prior to the sintering step 52.

As described above, most of the total volume of the particles in the pores 26 may be substantially non-densified and sintered as described above. In one embodiment, at least about 60% of the total volume of the particles in the pores 26 are substantially non-densified and sintered. In another embodiment, at least about 70% of the total volume of the particles in the pores 26 are substantially non-densified and sintered. In yet another embodiment, at least about 80% of the total volume of the particles in the pores 26 are substantially non-densified and sintered. In yet another embodiment, at least about 90% of the total volume of the particles in the pores 26 are substantially non-densified and sintered. For example, in one particular embodiment, at least about 95% of the total volume of particles in the pores 26 is substantially non-densified and sintered. More particularly, in one embodiment, about 100% of the total volume of particles in the pores 26 is substantially non-densified and sintered. It should be understood that at least a portion of the fill defined by the non-densified and sintered particles 62 in the pores 26 may contact the inner surface of the substrate 20 extending from the first surface 22 to the second surface 24 and at least partially define the pores.

The sintering step 52 may occur at a sintering temperature in the range of about 100°C to about 400°C. In one embodiment, the temperature may be in the range of about 200°C to about 400°C. For example, the temperature may be in the range of about 300°C to about 350°C. For example, the sintering temperature may be about 325°C.

The sintering step 52 may occur for any suitable duration within any of the above temperature ranges as desired to sinter the particles 62 without substantially densifying the particles 62 as described above. For example, the duration may be in the range of about 15 minutes to about 4 hours. In one embodiment, the duration may be in the range of about 30 minutes to about 2 hours. For example, the duration may be about 1 hour.

Advantageously, as described above, the particles 62 can be ductile and malleable. Thus, the particles 62 can have a mismatched coefficient of thermal expansion (CTE) relative to the substrate 20 without damaging the substrate 20 during sintering. In particular, for example, the malleability of the silver particles 62 allows for non-densified sintering while maintaining the structural integrity of the substrate. Thus, it is understood that no material is added to either of the suspensions 60a and 60b that is intended to bring the resulting CTE of the particles 62 closer to that of the substrate 20. Thus, the sintered particles 62 are free of residual material that is a product of the burned CTE matching agent. For example, each of the first and second suspensions 60 may be free of glass frits, or may be frit-free. Furthermore, in instances where the conductive material of the particles 62 is metal, the resulting vias 34 may define a single homogeneous metal from the first surface 22 to the second surface 24 of the substrate 20. For example, the first particles 62 and the second particles 62b may be the same metal. In one example, the same metal may be silver. In another example, the same metal may be copper.

Alternatively or more preferably, the sintering step 52 may include the step of applying a radio frequency (RF) current to the particles 62 sufficient to generate an eddy current that causes the particles 62 to sinter without being substantially densified.

It is recognized that the resulting via 34 contains substantially only conductive material as described above and air, except for any metal introduced into the hole during the sealing step as described above (if applicable). Moreover, as will now be described, the resulting via 34 can be airtight.

In particular, referring again to FIG. 3 , once the substrate 20 is sintered in step 52, the particles 62 may be subjected to a hard pressing step. Referring to FIGS. 21A to 21B , the hard pressing step 53 may be performed in a hard pressing machine 140. In particular, the hard pressing machine 140 may include first and second pressing surfaces 142 that may contact the substrate 20 at the same time and press toward the first surface 22 and the second surface 24 of the substrate 20. In particular, the first and second pressing surfaces 142 may be uniaxially movable toward each other and toward the respective first surface 22 and second surface 24. Therefore, the pressing step may be referred to as a uniaxial pressing step. The pressing surface 142 may contact the particles 62 extending from the first surface 22 and the second surface 24, which are also referred to as overfilled particles 62. As the pressing surfaces 142 continue toward each other and thus toward the substrate 20, the pressing surfaces 142 press the overfilled particles 62 against the first surface 22 and the second surface 24, respectively. Thus, the particles 62 may define an I-beam structure having a stem 144 extending to the first surface 22 and the second surface 24 within the hole 26, and an outer protrusion 146 pressing against the first surface 22 and the second surface 24, respectively. The outer protrusion 146 may be a flat outer protrusion 146 that is parallel to the first surface 22 and the second surface 24, respectively, of the substrate 20. In addition, the bump 146 may extend relative to the hole 26 and thus relative to the via 34 in a direction perpendicular to the hole 26 and thus relative to the via 34.

