A fine-grained SnBiIn alloy, its preparation method and application

Abstract

The present invention provides a fine-grained SnBiIn alloy, its preparation method and application, relating to the technical field of manufacturing electronic packaging chip interconnection materials. The present invention provides a fine-grained SnBiIn alloy. By atomic percentage, the content of Sn is 30-50 at%, the content of Bi is 20-40 at%, and the content of In is 30-50 at%. The fine-grained SnBiIn alloy is prepared by a ball milling method. The present invention also provides a SnBiIn alloy solder, which includes a SnBiIn alloy solder sheet or a SnBiIn alloy solder paste. By adjusting the proportions of various elements and adopting the preparation methods of vacuum induction melting and ball milling, the present invention enables In to fully react with Bi, inhibits the precipitation of brittle Bi phase, has a uniform and fine structure, a low melting point, improves the electromigration performance, thermal fatigue performance and mechanical properties of solder joints, reduces the degree of chip warping and the probability of solder joint failure.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic packaging chip interconnection material manufacturing, and particularly to a fine-grained SnBiIn alloy, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid development of artificial intelligence, people's demand for high-computation and high-integration chips is becoming increasingly urgent. According to Moore's Law, it has become increasingly difficult to improve chip integration by further miniaturizing transistors. Therefore, three-dimensional packaging is currently the most viable technical approach. To achieve high-integration vertical interconnection, it is necessary to perform multiple reflows using three different melting-point solders with high, medium, and low melting points simultaneously. Currently, mature low-melting-point solders include SnBi-based and SnIn-based solders. The inherent brittleness of the Bi phase in SnBi-based solders greatly reduces the service reliability of SnBi-based solders. And due to the high price of In element, the application of SnIn-based solders is restricted. At the same time, since the chip warpage increases with the increase of the reflow temperature, high warpage leads to low yield and low reliability. Low-temperature solder effectively reduces the reflow temperature and is the most effective way to solve the SMT warpage problem.

[0003] With the development of electronic products towards miniaturization and intelligentization, the spacing between solder joints and wires is getting finer and finer, and there will be a certain amount of residue aggregation on the surface or around the solder joints during the formation process. When these residues contain strongly corrosive ionic substances, it will bring reliability problems of corrosion and leakage to the solder joints and even the entire electronic component assembly. The main mechanism of this problem is the occurrence of electrochemical migration (ECM). The mechanism and process of electromigration can be simply described as follows: First, the metal on the surface of the solder joint is first oxidized to form an oxide in the atmospheric environment; Second, the residue absorbs moisture and ionizes active ions; Third, the active ions react with the metal oxide with the help of moisture in the air and generate metal ions; Fourth, a potential difference is generated between the solder joints during the operation of the device, and the metal ions move towards the cathode; Fifth, the electric field during the movement of the metal ions causes the ions to crystallize and dissolve repeatedly; The third to fifth steps are repeated in cycles, and finally dendrites and leakage are generated. The metal elements that are most likely to generate electromigration or dendrites are silver, lead, tin, and copper. During the service process of power devices, the thermal fatigue load caused by the change of the external temperature will cause reliability problems and lead to the failure of solder joints. And this kind of failure is often not the failure of one or two samples, but the entire batch of products will malfunction, resulting in huge losses. The traditional melting method is likely to cause the microstructure inside the alloy to be coarse, and the electrochemical migration performance, thermal fatigue performance, and mechanical performance of the solder are poor, which will cause reliability problems and lead to the failure of solder joints.

[0004] Grain refinement strengthening is one of the effective ways to improve the strength of materials. By changing the preparation method or adjusting the composition of the alloy, the effect of grain refinement can be achieved. Similarly, in the field of electronic packaging, refining the microstructure of the joining material can also achieve the purpose of improving the solder joint performance.

