High-performance tin-bismuth alloy solder for semiconductor packaging

Abstract

The application relates to a high-performance tin-bismuth alloy solder for semiconductor packaging, which is composed of the following components in percentage by weight: Bi: 40.0-58.0%; Ni: 0.3-0.8%; TiC nanoparticles: 0.05-0.2%; and the balance of Sn and inevitable impurities. The application utilizes the organic cooperation of Sn-Bi-Ni-TiC four components, wherein the Bi content is controlled in the range of 40.0%-58.0%, so as to utilize the eutectic reaction to reduce the melting point and reduce thermal damage, and through the solid solution strengthening and brittle phase precipitation of the appropriate Bi, the tensile strength and creep resistance are synergistically improved, and the sharp deterioration of plasticity is avoided; the introduction of Ni provides a strength basis by being dissolved in the beta-Sn matrix, generates fine Ni3Sn4 particles to pin the grain boundary and inhibit the Bi phase from being coarsened, optimizes the interface IMC layer structure, inhibits the excessive growth of Cu6Sn5 and forms a thinner and denser (Cu, Ni)6Sn5 layer, and significantly improves the interface thermal stability and anti-peeling capacity.

Description

Technical Field

[0001] This invention belongs to the field of tin-based alloy soldering powder technology, and specifically relates to a high-performance tin-bismuth alloy solder for semiconductor packaging. Background Technology

[0002] Tin-bismuth alloy solder is widely used in temperature-sensitive electronic packaging applications. Its eutectic composition, Sn-58Bi, has a melting point of only 138℃, which is much lower than the 217℃ of Sn-Ag-Cu (SAC) solder. This can effectively reduce the soldering heat budget and reduce thermal damage to heat-sensitive components, while also offering cost advantages and good tensile strength.

[0003] However, in practical applications, it has at least the following problems:

[0004] 1) Brittleness of Bi phase

[0005] Sn and Bi are almost mutually insoluble in the solid state. The typical microstructure of eutectic Sn-Bi alloy is a lamellar alternating distribution of Sn-rich and Bi-rich phases. Among them, the Bi-rich phase is a hard and brittle phase with poor intrinsic plasticity and limited deformation capacity. When the weld joint is under stress, it is easy to become a preferential channel for crack initiation and propagation. Macroscopically, this manifests as insufficient overall plasticity and toughness of the weld joint, and the elongation is usually low.

[0006] 2) The tissue is prone to coarsening.

[0007] At service temperatures, in order to reduce interfacial energy, the Bi-rich phase in the Sn-Bi eutectic system spontaneously coarsens and grows, a microstructure evolution process dominated by the Ostwald ripening mechanism. Aging experiments show that Sn-Bi solder undergoes significant two-phase coarsening during aging at 50℃, and Sn at the solder / substrate interface becomes depleted. Simultaneously, the intermetallic compound (IMC) layer continues to grow. This coarsening not only weakens the grain-refining strengthening effect but also increases the size of the Bi-rich brittle phase, exacerbating the stress concentration tendency.

[0008] 3) Insufficient mechanical properties of the weld joint

[0009] The combined effect of the brittleness of the Bi phase and the coarsening of the microstructure ultimately manifests as a deterioration in the mechanical properties of the solder joint. On the one hand, the coarsened Bi-rich phase, due to its brittle nature, is more prone to cleavage fracture under stress; on the other hand, although the maximum shear stress of the Sn-Bi solder joint may increase slightly after aging, the changes in ductility and the shift in failure mode reduce the reliability of the solder joint under impact loads. Summary of the Invention

[0010] To achieve the above objectives, the present invention provides a high-performance tin-bismuth alloy solder for semiconductor packaging, which, by weight percentage, comprises the following components:

[0011] Bi: 40.0~58.0%;

[0012] Ni: 0.3~0.8%;

[0013] TiC nanoparticles: 0.05~0.2%;

[0014] The balance is Sn and unavoidable impurities.

[0015] Preferably, the TiC nanoparticles have a particle size of 10~100nm and a purity of ≥99.9%.

[0016] Preferably, it is composed of the following components by weight percentage: Bi: 50%, Ni: 0.6%, TiC: 0.15% and balance Sn.

[0017] Preferably, it is composed of the following components by weight percentage: Bi: 52%, Ni: 0.5%, TiC: 0.1% and balance Sn.