It is recognized that the bump 146, which artificially extends the hole 26 and, therefore, the via 34, beyond one or both of the first surface 22 and the second surface 24, can be formed without adding any additional layers to the substrate. For example, the bump 146 can be formed without adding a sacrificial layer, such as a dry film photoresist, onto one or both of the first surface 22 and the second surface 24 of the substrate 20, thereby artificially extending the hole 26 and, therefore, the via 34, beyond one or both of the first surface 22 and the second surface 24. In this regard, the filling step 46 can be performed without first adding a dry film photoresist onto the surface 22 and the surface 24. Thus, in one embodiment, no portion of the hole 26 or the via 34 is defined by a photoresist layer extending from either the first surface 22 or the second surface 24. Furthermore, the hole 26 and thus the via 34 may be filled with particles 62 without depositing a conductive layer (e.g., gold or titanium) over the first surface 22 and the second surface 24, thereby artificially extending the hole 26 beyond the first surface 22 and the second surface 24. Thus, in one embodiment, no portion of the hole is defined by a titanium layer or a gold layer extending from either the first surface 22 or the second surface 24.

Compressing the flat outer protrusion 146 against the first surface 22 and the second surface 24, respectively, can seal the end of the via 34 at both the surface 22 and the surface 24 of the substrate. In addition, it should be understood that at least some of the non-densified sintered particles 62 can contact the substrate at one or both of the first surface 22 and the second surface 24. Therefore, the via 34 can be airtight. Therefore, the conductive material of the sintered particles 62, and therefore the conductive material of the via 34, can be non-porous at each of the first surface 22 and the second surface 24. In addition, the interference between the flat outer end and the substrate 20 can resist or prevent the migration of the conductive fill 35 during operation. The pressing surface 142 can also apply a compressive force to at least some of the particles 62 inside the hole 26. Thus, at least some of the particles 62 may define a highly packed powder, thereby densifying the powder. Thus, the method 40 may also include a step of non-sintering densification of the conductive material in the hole 26. While the vias described herein provide improved electrical performance, and without wishing to be bound by theory, it is believed that further densification of the conductive material may further improve certain aspects of the electrical performance of the resulting vias.

Each of the first and second hard planar pressing surfaces 142 may be defined by respective first and second pressing members 148. The pressing members 148 may be defined by glass or any suitable substitute having suitable hardness to compress the particles 62 without deformation. In addition, the pressing surfaces 142 may be flat before the pressing surfaces contact the particles 62 and after the hard pressing step is completed, because they press the particles 62 against the substrate 20. In particular, the planar pressing surfaces 142 may be parallel to the first and second surfaces 22, 24 of the substrate 20, respectively. The pressing members 148 may be disposed within a housing of the type described above with reference to FIGS. 8A-8B. The housing may be made of mylar or any suitable substitute material. The substrate 20 can be placed in the housing between the opposing pressed members 148 so that the first surface 22 faces the first pressed member and the second surface 24 faces the other pressed member 148. The pressed members 148 can be pulled toward each other to press the particles 62 in the manner described above. The hard pressing step can be performed under vacuum in the housing, or can be performed under normal atmospheric pressure. In addition, the hard pressing step can be a cold hard pressing step at room temperature, or a warm hard pressing step at a temperature above room temperature (such as about 120°C to about 250°C). In addition, the hard pressing step can be performed under vacuum. Alternatively, the hard pressing step can be performed in atmospheric pressure.

It is recognized that the hard pressing step may be performed after the sintering step 52 as described above. Alternatively, it is contemplated that the hard pressing step may alternatively be performed before the sintering step 52. Furthermore, the hard pressing step may be performed alone or in conjunction with one or more stacking steps 50. Alternatively, the hard pressing step may be performed in method 40 without performing the stacking step 50. Alternatively, method 40 may include one or more stacking steps 50 without performing the hard pressing step. When the method includes a hard pressing step but does not include a stacking step 50, a portion of the fill 35 may include particles 62 of the same density as particles 62 filled during the fill step 46.

