JP2010238615A - Conductive fine particles, anisotropic conductive material, and connection structure - Google Patents

Abstract

Disclosed are conductive fine particles capable of preventing deformation during storage and reducing mounting defects, an anisotropic conductive material using the conductive fine particles, and a connection structure.
A conductive fine particle having a low melting point metal layer formed on the surface of a substrate fine particle, and the low melting point metal layer has a peak intensity of a first preferred orientation when XRD measurement is performed. On the other hand, conductive fine particles containing tin having 6 or more crystal orientations having a peak intensity with an intensity ratio of 30% or more.
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Description

The present invention relates to conductive fine particles capable of preventing deformation during storage and reducing mounting defects, an anisotropic conductive material using the conductive fine particles, and a connection structure.

Conventionally, in an electronic circuit board, ICs and LSIs are connected by soldering electrodes to a printed circuit board. However, soldering cannot efficiently connect the printed circuit board to the IC or LSI. In addition, it is difficult to improve the mounting density of ICs and LSIs by soldering.
In order to solve this problem, a BGA (ball grid array) has been developed in which the solder is made into a spherical shape, so-called “solder balls” that connect the IC or LSI to the substrate. According to this technique, an electronic circuit that achieves both high productivity and high connection reliability can be configured by melting a solder ball mounted on a chip or a substrate at a high temperature and connecting the substrate and the chip.

However, in recent years, since the number of substrates has been increased and multilayer substrates are easily affected by the use environment, there has been a problem that distortion and expansion / contraction occur in the substrates and disconnection occurs in the connection portion between the substrates.

For such a problem, Patent Document 1 discloses that a metal layer containing a highly conductive metal is formed on the surface of resin fine particles, and further, a low melting point metal made of a metal such as tin on the surface of the metal layer. A conductive fine particle in which a layer (solder layer) is formed is disclosed. If such conductive fine particles are used, the stress applied to the conductive fine particles by the flexible resin fine particles can be relaxed, and the low melting point metal layer can be formed on the outermost surface to easily conduct conductive connection between the electrodes. it can.

However, the low melting point metal layer formed on the surface of the conductive fine particles is composed of a metal having low hardness and high ductility. The low melting point metal layer may be deformed by the contact, and the sphericity of the conductive fine particles may be lowered. As a result, there is a problem in that the ball mounter is attracted in the mounting process, resulting in a mounting defect.

JP 2001-220691 A

The present invention provides conductive fine particles capable of preventing deformation during storage and reducing defective mounting, an anisotropic conductive material using the conductive fine particles, and a connection structure. With the goal.

The present invention is a conductive fine particle having a low melting point metal layer formed on the surface of a substrate fine particle, and the low melting point metal layer has a peak intensity of the first preferred orientation when XRD measurement is performed. On the other hand, it is a conductive fine particle containing tin having 6 or more crystal orientations having a peak intensity with an intensity ratio of 30% or more.
The present invention is described in detail below.

The conductive fine particles of the present invention are conductive fine particles in which a low melting point metal layer is formed on the surface of the substrate fine particles, and the low melting point metal layer is first preferentially oriented when XRD measurement is performed. It contains tin having 6 or more crystal orientations having a peak intensity of 30% or more with respect to the peak intensity.

The substrate fine particles are not particularly limited, and examples thereof include resin fine particles, inorganic fine particles, organic-inorganic hybrid fine particles, and metal fine particles. As the substrate fine particles, resin fine particles are particularly preferable.

The resin fine particles are not particularly limited, and include, for example, polyolefin resin, acrylic resin, polyalkylene terephthalate resin, polysulfone resin, polycarbonate resin, polyamide resin, phenol formaldehyde resin, melamine formaldehyde resin, benzoguanamine formaldehyde resin, urea formaldehyde resin, and the like. Resin fine particles.
The polyolefin resin is not particularly limited, and examples thereof include polyethylene resin, polypropylene resin, polystyrene resin, polyisobutylene resin, and polybutadiene resin. The acrylic resin is not particularly limited, and examples thereof include polymethyl methacrylate resin and polymethyl acrylate resin. These resins may be used alone or in combination of two or more.

