CN115411007B - A kind of special-shaped multi-applicability lead-free composite solder and its preparation method - Google Patents

Abstract

The invention discloses a special-shaped multi-applicability lead-free composite solder and a preparation method thereof, comprising a lead-free composite solder body, the lead-free composite solder body includes a special-shaped matrix, a first connection surface and a second connection surface, and The lead-free composite solder body is composed of a special-shaped substrate, a solder alloy film on the first connection surface and the second connection surface, and the spatial orientation and size between the first connection surface and the second connection surface are based on the components to be connected. The structure of the pad on the chip is determined. In the spatial coordinate system, the angle between the corresponding coordinate axes determined by the two connection surfaces of the composite solder is determined according to the bump structure on the chip to be connected. The first connection surface The projection of the line connecting the centers of the two connecting surfaces with the second connecting surface in the datum coordinate system. The special-shaped multi-applicability lead-free composite solder and the preparation method disclosed by the invention break through the traditional idea of designing and manufacturing micro solder joints, and provide a new idea and approach for comprehensively improving the reliability of electronic products.

Description

A kind of special-shaped multi-applicability lead-free composite solder and its preparation method

technical field

The invention relates to the technical field of metal material processing, in particular to a special-shaped multi-applicability lead-free composite solder and a preparation method thereof.

Background technique

With the continuous pursuit of miniaturization, multi-functionality and high reliability, the packaging density of electronic products is getting higher and higher. With the development of packaging structure in three-dimensional direction, the size and spacing of interconnection solder joints continue to decrease. The above changes Many reliability issues can arise. First, the three-dimensional packaging structure is becoming more and more complex, and more and more asymmetric solder joints will be used in the packaging system, making circuit design and manufacturing more and more difficult; second, the heat dissipation of the three-dimensional packaging structure is difficult, which easily leads to thermal stress loss. thirdly, the reduction of solder joint size requires higher and higher current density in a single solder joint, and the high-density current is easy to drive the metal atoms in the solder joint to undergo directional diffusion and migration, resulting in electromigration problems; fourth, The reduced size of the solder joint greatly weakens the strength of itself and the entire packaging system.

However, most of the improvement measures in the past were mainly aimed at one of the problems. For example, in order to solve the problem of complex structure, the technology of combining ball array and wire bonding is often used in packaging, but the manufacturing process is complicated; in order to solve the problem of heat dissipation, a heat dissipation layer is often inserted in the stacked structure to enhance the heat dissipation effect, but this weakens The high density of the package; particle reinforcement or optimization of the solder joint structure is the most common method to improve the electromigration resistance and mechanical properties of the solder joint, but it will cause thermal stress problems. While the above approach can solve one problem, it cannot fully solve other reliability problems. At present, the packaging field still lacks ideas and technologies to comprehensively solve the above problems.

Contents of the invention

The invention discloses a special-shaped multi-applicability lead-free composite solder and its preparation method. The purpose of the invention is to overcome the complex process, thermal stress mismatch and electromigration that occur in the process of manufacturing and serving micro solder joints in existing electronic products problem, and provide a kind of idea and method for connecting different angles and different shapes of pads in the packaging system, corresponding to it is a kind of special-shaped multi-applicability composite solder with asymmetric structure and its preparation method, the composite Solder will break through the traditional ideas of micro-solder joint design and manufacture, and provide new ideas and ways for comprehensively improving the reliability of electronic products.

In order to achieve the above object, the present invention adopts the following technical solutions:

A special-shaped multi-applicability lead-free composite solder, comprising a lead-free composite solder body, the lead-free composite solder body includes a special-shaped matrix 2, a first connection surface 1 and a second connection surface 3, and the lead-free composite The solder body is composed of a special-shaped substrate 2, a solder alloy film on the first connection surface 1 and the second connection surface 3, and the spatial orientation and size between the first connection surface 1 and the second connection surface 3 are based on the desired In the spatial coordinate system, the corresponding coordinate axes ox and o'x', oy and o'y', oz determined by the two connection surfaces of the lead-free composite solder body The angles α, β, and γ between o'z' and o'z' are determined according to the bump structure on the chip to be connected, and their values are adjusted between 0~2π, 0~π, and 0~π respectively. The first connection The projection of the center line of the two connection surfaces of surface 1 and second connection surface 3 in the reference coordinate system, that is, the distances a, b, and c are determined according to the structure and size of the bumps on the connection chip, and the size is from a few microns to several Varies between hundreds of microns.