In some embodiments, method 40 may include a step 54 of sealing the via. In one embodiment, the sealing step may be performed by surface processing the particles 62.

In particular, as shown in FIGS. 16A to 16B , the facing outer surface of the sintered particles 62 at each of the first surface 22 and the second surface 24 may be pressed by a rod 166. The hardness of the rod 166 may be greater than the hardness of the conductive material and less than the hardness of the substrate. For example, its hardness may be greater than silver or copper and less than glass. Therefore, the rod 166 may cause the sintered particles 62 at each of the first surface 22 and the second surface 24 to change its shape without damaging the integrity of the substrate. In particular, the rod 166 may change the shape of the overfilled portion of the sintered particles at each of the first surface and the second surface, thereby sealing the opening of the via at one or more interfaces between the conductive material and the substrate 20. For example, the interfaces may be disposed at the first surface 22 and the second surface 24 of the substrate, respectively. In one example, the rod 166 can be made of nickel. It is recognized that the sintered particles 62 at the first surface 22 and the second surface 24 can be defined by the final fill described above. Therefore, it can be said that the final fill defines the end cap 161 of the via 34. In addition, the end cap can hermetically seal the via.

The rod 166 may be pressed into the final fill and moved in the final fill, thereby smearing the particles along the outer surface of the glass before the coating and/or redistribution layer is applied. The smearing step may cause the gaps in the final fill to be blocked and become non-porous at the outer surface. The ductility of the silver or copper final fill is particularly suitable for this purpose. In addition, the final fill may be pressed at the interface with the opening of the hole 26 at each of the first surface 22 and the second surface 24 of the substrate. In one embodiment, the sealing step may be performed in a vacuum so that both the substrate 20 and the rod 166 can be placed in a vacuum environment during the surface processing of the conductive material. It should be understood that the step of surface processing the conductive material can further flatten the conductive material. Alternatively or more preferably, the sealing step may include the step of applying vacuum deposition of a conductive material to the conductive material at the end of the via hole, thereby achieving one or both of the following: 1) plugging a plurality of gaps, and 2) filling the opening at the interface between the conductive material and the substrate 20. Alternatively or more preferably, the sealing step may include vacuum melting the conductive material, thereby achieving one or both of the following: 1) plugging a plurality of gaps, and 2) filling the opening at the interface between the conductive material and the substrate 20.

The result is a hermetic via that can have a hermeticity of less than about ^10-7 . For example, the hermeticity can be less than about ^10-8 . For example, the hermeticity can be less than about ^10-9 . For example, the hermeticity can be less than about ^10-10 . For example, the hermeticity can be less than about ^10-11 . Alternatively, the coating step can be omitted and the coating can be applied and/or the redistribution layer can be applied without smearing particles along the outer surface of the glass.

However, it is recognized that hard pressing step 53 and subsequent steps may replace sealing step 54. Therefore, method 40 may include hard pressing step 53 and omit sealing step 54. Alternatively, method 40 may include sealing step 54 and omit hard pressing step 53. Still alternatively, it is contemplated that the method may include both sealing step 54 and hard pressing step 53. Hard pressing step 53 may be performed before sealing step 54. Alternatively, hard pressing step 53 may be performed after sealing step 54. As shown in FIGS. 16A-16B , it is understood that sealing step 54 may seal the ends of via 34 at first and second sides of the substrate, the first and second sides defining first surface 22 and second surface 24, respectively. Thus, via 34 may be airtight. Thus, the conductive material of the sintered particles 62, and therefore the conductive material of the vias 34, can be non-porous at each of the first surface 22 and the second surface 24. In particular, the rod can apply the particles along the outer surface of the glass.

