High-performance low-silver lead-free solder and preparation method thereof

Abstract

The invention relates to the technical field of electronic packaging materials, and particularly discloses a high-performance low-silver lead-free solder and a preparation method thereof. The solder is prepared from the following components in percentage by mass: 0.1 to 1 percent of Ag, 0.01 to 1 percent of Cu, 0.1 to 3.8 percent of Bi, 0.002 to 0.3 percent of Ni, 0.02 to 2 percent of In, 0.001 to 0.5 percent of Co, 0.001 to 0.5 percent of Ce and the balance of Sn. 0.05 to 0.2 percent of at least one of Ga, Ge and P can be selectively added. The components of the solder must simultaneously meet the following two relational expressions: 0.15 < = (Ni + Co) / In < = 3.5 (1); (Ag-0. 5) + (Bi-2) / 4 < = 1 (2), wherein each element symbol represents the mass percent. The mass ratio of Ni to Co to In is controlled through a relational expression (1), and a (Cu, Ni, Co) 6 (Sn, In) 5 tough interface layer is promoted to be formed; contents of Ag and Bi are synergistically limited in an optimal elliptical interval through a relational expression (2), and brittleness is avoided while the strength is guaranteed. The solder has excellent wettability, mechanical property and thermal fatigue resistance reliability while remarkably reducing the silver content, and is suitable for the field of electronic packaging.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic packaging soldering of electronic and electrical products, and in particular to a high-performance low-silver lead-free solder and a preparation method thereof. BACKGROUND

[0002] In recent years, with the enhancement of environmental awareness, electronic packaging lead-free has become a global consensus. Among the many lead-free solder systems, Sn-Ag-Cu alloy is considered as the most ideal substitute for traditional Sn-Pb solder due to its excellent comprehensive performance. One of the current industry's clear research directions is to develop low-silver (Ag < 1.0%) or even ultra-low-silver (Ag < 0.5%) Sn-Ag-Cu solder. However, simply reducing the silver content is a "double-edged sword": while reducing the cost and reducing the internal Ag3Sn phase, it also causes a new technical bottleneck, specifically manifested as uncontrolled interfacial reaction: the reduction of silver content weakens its inhibition of copper (Cu) element dissolution, leading to an increase in interfacial reaction between the solder and the copper substrate during reflow soldering and subsequent service, which will form an excessively thick Cu6Sn5 and Cu3Sn intermetallic compound layer. This intermetallic compound (IMC) layer is not only a weak link of stress, but its excessive growth will also consume the plastic solder matrix of the solder joint itself, directly leading to a decrease in solder joint connection strength, an increase in resistance, and the initiation of cracks under thermal cycle loading, ultimately causing early failure.

[0003] Therefore, the existing low-silver Sn-Ag-Cu solder technology has obvious deficiencies in the precise regulation of interfacial IMC. Developing a new type of low-silver solder that can actively inhibit the excessive growth of interfacial IMC has become a key technical bottleneck for improving the long-term service reliability of the next generation of electronic products. SUMMARY

[0004] In order to solve the core technical bottleneck of "interfacial stability" caused by the reduction of silver content in existing low-silver / ultra-low-silver Sn-Ag-Cu solder, the present application provides a high-performance low-silver lead-free solder, which is based on quantitative component design and can precisely regulate interfacial reaction and actively inhibit the excessive growth of interfacial intermetallic compound (IMC) of the solder joint, avoiding it from becoming a weak link of reliability.

[0005] In the first aspect, the present application provides a high-performance low-silver lead-free solder, which adopts the following technical scheme:

[0006] A high-performance low-silver lead-free solder, comprising the following components and their mass percentages: 0.1-1% of Ag, 0.01-1% of Cu, 0.1-3.8% of Bi, 0.002-0.3% of Ni, 0.02-2% of In, 0.001-0.5% of Co, 0.001-0.5% of Ce, and the balance being Sn, and the mass percentages of the components satisfy the following (1) formula and (2) formula:

[0007] 0.15≤(Ni+Co) / In≤3.5 (1) Formula;

[0008] (Ag-0.5)²+(Bi-2)² / 4≤1 (2) Formula.

[0009] By adopting the above technical solution, this invention adds 0.1-1% Ag to the Sn-Ag-Cu solder. Ag in the alloy mainly reacts with Sn to form fine Ag3Sn intermetallic compounds. These dispersed strengthening phases effectively improve the strength and hardness of the alloy. Simultaneously, Ag also improves the electrical and thermal conductivity of the alloy. However, excessive Ag leads to coarsening of the Ag3Sn phase, which reduces the alloy's plasticity, and also increases raw material costs. Therefore, considering the overall solution of this invention, the optimal addition amount is 0.1%-1%.

[0010] This invention incorporates 0.01-1% Cu into the Sn-Ag-Cu solder. Cu primarily forms Cu6Sn5 intermetallic compounds in the alloy, which are dispersed in the matrix and act as a second-phase reinforcement. Furthermore, Cu can form a good metallurgical bond with the substrate; however, excessively high Cu content will increase the alloy's melting point and deteriorate its processing performance. Therefore, considering the overall design of this invention, the optimal addition amount is 0.01-1%.

[0011] This invention incorporates 0.1-3.8% Bi into Sn-Ag-Cu solder. Bi exhibits significant solid solution strengthening in the Sn matrix, effectively improving the alloy's strength and hardness. Simultaneously, the addition of Bi significantly lowers the alloy's melting point, improving welding process performance. However, excessive Bi can cause brittleness, necessitating strict control of its content. Therefore, considering the overall design of this invention, the optimal addition amount is 0.1-3.8%.

[0012] This invention incorporates 0.002-0.3% Ni into Sn-Ag-Cu solder. The addition of Ni effectively inhibits excessive dissolution of Cu into the solder, refines the interfacial IMC layer by forming the (Cu,Ni)6Sn5 phase, and improves interfacial bonding strength. Ni also promotes grain refinement, improves the overall mechanical properties of the alloy, and increases the melting point. Research indicates that the optimal addition amount is 0.002-0.3%.

[0013] This invention incorporates 0.02-2% In into Sn-Ag-Cu solder. In effectively lowers the alloy's melting point and improves wetting properties. More importantly, In can dissolve into the IMC layer to form a (Cu,Ni)6(Sn,In)5 composite phase. This phase exhibits better toughness and significantly enhances interfacial reliability. Studies have shown that the optimal addition amount is 0.02-2%.