[0018] Preferably, it is composed of the following components by weight percentage: Bi: 55%, Ni: 0.4%, TiC: 0.08% and balance Sn.

[0019] On the other hand, a method for preparing solder powder for the tin-bismuth alloy solder is provided, comprising the following steps:

[0020] S01 Weigh each raw material according to the ratio, heat pure tin to 350~400℃ to melt, add pure bismuth and Ni source, keep warm for 30~60 minutes, melt evenly, and obtain Sn-Bi-Ni liquid alloy.

[0021] S02 is used to pre-treat TiC nanoparticles by vacuum drying;

[0022] S03 adds TiC nanoparticles to the liquid alloy of S01 and uses ultrasonic dispersion treatment to make the TiC nanoparticles uniformly dispersed in the liquid alloy.

[0023] S04 controls the temperature of the molten alloy with uniformly dispersed TiC nanoparticles at 345~355℃ and conveys it to the atomization chamber for atomization and powder production.

[0024] S05 collects alloy powder, which is then cooled and sieved to obtain tin-based alloy solder powder with a particle size of T5~T6.

[0025] Preferably, the Ni source in S01 is a Sn-Ni master alloy.

[0026] Preferably, the ultrasonic dispersion treatment in S03 has a frequency of 15~30kHz, a power of 1~10kW, and a treatment time of 30~90 minutes.

[0027] Preferably, the atomization method described in S04 is nitrogen atomization.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] This invention utilizes the organic combination of four components, Sn-Bi-Ni-TiC, with the Bi content controlled at 40.0%~58.0%. This not only lowers the melting point and reduces thermal damage through eutectic reaction, but also enhances tensile strength and creep resistance through solid solution strengthening of appropriate Bi and precipitation of brittle phase, thus avoiding rapid deterioration of plasticity.

[0030] The introduction of Ni provides a strength basis by solidifying in the β-Sn matrix, and generates fine Ni3Sn4 particles to pin grain boundaries and suppress Bi phase coarsening. At the same time, it optimizes the interface IMC layer structure, suppresses the excessive growth of Cu6Sn5 and forms a thinner and denser (Cu,Ni)6Sn5 layer, which significantly improves the interface thermal stability and anti-peeling ability.

[0031] Based on this, TiC nanoparticles are uniformly distributed in the matrix as an inert, non-decomposing, and non-reactive dispersed phase. They hinder dislocation movement through the Orowan mechanism, pin grain boundaries and phase interfaces through the Zener effect, further consolidate the Ni-refined structure, inhibit the coarsening of the Bi phase during repeated reflows and high-temperature aging, reduce solder surface tension, improve wettability, and reduce void defects.

[0032] The three components form a clear synergistic chain, which maintains the advantage of Sn-Bi eutectic low melting point (about 139°C) to meet the requirements of low temperature packaging, while solving the problems of Bi phase brittleness, microstructure coarsening and insufficient mechanical properties of solder joints. Detailed Implementation

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1

[0035] A high-performance tin-bismuth alloy solder for semiconductor packaging, comprising the following components by weight percentage: Bi: 40.0~58.0%; Ni: 0.3~0.8%; TiC nanoparticles: 0.05~0.2%; with the balance being Sn and unavoidable impurities.

[0036] Bismuth (Bi) forms a eutectic structure with Sn, significantly lowering the solder melting point to around 139°C. This allows the solder to meet the requirements of low-temperature packaging processes, reducing thermal damage to heat-sensitive components and the substrate. Simultaneously, Bi dissolves in the Sn matrix, providing solid solution strengthening and precipitating dispersed brittle Bi phases, greatly improving the tensile strength and hardness of the solder and enhancing the creep resistance of the solder joint. Excessive Bi content leads to an increased melting point and insufficient strength, while insufficient Bi content results in a sharp increase in solder brittleness, a significant decrease in elongation and impact resistance, and reduced solder joint reliability. Therefore, this embodiment limits the Bi content to the range of 40.0% to 58.0%, achieving an optimal balance between low-temperature properties, mechanical strength, and ductility / toughness.