Alternatively, as described above, the sealing step 54 may be omitted in the method 40. Alternatively, after the sintering step 52, a conductive conformal coating may be applied to the ends of the vias. In this regard, the conformal coating may be applied after the hard pressing step 53. Alternatively, the conformal coating may be applied before the hard pressing step 53 is performed. Alternatively, when the method 40 does not include the hard pressing step 53, the conformal coating may be applied. For example, the conformal coating may be applied to a fill that is substantially planar with the surfaces 22 and 24 of the substrate 20. The conformal coating may be applied to the ends of the vias using any deposition technique as desired. In one embodiment, if a final fill step is performed, the conformal coating may be applied to the final fill particles 62 at the ends of the vias. Alternatively, a conformal coating may be applied to the bulk filled particles 62 at the ends of the vias. In one embodiment, the conformal coating may be electroplated to the particles 62. Alternatively, the conformal coating may be deposited by variations of techniques such as evaporation, PVD, or chemical vapor deposition (CVD) such as atomic layer deposition (ALD). Still alternatively, the conformal coating may be applied during a chemical plating step. It is recognized that the conformal coating may occupy, and in some cases, fill, the gaps defined between adjacent particles as described above.

The ends of the vias may then be further sealed to the first and second surfaces 22 and 24 of the substrate 20. For example, the ends of the vias that are substantially planar and/or flush with the first and second surfaces 22 and 24 of the substrate may be sealed. Alternatively, the flat outer ends or bumps 146 (see FIG. 21B ) may be further sealed to the surfaces 22 and 24 of the substrate 20. In one embodiment, the sealing step may be performed under vacuum to prevent gaseous contaminants from entering the vias. For example, the sealing step may prevent gaseous contaminants from entering the gaps between adjacent particles. Alternatively or more preferably, the sealing step may prevent gaseous contaminants from entering the holes of the conductive material.

Finally, a redistribution layer (RDL) may be applied to the substrate 20 as desired. For example, referring now to FIGS. 17-18B , a redistribution layer 37 may be applied to one or both of the first and second surfaces 22, 24 of the substrate 20 to electrically communicate with the vias 34 and thus with the conductive material in the vias. For example, a sputtering layer may be applied, and a conductive metal coating applied over the sputtering layer in a conventional manner. As shown in FIG. 18A , a trench 170 may alternatively be formed on at least one of the first and second surfaces 22, 24. It should be understood that the trench 170 may be open to the hole 26 and the via. Thus, methods used to force particles into holes, such as vacuum, centrifugal force, and electrostatic force, may also be used to force particles into the trench. The particles may be dried, stacked and sintered as described above to define a redistribution layer 37.

Referring again to FIGS. 1A-4 , the resulting vias define the conductive material of particles 62, which may be metal, and voids defined by spaces between adjacent particles in the solid material, which may also be referred to as pores, defined by the spaces not filled during method 40 as described above. If a conformal coating is applied as described above, it may be further defined by the resulting vias. The conductive material of particles 62 may define a support matrix designed with internal air gaps or pores that are arranged along a majority of the length of the hole from the first surface 22 to the second surface 24. The sintered conductive material defines a conductive path from the first surface to the second surface. In certain embodiments, the pores may define at least 25% to as much as 75% of the total volume of the vias. However, it is understood that in other embodiments, the pores may define less than 25% of the total volume of the via. In addition, the pores may be substantially uniformly arranged along a majority of the length of the via. The resulting via may define a nonlinear conductive path from the first surface 22 to the second surface 24. The mesh substrate may define at least one airflow path extending from a first end of the mesh substrate to a second end of the mesh substrate. The first end and the second end may be defined by non-porous end caps.

Thus, the mesh matrix may include a conductive material including sintered and surface processed particles that define a continuous conductive interconnect network for a majority of the length of the via from the first surface 22 to the second surface 24, wherein the conductive material is not fused to the substrate in the via 26, and wherein the conductive material defines a conductive path along the entire length of the via.

The conductive fill 35 of the via 34 may be defined by a matrix of a plurality of conductive particles which are stacked and subsequently sintered to bond adjacent particles to each other. As will be understood from the following, the conductive path may be defined in any shape as desired. It is contemplated that at least a portion of the conductive path is non-linear.

Additionally, the conductive fill may include silver or copper particles, which may be mixed with other conductive materials to produce a particle distribution whereby the conductive other conductive materials may occupy some of the gaps. Other conductive materials may include one or more conductive polymers, conductive metals, conductive ceramics, conductive compounds, and the like, such as graphene, conductive carbides, and intermetallic composites. Alternatively or more, a supercritical fluid has extremely low surface tension and may be used to deposit metal. It is envisioned that it may at least partially fill the gaps in the vias after the sintering step. The supercritical fluid carries the metal with low surface tension, so the metal can enter narrow spaces. Thus, the metal may be deposited in the holes 26. Another option is to deposit the nanoparticles supercritically in the pores, thereby occupying at least a portion of the interstitial space.