[0014] The present application adds 0.001-0.5% Co in Sn-Ag-Cu solder. Co as grain refiner, can effectively hinder grain boundary movement, inhibit grain growth. Co can also form small intermetallic compounds with Sn, further improve the strength of the alloy, Co can also increase the melting point. Studies have shown that the best amount of addition is 0.001-0.5%.

[0015] The present application adds 0.001-0.5% Ce in Sn-Ag-Cu solder. Ce is a strong rare earth modifier, can effectively purify alloy melt, remove impurities. Ce can also promote nucleation, refine the grain, inhibit the growth of interface IMC, and form a protective film on the alloy surface, improve the oxidation resistance. Studies have shown that the best amount of addition is 0.001-0.5%.

[0016] The present application is Sn, but does not exclude the rest of the inevitable impurities.

[0017] It is worth pointing out that, through in-depth research, the present application found that under the constraint condition that the silver content is not more than 1%, the solder performance is dominated by two core mechanisms: one is the "interface behavior regulation" with Ni, Co, In interaction as the core; the second is the "matrix strengthening synergy" with Ag, Bi ratio as the core. For interface regulation, the present application found that since Ni and Co belong to transition elements, their atomic radii and chemical properties are similar. During reflow soldering, they can be jointly dissolved into the interface Cu6Sn5 phase to form (Cu, Ni, Co)6(Sn, In)5. This multi-component solid solution phase has higher lattice distortion energy and lower interface energy than the binary Cu6Sn5, thereby significantly refining the IMC grains and inhibiting their excessive growth and coarsening. In atoms can be dissolved into the Sn matrix and the IMC on the Sn side. Its addition will lower the overall surface energy of the solder and change the atomic diffusion dynamics. More importantly, we found that an appropriate amount of In can promote Ni and Co elements to participate in the interface reaction more effectively, playing the role of "activation" and "carrier". However, excessive In will excessively lower the melting point and possibly weaken the interface. The present application found that Ni and Co have a synergistic effect in inhibiting IMC growth and have a quantitative dependence on In, with the mass percentage satisfying: 0.15≤(Ni+Co) / In≤3.5. When (Ni+Co) / In<0.15, it means that the total amount of interface modification elements (Ni+Co) is severely insufficient relative to In. At this time, the "regulation" effect of In dominates, but there is a lack of sufficient Ni / Co to form stable (Cu, Ni, Co)6(Sn, In)5 strengthening phase, resulting in an excessively thin interface IMC layer, which reduces the mechanical bonding strength of the solder joint, and the structure is loose, the mechanical properties are poor, and the solder joint has weak shear and tensile resistance. When (Ni+Co) / In>3.5, it means that the content of Ni and Co is relatively high. Excess Ni and Co not only consume the regulation effect of In, but also can react with Sn to form brittle Ni3Sn4, CoSn3, and other independent phases. These hard particles will cut the solder matrix, causing a sharp decrease in plasticity and making the solder joint brittle. At the same time, excessive Ni / Co unnecessarily increases the alloy melting point. When 0.15≤(Ni+Co) / In≤3.5, the "IMC growth inhibition" effect of Ni and Co and the "diffusion optimization and synergy" effect of In reach a precise balance. Experiments show that at this time, a continuous, dense, and appropriately thick (Cu, Ni, Co)6(Sn, In)5 interface layer can be formed. This layer is firmly bonded to the copper substrate and can effectively block the mutual diffusion of Sn and Cu atoms, thereby obtaining a solder joint with high strength and excellent reliability. Based on this, the present application innovatively proposes the concept of "interface synergistic regulation factor" and quantifies it as (Ni+Co) / In.

[0018] In addition, the mass percentage of Bi and Ag satisfies the relationship (Ag-0.5) 2+(Bi-2) 2 / 4≤1. Ag provides second-phase strengthening by forming Ag3Sn phase, and the content of Ag is optimal at 0.5% in the low silver content range. When the content of Ag deviates from 0.5%, the content of Bi needs to be adjusted to compensate, so as to prevent high cost or brittleness caused by too high Ag and plasticity reduction caused by too high Bi. The addition of Bi has the effects of reducing the melting point, increasing the wettability and solid solution strengthening, and the solid solution strengthening of the solder is optimal at 2% content. Therefore, when Bi and Ag satisfy the relationship (Ag-0.5) 2+(Bi-2) 2 / 4≤1, the contents of Bi and Ag are kept in the optimal interval of the elliptical shape centered on (0.5% Ag, 2% Bi), the synergistic effect of Bi and Ag is optimal, and the comprehensive performance of the solder, such as the mechanical strength and toughness, is best. Based on this, the application innovatively proposes the concept of “material strengthening factor” and quantifies it as (Ag-0.5) 2+(Bi-2) 2 / 4.

[0019] The high-performance low-silver lead-free solder has excellent comprehensive performance, specifically, the solder can maintain good wettability, spreading ability, melting point, mechanical strength and creep resistance in a low-silver environment, meets the higher reliability requirements of micro-welding points for miniaturization and high-density packaging, and solves the problem of imbalance between interface stability and comprehensive performance in the prior art. Therefore, the high-performance low-silver lead-free solder of the application is a new type of low-silver solder which can actively inhibit the excessive growth of interface IMC, and simultaneously has excellent wettability, mechanical performance and process feasibility.

[0020] Preferably, the high-performance low-silver lead-free solder comprises the following components and mass percentages: 0.25-0.81% of Ag, 0.1-0.7% of Cu, 0.69-2.1% of Bi, 0.007-0.15% of Ni, 0.05-1% of In, 0.045-0.1% of Co, 0.05-0.2% of Ce, and the balance of Sn.

[0021] Preferably, at least one of Ga, Ge and P with a mass percentage of 0.05-0.2% is further included.

[0022] By adopting the above technical solution, Ga, Ge and P are used as auxiliary elements to further optimize the wettability and oxidation resistance. The application adds 0-0.2% of Ga, Ge or P in the Sn-Ag-Cu solder. Ga can further reduce the melting point of the alloy and improve the wettability; Ge and P are effective oxidation resistance elements and can reduce the generation of oxidation slag in the welding process.