[0037] Ni partially dissolves in the β-Sn matrix, producing a solid solution strengthening effect. Simultaneously, it reacts with Sn to form fine Ni3Sn4 intermetallic compound particles, uniformly distributed within and around the grain boundaries. This effectively pins the grain boundaries, inhibits the coarsening and growth of the Bi phase, refines the solder microstructure, and improves the alloy's plasticity. Secondly, the addition of Ni significantly reduces the interfacial reaction rate between the solder and the Cu substrate, suppressing the excessive growth of the Cu6Sn5 layer and forming a (Cu,Ni)6Sn5 ternary compound layer. This compound layer is thinner, denser, and has better thermal stability, thus effectively improving the interfacial bonding reliability and anti-peeling ability of the solder joint under high-temperature aging and thermal cycling conditions. If the Ni content is too low, the microstructure refinement and interfacial regulation effects are not significant; if it is too high, it will lead to an increase in the solder melting point, and excessive Ni will promote the abnormal growth of needle-like (Cu,Ni)6Sn5, thus deteriorating the mechanical properties of the solder joint. Therefore, in this embodiment, the Ni content is limited to the range of 0.3% to 0.8% to achieve the best microstructure regulation and interfacial modification effects.

[0038] TiC nanoparticles possess extremely high hardness and elastic modulus, excellent thermal stability, and chemical inertness. During solder melting and reflow soldering, they do not decompose or react with the matrix, maintaining their intact particle morphology and uniformly dispersed within the Sn-Bi matrix. They form numerous nanoscale barriers along dislocation movement paths, effectively hindering dislocation slip and climb, significantly improving the solder's creep resistance and high-temperature strength. Furthermore, the dispersed distribution of TiC nanoparticles at grain boundaries creates a Zener pinning effect, effectively inhibiting the coarsening and growth of the Bi phase during repeated reflows and high-temperature aging, stabilizing the solder microstructure, and delaying solder joint performance degradation.

[0039] Furthermore, the addition of TiC nanoparticles can improve solder wettability, reduce solder surface tension, promote the spread of molten solder on the substrate, reduce porosity and voids within the solder joint, and increase solder joint density. When the TiC nanoparticle content is too low, the reinforcing effect is weak, making it difficult to exert significant dispersion strengthening and microstructure stabilization effects; when it is too high, it will lead to an increased tendency for nanoparticle agglomeration, with excessively small particle spacing, which will become stress concentration sources and crack initiation points, deteriorating the solder's plasticity and processing properties. Therefore, in this embodiment, the TiC nanoparticle content is limited to 0.05~0.2%, and the particle size is controlled within the range of 10~100nm to ensure uniform dispersion of nanoparticles in the solder matrix and optimal reinforcing effect.

[0040] The balance consists of Sn and unavoidable impurities. Sn, as a matrix component of the solder alloy, provides excellent electrical conductivity, thermal conductivity, and wettability. Together with Bi, Ni, and TiC nanoparticles, it forms a composite solder system, ensuring the overall solderability and comprehensive service performance of the solder. Unavoidable impurities mainly originate from raw materials and are introduced during the production process. Their total content must be strictly controlled to ≤0.05% to prevent impurity elements from adversely affecting the solder melting point, wettability, and solder joint reliability.

[0041] In other words, the solid solution strengthening of Ni provides the foundation for matrix strength, while the Orowan dispersion strengthening and grain refinement strengthening of TiC nanoparticles achieve a secondary improvement in mechanical properties on this basis. In terms of microstructure stability, Ni refines the eutectic structure, providing a finer grain boundary network for the uniform dispersion of TiC nanoparticles, while the pinning effect of TiC nanoparticles on grain boundaries and phase interfaces further consolidates the Ni-refined structure. Together, they inhibit Bi phase coarsening and grain growth, delaying solder performance degradation. In terms of interface reliability, Ni optimizes the intermetallic compound layer structure at the interface to reduce interface brittleness, while TiC nanoparticles alleviate stress concentration near the interface by increasing the strength of the solder matrix itself. Together, they synergistically enhance the solder joint's resistance to electromigration, thermal fatigue, and long-term service reliability.

[0042] A method for preparing solder powder for the above-mentioned tin-bismuth alloy solder includes the following steps: S01 Weigh each raw material according to the ratio, heat pure tin to 350~400℃ to melt, add pure bismuth and Ni source, keep warm for 30~60 minutes, melt uniformly, and obtain Sn-Bi-Ni liquid alloy; S02 Perform vacuum drying pretreatment on TiC nanoparticles.