It is recognized that a method of cleaning the substrate 20 can be provided. For example, residual suspension can be removed from the first surface 22 and the second surface 24 as needed, including before the accumulation step, before the sintering step, before the surface processing step, and after the surface processing step. For example, the residual suspension can be removed using a suitable rod (such as a Teflon rod). Alternatively or more, alcohols such as IPA and soft semi-abrasives can clean the residual powder.

FIG. 22 shows an overview of an exemplary assembly 500 of the assemblies discussed above and throughout the text according to one aspect of the systems and methods disclosed herein. In this embodiment, multiple devices may be mounted to the interposer 21, with additional devices at the bottom. The interposer 21 may have portions of glass vias or through silicon vias of the type described above. Additional interposers or other types of layers are shown in green as part of the assembly structure of the devices. Such layers may be used for additional interconnects. Some interconnects may be made on the top or bottom of the interposer 21. In one embodiment, a dedicated integrated circuit may be mounted to the substrate 20, thereby at least partially defining the die package. In another embodiment, a silicon photonics ship may be mounted on the substrate so as to be optically connected to the substrate 20. In yet another embodiment, the transceiver may be mounted on a glass substrate so as to be electrically connected to the conductive material.

It should be understood that the illustration and discussion of the embodiments shown in the drawings are for illustrative purposes only and should not be construed as limiting the present disclosure. A person of ordinary skill in the art to which the present invention pertains will understand that the present disclosure contemplates various specific embodiments. Furthermore, it should be understood that the concepts described above in conjunction with the above specific embodiments may be used alone or in conjunction with any other specific embodiments described above. It should be further understood that the various alternative specific embodiments described above with respect to one illustrated specific embodiment may apply to all specific embodiments as described herein, unless otherwise stated.

26: Holes

65: First filling

67: Powder accumulation/filling

77: Highly stacked powder

130: Stacking main body filling

132: Final accumulation of powder

134: Final filling

Claims (72)