In a preferred solution, the shape of the two connection surfaces of the first connection surface 1 and the second connection surface 3 is any one of a circle, a rectangle, or a compound shape combining a circle and a rectangle, or one of them any combination between; the shape between the first connection surface 1 and the second connection surface 3 depends on the shape of the mask after processing, and the surface of the first connection surface 1 and the second connection surface 3 The thickness of the solder alloy on the board is between 1 and 6 μm, and the alloy used is a common commercial lead-free solder that does not involve claims in other patents. The shape of the matrix of the lead-free composite solder body is determined by the structure of the chip to be connected. It is determined that its material is an easily conductive and thermally conductive material, and it is prepared by sputtering or electroplating with the help of a mask during molding.

In a preferred solution, the base material of the lead-free composite solder body is pure copper, while other easily conductive and thermally conductive materials are not excluded, and the lead-free composite solder body is connected to the first connection surface 1 and the second connection surface 1. The angle relationship between the surfaces 3 is: when α=90°, β=0°, γ=90°, the cross section of the lead-free composite solder body is a right triangle, and when α=β=0°, When γ=180°, a composite solder with a linear or tapered cross section is formed.

A method for preparing a special-shaped multi-applicability lead-free composite solder mainly includes the following steps:

S1: Preparation of brazing alloy film: place the bottom mold on a flat plate, and assemble the first mask on the bottom mold, and prepare a brazing alloy film by sputtering or electroplating, and the thickness of the alloy film is controlled between 1 and 6 μm ;

S2: Preparation of special-shaped substrate: remove the first mask, assemble the second mask on the bottom mold, and prepare a special-shaped copper substrate by sputtering or electroplating. The size and shape of the substrate depend on the mask;

S3: Preparation of solder alloy thin film Install the upper mold on the second mask, and prepare a solder alloy thin film with a thickness of 1-6 μm on the other connecting surface by sputtering or electroplating again;

S4: Turn over and remove the upper mold, and place the bottom mold, the second mask and the composite solder on the flat plate after turning over together;

S5: heat preservation and demoulding, heat preservation at 3-5°C above the melting point of the solder for 10-30s, remove the bottom mold and the second mask in turn to form the aforementioned special-shaped multi-applicability composite solder;

The special-shaped multi-applicability composite solder needs to be kept at 3-5°C above the melting point of the solder alloy for 10-30s, and the thickness of the intermetallic compound formed at the interface should not exceed 1/4 of the thickness of the solder layer. In order to simplify the packaging process , if the two connecting surfaces of the composite solder have different sizes, the larger connecting surface should be used as the bottom surface after demolding.

It can be seen from the above that a lead-free composite solder with special shape and multiple applicability includes a lead-free composite solder body, and the lead-free composite solder body includes a special-shaped matrix 2, a first connecting surface 1 and a second connecting surface 3, And the lead-free composite solder body is composed of a special-shaped substrate 2, a solder alloy film on the first connection surface 1 and the second connection surface 3, and the spatial orientation between the first connection surface 1 and the second connection surface 3 is and dimensions are determined according to the pad structure on the chip to be connected. In the spatial coordinate system, the corresponding coordinate axes ox and o'x', oy and o' determined by the two connection surfaces of the lead-free composite solder body The angles α, β, and γ between y', oz, and o'z' are determined according to the bump structure on the chip to be connected, and their values are adjusted between 0~2π, 0~π, and 0~π respectively. Describe the projection of the center line of the two connection surfaces of the first connection surface 1 and the second connection surface 3 in the reference coordinate system, that is, the distances a, b, and c are determined according to the bump structure and size on the connection chip, and the size is between ranging from a few microns to hundreds of microns. The special-shaped multi-applicability lead-free composite solder and the preparation method provided by the invention have the following technical effects:

1. Wide range of applications: Since the structure of the solder can be determined by the spatial orientation, size and shape between the two pads on the chip to be connected, and the angle, distance and area between the two connection surfaces can be adjusted, the The idea can meet different packaging structures and has a wide range of applications;

2. Simple structure: Although the composite solder has an asymmetric structure, it is only composed of a solder alloy film on the substrate and the connecting surface, and the structure is very simple;

3. Good overall performance: Since copper is the common metal with the best electrical and thermal conductivity, the introduction of the overall copper matrix can increase the heat dissipation capacity of the packaging system. At the same time, the control of the thickness of the solder alloy film limits the solder alloy in the composite solder. The total amount can greatly improve the strength and anti-electromigration performance of micro solder joints;

4. The process is simple: the shape and size of the brazing material are mainly controlled by a mask during the forming process, and the preparation can be completed by simple installation, flipping and demoulding.