The method for producing the resin fine particles is not particularly limited, and examples thereof include a polymerization method, a method using a polymer protective agent, and a method using a surfactant.
The polymerization method is not particularly limited, and examples thereof include emulsion polymerization, suspension polymerization, seed polymerization, dispersion polymerization, and dispersion seed polymerization.

The inorganic fine particles are not particularly limited, and examples thereof include fine particles composed of metal oxides such as silica and alumina. The organic-inorganic hybrid fine particles are not particularly limited, and examples thereof include hybrid fine particles containing an acrylic polymer in an organosiloxane skeleton.
The metal fine particles are not particularly limited, and examples thereof include fine particles made of metals such as aluminum, copper, nickel, iron, gold, and silver. Of these, copper fine particles are preferred. The copper fine particles may be copper fine particles formed substantially only of copper metal, or may be copper fine particles containing copper metal. In addition, when the said base material microparticles | fine-particles are copper microparticles | fine-particles, it is not necessary to form the conductive layer mentioned later.

When the substrate fine particles are resin fine particles, the preferred lower limit of the 10% K value of the fine resin particles is 1000 MPa, and the preferred upper limit is 15000 MPa. If the 10% K value is less than 1000 MPa, the resin fine particles may be destroyed when the resin fine particles are compressed and deformed. When the 10% K value exceeds 15000 MPa, the conductive fine particles may damage the electrode. The more preferable lower limit of the 10% K value is 2000 MPa, and the more preferable upper limit is 10,000 MPa.

The 10% K value is obtained by using a micro compression tester (for example, “PCT-200” manufactured by Shimadzu Corporation), and using a smooth indenter end face of a diamond cylinder having a diameter of 50 μm and a compression speed of 2.6 mN / The compression displacement (mm) when compressed under conditions of seconds and a maximum test load of 10 g can be measured and determined by the following equation.
K value ^{(N / mm 2) = (} 3 / √2) · F · S -3/2 · R -1/2
F: Load value at 10% compression deformation of resin fine particles (N)
S: Compression displacement (mm) in 10% compression deformation of resin fine particles
R: radius of resin fine particles (mm)

The average particle diameter of the substrate fine particles is not particularly limited, but a preferable lower limit is 1 μm and a preferable upper limit is 2000 μm. When the average particle diameter of the above-mentioned substrate fine particles is less than 1 μm, the substrate fine particles are likely to aggregate. When conductive fine particles in which a low melting point metal layer is formed on the surface of the aggregated substrate fine particles are used, a gap between adjacent electrodes can be obtained. May cause a short circuit. When the average particle diameter of the base material fine particles exceeds 2000 μm, the range suitable for connection between electrodes such as a circuit board may be exceeded. The more preferable lower limit of the average particle diameter of the substrate fine particles is 3 μm, and the more preferable upper limit is 1000 μm.
The average particle size of the above-mentioned substrate fine particles is obtained by measuring the particle size of 50 randomly selected substrate fine particles using an optical microscope or an electron microscope and arithmetically averaging the measured particle sizes. Can do.

The coefficient of variation of the average particle diameter of the substrate fine particles is not particularly limited, but is preferably 10% or less. If the coefficient of variation exceeds 10%, the connection reliability of the conductive fine particles may be lowered. The coefficient of variation is a numerical value obtained by dividing the standard deviation obtained from the particle size distribution by the average particle size and expressed as a percentage (%).

The shape of the substrate fine particles is not particularly limited as long as the distance between the opposing electrodes can be maintained, but a true spherical shape is preferable. Further, the surface of the substrate fine particles may be smooth or may have a protrusion.