[0023] In the second aspect, the application provides a preparation method of the high-performance low-silver lead-free solder, which adopts the following technical solution:

[0024] The preparation method of the high-performance low-silver lead-free solder in the scheme comprises the following steps in sequence according to a processing procedure:

[0025] S1: Ni, Co, Ce, P and part of Sn are respectively smelted into Sn-1Ni, Sn-1Co, Sn-5Ce and Sn-2P intermediate alloys at 550-650 DEG C in a vacuum environment;

[0026] S2: the remaining Sn is heated to 430-470 DEG C under the protection of a high-purity argon atmosphere, so that the Sn is completely melted; Ag, Cu, Bi and In are added, each is stirred for 10-20 minutes after being added, then the Sn-1Ni and Sn-1Co intermediate alloys are added, and the stirring is continued for 15-20 minutes, so that the intermediate alloys and the single elements are completely dissolved and uniformly distributed, and a uniform base melt is formed;

[0027] S3: the temperature of the base melt is reduced to 390-410 DEG C, the pre-prepared Sn-5Ce and Sn-2P intermediate alloys and Ga and Ge single elements are added, and ultrasonic vibration is performed for 5-10 minutes, and then electromagnetic stirring is performed for 10-20 minutes, so that the intermediate alloys and the single elements are completely dissolved, and the Ce, Ga, Ge and P elements are dispersed at a nanometer level, and the high-performance low-silver lead-free solder is obtained.

[0028] By adopting the technical scheme, in S1, since the melting points of Ni, Co and Ce are high, the Sn melt is easy to segregate and oxidize if the Ni, Co and Ce are directly added into the Sn melt, the Ni, Co and Ce are first prepared into intermediate alloys and then added into the Sn, so that the uniform dissolution can be ensured. In addition, the Ce is easy to oxidize, the Sn-5Ce is prepared, so that the stability after the Ce is added can be improved, and the yield of the active element can be controlled. This is a prerequisite for realizing the accurate control of the formula components and the effective play of the elements, and if the components are not uniformly added, the local Ni / Co concentration is too high, which may promote the abnormal growth of the IMC, and the opposite effect is brought.

[0029] In S3, since the properties of Ce, P, Ga and Ge are active or volatile, the addition at a low temperature can greatly reduce the burning loss, and the yield can be ensured. In addition, through the low temperature, ultrasonic vibration, electromagnetic stirring and intermediate alloy form, the purpose is to let these trace active elements exist in the form of small and dispersed particles or solid solutions, rather than aggregation. If the elements of Ce and P are dispersed at a nanometer level, the crystal boundary can be strongly pinned, the crystal grains can be refined, and the transverse growth and coarsening of the IMC layer can be inhibited in the subsequent welding, so that the strength (fine-grain strengthening) and toughness of the solder can be simultaneously improved. This is the core bridge between the connection preparation process and the final performance, and is also the most critical step in the preparation process.

[0030] Preferably, S4: the high-performance low-silver lead-free solder is kept at 340-360 DEG C for 50-60 minutes, and is poured into a metal mold preheated to 150-200 DEG C under the protection of argon, and the alloy ingot is obtained after cooling.

[0031] Preferably, in S4, the alloy ingot is subjected to thermal mechanical processing to further process into solder column, solder strip, solder wire, solder ball, solder powder or preformed solder sheet.

[0032] Compared with the prior art, the present application has the following advantages and technical effects:

[0033] 1. Accurate interface reaction control: when the mass percentage of Ni, Co and In satisfies the formula 0.15 ≤ (Ni+Co) / In ≤3.5 through the relationship (1), a (Cu, Ni, Co)6(Sn, In)5 intermetallic compound layer is formed at the interface. The IMC layer has excellent toughness and thermal stability, effectively inhibits the excessive growth of the interface IMC, and controls the IMC layer thickness after reflow soldering to be below 3 μm, significantly improving the thermal fatigue resistance of the solder joint.

[0034] 2. Optimal balance of comprehensive performance: the relationship (2) limits the content of Ag and Bi within an elliptical region centered at (0.5%, 2%), achieving the optimal ratio of melting strengthening elements and second phase strengthening elements. This design enables the solder to maintain excellent comprehensive performance under low silver conditions, with a wetting and spreading rate greater than 79%, a tensile strength exceeding 48 MPa, and a shear strength exceeding 33 MPa.

[0035] 3. Stable and reliable preparation process: the use of intermediate alloy form and closed-loop feedback adjustment process ensures accurate addition of active elements and precise control of composition, solving the technical problem of difficulty in ensuring the uniformity of multi-element micro-alloyed solder composition, and providing reliable guarantee for industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 Interface microstructure photo of high-performance low-silver lead-free solder prepared in Example 1 after soldering on a copper pad. DETAILED DESCRIPTION

[0037] The present application will be further described in conjunction with specific examples, but the scope of implementation and protection of the present application is not limited thereto.

[0038] The raw materials in the examples are obtained by market purchase.

[0039] Example 1

[0040] A high-performance low-silver lead-free solder, comprising the following ingredients and their mass percentages: Ag: 0.3%, Cu: 0.7%, Bi: 3.8%, Ni: 0.002%, In: 0.02%, Co: 0.05%, Ce: 0.001%, Sn: 95.127%. It comprises the following steps in order according to the processing procedure:

[0041] S1: Preparation of raw materials and master alloys: Sn, Ag, Cu, Bi and In metals with purity not less than 99.9% were prepared, and 0.2 g of Ni, 5 g of Co and 0.1 g of Ce were respectively smelted into Sn-1Ni, Sn-1Co and Sn-5Ce master alloys in a vacuum induction furnace at 550°C, respectively;

[0042] S2: Smelting of base solder alloy: 899.6 g of the remaining Sn was heated to 430°C in a smelting furnace under a protective atmosphere of high-purity argon to completely melt it; 3 g of Ag, 7 g of Cu, 38 g of Bi and 0.2 g of In were sequentially added, and stirred for 10 minutes after each addition; then, 2 g of Sn-1Ni and 50 g of Sn-1Co master alloys were added, i.e. Ni was added in the form of Sn-1Ni master alloy and Co was added in the form of Sn-1Co master alloy, and stirred for another 15 minutes until they were completely dissolved and uniformly distributed, forming a uniform base melt;

[0043] S3: Addition and dispersion of active element Ce: the temperature of the base melt was reduced to the active element addition window of 390°C, 0.2 g of the pre-prepared Sn-5Ce master alloy was added, and ultrasonic vibration was performed for 6 minutes, followed by electromagnetic stirring for 10 minutes, so that the master alloy was completely dissolved and the Ce element was dispersed at the nanoscale, obtaining a high-performance low-silver lead-free solder melt;

[0044] S4: Microstructure stabilization and shaping: the high-performance low-silver lead-free solder melt after composition adjustment was kept at 340°C for 50 minutes to promote melt homogenization and let impurities float; under argon protection, it was poured into a metal mold preheated to 150°C, and cooled to obtain an alloy ingot, i.e. 1000 g of high-performance low-silver lead-free solder.