Description of drawings

Fig. 1 is a schematic diagram of the projection relationship between the centers of the space coordinate system of the connection surface of a special-shaped multi-adaptability lead-free composite solder and the preparation method proposed by the present invention.

Fig. 2 is a schematic diagram of the shape of the connection surface of a special-shaped multi-adaptability lead-free composite solder and its preparation method proposed by the present invention.

Fig. 3 is a schematic diagram of a special-shaped composite solder with a combination of rectangular and rectangular joint surfaces according to a special-shaped multi-applicability lead-free composite solder and its preparation method proposed by the present invention.

Fig. 4 is a schematic diagram of a special-shaped composite solder after combining circular and circular combined joint surfaces of a special-shaped multi-applicability lead-free composite solder and its preparation method proposed by the present invention.

FIG. 5 is a schematic diagram of a special-shaped composite solder after combining rectangular and rectangular combined connection surfaces of a special-shaped multi-applicability lead-free composite solder and its preparation method proposed by the present invention.

Fig. 6 is a schematic diagram of a special-shaped composite solder with multiple applicability and its preparation method after combining a rectangle and a composite connection surface according to the present invention.

Fig. 7 is a schematic cross-sectional view of a special-shaped multi-applicability lead-free composite solder and the composite solder of the preparation method proposed by the present invention.

Fig. 8 is a schematic diagram of mold assembly and operation process in the preparation process of a special-shaped multi-adaptability lead-free composite solder and its preparation method proposed by the present invention.

Fig. 9 is a structural schematic diagram of a special-shaped multi-applicability lead-free composite solder and a preparation method of a special-shaped substrate proposed by the present invention.

In the figure: 1 - the first connection surface; 2 - the special-shaped base; 3 - the second connection surface.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention.

A special-shaped multi-applicability composite solder is composed of a special-shaped copper substrate with an asymmetric structure or other easily conductive and heat-conductive material substrates and solder alloy films on two connecting surfaces. Among them, the shape and size of the special-shaped copper substrate or other material substrates are determined according to the orientation and size of the pads on the chip to be connected, and the composition and purity of the substrate material can be determined according to electrical and thermal conductivity and strength; solder alloy film The thickness is 1-6 μm, and the solder alloy is common commercial lead-free solder.

A preparation method of special-shaped multi-applicability composite solder is realized through the following steps:

1. The production of the bottom mold, the first mask and the second mask and the upper mold selects an aluminum material that is similar to Sn and does not have a metallurgical reaction as the base material of the above-mentioned mold. The size and shape of the second mask depends on the size and shape of the connection surface, and the spatial orientation of the connection surface corresponds to the spatial orientation of the other connection surface to meet the purpose of connecting two specific pads; the shape and size of the second mask are based on the two It depends on the spatial orientation and processing conditions between the connecting surfaces;

2. Preparation of solder alloy film on the connecting surface of the bottom mold Place the bottom mold on a flat plate, and assemble the first mask on the bottom mold, and prepare the solder alloy film by sputtering or electroplating. The thickness of the alloy film is controlled at 1~ Between 6μm;

3. Preparation of special-shaped copper substrate or special-shaped substrate of other materials Remove the first mask, assemble the second mask on the bottom mold, and prepare special-shaped copper substrate or other materials of special-shaped substrate by sputtering or electroplating;

4. Preparation of solder alloy thin film on the connection surface of the upper mold Install the upper mold on the second mask, and prepare a solder alloy film with a thickness of 1-6 μm on the other connection surface by sputtering or electroplating again;

5. Turn over and remove the upper mold. Turn the bottom mold, the second mask and the composite solder together and place them on the flat plate, then remove the upper mold;

6. Insulation and demolding Heat preservation at 3-5°C above the melting point of the solder for 10-30s, remove the bottom mold and the second mask in turn to form a special-shaped multi-applicability composite solder

design phase:

As shown in accompanying drawing 9, composite solder among the present invention is made up of special-shaped copper substrate 2 and the lead-free solder alloy thin film 1 and 3 that are formed on the connecting surface by sputtering or electroplating method, and this composite solder is designed The spatial orientation between the two connection surfaces of the first connection surface and the second connection surface is determined according to the pad structure on the chip to be connected. In the spatial coordinate system, the two connection surfaces of the first connection surface and the second connection surface The determined angles α, β, and γ between the corresponding coordinate axes ox and o'x', oy and o'y', oz and o'z' can be respectively in the range of 0 to 2π according to the bump structure on the connected chip , 0 ~ π, 0 ~ π adjustment, as shown in Figure 1 of the specification. At the same time, the projection of the center line of the two connection surfaces in the reference coordinate system, that is, the distances a, b, and c are determined according to the structure and size of the bumps on the connected chip, and the size varies from several microns to hundreds of microns. As shown in Figure 1 of the description. In addition, the shape of the connection surface of the composite solder can be arbitrarily selected from the composite shape shown in Figure 2 as rectangle, circle or the combination of circle and rectangle, and can also be any combination of them. The shape of the transition between them depends on the shape of the mask after processing.