When the XRD measurement is performed, the low-melting-point metal layer contains tin having 6 or more crystal orientations having a peak intensity with a strength ratio of 30% or more with respect to the peak intensity of the first preferential orientation.
In the present invention, “XRD measurement” refers to a crystal analysis method by X-ray diffraction measurement. Specifically, X-rays are incident on the crystal to be measured, and the intensity of Bragg reflection at each crystal orientation is measured. Thereby, the existence ratio of each crystal orientation is obtained from the kind of crystal orientation existing in the crystal and its intensity ratio.
The “first preferred orientation” refers to a crystal orientation having the highest peak intensity when 2θ is within a range of 30 to 90 ° in the XRD measurement. The “intensity ratio” means the intensity ratio when the peak intensity of the crystal orientation defined as the first preferred orientation is 100%. The number of “crystal orientations having a peak intensity with an intensity ratio of 30% or more with respect to the peak intensity of the first preferential orientation” includes the first preferential orientation itself.

The tin has 6 or more crystal orientations having a peak intensity with an intensity ratio of 30% or more with respect to the peak intensity of the first preferred orientation defined as described above. Having 6 or more crystal orientations in which the intensity ratio is 30% or more means that the tin has a large orientation. By containing such tin, the hardness of the low-melting-point metal layer increases and the ductility decreases, so that the low-melting-point metal is rubbed by rubbing between conductive fine particles during storage and contact with equipment during mounting. It is possible to prevent the layer from being deformed, and as a result, it is possible to reduce inconveniences in the mounting process, such as poor adhesion of the ball mounter.
When the crystal orientation having a peak intensity with a strength ratio of 30% or more is less than 6, the low melting point metal layer has low hardness and high ductility, leading to poor mounting. In the present invention, it is more preferable that the intensity ratio has a crystal orientation having a peak intensity of 30% or more, and more preferably 10 or less.

The low melting point metal layer may contain an element other than the tin. Moreover, it is good also as an alloy of the said tin and another metal. The said alloy is not specifically limited, For example, a tin-copper alloy, a tin-silver alloy, a tin-bismuth alloy, a tin-zinc alloy, a tin-indium alloy etc. are mentioned. Among these, a tin-silver alloy is preferable because the melting point of the low melting point metal layer to be formed can be lowered.

Further, in order to improve the bonding strength between the low-melting-point metal layer and the electrode, the low-melting-point metal layer includes nickel, antimony, aluminum, iron, gold, titanium, phosphorus, germanium, tellurium, gallium, cobalt, manganese, A metal such as chromium, molybdenum, palladium, or indium may be contained. Especially, since it is excellent in the effect which improves the joining strength of the said low melting metal layer and an electrode, it is suitable to make the said low melting metal fine particle contain nickel, antimony, and aluminum.
The content of the metal in the total of metals contained in the low melting point metal layer is not particularly limited, but a preferred lower limit is 0.0001% by weight and a preferred upper limit is 2% by weight. When the content of the metal is less than 0.0001% by weight, the bonding strength between the low melting point metal layer and the electrode may not be sufficiently obtained. If the metal content exceeds 2% by weight, the melting point of the conductive fine particles may change.

The tin content in the low melting point metal layer is preferably 40% by weight or more. When the content is less than 40% by weight, the effects of the present invention cannot be sufficiently obtained, and mounting defects may be caused. The content of tin in the low melting point metal layer means the ratio of tin to the total of elements contained in the low melting point metal layer, and the tin content of the low melting point metal layer is the high frequency inductively coupled plasma. It can be measured using an emission spectroscopic analyzer (“ICP-AES” manufactured by Horiba, Ltd.), a fluorescent X-ray analyzer (“EDX-800HS” manufactured by Shimadzu).

Although the thickness of the said low melting metal layer is not specifically limited, A preferable minimum is 0.1 micrometer and a preferable upper limit is 200 micrometers. When the thickness of the low-melting-point metal layer is less than 0.1 μm, it may not be able to be sufficiently bonded to the electrode even when reflowed and melted. When the thickness of the low-melting-point metal layer exceeds 200 μm, Aggregation tends to occur when the melting point metal layer is formed, and the aggregated conductive fine particles may cause a short circuit between adjacent electrodes. The minimum with more preferable thickness of the said low melting metal layer is 0.2 micrometer, and a more preferable upper limit is 50 micrometers.
The thickness of the low melting point metal layer is a thickness obtained by observing and measuring a cross section of 10 randomly selected conductive fine particles with a scanning electron microscope (SEM) and arithmetically averaging the measured values. .