[0045] Examples 2-5

[0046] Examples 2-5 all disclose a high-performance low-silver lead-free solder, which differs from Example 1 in the mass percentage of the composition and the preparation conditions, as shown in Table 1 and Table 2.

[0047] Example 6

[0048] Example 6 discloses a high-performance low-silver lead-free solder, which differs from Example 1 in the composition and its mass percentage, as shown in Table 1. It comprises the following steps in turn according to the processing procedure:

[0049] S1: Raw material and intermediate alloy preparation: Prepare Sn, Ag, Cu, Bi and In metals with a purity of not less than 99.9%, and melt 0.2g Ni with 19.8g Sn, 5g Co with 495g Sn, and 0.1g Ce with 1.9g Sn in a vacuum induction furnace at 550℃ to prepare Sn-1Ni, Sn-1Co and Sn-5Ce intermediate alloys respectively;

[0050] S2: Melting of the base solder alloy: Under a protective atmosphere of high-purity argon, heat 897.6g of the remaining Sn in a melting furnace to 430℃ until it is completely melted; add 3gAg, 7gCu, 38gBi, and 0.2gIn in sequence, stirring for 10 minutes after each addition. Then, add 2gSn-1Ni and 50gSn-1Co master alloys, i.e., add Ni in the form of Sn-1Ni master alloy and Co in the form of Sn-1Co master alloy, and stir for another 15 minutes until it is completely dissolved and evenly distributed to form a homogeneous base melt.

[0051] S3: Addition and dispersion of active elements Ce and Ge: The temperature of the base melt is reduced to the active element addition window of 390℃. 0.2g of pre-made Sn-5Ce master alloy and 2g of elemental Ge are added and ultrasonically vibrated for 6 minutes, followed by electromagnetic stirring for 10 minutes to completely dissolve the master alloy and achieve nanoscale dispersion of Ce and Ge elements, resulting in a high-performance low-silver lead-free solder melt.

[0052] S4: Structure stabilization and molding: The high-performance low-silver lead-free solder melt with adjusted composition is kept at 340℃ for 50 minutes to promote the homogenization of the melt and allow impurities to float to the surface; under argon protection, it is poured into a metal mold preheated to 150℃ and cooled to obtain an alloy ingot, which yields 1000g of high-performance low-silver lead-free solder.

[0053] Example 7

[0054] Example 7 discloses a high-performance low-silver lead-free solder, which differs from Example 1 in its composition and mass percentage, as detailed in Table 1. The processing steps are as follows:

[0055] S1: Raw material and intermediate alloy preparation: Prepare Sn, Ag, Cu, Bi and In metals with a purity of not less than 99.9%, and melt 0.2g Ni with 19.8g Sn, 5g Co with 495g Sn, and 0.1g Ce with 1.9g Sn in a vacuum induction furnace at 550℃ to prepare Sn-1Ni, Sn-1Co and Sn-5Ce intermediate alloys respectively;

[0056] S2: Melting of base solder alloy: 898.6 g of Sn was heated to 430 °C in a melting furnace under a protective atmosphere of high-purity argon to completely melt it; 3 g of Ag, 7 g of Cu, 38 g of Bi, and 0.2 g of In were added in sequence, and stirred for 10 minutes after each addition; then, 2 g of Sn-1Ni and 50 g of Sn-1Co master alloys were added, i.e., Ni was added in the form of Sn-1Ni master alloy, and Co was added in the form of Sn-1Co master alloy, and stirred for another 15 minutes until they were completely dissolved and uniformly distributed, forming a uniform base melt;

[0057] S3: Addition and dispersion of active elements Ce, Ga, and Ge: the temperature of the base melt was reduced to the active element addition window of 390 °C, and pre-prepared 0.2 g of Sn-5Ce master alloy, 0.5 g of Ga, and 0.5 g of Ge were added, and ultrasonic vibration was performed for 6 minutes, followed by electromagnetic stirring for 10 minutes, so that the master alloy was completely dissolved, and the elements Ce, Ga, and Ge were nano-dispersed, obtaining a high-performance low-silver lead-free solder melt;

[0058] S4: Organization stabilization and shaping: the high-performance low-silver lead-free solder melt after composition adjustment was kept at 340 °C for 50 minutes to promote melt homogenization and let impurities float up; under argon protection, it was poured into a metal mold preheated to 150 °C, and cooled to obtain an alloy ingot, i.e., 1000 g of high-performance low-silver lead-free solder.

[0059] Example 8

[0060] Example 8 discloses a high-performance low-silver lead-free solder, which differs from Example 1 in composition and mass percentage, as shown in Table 1. It comprises the following steps in sequence according to the processing procedure:

[0061] S1: Raw materials and master alloy preparation: Sn, Ag, Cu, Bi, and In metals with a purity of not less than 99.9% were prepared, and 0.2 g of Ni, 19.8 g of Sn, 5 g of Co, 495 g of Sn, 0.1 g of Ce, 1.9 g of Sn, 5 g of P, and 245 g of Sn were respectively melted into Sn-1Ni, Sn-1Co, Sn-5Ce, and Sn-2P master alloys in a vacuum induction furnace at 550 °C;

[0062] S2: Melting of base solder alloy: 874.6 g of Sn was heated to 430 °C in a melting furnace under a protective atmosphere of high-purity argon to completely melt it; 3 g of Ag, 7 g of Cu, 38 g of Bi, and 0.2 g of In were sequentially added, and each was stirred for 10 minutes; then, 2 g of Sn-1Ni and 50 g of Sn-1Co intermediate alloy were added, i.e., Ni was added in the form of Sn-1Ni intermediate alloy, and Co was added in the form of Sn-1Co intermediate alloy, and the mixture was stirred for another 15 minutes until the intermediate alloy was completely dissolved and uniformly distributed, forming a uniform base melt;

[0063] S3: Addition and dispersion of active elements Ce and P: the temperature of the base melt was reduced to the active element addition window of 390 °C, 0.2 g of Sn-5Ce and 25 g of Sn-2P intermediate alloy were added, and ultrasonic vibration was performed for 6 minutes, followed by electromagnetic stirring for 10 minutes, so that the intermediate alloy was completely dissolved, and the Ce and P elements were dispersed at the nanoscale, obtaining a high-performance low-silver lead-free solder melt;

[0064] S4: Organization stabilization and shaping: the high-performance low-silver lead-free solder melt after component adjustment was kept at 340 °C for 50 minutes to promote melt homogenization and allow impurities to float; under argon protection, it was poured into a metal mold preheated to 150 °C, and cooled to obtain an alloy ingot, i.e., 1000 g of high-performance low-silver lead-free solder.