[0005] Aiming at the problems existing in the existing low-temperature solders, it is necessary to research and develop a grain-refined SnBiIn alloy. By adjusting the preparation method, changing the microstructure of the solder, reducing the reflow temperature, improving the electrochemical migration performance, thermal fatigue performance and mechanical properties of the solder, and solving the problem of solder joint reliability, which has important economic benefits for the development of the electronic packaging field. Summary of the Invention

[0006] The purpose of the present invention is to provide a grain-refined SnBiIn alloy and its preparation method and application to solve the problems existing in the above-mentioned prior art.

[0007] To achieve the above purpose, the present invention provides the following solutions:

[0008] The present invention provides a grain-refined alloy. In the grain-refined SnBiIn alloy, by atomic percentage, the content of Sn is 30-50 at%, the content of Bi is 20-40 at%, and the content of In is 30-50 at%;

[0009] The grain-refined SnBiIn alloy is prepared by ball milling the SnBiIn alloy;

[0010] The particle size of the grain-refined SnBiIn alloy is ≤10 μm.

[0011] The present invention also provides an SnBiIn alloy solder, and the SnBiIn alloy solder contains the above-mentioned grain-refined SnBiIn alloy; the SnBiIn alloy solder contains an SnBiIn alloy solder sheet or an SnBiIn alloy solder paste.

[0012] As a further preference of the present invention, the SnBiIn alloy solder sheet is obtained by spark plasma sintering the grain-refined SnBiIn alloy; the SnBiIn alloy solder paste is obtained by mixing the grain-refined SnBiIn alloy and a flux.

[0013] As a further preference of the present invention, the temperature of the spark plasma sintering is 50-60 °C, more preferably 55 °C, the pressure of the spark plasma sintering is 1-2 MPa, more preferably 1.5 MPa, and the current of the spark plasma sintering is 1-2 kA, more preferably 1.5 kA;

[0014] The soldering flux is soldering paste KL-558 and / or soldering paste KE-500, and the dosage of the soldering flux is 5-15% of the mass fraction of the fine-grained SnBiIn alloy, more preferably 10%.

[0015] The present invention also provides a preparation method of the fine-grained SnBiIn alloy, comprising the following steps: ball-milling the SnBiIn alloy to obtain the fine-grained SnBiIn alloy;

[0016] The ball-to-material ratio of the ball-milling is 15-30:1; the rotation speed of the ball-milling is 100-250 r / min.

[0017] As a further preference of the present invention, the SnBiIn alloy adopts an SnBiIn alloy ingot, and the SnBiIn alloy ingot is obtained by vacuum induction melting;

[0018] The vacuum degree of the vacuum induction melting is 2.5×10 -3 ~5×10 -3 Pa, the power is 0.5-1 KJ, the time is 20-50 s, and the more preferred vacuum degree is 3×10 -3 ~4×10 -3 Pa, the power is 0.6-0.8 KJ, and the time is 30-40 s.

[0019] As a further preference of the present invention, it also includes crushing the SnBiIn alloy ingot to obtain intermediate powder, and the particle size of the intermediate powder is ≤100 μm, more preferably ≤80 μm.

[0020] The present invention also provides a preparation method of the SnBiIn alloy solder, sintering the fine-grained SnBiIn alloy by spark plasma sintering to obtain the SnBiIn alloy solder sheet; or mixing the fine-grained SnBiIn alloy and the soldering flux to obtain the SnBiIn alloy solder paste.

[0021] As a further preference of the present invention, the temperature of the spark plasma sintering is 50-60 °C, more preferably 55 °C, the pressure of the spark plasma sintering is 1-2 MPa, more preferably 1.5 MPa, and the current of the spark plasma sintering is 1-2 KA, more preferably 1.5 KA;

[0022] The soldering flux is soldering paste KL-558 and / or soldering paste KE-500, and the dosage of the soldering flux is 5-15% of the mass fraction of the fine-grained SnBiIn alloy, more preferably 10%.

[0023] The present invention also provides the application of the fine-grained SnBiIn alloy or the SnBiIn alloy solder in the field of electronic packaging.