The low melting point metal layer may be formed directly on the surface of the substrate fine particles. In the low melting point metal layer, a conductive layer (underlying metal layer) may be further formed between the low melting point metal layer and the base particle.
The metal forming the conductive layer is not particularly limited, and examples thereof include gold, silver, copper, zinc, iron, lead, tin, aluminum, cobalt, indium, nickel, chromium, antimony, bismuth, germanium, and cadmium. . Especially, since it is excellent in electroconductivity, it is preferable that the metal which forms the said conductive layer is gold, copper, or nickel.

The method for forming the conductive layer on the surface of the substrate fine particles is not particularly limited, and examples thereof include an electroless plating method, an electrolytic plating method, a vacuum deposition method, an ion plating method, and an ion sputtering method.

Although the thickness of the said conductive layer is not specifically limited, A preferable minimum is 0.1 micrometer and a preferable upper limit is 100 micrometers. If the thickness of the conductive layer is less than 0.1 μm, sufficient conductivity may not be obtained. When the thickness of the conductive layer exceeds 100 μm, the flexibility of the conductive fine particles may be lowered. A more preferable lower limit of the thickness of the conductive layer is 0.2 μm, and a more preferable upper limit is 50 μm.
The thickness of the conductive layer is a thickness obtained by observing and measuring a section of 10 randomly selected conductive fine particles with a scanning electron microscope (SEM) and arithmetically averaging them.

The method for producing conductive fine particles of the present invention is not particularly limited as long as it is a method for obtaining tin as described above. For example, the low-melting-point metal fine particles containing tin are brought into contact with the base fine particles, and shear compression is performed. It can be manufactured by a method having a step of forming a low melting point metal layer on the substrate fine particles by melting the low melting point metal fine particles.

Specifically, for example, a method using a theta composer (manufactured by Tokuju Kogakusha Co., Ltd.) can be mentioned. The theta composer includes a vessel having an elliptical cavity, and a rotor that is separately rotated on the same axis as the vessel in the cavity. A shear compressive force can be applied in the gap in the vicinity where the minor axis of the cavity and the major axis of the rotor coincide. Conducting fine particles having a low-melting-point metal layer formed on the surface of the substrate fine particles is produced by repeatedly melting and softening the low-melting-point metal fine particles by the shear compression and attaching the low-melting-point metal fine particles to the substrate fine particles. be able to.

The average particle diameter of the low melting point metal fine particles used when forming the low melting point metal layer is not particularly limited, but the preferred lower limit is 0.1 μm and the preferred upper limit is 100 μm. When the average particle diameter of the low melting point metal fine particles is less than 0.1 μm, the low melting point metal fine particles are likely to aggregate, and it may be difficult to form the low melting point metal layer. When the average particle diameter of the low melting point metal fine particles exceeds 100 μm, the low melting point metal layer may not be melted during shear compression and it may be difficult to form a low melting point metal layer. The average particle size of the low-melting-point metal fine particles is obtained by measuring the particle sizes of 50 low-melting-point metal fine particles selected at random using an optical microscope or an electron microscope, and arithmetically averaging the measured particle sizes. Can be sought.
Moreover, it is preferable that the average particle diameter of the said low melting metal fine particle is 1/10 or less of the average particle diameter of the said base particle. When the average particle size of the low melting point metal fine particles exceeds 1/10 of the average particle size of the substrate fine particles, the low melting point metal fine particles cannot adhere to the substrate fine particles and form a film during shear compression. There is.

The low melting point metal layer obtained by such a manufacturing method has 6 or more crystal orientations having a peak intensity with an intensity ratio of 30% or more with respect to the peak intensity of the first preferred orientation when XRD measurement is performed. It will contain tin. Therefore, since the obtained conductive fine particles increase the hardness of the low melting point metal layer and decrease the ductility, the low melting point metal layer is rubbed by rubbing between the conductive fine particles during storage and contact with the equipment during mounting. Can be prevented from being deformed, and as a result, defects in the mounting process such as poor adsorption of the ball mounter can be reduced.
Moreover, the said manufacturing method can form a low melting metal layer suitably also to base-material microparticles | fine-particles with a small particle diameter like a particle diameter of 200 micrometers or less. Moreover, a low melting point metal layer having a desired composition can be formed by selecting low melting point metal fine particles. Furthermore, it is not necessary to perform complicated steps such as preparation of a plating solution and an electrodeposition step, and conductive fine particles can be produced at a low cost by a simple method.