[0065] Comparative Example 1

[0066] The raw material components and their mass percentages are as follows: Ag: 0.3%, Cu: 0.7%, Sn: 99%.

[0067] In a melting furnace, 990 g of Sn raw material was melted at a temperature of 450 °C, and then 3 g of Ag and 7 g of Cu were added, and the mixture was stirred and kept for 2 h, thereby obtaining 1000 g of Sn-0.3Ag-0.7Cu lead-free solder.

[0068] Comparative Example 2

[0069] The raw material components and their mass percentages are as follows: Ag1: 3.0%, Cu: 0.5%, Sn: 96.5%.

[0070] In a melting furnace, 965 g of Sn raw material was melted at a temperature of 450 °C, and then 30 g of Ag and 5 g of Cu were added, and the mixture was stirred and kept for 2 h, thereby obtaining 1000 g of Sn-3.0Ag-0.5Cu lead-free solder.

[0071] Comparative Examples 3-8

[0072] Comparative Examples 3-8 all disclose a high-performance low-silver lead-free solder, which differs from Example 1 in the mass percentages of the components, as shown in Table 1.

[0073] Comparative Example 9

[0074] Comparative Example 9 discloses a high-performance low-silver lead-free solder, which differs from Example 1 in the preparation method. In Comparative Example 9, Ni, Co and Ce are not smelted into an intermediate alloy in S1, but Ni and Co are directly added to Sn in S2, and Ce is directly added to Sn in S3.

[0075] Comparative Example 10

[0076] Comparative Example 10 discloses a high-performance low-silver lead-free solder, which differs from Example 1 in the preparation method. In Comparative Example 10, after adding the intermediate alloy in S3, ordinary mechanical stirring is used instead of ultrasonic vibration and electromagnetic stirring, and the stirring time is 22 minutes.

[0077] Comparative Example 11

[0078] Comparative Example 11 discloses a high-performance low-silver lead-free solder, which differs from Example 1 in the preparation method. In Comparative Example 11, the ultrasonic vibration time in S3 is 4 minutes, and the electromagnetic stirring time is 8 minutes.

[0079] Table 1 Composition of each example and comparative example and its mass percentage and value of two relationship formulas

[0080] Ingredients / % Example / Comparative Example Ag Cu Bi Ni In Co Ce Ga Ge P Sn (Ni+Co) / In (results retained to two decimal places) (Ag-0.5)2+(Bi-2)2 / 4 (results retained to two decimal places) Example 1 0.3 0.7 3.8 0.002 0.02 0.05 0.001 0 0 0 95.127 2.6 0.85 Example 2 0.25 1 1.85 0.3 2 0.001 0.5 0 0 0 94.099 0.15 0.07 Example 3 0.1 0.1 0.69 0.15 1 0.1 0.1 0 0 0 97.76 0.25 0.59 Example 4 1 0.5 2.1 0.06 0.16 0.5 0.2 0 0 0 95.48 3.5 0.25 Example 5 0.81 0.01 0.1 0.007 0.05 0.045 0.05 0 0 0 98.928 1.04 1.00 Example 6 0.3 0.7 3.8 0.002 0.02 0.05 0.001 0 0.2 0 94.927 2.6 0.85 Example 7 0.3 0.7 3.8 0.002 0.02 0.05 0.001 0.05 0.05 0 95.027 2.6 0.85 Example 8 0.3 0.7 3.8 0.002 0.02 0.05 0.001 0 0 0.05 95.077 2.6 0.85 Comparative Example 1 0.3 0.7 0 0 0 0 0 0 0 0 99 / / Comparative Example 2 3 0.5 0 0 0 0 0 0 0 0 96.5 / / Comparative Example 3 0.3 0.7 3.8 0.002 0.04 0.4 0.02 0 0 0 94.738 10.05 0.85 Comparative Example 4 0.3 0.7 3.8 0.1 1.5 0.003 0.001 0 0 0 93.596 0.07 0.85 Comparative Example 5 1 0.7 3.8 0.002 0.02 0.05 0.001 0 0 0 94.427 2.6 1.06 Comparative Example 6 0.08 0.7 3.8 0.002 0.01 0.002 0.001 0 0 0 95.405 0.4 0.99 Comparative Example 7 0.3 0.7 3.8 0.002 2.05 0.8 0.001 0 0 0 92.347 0.39 0.85 Comparative Example 8 0.065 0.7 3.8 0.41 2.4 0.05 0.001 0 0 0 92.574 0.19 1.00 Comparative Example 9 0.3 0.7 3.8 0.002 0.02 0.05 0.001 0 0 0 95.127 2.6 0.85 Comparative Example 10 0.3 0.7 3.8 0.002 0.02 0.05 0.001 0 0 0 95.127 2.6 0.85 Comparative Example 11 0.3 0.7 3.8 0.002 0.02 0.05 0.001 0 0 0 95.127 2.6 0.85

[0081] Table 2 Preparation conditions of each example and comparative example

[0082] Example / Comparative Example Preparation Conditions Example 1 Example 2 Example 3 Example 4 Example 5 S1 Melting temperature / °C 550 650 600 580 650 S2 Heating temperature / °C 430 470 450 460 450 S2 Element stirring time / min 10 20 15 14 10 S2 Alloy stirring time / min 15 20 18 18 20 S3 Cooling temperature / °C 390 410 400 410 390 S3 Ultrasonic time / min 6 7 10 5 8 S3 Stirring time / min 10 15 18 13 20 S4 Holding temperature / °C 340 360 350 355 360 S4 Holding time / min 50 60 55 55 50 S4 Preheating temperature / °C 150 200 180 170 180

[0083] Performance test

[0084] The present application tests the performance of each example and comparative example of high-performance low-silver lead-free solder under the same test conditions, and the test method is as follows. The test results are shown in Table 3.