According to the above ideas, the orientation, shape and size of the two connecting surfaces of the composite solder in the present invention can be flexibly determined according to the packaging structure to be connected, which will break through the shortcomings of the single shape and size of the composite solder in the past, and have multi-applicability advantage. In particular, the following specific implementation examples can be cited:

Example 1

According to the shape of the connecting surface, the two connecting surfaces in the composite solder can be designed as a combination of rectangle and circle, rectangle and rectangle, circle and circle, circle or rectangle and composite type, respectively as shown in the abstract drawings and As shown in Figure 3 of the description. The size of the connection surface depends on the size of the pads to be connected, and at the same time, other shapes and combinations thereof are not excluded in this implementation process.

Example 2

According to the spatial angle relationship between the connecting surfaces, the angles α, β, and γ between the two connecting surfaces of the composite solder can be adjusted between 0-2π, 0-π, and 0-π respectively. In particular, γ is 180° for a linear structure, and γ can also be designed as a right-angled structure with an angle of 90° or other angles, wherein the latter can be seen in Figures 3-6 of the specification.

Example 3

According to the spatial angle relationship between the surfaces to be connected, the projections a, b and c of the center line of the two connection surfaces of the composite solder in the reference coordinates can be adjusted from several microns to hundreds of microns.

The implementation examples listed above are only to explain the design ideas of the present invention, and should not be considered as limitations to the design ideas of the present invention. Any changes or improvements carried out according to the design ideas and technical solutions of the present invention should be included in the protection scope of the present invention within.

Preparation stage:

According to the aforementioned design ideas, the preparation process is illustrated by taking the composite solder shown in Figures 3 and 7 as an example, including:

(1) Preparation of solder alloy film on the first connection surface Place the bottom mold on a flat plate and assemble the first mask on the bottom mold, see Figure 5; prepare the solder alloy film by sputtering or electroplating, the thickness Controlled between 1 ~ 6μm;

(2) Preparation of special-shaped substrate: remove the first mask, and assemble the second mask on the bottom mold; use sputtering or electroplating to prepare special-shaped copper or other material substrates, and the size and shape of the substrate are determined by the mask;

(3) Preparation of solder alloy film on the second connection surface: install the upper mold on the second mask; again prepare a solder alloy film with a thickness of 1-6 μm on the other connection surface by sputtering or electroplating ;

(4) Turn over and remove the upper mold, turn over the bottom mold, the second mask and the composite solder together and place them on the flat plate;

(5) Heat preservation and demoulding. Heat preservation at 3-5°C above the melting point of the solder for 10-30s to ensure that the metallurgical reaction between the solder alloy on the two joint surfaces and the joint surface occurs and an intermetallic compound at the interface is formed. No more than 1/4 of the thickness of the solder alloy film; finally remove the bottom mold and the second mask in sequence to form the aforementioned special-shaped multi-applicability composite solder.

In particular, according to the above preparation process, the following specific implementation examples can also be enumerated:

Example 4

Each mold shown in Figure 5 is an integral mold. According to the spatial relationship between the pads to be connected and the corresponding design ideas, if necessary, the above-mentioned integral mold can be changed into an assembled mold, such as half-and-half, multiple mold assembly, etc. The material of the mold should be a material that does not easily react with the solder alloy, such as aluminum; but it does not exclude cemented carbide or other materials.

Example 5

The material of the special-shaped substrate with an asymmetric structure is selected from materials that are easy to conduct electricity and heat, usually industrial pure copper, or other materials that meet the above requirements, including other metal or non-metal materials.

Example 6

The solder alloy is selected from lead-free solder that is commercially available and does not involve claims in other patents. Before the composite solder is demoulded, it needs to be kept at 3-5°C above the melting point of the solder for 10-30s to ensure the metallurgical reaction between the solder alloy and the matrix and form a stable interface intermetallic compound layer, and to control the thickness of the compound in the alloy. Within 1/4 of the film thickness.