[0043] S03 Add TiC nanoparticles to the liquid alloy in S01 and use ultrasonic dispersion treatment to make the TiC nanoparticles uniformly dispersed in the liquid alloy; S04 Control the temperature of the molten alloy with uniformly dispersed TiC nanoparticles at 345~355℃ and transport it to the atomization chamber for atomization powder making; S05 Collect the alloy powder, cool it and sieve it to obtain tin-based alloy solder powder with T5~T6 particle size.

[0044] Specifically, weigh out pure tin, pure bismuth, and Sn-10Ni master alloy according to the specified ratio. Place the pure tin in a crucible and heat it to 350~400℃ to melt it. Then add pure bismuth and Ni source in sequence and keep it at that temperature for 30~60 minutes. During this time, stir regularly with a tungsten rod or quartz rod to ensure that the alloy elements are fully and uniformly dissolved.

[0045] The temperature of the uniformly melted Sn-Bi-Ni liquid alloy was maintained at 350~380℃, and weighed TiC nanoparticles were added. Before adding, the TiC nanoparticles were dried in a vacuum oven at 130℃ for 3 hours to remove surface-adsorbed moisture and gas. After adding the TiC nanoparticles, high-power ultrasonic dispersion treatment was used, with an ultrasonic frequency of 15~30kHz, a power of 1~10kW, and a treatment time of 30~90 minutes, so that the TiC nanoparticles were fully dispersed in the liquid alloy and agglomeration was avoided.

[0046] The temperature of the molten alloy with uniformly dispersed TiC nanoparticles is controlled at 345~355℃, and it is transported to the atomization chamber for atomization dispersion and molding treatment. The atomization method is gas atomization, and the working conditions of the atomization chamber are controlled at 0~50℃ and the oxygen content is controlled at 400~2000ppm. If the temperature is too low, the nanoparticles will be easily oxidized, and if the temperature is too high, the alloy will be severely oxidized.

[0047] The atomized alloy powder is rapidly cooled into fine metal particles, and the desired particle size distribution of the welding powder is obtained by sieving, specifically welding powder with a particle size of T5~T6.

[0048] Example 2

[0049] A method for preparing solder powder for the above-mentioned tin-bismuth alloy solder includes the following steps:

[0050] S01 Weigh each raw material according to the ratio, heat pure tin to 350~400℃ to melt, add pure bismuth and Ni source, keep warm for 30~60 minutes, melt evenly, and obtain Sn-Bi-Ni liquid alloy.

[0051] S02 is used to pre-treat TiC nanoparticles by vacuum drying;

[0052] S03 adds TiC nanoparticles to the liquid alloy of S01 and uses ultrasonic dispersion treatment to make the TiC nanoparticles uniformly dispersed in the liquid alloy.

[0053] S04 controls the temperature of the molten alloy with uniformly dispersed TiC nanoparticles at 345~355℃ and conveys it to the atomization chamber for atomization and powder production.

[0054] S05 collects alloy powder, which is then cooled and sieved to obtain tin-based alloy solder powder with a particle size of T5~T6.

[0055] Furthermore, the Ni source in SO1 is pure Ni or Sn-Ni master alloy. When using Sn-Ni master alloy, the Ni content in the Sn-Ni master alloy is 5~20wt%, preferably 10wt%. Adding it in the form of Sn-Ni master alloy can reduce the melting temperature of Ni, shorten the melting time, and improve the dispersion uniformity of Ni element in Sn-Bi melt. This avoids the problem that pure Ni is difficult to completely dissolve at conventional melting temperatures due to its high melting point (1455℃). The amount of Sn-Ni master alloy added is determined based on the final Ni content in the target solder.

[0056] Pure Ni can also be used as the Ni source. The particle size of pure Ni is controlled to be ≤1mm, preferably 200~500 mesh powder, in order to increase the specific surface area and accelerate dissolution. If Sn-Ni master alloy is used as the Ni source, the Sn-Ni master alloy is pre-crushed into blocks or granules of ≤5mm to facilitate rapid melting into Sn-Bi melt.

[0057] Example 3

[0058] A method for preparing solder powder for the above-mentioned tin-bismuth alloy solder includes the following steps:

[0059] S01 Weigh each raw material according to the ratio, heat pure tin to 350~400℃ to melt, add pure bismuth and Ni source, keep warm for 30~60 minutes, melt evenly, and obtain Sn-Bi-Ni liquid alloy.