[0085] Method for testing the thickness of the interfacial IMC layer after reflow soldering

[0086] The solder and the pure copper substrate are soldered under the standard reflow curve, and then cold inlaid with epoxy resin, polished to a mirror surface by step-by-step sandpaper grinding and diamond polishing liquid. A nitrate acid alcohol solution of 2% HNO3+3% HCl+98% C2H5OH (volume ratio) is used for slight corrosion for a few seconds to clearly show the IMC layer. The field emission scanning electron microscope is used to observe in the backscattered electron mode, and the IMC layer and the solder / substrate have obvious contrast differences. 20 different positions are randomly selected at the interface, and the selected positions should uniformly cover the thick, thin and transition regions of the IMC layer. The image analysis software is used to directly measure the thickness (µm) of the IMC layer, and the average value is taken as the test result.

[0087] Melting temperature test method

[0088] Before the test, a small piece of solder with a mass of about 20 mg is accurately weighed on a centesimal balance, then placed in an ultrasonic instrument to clean the grease and dirt on its surface with anhydrous ethanol, and finally placed in a DSC Q200 instrument in a nitrogen atmosphere for testing the melting interval. The test conditions are that the temperature range is 45-260℃, and the temperature rising rate is 5℃ / min.

[0089] Expansion rate test method

[0090] The expansion rate is a quantitative measure of the wetting and spreading ability of the solder, and reflects its soldering processability. The expansion rate test method of the examples and the comparative examples refers to the "solder ball expansion rate test method" of JIS Z 3198, that is, the solder is made into a solder ball with a mass of 0.3 g, and welded to a Cu sheet. After the welding is completed, an optical microscope and image analysis software are used to measure the maximum expansion diameter (D) and height (H) of the solder joint. The expansion rate is calculated as: expansion rate (%) = [(D-H) / D] x 100%, or the spreading area is directly used for comparison.

[0091] Tensile strength test method

[0092] The prepared solder is cast into a dog bone-shaped tensile specimen with a length of 100 mm and a diameter of 6 mm, and tensile testing is performed on a universal material testing machine. The test temperature is room temperature, the force loading mode is a tensile rate of 1 N / min, the stress-strain curve is recorded, the tensile strength (MPa) and the elongation after fracture (%) are directly read, and the average value of 10 effective specimens is taken as the tensile strength test result.

[0093] Shear strength test method

[0094] The prepared solder is prepared into a solder joint on a Cu plate, and a shear strength test is performed on a push-pull force testing instrument. A push force is applied from the side of the solder joint at a shear rate of 0.2 mm / s, until fracture, the maximum shear force is recorded, and the fracture mode is observed.

[0095] Table 3: Test results of various properties of each example and comparative example

[0096] Test Item Example / Comparative Example Interfacial IMC thickness after reflow soldering (pm) Melting range (°C) Expansion rate (%) Tensile strength (MPa) Shear strength (MPa) Example 1 2.7 218.1-223.5 82.5 48.2 35.1 Example 2 2.3 216.8-228.1 79.6 51.5 37.8 Example 3 2.4 217.2-224.7 82.3 53.8 39.5 Example 4 2.9 219.6-226.4 79.1 55.5 33.9 Example 5 2.6 217.3-225.2 80.6 49.7 36.2 Example 6 2.8 218.3-223.6 84.5 49.1 35.5 Example 7 2.7 216.0-221.8 84.1 48.8 36.0 Example 8 2.8 217.5-223.2 83.9 48.6 34.9 Comparative Example 1 3.3 217.2-227.5 73.5 38.4 28.7 Comparative Example 2 4.5 217.4-221.8 75.0 45.0 34.9 Comparative Example 3 3.2 217.8-224.2 80.9 40.0 35.8 Comparative Example 4 2.2 218.6-225.9 83.5 42.6 32.4 Comparative Example 5 2.7 218.4-226.3 78.8 41.7 34.9 Comparative Example 6 2.8 221.2-225.6 76.2 43.5 31.0 Comparative Example 7 2.6 219.6-224.9 84.5 50.5 36.9 Comparative Example 8 2.7 219.2-225.5 85.6 48.5 34.9 Comparative Example 9 3.0 218.3-224.2 82.1 49.0 35.5 Comparative Example 10 3.1 217.5-223.0 81.9 48.6 34.6 Comparative Example 11 3.0 217.7-223.6 82.5 47.7 35.4

[0097] As can be seen from Table 3 in combination with Examples 1-5, the interface IMC thickness of the high-performance low-silver lead-free solder of the present application can be as low as 3 μm or less after reflow soldering, and in combination with Figure 1 as shown in Figure 1The interface microstructure photos of the high-performance low-silver lead-free solder prepared in Example 1 after soldering on the copper pad can clearly observe that a continuous, dense and moderate thickness (Cu, Ni, Co)6(Sn, In)5 interface thin layer is formed at the soldering interface, which indicates that the high-performance low-silver lead-free solder of the application has the ability to precisely control the interface reaction and actively inhibit the excessive growth of the solder joint interface IMC through the quantitative composition design, so that the interface IMC thickness after reflow soldering is kept below 3 μm, showing excellent interface stability. In addition, there are a large number of dispersed Ag3Sn phases (large particle) in the solder area near the solder joint interface, which can significantly improve the mechanical strength of the solder. At the same time, the melting range of the high-performance low-silver lead-free solder of the application is between 216-230℃, the wetting expansion rate is more than 79%, the tensile strength is greater than 48 MPa, and the shear resistance is greater than 33 MPa, which takes into account the excellent melting capacity, wetting and spreading capacity, mechanical properties and process feasibility, so the high-performance low-silver lead-free solder of the application not only effectively solves the problem of IMC overgrowth, but also solves the problem of imbalance between interface stability and comprehensive performance in the prior art.

[0098] As can be seen from Examples 1 and 6-8, Examples 6-8 add at least one auxiliary element Ga, Ge and P on the basis of Example 1, and the expansion rate is improved to different degrees, which is due to the addition of antioxidant elements to reduce oxidation and improve wetting, thereby improving the expansion rate.

[0099] As can be seen from Examples 1-5 and Comparative Examples 1-2, Comparative Examples 1 and 2 are Sn-0.3Ag-0.7Cu low-silver lead-free solder and Sn-3.0Ag-0.5Cu high-silver lead-free solder commonly used in the industry at present, under the same test conditions, compared with conventional silver-containing lead-free solder, the high-performance low-silver lead-free solder of the application has a thinner interface IMC thickness after reflow soldering, and the effect is better. By comparing Examples 1-5 with Comparative Example 1, it can be found that the high-performance low-silver lead-free solder of the application is obviously better than Sn-0.3Ag-0.7Cu low-silver lead-free solder in basically all aspects. In addition, by comparing Examples 1-5 with Comparative Example 2, the mechanical properties of the high-performance low-silver lead-free solder of the application are close to those of Sn-3.0Ag-0.5Cu high-silver lead-free solder, but the Ag content of the high-performance low-silver lead-free solder of the application is lower than 1%, which can not weaken the mechanical properties in a low-silver environment. Such lead-free solder not only has a thin IMC thickness, but also has low cost, high wettability, good weldability, high reliability and high cost performance.