An anisotropic conductive material can be produced by dispersing the conductive fine particles of the present invention in a binder resin. Such an anisotropic conductive material is also one aspect of the present invention.

Examples of the anisotropic conductive material of the present invention include anisotropic conductive paste, anisotropic conductive ink, anisotropic conductive adhesive, anisotropic conductive film, and anisotropic conductive sheet.

The binder resin is not particularly limited, but an insulating resin is used, and examples thereof include a vinyl resin, a thermoplastic resin, a curable resin, a thermoplastic block copolymer, and an elastomer.
Although the said vinyl resin is not specifically limited, For example, a vinyl acetate resin, an acrylic resin, a styrene resin etc. are mentioned.
Although the said thermoplastic resin is not specifically limited, For example, polyolefin resin, ethylene-vinyl acetate copolymer, a polyamide resin etc. are mentioned.
Although the said curable resin is not specifically limited, For example, an epoxy resin, a urethane resin, a polyimide resin, an unsaturated polyester resin etc. are mentioned. The curable resin may be a room temperature curable resin, a thermosetting resin, a photocurable resin, or a moisture curable resin. The curable resin may be used in combination with a curing agent.
The thermoplastic block copolymer is not particularly limited. For example, styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, hydrogenated product of styrene-butadiene-styrene block copolymer, styrene -Hydrogenated product of isoprene-styrene block copolymer.
The elastomer is not particularly limited, and examples thereof include styrene-butadiene copolymer rubber and acrylonitrile-styrene block copolymer rubber.
These resins may be used alone or in combination of two or more.

In addition to the conductive fine particles of the present invention and the above-mentioned binder resin, the anisotropic conductive material of the present invention is, for example, an extender, a plasticizer, and improved adhesiveness within a range that does not hinder the achievement of the present invention. Agents, antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, colorants, flame retardants, organic solvents, and the like.

The method for producing the anisotropic conductive material of the present invention is not particularly limited. For example, the conductive fine particles of the present invention are added to the binder resin, and the mixture is uniformly mixed and dispersed. Examples thereof include a method for producing an anisotropic conductive ink, an anisotropic conductive adhesive, and the like. Further, the conductive fine particles of the present invention are added to the binder resin and uniformly dispersed or dissolved by heating, and a predetermined film thickness is applied to a release treatment surface of a release material such as release paper or release film. For example, a method for producing an anisotropic conductive film, an anisotropic conductive sheet or the like by coating may be used.
Moreover, it is good also as an anisotropic conductive material by using separately the said binder resin and the electroconductive fine particles of this invention, without mixing.

A connection structure using the conductive fine particles of the present invention or the anisotropic conductive material of the present invention is also one aspect of the present invention.

The connection structure of the present invention is a conductive connection structure in which a pair of circuit boards are connected by filling the pair of circuit boards with the conductive fine particles of the present invention or the anisotropic conductive material of the present invention. is there.

According to the present invention, there are provided conductive fine particles capable of preventing deformation during storage and reducing defective mounting, an anisotropic conductive material using the conductive fine particles, and a connection structure. can do.