[0024] The present invention discloses the following technical effects:

[0025] 1) By using the concept of multi - principal - element alloy and adjusting the proportion of each element in the SnBiIn system, the present invention enables In to fully react with Bi to form the InBi phase, so that there is no elemental Bi in the material, thereby reducing the inherent brittleness of the solder. The reduction of the brittle phase Bi can improve the electromigration performance, thermal fatigue performance and mechanical properties of the solder joint, and can greatly reduce the probability of solder joint failure.

[0026] 2) In the present invention, not only can the brittleness of Bi be alleviated, but also due to its low melting point, the temperature during the reflow process of the device is relatively low, and the degree of chip warping is greatly reduced.

[0027] 3) The present invention prepares the fine - grained SnBiIn alloy by a method combining vacuum induction melting and ball milling. The prepared fine - grained SnBiIn alloy has a uniform and fine microstructure, forming a eutectic structure mixed with the Sn(In) solid solution and the InBi phase. Among them, In and Bi form the InBi phase, which inhibits the precipitation of the brittle Bi phase, thereby improving the thermal fatigue performance, electromigration performance and mechanical properties of the solder joint and enhancing the solder joint reliability. Brief Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0029] Figure 1 is the flowchart of Embodiment 1;

[0030] Figure 2 is the micro - morphological diagram of Embodiment 1, where a is the micro - morphological diagram of the SnBiIn alloy ingot, and b is the micro - morphological diagram of the fine - grained SnBiIn alloy;

[0031] Figure 3 is the XRD diagram of the SnBiIn alloy prepared in Embodiment 1;

[0032] Figure 4 is the DSC diagram of the SnBiIn alloy prepared in Embodiment 1;

[0033] Figure 5 is the tensile strength of the sandwich solder joints prepared in Embodiment 1 and Comparative Example 1, where A is Embodiment 1 and B is Comparative Example 1. Detailed Description of the Embodiments

[0034] The various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and implementation schemes of the present invention.

[0035] It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0036] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0037] Without departing from the scope or spirit of the present invention, various improvements and variations can be made to the specific embodiments of the present invention specification, which are obvious to those skilled in the art. Other embodiments obtained from the specification of the present invention are obvious to those skilled in the art. The specification and examples of the present invention are merely exemplary.

[0038] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0039] The technical solution of the present invention will be further described in detail below in conjunction with embodiments.

[0040] Example 1

[0041] Metal particles with a composition of 30 at% Sn, 30 at% Bi, and 40 at% In were placed in a vacuum induction melting furnace. Under the conditions of a vacuum degree of 2.5×10-3 Pa and a power of 0.5 KJ, vacuum induction melting was carried out for 30 s. After cooling, the melting was repeated 3 times under the above conditions to obtain a SnBiIn alloy ingot. The SnBiIn alloy ingot was crushed to obtain intermediate powder with a particle size of 90 μm. The intermediate powder and stainless steel grinding balls were placed in a ball milling tank containing absolute ethanol according to a ball-to-material ratio of 20:1. The mass percentage of the intermediate powder to absolute ethanol was 10:1, and ball milling was carried out at a rotation speed of 150 r / min for 50 h to obtain a fine-grained SnBiIn alloy.

[0042] The fine-grained SnBiIn alloy was subjected to spark plasma sintering at a temperature of 60 °C, a pressure of 2 MPa, and a current of 2 kA to obtain a SnBiIn alloy solder sheet.

[0043] The SnBiIn alloy solder sheet and the copper plate to be welded were made into a sandwich solder joint with copper plates on the upper and lower layers and the solder sheet in the middle at a temperature of 75 °C and a pressure of 2 MPa.

[0044] The flow chart of this embodiment is as Figure 1 shown.

[0045] The SnBiIn alloy ingot and the fine-grained SnBiIn alloy prepared in this embodiment were subjected to microstructural morphology analysis. The results are as Figure 2 shown, where a is the microstructural morphology diagram of the SnBiIn alloy ingot and b is the microstructural morphology diagram of the fine-grained SnBiIn alloy. It can be seen from the microstructural morphology diagram that the fine-grained SnBiIn alloy is composed of Sn and InBi phases, and no single Bi phase is observed. Comparing Figure a and Figure b, it can be seen that the alloy structure obtained by one-step vacuum induction melting is coarse, and the alloy structure prepared by the method combining vacuum induction melting and ball milling is fine.