Example 7

The method of sputtering or electroplating is used in the preparation of the substrate, and one of nitrogen, argon or other protective gases is used for protection during sputtering; electroplating is a common electroplating process.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto, any person familiar with the technical field within the technical scope disclosed in the present invention, according to the technical solution of the present invention Any equivalent replacement or change of the inventive concepts thereof shall fall within the protection scope of the present invention.

Claims (7)

1. The lead-free composite solder body comprises a special-shaped matrix (2), a first connecting surface (1) and a second connecting surface (3), and is composed of solder alloy films on the special-shaped matrix (2), the first connecting surface (1) and the second connecting surface (3), wherein the space orientation and the size between the first connecting surface (1) and the second connecting surface (3) are determined according to the structure of a bonding pad on a chip to be connected, in a space coordinate system, the included angles alpha, beta and gamma between corresponding coordinate axes ox and o 'x', oy and o 'y', oz and o 'z' determined by the two connecting surfaces of the lead-free composite solder body are determined according to the bump structures on the chip to be connected, the values of the included angles are respectively adjusted between 0 pi, 0 pi and pi, and 0 pi, the projection line of the central coordinate system of the first connecting surface (1) and the second connecting surface (3) between the two connecting surfaces in the reference coordinate system, namely, the projection distance between the two connecting surfaces a, c and the chip in a micrometer range is determined according to the change in a micrometer range from a micrometer to a micrometer range, and the micrometer range from a micrometer to a micrometer.

2. The special-shaped multi-applicability lead-free composite solder according to claim 1, wherein the shape of the first connecting surface (1) and the second connecting surface (3) is any one of a round shape, a rectangular shape or a composite shape formed by combining a round shape and a rectangular shape, or any combination of the round shape and the rectangular shape; the shape between the first connecting surface (1) and the second connecting surface (3) depends on the shape of the mask after processing.

3. A shaped multi-applicability lead free composite solder according to claim 1, characterized in that the solder alloy thickness on the surface of the first (1) and second (3) joining surfaces is between 1 and 6 μm.

4. The special-shaped multi-applicability lead-free composite solder according to claim 1, wherein the matrix shape of the lead-free composite solder body is determined by the chip structure to be connected, the lead-free composite solder body is made of a material which is easy to conduct electricity and heat, and the lead-free composite solder is prepared by a mask and by a sputtering or electroplating method during molding.

5. The special-shaped multi-applicability lead-free composite solder according to claim 4, wherein the matrix material of the lead-free composite solder body is pure copper, and the included angle relation between the lead-free composite solder body and the first connecting surface (1) and the second connecting surface (3) is as follows: when α=90 °, β=0°, γ=90°, the lead-free composite solder body has a right triangle cross section, and when α=β=0°, γ=180°, a composite solder having a linear or tapered cross section is formed.

6. A method for preparing a special-shaped multi-applicability lead-free composite solder, which is applied to the special-shaped multi-applicability lead-free composite solder as claimed in any one of claims 1 to 5, and is characterized by mainly comprising the following steps:

s1: preparing a solder alloy film: placing a bottom die on a flat plate, assembling a first mask on the bottom die, and preparing a brazing alloy film by utilizing a sputtering or electroplating method, wherein the thickness of the alloy film is controlled between 1 and 6 mu m;

s2: preparing a special-shaped matrix: removing the first mask, assembling the second mask on the bottom die, and preparing a special-shaped copper matrix by utilizing a sputtering or electroplating method, wherein the size and shape of the matrix are determined according to the mask;

s3: the upper die is arranged on the second mask, and the brazing alloy film with the thickness of 1-6 mu m is prepared on the other connecting surface by a sputtering or electroplating method;

s4: the upper die is removed through overturning, and the bottom die, the second mask and the composite solder are put on a flat plate after being overturned together;

s5: and (3) preserving heat and demoulding, namely preserving heat for 10-30 s at a temperature of 3-5 ℃ above the melting point of the brazing filler metal, and sequentially removing the bottom die and the second mask to form the special-shaped multi-applicability composite brazing filler metal.

7. The method for preparing the special-shaped multi-applicability lead-free composite solder according to claim 6, wherein the special-shaped multi-applicability lead-free composite solder is required to be subjected to heat preservation for 10-30 s at a temperature of 3-5 ℃ above the melting point of a solder alloy, and the thickness of the formed interface intermetallic compound is not more than 1/4 of the thickness of a solder layer.