It is a chart which shows the XRD measurement result of the electroconductive fine particles obtained in the Example. It is a chart which shows the XRD measurement result of the electroconductive fine particles obtained by the comparative example.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

Example 1
A copper layer having a thickness of 10 μm was formed by electroplating on the surface of resin fine particles (average particle diameter of 240 μm) made of a copolymer of tetramethylolmethane tetraacrylate and divinylbenzene to obtain substrate fine particles.
Subsequently, the obtained base material fine particles and tin 96.5 silver 3.5 alloy fine particles (particle size distribution: 5 to 15 μm) were put into a Theta composer (manufactured by Tokuju Kogakusha Co., Ltd.) and mixed. As a result, tin 96.5 silver 3.5 fine particles are adhered to the base fine particles and formed into a film, thereby forming a 25 μm thick tin 96.5 silver 3.5 alloy layer on the surface of the base fine particles. Fine particles were obtained. The sphericity measured by measuring the sphericity of 50 randomly selected conductive particles using an optical microscope or an electron microscope and arithmetically averaging the measured sphericity was 99.4%. It was. The sphericity was calculated from the following equation by obtaining the area of the circumscribed circle in contact with the conductive fine particles and the area of the inscribed circle from a projection photograph taken using an optical microscope or an electron microscope.
Sphericality = {1-((area of circumscribed circle−area of inscribed circle) / area of circumscribed circle)} × 100
Further, when mixing using a theta composer, the rotating container (vessel) was reversely rotated at 35 rpm and the rotating blade (rotor) was rotated at 2500 rpm so that a shear compression force was applied. The mixing time was 300 minutes.

(Comparative Example 1)
A copper layer having a thickness of 10 μm was formed by electroplating on the surface of resin fine particles (average particle diameter of 240 μm) made of a copolymer of tetramethylolmethane tetraacrylate and divinylbenzene to obtain substrate fine particles.
Subsequently, a tin 96.5 silver 3.5 alloy layer having a thickness of 25 μm was formed on the surface of the obtained base material fine particles by electroplating to obtain conductive fine particles. The sphericity was 99.5%.

<Evaluation>
The following evaluation was performed about the electroconductive fine particles obtained by the Example and the comparative example. The results are shown in Table 1.

(1) XRD measurement About the obtained electroconductive fine particles, XRD measurement was performed using the X-ray-diffraction apparatus (RINT1000, Rigaku Co., Ltd.), and the intensity ratio with respect to the peak intensity of the 1st priority orientation in each crystal orientation was measured. . The results are shown in Table 1. Table 1 shows eight peaks with high intensity.
In addition, the XRD measurement result of the electroconductive fine particles obtained in the Example is shown in FIG. 1, and the XRD measurement result of the electroconductive fine particles obtained in the comparative example is shown in FIG. As shown in FIGS. 1 and 2, Sn (101) is the first preferred orientation in the examples and comparative examples.

(2) Deformation by contact The obtained conductive fine particles and water were mixed in a container, and ultrasonic waves were applied to promote contact between the conductive fine particles (acceleration test). Next, the sphericity of the conductive fine particles after application of ultrasonic waves was determined.

(3) Ball mounter mounting failure Conductive fine particles after performing the “(2) Deformation by contact” test are mounted on the electrodes on the substrate using the ball mounter, and the conductive fine particles generated at that time are mounted. The percentage of defects was determined.

According to the present invention, there are provided conductive fine particles capable of preventing deformation during storage and reducing mounting defects, an anisotropic conductive material using the conductive fine particles, and a connection structure. can do.

Claims (7)

Conductive fine particles in which a low melting point metal layer is formed on the surface of the base fine particles,
The low-melting-point metal layer contains tin having 6 or more crystal orientations having a peak intensity of 30% or more with respect to the peak intensity of the first preferential orientation when XRD measurement is performed. Conductive fine particles. 2. The conductive fine particles according to claim 1, wherein the low melting point metal layer is made of tin or an alloy of tin and another metal. The conductive fine particles according to claim 1, wherein the substrate fine particles are resin fine particles. The conductive fine particles according to claim 1, wherein the substrate fine particles are copper fine particles. The conductive fine particles according to claim 1, 2, 3, or 4, further comprising a conductive layer between the substrate fine particles and the low melting point metal layer. An anisotropic conductive material, wherein the conductive fine particles according to claim 1, 2, 3, 4 or 5 are dispersed in a binder resin. A connection structure comprising the conductive fine particles according to claim 1, 2, 3, 4 or 5, or the anisotropic conductive material according to claim 6.

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