[0060] S02 is used to pre-treat TiC nanoparticles by vacuum drying;

[0061] S03 adds TiC nanoparticles to the liquid alloy of S01 and uses ultrasonic dispersion treatment to make the TiC nanoparticles uniformly dispersed in the liquid alloy.

[0062] S04 controls the temperature of the molten alloy with uniformly dispersed TiC nanoparticles at 345~355℃ and conveys it to the atomization chamber for atomization and powder production.

[0063] S05 collects alloy powder, which is then cooled and sieved to obtain tin-based alloy solder powder with a particle size of T5~T6.

[0064] Furthermore, during the S01 smelting process, in order to effectively prevent oxidation of the molten alloy surface and reduce the volatilization loss of alloying elements, a covering protection or atmosphere protection method can be adopted.

[0065] The protective coating uses a KCl-LiCl molten salt coating agent with a mass ratio of 1.25:1. This molten salt is in a molten state at a melting temperature of 350~400℃, and its density is lower than that of the Sn-Bi alloy melt. It can spread evenly on the surface of the melt to form a complete and dense liquid protective layer, effectively isolating the air from contact with the melt. Furthermore, this molten salt coating agent does not chemically react with the Sn-Bi-Ni alloy, and can be completely separated from the alloy melt after melting by allowing it to stand and separate into layers or by decanting. Rosin can also be used as a protective coating agent. Rosin melts at the melting temperature and spreads on the liquid surface to form an organic protective film. Its advantage is that no additional removal process is required afterward, as the rosin volatilizes during atomization, making the operation simple. However, its protective effect is slightly inferior to that of KCl-LiCl molten salt.

[0066] For atmosphere protection, a vacuum or inert atmosphere is selected. When vacuum protection is used, the vacuum degree is controlled at ≤10Pa. When inert atmosphere protection is used, high-purity nitrogen or argon is continuously introduced into the melting furnace at a flow rate of 0.5~2L / min to ensure that the oxygen content in the furnace is reduced to ≤100ppm. Atmosphere protection can avoid additional impurity contamination introduced by the covering agent and is especially suitable for the preparation of high-purity solder alloys.

[0067] Example 4

[0068] A method for preparing solder powder for the above-mentioned tin-bismuth alloy solder includes the following steps:

[0069] S01 Weigh each raw material according to the ratio, heat pure tin to 350~400℃ to melt, add pure bismuth and Ni source, keep warm for 30~60 minutes, melt evenly, and obtain Sn-Bi-Ni liquid alloy.

[0070] S02 is used to pre-treat TiC nanoparticles by vacuum drying;

[0071] S03 adds TiC nanoparticles to the liquid alloy of S01 and uses ultrasonic dispersion treatment to make the TiC nanoparticles uniformly dispersed in the liquid alloy.

[0072] S04 controls the temperature of the molten alloy with uniformly dispersed TiC nanoparticles at 345~355℃ and conveys it to the atomization chamber for atomization and powder production.

[0073] S05 collects alloy powder, which is then cooled and sieved to obtain tin-based alloy solder powder with a particle size of T5~T6.

[0074] Furthermore, the SO3 atomization method can be selected from any one of gas atomization, centrifugal atomization, or ultrasonic atomization.

[0075] Gas atomization uses high-pressure, high-speed airflow to impact the molten alloy liquid flow, utilizing the kinetic energy of the airflow to break the melt into fine droplets and rapidly condense them into powder. It is suitable for Sn-Bi alloys with low melting points and good fluidity, and can obtain alloy powders with good sphericity and concentrated particle size distribution. It has high production efficiency and relatively low cost, which is conducive to industrial mass production.

[0076] Centrifugal atomization involves feeding molten alloy onto a high-speed rotating atomizing disc or cup, where centrifugal force throws the melt out and breaks it into tiny droplets. The droplets spherize and cool during flight, solidifying into powder. This method is suitable for preparing welding powder with high sphericity and narrow particle size distribution.

[0077] Ultrasonic atomization utilizes ultrasonic vibration energy to excite capillary waves on the surface of a melt. When the vibration intensity reaches a critical value, the capillary waves break into micron-sized droplets and detach from the liquid surface. The droplets are then carried and cooled into powder by an inert gas flow. This method can be operated at lower temperatures, producing fine and uniform powder particles. It is particularly suitable for preparing submicron to micron-sized fine powders. However, it has low production efficiency and high energy consumption, making it suitable for preparing small batches of high-value-added welding powders.