[0046] The average grain diameter of the fine-grained SnBiIn alloy prepared in this embodiment is 10 μm.

[0047] The fine-grained SnBiIn alloy prepared in this embodiment was subjected to XRD phase analysis. The results are as Figure 3 shown. By comparing with the PDF card, it is concluded that the fine-grained SnBiIn alloy is composed of Sn and InBi phases, and no single Bi phase is observed.

[0048] The fine-grained SnBiIn alloy prepared in this embodiment was subjected to DSC analysis. The results are as Figure 4 shown. The melting point of the fine-grained SnBiIn alloy in this embodiment is 85.7 °C, which meets the standard of low-temperature solder.

[0049] Example 2

[0050] The preparation method of the fine-grained SnBiIn alloy in this embodiment is the same as that in Example 1.

[0051] The fine-grained SnBiIn alloy was mixed with the soldering paste KL-558, and the dosage of the soldering paste KL-558 was 10% of the mass fraction of the fine-grained SnBiIn alloy. The mixture was stirred for 30 min and ultrasonically vibrated for 10 min while stirring to obtain a SnBiIn alloy solder paste.

[0052] The SnBiIn alloy solder paste and the copper plate to be welded are made into a sandwich solder joint with two layers of copper plates on the upper and lower sides and the solder paste in the middle under the conditions of a temperature of 80 °C and a pressure of 2 MPa.

[0053] Example 3

[0054] Adjust the raw material ratio to 30 at% Sn, 20 at% Bi, and 50 at% In, and the other conditions are the same as those in Example 1.

[0055] Example 4

[0056] Adjust the raw material ratio to 40 at% Sn, 30 at% Bi, and 30 at% In, and the other conditions are the same as those in Example 1.

[0057] Example 5

[0058] Adjust the raw material ratio to 50 at% Sn, 20 at% Bi, and 30 at% In, and the other conditions are the same as those in Example 1.

[0059] Example 6

[0060] Adjust the ball-to-material ratio of ball milling to 15:1, and the other conditions are the same as those in Example 1.

[0061] Example 7

[0062] Adjust the ball-to-material ratio of ball milling to 30:1, and the other conditions are the same as those in Example 1.

[0063] Comparative Example 1

[0064] Metal particles with a ratio of 30 at% Sn, 30 at% Bi, and 40 at% In are added with a ZnCl2 melting covering agent, heated to 650 °C, and held for 30 min. After stirring the obtained melt for 30 min, the surface covering agent is removed. The molten liquid is atomized to form small droplets, the atomization pressure is 75 bar, and the atomization gas is helium. After atomization, SnBiIn solder is obtained.

[0065] Refer to the method of Example 1 to prepare SnBiIn alloy solder sheets from SnBiIn solder, and then make sandwich solder joints with the copper plates to be welded.

[0066] Tensile strength tests are carried out on the solder joints made in Example 1 and Comparative Example 1. The test results are as Figure 5 shown. Among them, A is the tensile strength of the sandwich solder joint made in Example 1, and B is the tensile strength of the sandwich solder joint made in Comparative Example 1. It can be seen from Figure 5 that the tensile strength of the solder joint in Example 1 is higher than that of the solder joint in Comparative Example 1.

[0067] Comparative Example 2

[0068] Adjust the raw material ratio to 48 at% Sn, 4 at% Bi, and 48 at% In, and keep other conditions the same as in Example 1.

[0069] Perform microscopic morphology analysis and XRD phase analysis on this comparative example. The phase composition of the obtained SnBiIn alloy is Sn phase, BiIn2 phase, and In3Sn phase, and the average grain diameter is 30 μm.