[0100] It can be seen from Example 1 and Comparative Examples 3-4 that Comparative Examples 3-4 all use appropriate amounts of various raw materials, but the value of (Ni+Co) / In of Comparative Example 3 is 10.05 and the value of (Ni+Co) / In of Comparative Example 4 is 0.07, both of which are not within the range of 0.15-3.5. The "interface behavior regulation" centered on the interaction of Ni, Co and In is the most important reason affecting the test results of the interface IMC layer thickness after reflow soldering. When (Ni+Co) / In < 0.15, it means that the total amount of interface modification elements (Ni+Co) is severely insufficient relative to In. At this time, the "regulation" effect of In is dominant, but there is a lack of sufficient Ni / Co to form a stable (Cu, Ni, Co)6(Sn, In)5 strengthening phase, resulting in an excessively thin interface IMC layer, which reduces the mechanical bonding strength of the solder joint, and the structure is loose, the mechanical properties are poor, and the solder joint has weak shear and tensile resistance. When (Ni+Co) / In > 3.5, it means that the content of Ni and Co is relatively high, resulting in a thick interface IMC layer. Moreover, the excess Ni and Co not only consume the regulation effect of In, but also can react with Sn to form brittle independent phases such as Ni3Sn4 and CoSn3, which will cut the solder matrix and cause a sharp decrease in plasticity, making the solder joint brittle. Therefore, the interface IMC thickness of Comparative Example 3 after reflow soldering is 3.2 μm, which is thicker than that of Example 1, and the interface IMC thickness of Comparative Example 4 after reflow soldering is 2.2 μm, which is thinner than that of Example 1. The above shows that under low-silver conditions, Co and Ni need to satisfy a specific ratio relationship to synergize with In to effectively regulate the interface. Thus, it is proved that Ni, Co and In have a synergistic effect rather than a simple additive effect, and it is also proved that not only do the various raw materials need to be appropriate and meet the relationship (Ag-0.5)²+(Bi-2)² / 4≤1, but also they need to meet the relationship 0.15≤(Ni+Co) / In≤3.5, so that the comprehensive performance of the solder is improved.

[0101] It can be seen from Example 1 and Comparative Example 5 that Comparative Example 5 also uses appropriate amounts of various raw materials, but the value of (Ag-0.5)²+(Bi-2)² / 4 of Comparative Example 5 is 1.06, which is greater than 1. After testing, the overall test results of Comparative Example 5 are not as good as those of Example 1, and the cost is also higher than that of Example 1. The Bi and Ag of Example 1 meet the relationship (Ag-0.5)²+(Bi-2)² / 4≤1, and the contents of Bi and Ag are kept within the optimal interval of the elliptical region centered on (0.5% Ag, 2% Bi), so the synergistic effect of Bi and Ag is best, and the comprehensive performance of the solder, such as mechanical strength and toughness, is best. Thus, it is proved that Ag and Bi have a synergistic effect rather than a simple additive effect, and it is also proved that not only do the various raw materials need to be appropriate and meet the relationship 0.15≤(Ni+Co) / In≤3.5, but also they need to meet the relationship (Ag-0.5)²+(Bi-2)² / 4≤1, so that the comprehensive performance of the solder is improved.

[0102] It can be seen from the combination of Example 1 and Comparative Examples 6-8 that Comparative Examples 6-8 all reduce, increase or simultaneously reduce and increase the amount of individual raw materials, but all keep the values of the two relational expressions within the set range. Due to the changes of different raw materials, Comparative Examples 6-8 respectively cause different performance effects: Comparative Example 6 reduces the strength and hardness of the solder alloy, increases the melting point, and reduces the wettability; the overall performance of Comparative Examples 7 and 8 is equivalent to that of Example 1, but since Comparative Examples 7 and 8 both use more expensive In, it is not conducive to reducing costs and does not meet the low-cost characteristics of the present application. The above test results show that there is a synergistic effect between Ni, Co and In, and a synergistic effect between Ag and Bi, but this synergistic effect is based on the appropriate amount of raw materials, thus proving that various raw materials must be appropriate even if they meet the relational expressions 0.15≤(Ni+Co) / In≤3.5 and (Ag-0.5)2+(Bi-2)2 / 4≤1, in order to improve the comprehensive performance of the solder.

[0103] It can be seen from the combination of Example 1 and Comparative Examples 3-8 that the high-performance low-silver lead-free solder of the present application not only requires the mass percentage of various raw materials to be within a certain range, but also requires the values of the two relational expressions to be within a certain range. Only when all three conditions are met can the synergistic effect between various raw materials be achieved to ensure that the solder achieves optimal comprehensive performance. If any of the conditions is not met, it will affect the comprehensive performance of the solder.

[0104] It can be seen from the combination of Example 1 and Comparative Example 9 that Comparative Example 9 does not first prepare Ni, Co and Ce into Sn-1Ni, Sn-1Co and Sn-5Ce intermediate alloys, but directly adds Ni, Co and Ce in the form of single elements to Sn. Ni, Co and Ce in the form of single elements are not easy to dissolve in Sn due to their high melting points or active properties, resulting in uneven addition and thus local Ni / Co concentration being too high, which in turn promotes the abnormal growth of IMC, resulting in an IMC thickness of up to 3 μm. Therefore, it is shown that first preparing Ni, Co and Ce into Sn-1Ni, Sn-1Co and Sn-5Ce intermediate alloys is a key and essential step for preparing the high-performance low-silver lead-free solder of the present application, and is a guarantee for the ideal interface IMC thickness.