[0078] It should be noted that the temperature of the molten alloy is controlled at 345~355℃ before atomization. This temperature range is slightly higher than the liquidus temperature of Sn-Bi alloy by 30~45℃. This ensures that the melt has sufficient fluidity to facilitate atomization and breakup, while avoiding excessive heat that could lead to increased interfacial reaction between nanoparticles and the matrix or increased volatilization loss of Bi element.

[0079] Example 5

[0080] A high-performance tin-bismuth alloy solder for semiconductor packaging, weighed by weight percentage: 52% Bi, 0.5% Ni, 0.1% TiC nanoparticles (average particle size 50nm), and the balance Sn (i.e., Sn-52Bi-0.5Ni-0.1TiC).

[0081] The method for preparing the solder powder of the above-mentioned tin-bismuth alloy solder includes the following steps:

[0082] S01 Weigh each raw material according to the ratio, heat pure tin to 380℃ to melt, add pure bismuth and Sn-10Ni intermediate alloy, keep warm for 45 minutes, melt evenly, and obtain Sn-Bi-Ni liquid alloy.

[0083] S02 is used to pre-treat TiC nanoparticles by vacuum drying;

[0084] S03 adds TiC nanoparticles to the liquid alloy of S01 and uses ultrasonic dispersion treatment to make the TiC nanoparticles uniformly dispersed in the liquid alloy.

[0085] S04 controls the temperature of the molten alloy with uniformly dispersed TiC nanoparticles at 350℃ and transports it to the atomization chamber for nitrogen atomization to produce powder.

[0086] S05 collects alloy powder, which is then cooled and sieved to obtain tin-based alloy solder powder with a particle size of T5~T6.

[0087] The ultrasonic dispersion conditions were: 20kHz, 5kW, and a processing time of 60min.

[0088] Nitrogen atomization powder production parameters: chamber temperature 25℃, oxygen content 800ppm.

[0089] Example 6

[0090] Weigh the following by weight percentage: Bi 50%, Ni 0.6%, TiC nanoparticles (average particle size 80nm) 0.15%, balance Sn.

[0091] The preparation process is the same as in Example 5.

[0092] Example 7

[0093] Weigh the following by weight percentage: Bi 55%, Ni 0.4%, TiC nanoparticles (average particle size 30nm) 0.08%, balance Sn.

[0094] The preparation process is the same as in Example 5.

[0095] Final performance test results (Part 1)

[0096] Performance indicators Example 5 Example 6 Example 7 Melting point (°C) 140-143 141-144 139-142 Tensile strength (MPa) 72 69 70 Elongation (%) 25 22 23 Average size of Bi phase (µm) 2.5 2.8 2.3 Electromigration lifetime (relative value) 4.8 4.2 4.5 Wetting angle (°) 18 20 19

[0097] Results analysis:

[0098] Example 5 (Sn-52Bi-0.5Ni-0.1TiC) exhibits the best overall performance, with a tensile strength of 72MPa, an elongation of 25%, an average Bi phase size of only 2.5μm, and a significantly refined microstructure.

[0099] Comparative Example 1

[0100] Sn-52Bi-0.5Ni, without the addition of TiC nanoparticles, the rest of the process is the same as in Example 5.

[0101] Comparative Example 2

[0102] Sn-52Bi-0.1TiC, without adding Ni element, the rest of the process is the same as in Example 5.

[0103] Comparative Example 3

[0104] Sn-58Bi, without any added strengthening elements or particles.

[0105] Final performance test results (Part 2)

[0106] Performance indicators Example 5 Comparative Example 1 Comparative Example 2 Comparative Example 3 Melting point (°C) 140-143 141-143 139-141 139 Tensile strength (MPa) 72 55 48 38 Elongation (%) 25 20 15 10 Average size of Bi phase (µm) 2.5 6.5 4.0 12.0 Electromigration lifetime (relative value) 4.8 2.5 1.8 1.0 Wetting angle (°) 18 22 25 28

[0107] Comparative Example 1 showed that the addition of TiC increased the tensile strength by 31%, refined the Bi phase size from 6.5 μm to 2.5 μm, and increased the electromigration lifetime by 92%, confirming the grain refinement and dispersion strengthening effects of TiC nanoparticles.