[0070] The above-described embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A fine-grained alloy for electronic packaging, characterized in that, The fine-grained SnBiIn alloy has, by atomic percentage, 30 to 50 at% of Sn, 20 to 40 at% of Bi, and 30 to 50 at% of In; The preparation steps of the fine-grained SnBiIn alloy for electronic packaging include: obtaining an SnBiIn alloy ingot by vacuum induction melting; ball-milling the SnBiIn alloy ingot to obtain the fine-grained SnBiIn alloy for electronic packaging; The vacuum degree of the vacuum induction melting is 2.5×10 -3 ~5×10 -3 Pa, the power is 0.5~1 KJ, and the time is 20~50 s; the ball-to-material ratio of the ball milling is 15~30:1, and the rotation speed of the ball milling is 100~250 r / min; The particle size of the fine-grained SnBiIn alloy for electronic packaging is ≤10 μm; The fine-grained SnBiIn alloy for electronic packaging is a eutectic structure mixed with Sn(In) solid solution and InBi phase.

2. A SnBiIn alloy solder for electronic packaging, characterized in that, The SnBiIn alloy solder raw material includes the fine-grained SnBiIn alloy for electronic packaging as claimed in claim 1; the SnBiIn alloy solder for electronic packaging is an SnBiIn alloy solder sheet or an SnBiIn alloy solder paste.

3. The SnBiIn alloy solder for electronic packaging according to claim 2, wherein, The SnBiIn alloy solder sheet is obtained by spark plasma sintering the fine-grained SnBiIn alloy for electronic packaging; the SnBiIn alloy solder paste is obtained by mixing the fine-grained SnBiIn alloy for electronic packaging and a flux.

4. The SnBiIn alloy solder for electronic packaging according to claim 3, characterized in that, The temperature of the spark plasma sintering is 50 to 60 °C□, the pressure of the spark plasma sintering is 1 to 2 MPa, and the current of the spark plasma sintering is 1 to 2 kA; The flux is flux paste KL-558 and / or flux paste KE-500, and the dosage of the flux is 5 to 15% of the mass fraction of the fine-grained SnBiIn alloy.

5. A method for preparing a fine-grained SnBiIn alloy for electronic packaging according to claim 1, characterized in that, It includes the following steps: ball-milling the SnBiIn alloy to obtain the fine-grained SnBiIn alloy for electronic packaging; The ball-to-material ratio of the ball-milling is 15 to 30:1, and the rotation speed of the ball-milling is 100 to 250 r / min.

6. The preparation method according to claim 5, characterized in that, The SnBiIn alloy uses an SnBiIn alloy ingot, and the SnBiIn alloy ingot is obtained by vacuum induction melting; The vacuum degree of the vacuum induction melting is 2.5×10 -3 ~5×10 -3 Pa, the power is 0.5~1 KJ, and the time is 20~50 s.

7. The preparation method according to claim 6, characterized in that, It also includes crushing the SnBiIn alloy ingot to obtain intermediate powder, and the particle size of the intermediate powder is ≤100 μm.

8. A preparation method of the SnBiIn alloy solder for electronic packaging according to any one of claims 2 to 4, characterized in that, Spark plasma sintering the fine-grained SnBiIn alloy for electronic packaging to obtain the SnBiIn alloy solder sheet; or, mixing the fine-grained SnBiIn alloy for electronic packaging and a flux to obtain the SnBiIn alloy solder paste.

9. The preparation method according to claim 8, characterized in that, The temperature of the spark plasma sintering is 50 to 60 °C□, the pressure of the spark plasma sintering is 1 to 2 MPa, and the current of the spark plasma sintering is 1 to 2 kA; The flux is flux paste KL-558 and / or flux paste KE-500, and the dosage of the flux is 5 to 15% of the mass fraction of the fine-grained SnBiIn alloy.

10. Application of the fine-grained SnBiIn alloy for electronic packaging as claimed in claim 1 or the SnBiIn alloy solder for electronic packaging as claimed in any one of claims 2 to 4 in the field of electronic packaging.

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