A method for manufacturing an electrical component comprises the following steps: performing an application step of applying an antioxidant to a plurality of copper particles; performing an introduction step of introducing a suspension of the copper particles in a liquid medium into a hole extending in a transverse direction from a first surface of a glass substrate through the glass substrate to a second surface of the glass substrate opposite to the first surface; performing an emptying step of emptying the liquid medium from the hole; performing a sintering step of sintering the copper particles to define a conductive matrix having a first end and a second end opposite to each other in the transverse direction, wherein the conductive matrix defines a conductive path from the first end to the second end. The method of claim 1, wherein the applying step is performed before the introducing step. A method as claimed in any one of claims 1 to 2, wherein the applying step comprises coating the copper particles with an anti-oxidation coating, the anti-oxidation coating preventing the copper particles from being exposed to oxygen. A method as claimed in claim 3, wherein the antioxidant coating comprises an anti-agglomeration coating. The method of claim 3, wherein the antioxidant coating comprises oleic acid. The method of claim 3, wherein the antioxidant coating comprises stearic acid. The method of claim 3, wherein the antioxidant coating comprises capric acid. A method as in any one of claims 1 to 2, wherein the applying step comprises coating the copper particles with an anti-oxidation coating that reduces oxidation formed on the copper particles. A method as claimed in claim 8, wherein the antioxidant comprises a getter material. The method of claim 8, wherein the antioxidant comprises titanium. The method of claim 8, wherein the antioxidant comprises carbon. The method of claim 8, wherein the antioxidant comprises neoalkoxy titanate. A method as claimed in any one of claims 1 to 2, wherein the evacuation step removes a certain amount of copper oxide from the pores. The method of claim 13, wherein the evacuating step comprises subjecting the suspension to a vacuum force. The method of claim 13, wherein the emptying step comprises subjecting the suspension to centrifugal force. A method as claimed in any one of claims 1 to 2, wherein the sintering step removes a certain amount of copper oxide from the hole. The method of claim 16, wherein the sintering step removes copper oxide produced by oxidation of the copper particles. A method as claimed in any one of claims 1 to 2, wherein the suspension is free of melt. A method for manufacturing an electrical component comprises the following steps: performing an introducing step of introducing a suspension of copper particles in a liquid medium into a hole extending in a transverse direction from a first surface of a glass substrate through the glass substrate to a second surface of the glass substrate opposite to the first surface; performing an emptying step of emptying the liquid medium from the hole; and performing a sintering step of sintering the copper particles substantially non-densified to define a conductive matrix having a first end and a second end opposite to each other in the transverse direction, wherein the conductive matrix defines a conductive path from the first end to the second end, wherein the sintering step substantially removes copper oxide from the copper particles. The method of claim 19 further comprises the step of applying an antioxidant to the copper particles. The method of claim 20, wherein the antioxidant comprises a getter material. The method of claim 20, wherein the antioxidant comprises titanium. The method of claim 20, wherein the antioxidant comprises carbon. The method of claim 20, wherein the antioxidant comprises titanium neoalkoxy ester. The method of claim 20, wherein the antioxidant comprises an anti-agglomerant. The method of claim 25, wherein the anti-agglomerating agent comprises oleic acid. The method of claim 20, wherein the antioxidant comprises stearic acid. The method of claim 20, wherein the antioxidant comprises capric acid. A method for manufacturing an electrical component, comprising the steps of: applying an anti-agglomeration agent to a plurality of copper particles; introducing a suspension of the plurality of copper particles in a liquid medium into a hole extending in a transverse direction from a first surface of a glass substrate through the glass substrate to a second surface of the glass substrate opposite to the first surface; draining the liquid medium from the hole; and sintering the copper particles to define a conductive matrix having a first end and a second end opposite to each other in the transverse direction, wherein the conductive matrix defines a conductive path from the first end to the second end, wherein the sintering step substantially removes copper oxide from the copper particles. The method of claim 29, wherein the anti-agglomerating agent is configured as an anti-agglomerating coating comprising oleic acid. The method of claim 29, wherein the anti-agglomeration agent is configured as an anti-agglomeration coating comprising stearic acid. The method of claim 29, wherein the anti-agglomeration agent is configured as an anti-agglomeration coating comprising capric acid. A method as claimed in any one of claims 29 to 32, wherein the anti-agglomeration agent comprises sonication applied to the particles during sonication of the suspension. A method for manufacturing an electrical component, comprising the steps of: performing an introducing step of introducing at least one suspension into a hole extending from a first surface of a glass substrate through the glass substrate to a second surface of the glass substrate, wherein the at least one suspension comprises first bimodal particles and second bimodal particles and a liquid medium, wherein the first bimodal particles and the second bimodal particles comprise different metals, and the melting point of the second bimodal metals is lower than The melting point of the first bimodal metals; performing an emptying step of emptying the liquid medium from the hole so that the second bimodal particles are disposed in the gap defined by the first bimodal particles; and performing a sintering step of sintering the first bimodal particles and the second bimodal particles in the hole, thereby defining a conductive matrix having a first end and a second end opposite to each other in a transverse direction, wherein the conductive matrix defines a conductive path from the first end to the second end. The