[0108] Comparative Example 2 showed that the addition of Ni increased tensile strength by 50% and electromigration lifetime by 167%, confirming the solid solution strengthening and interface stabilization effects of Ni.

[0109] Comparative Example 3 shows that (traditional Sn-58Bi) has a coarse Bi phase (12μm), an elongation of only 10%, and the worst mechanical properties and electromigration lifetime.

[0110] Example 8

[0111] A tin-bismuth alloy solder paste is prepared by mixing and stirring the tin-bismuth alloy solder powder obtained in Example 5 with a flux in a certain proportion, wherein the content of solder or solder powder is 78~92wt% and the content of flux is 8~22wt%.

[0112] The flux composition specifically includes: resin (25~40%), solvent (20~40%), organic acid activator (5~15%), thixotropic agent (1~10%), corrosion inhibitor (0.5~3%), etc.

[0113] In the actual preparation process, the components of the flux should be weighed according to the ratio and placed in a mixing tank. The mixture should be heated in a water bath at 25~60℃ and stirred at 200~1000rpm until all components are completely dissolved into a uniform transparent liquid. After cooling to room temperature, the weighed tin-bismuth alloy solder powder should be added. The mixture should be mixed and dispersed evenly using a planetary mixer or a three-roll mill at a stirring speed of 500~3000rpm for 15~60 minutes to finally produce a homogeneous solder paste.

[0114] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0115] The above description is only used to illustrate the technical solution of the present invention and is not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention, as long as they do not depart from the spirit and scope of the technical solution of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A high-performance tin-bismuth alloy solder for semiconductor packaging, characterized in that, By weight percentage, it consists of the following components: Bi: 40.0~58.0%; Ni: 0.3~0.8%; TiC nanoparticles: 0.05~0.2%; The balance is Sn and unavoidable impurities.

2. The high-performance tin-bismuth alloy solder for semiconductor packaging according to claim 1, characterized in that, The TiC nanoparticles have a particle size of 10~100nm and a purity of ≥99.9%.

3. The high-performance tin-bismuth alloy solder for semiconductor packaging according to claim 1, characterized in that, It consists of the following components by weight percentage: Bi: 50%, Ni: 0.6%, TiC: 0.15% and balance Sn.

4. The high-performance tin-bismuth alloy solder for semiconductor packaging according to claim 1, characterized in that, By weight percentage, it consists of the following components Composition: Bi: 52%, Ni: 0.5%, TiC: 0.1% and balance Sn.

5. The high-performance tin-bismuth alloy solder for semiconductor packaging according to claim 1, characterized in that, It consists of the following components by weight percentage: Bi: 55%, Ni: 0.4%, TiC: 0.08% and balance Sn.

6. A method for preparing solder powder for a tin-bismuth alloy solder as described in any one of claims 1-5, characterized in that, Includes the following steps: S01 Weigh each raw material according to the ratio, heat pure tin to 350~400℃ to melt, add pure bismuth and Ni source, keep warm for 30~60 minutes, melt evenly, and obtain Sn-Bi-Ni liquid alloy. S02 is used to pre-treat TiC nanoparticles by vacuum drying; S03 adds TiC nanoparticles to the liquid alloy of S01 and uses ultrasonic dispersion treatment to make the TiC nanoparticles uniformly dispersed in the liquid alloy. S04 controls the temperature of the molten alloy with uniformly dispersed TiC nanoparticles at 345~355℃ and conveys it to the atomization chamber for atomization and powder production. S05 collects alloy powder, which is then cooled and sieved to obtain tin-based alloy solder powder with a particle size of T5~T6.

7. A method for preparing solder powder for a tin-bismuth alloy solder as described in any one of claims 6, characterized in that, The Ni source mentioned in S01 is a Sn-Ni master alloy.

8. A method for preparing solder powder for a tin-bismuth alloy solder as described in any one of claims 6, characterized in that, The ultrasonic dispersion treatment described in S03 has a frequency of 15~30kHz, a power of 1~10kW, and a treatment time of 30~90 minutes.

9. A method for preparing solder powder for a tin-bismuth alloy solder as described in any one of claims 6, characterized in that, The atomization method described in S04 is nitrogen atomization.