[0105] It can be seen from the combination of Example 1 and Comparative Example 10 that, in Comparative Example 10, ordinary mechanical stirring (such as stirring by a paddle stirrer) is used instead of ultrasonic vibration and electromagnetic stirring in S3, and the stirring time is 22 minutes. Compared with Example 1, in Example 1, ultrasonic vibration is first performed for 6 minutes, and then electromagnetic stirring is performed for 10 minutes in S3. Although the stirring time of Comparative Example 10 is 6 minutes longer than that of Example 1, the solder prepared in Comparative Example 10 has poorer performance, and the thickness of the IMC at the interface after reflow soldering is 3.1 μm. This is because the intensity of mechanical stirring is far lower than that of ultrasonic vibration plus electromagnetic stirring. The elements such as Ce, P, Ga, and Ge that are active or volatile in nature need to be dispersed in the form of fine, dispersed particles or solid solutions to achieve nanodispersion to inhibit the lateral growth and coarsening of the IMC layer. However, mechanical stirring alone cannot ensure nanodispersion. Even if the mechanical stirring time is longer, it cannot replace ultrasonic vibration plus electromagnetic stirring. Therefore, ultrasonic vibration plus electromagnetic stirring is a key link between the preparation process and the final performance, and is one of the most critical steps in the preparation process.

[0106] It can be seen from the combination of Example 1 and Comparative Example 11 that, in Comparative Example 11, the ultrasonic vibration time and the electromagnetic stirring time in S3 are each reduced by 2 minutes, which results in an increase of 3 μm in the thickness of the IMC at the interface after reflow soldering. This shows that the ultrasonic vibration time and the electromagnetic stirring time are important factors affecting the thickness of the IMC. If the ultrasonic vibration time and the electromagnetic stirring time are not sufficient, individual raw materials cannot be completely dissolved and uniformly distributed, which weakens the inhibition of the excessive growth of the IMC, and makes the IMC layer thicker.

[0107] It can be seen from the combination of Example 1 and Comparative Examples 9-11 that the influence of the process on the performance of the high-performance low-silver lead-free solder of the application is not less than the influence of the formula composition on the performance of the high-performance low-silver lead-free solder. Only when the preparation method and the preparation conditions are closely matched with the formula composition elements can both of them play the maximum role together to achieve the preparation of low-silver lead-free solder with low cost and high performance.

[0108] It can be seen from the combination of Comparative Examples 1-2 and Comparative Examples 3-11 that, although the comprehensive performance of Comparative Examples 3-11 is not as good as that of Examples 1-8, it is still better than that of Comparative Examples 1-2. This shows that the high-performance low-silver lead-free solder of the application is a new type of low-silver solder compared with the prior art, and has excellent comprehensive performance, which helps to improve the long-term service reliability of the next generation of electronic products.

[0109] To sum up, the high-performance low-silver lead-free solder of the present application solves the technical problem of how to precisely control the multi-element micro-alloying while ensuring the stability of the solder joint interface and the overall mechanical properties by defining the "material strengthening factor", i.e., (Ag-0.5) 2+(Bi-2) 2 / 4, and the "interface synergistic control factor", i.e., (Ni+Co) / In. The present application can maintain the balance between "interface stability" and "overall performance" while reducing the silver content. Specifically, the present application has the following excellent effects: (1) Precise control of interface reaction, active inhibition of excessive growth of solder joint interface intermetallic compounds (IMC), and avoidance of becoming a weak link of reliability. (2) Breakthrough in performance imbalance, simultaneous realization of excellent wettability, high mechanical strength and good creep resistance under the premise of low silver. (3) Provide an industrialized and feasible preparation scheme to ensure that the above performance improvement can be stably and repeatedly achieved, and fundamentally overcome the defects of the prior art. The high-performance low-silver lead-free solder alloy ingot of the present application is subjected to thermal mechanical processing to further process into solder columns, solder strips, solder wires, solder balls, solder powder and pre-formed solder tabs, etc., which are suitable for use in the electronic packaging soft soldering field in wave soldering, reflow soldering, immersion soldering and manual soldering processes, and have very wide applications.

[0110] The specific embodiments are only an explanation of the present application, and are not a limitation of the present application. Those skilled in the art can make modifications to the embodiments without creative contribution after reading the present specification, as long as the modifications are within the scope of the claims of the present application.

Claims

1. A high-performance, low-silver, lead-free solder, characterized in that: It includes the following components and their mass percentages: 0.1-1% Ag, 0.01-1% Cu, 0.1-3.8% Bi, 0.002-0.3% Ni, 0.02-2% In, 0.001-0.5% Co, 0.001-0.5% Ce, with the balance being Sn, and the mass percentages of the components satisfy the following equations (1) and (2): 0.15≤(Ni+Co) / In≤3.5 (1) Formula; (Ag-0.5)²+(Bi-2)² / 4≤1 (2) Formula.

2. The high-performance low-silver lead-free solder according to claim 1, characterized in that: The high-performance low-silver lead-free solder comprises the following components and their mass percentages: 0.25-0.81% Ag, 0.1-0.7% Cu, 0.69-2.1% Bi, 0.007-0.15% Ni, 0.05-1% In, 0.045-0.1% Co, 0.05-0.2% Ce, with the balance being Sn.

3. The high-performance low-silver lead-free solder according to claim 1, characterized in that: It also includes at least one of Ga, Ge and P in a mass percentage of 0.05-0.2%.

4. The method for preparing the high-performance low-silver lead-free solder according to any one of claims 1-3, characterized in that: The processing steps are as follows: S1: Ni, Co, Ce, P and a portion of Sn are melted in a vacuum environment at 550-650℃ to form Sn-1Ni, Sn-1Co, Sn-5Ce and Sn-2P master alloys, respectively. S2: Under a protective atmosphere of high-purity argon, heat the remaining Sn to 430-470℃ until it is completely melted; add Ag, Cu, Bi and In elements, stirring for 10-20 minutes after each addition; then add Sn-1Ni and Sn-1Co master alloys, and stir for another 15-20 minutes until they are completely dissolved and evenly distributed to form a homogeneous base melt; S3: Reduce the temperature of the base melt to 390-410℃, add the pre-made Sn-5Ce, Sn-2P master alloy and Ga, Ge elements, and ultrasonically vibrate for 5-10 minutes, then electromagnetically stir for 10-20 minutes to completely dissolve the master alloy and elements, and achieve nanoscale dispersion of Ce, Ga, Ge and P elements to obtain high-performance low-silver lead-free solder.

5. The method for preparing high-performance low-silver lead-free solder according to claim 4, characterized in that: It also includes S4: holding the high-performance low-silver lead-free solder at 340-360℃ for 50-60 minutes, then pouring it into a metal mold preheated to 150-200℃ under argon protection, and cooling it to obtain an alloy ingot.

6. The method for preparing high-performance low-silver lead-free solder according to claim 5, characterized in that: In step S4, the alloy ingot is subjected to thermomechanical processing to further process it into solder pillars, solder bars, solder wires, solder balls, solder powder, or preformed solder sheets.

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