method of claim 34, wherein the first bimodal particles comprise silver or copper. A method as claimed in any one of claims 34 to 35, wherein the second bimodal particles comprise indium. A method as claimed in any one of claims 34 to 35, wherein the second bimodal particles comprise tin. The method of any of claims 34 to 35, wherein the first bimodal particles have a first bimodal average particle size, the second bimodal particles have a second bimodal average particle size, and the first bimodal average particle size and the second bimodal average particle size are defined in a ratio ranging from about 4:1 to about 10:1. The method of claim 38, wherein the ratio is approximately 7:1. A method as in any of claims 34 to 35, wherein the sintering step alloys the second bimodal particles with the first bimodal particles. The method of claim 40, wherein the sintering step causes the bimodal particles to define a porous through-path from the first end to the second end. The method of claim 41, further comprising the step of adjusting the porosity of the matrix at least in part by controlling at least one of the volume and average size of the second bimodal particles relative to the first bimodal particles. The method of any of claims 34 to 35, wherein the second bimodal particles are present in an amount ranging from 5% of the pore volume to about 20% of the pore volume. The method of claim 43, wherein the volume of the second bimodal particles present is about 10% relative to the volume of the pores. A method as claimed in any one of claims 34 to 35, wherein the first bimodal particles and the second bimodal particles comprise bulk fill. A method as claimed in any one of claims 34 to 35, wherein the first bimodal particles and the second bimodal particles comprise a final fill. The method of claim 46 further comprises the steps of introducing a main body fill suspension into the hole and draining the liquid medium from the main body fill before performing the introducing and draining steps for the final filling. A method as claimed in any one of claims 34 to 35, wherein the first bimodal particles and the second bimodal particles comprise first trimodal particles and second trimodal particles, and the at least one suspension further comprises third trimodal particles. The method of claim 48, wherein the third trimodal particles contain silver or copper. The method of claim 48, wherein the third trimodal particles contain indium. The method of claim 48, wherein the third trimodal particles contain tin. The method of claim 48, wherein the second trimodal particles have an average particle size, the third trimodal particles have an average particle size, and the average particle size of the second trimodal particles and the average particle size of the third trimodal particles define a ratio ranging from about 4:1 to about 10:1. The method of claim 52, wherein the ratio is approximately 7:1. A method as in any one of claims 34 to 35, further comprising the step of performing a final filling operation. The method of claim 34 further comprises the step of applying a redistribution layer to one or both of the first surface and the second surface. The method of claim 55 further comprises the step of performing a final filling operation. The method of claim 55, wherein the subsequent introduction step is implemented without using a final fill. The method of claim 55, further comprising the step of applying a sacrificial layer to at least one of the first surface and the second surface, the sacrificial layer having holes aligned with the holes so that the particles extend into the holes after the evacuation step. The method of claim 58 further comprises a step of removing the sacrificial layer. The method of any one of claims 58 to 59 further comprises a step of compressing the particles before the sintering step. The method of any one of claims 58 to 59 further comprises the step of applying a conductive layer to at least one of the first surface and the second surface before the introducing step. The method of claim 61, wherein the conductive layer comprises titanium. The method of claim 61, wherein the applying step further comprises: coating at least one outer portion of the inner surface of the hole with the conductive layer. The method of claim 63 further comprises a step of compressing the particles before the sintering step. A method for manufacturing an electrical component comprises the following steps: introducing at least one suspension into a hole, the hole extending in a lateral direction from a first surface of a glass substrate through the glass substrate to a second surface of the glass substrate opposite to the first surface, wherein the at least one suspension comprises first bimodal particles, second bimodal particles and a liquid medium; and draining the suspension from the hole. A step of draining the liquid medium so that the second bimodal particles are disposed in the gap defined by the first bimodal particles; and a step of sintering the first bimodal particles and the second bimodal particles in the hole, thereby defining a conductive matrix having a first end and a second end opposite to each other along the transverse direction, wherein the conductive matrix defines a conductive path from the first end to the second end. The method of claim 65, wherein the first bimodal particles have a first bimodal average particle size, the second bimodal particles have a second bimodal average particle size, and the first bimodal average particle size and the second bimodal average particle size are defined in a ratio ranging from about 4:1 to about 10:1. The method of claim 66, wherein the ratio is approximately 7:1. The method of any of claims 65 to 67, wherein the second bimodal particles are present in an amount ranging from 5% of the pore volume to about 20% of the pore volume. The method of claim 68, wherein the volume of the second bimodal particles present is about 10% relative to the volume of the pores. A method as claimed in any one of claims 66 to 67, wherein the first bimodal particles and the second bimodal particles comprise first trimodal particles and second trimodal particles, and the at least one suspension further comprises third trimodal particles. The method of claim 70, wherein the second trimodal particles have an average particle size, the third trimodal particles have an average particle size, and the average particle size of the second trimodal particles and the average particle size of the third trimodal particles define a ratio ranging from about 4:1 to about 10:1. The method of claim 71, wherein the ratio is approximately 7:1.