Low-silver alloy soldering tin material and preparation method thereof

Abstract

The invention relates to the technical field of soldering tin material processing, in particular to a low-silver alloy soldering tin material and a preparation method thereof.The low-silver alloy soldering tin material is prepared from, by weight, 0.05%-1% of silver, 0.4%-0.8% of copper, 0.1%-3.8% of bismuth, 0.01%-0.3% of indium, 0.01%-0.2% of antimony, 0.01%-0.05% of titanium, 0.05%-0.1% of rare earth oxide, 0.1%-0.5% of wetting agent and the balance tin. According to the invention, collaborative improvement of 240-245 DEG C low-temperature welding wettability and welding spot reliability is realized, low-temperature welding is realized, PCB thermal damage is avoided, the material cost is reduced, and the market competitiveness is improved.

Description

Technical Field

[0001] This application relates to the field of solder material processing technology, and more specifically, to a low-silver alloy solder material and its preparation method. Background Technology

[0002] With the miniaturization and high-density development of electronic components, surface mount technology has become the mainstream process for PCB assembly. Reflow soldering is a crucial step in achieving electrical connections between components and the circuit board. During reflow soldering, the solder alloy is heated and melted in a reflow oven to form solder joints. However, the heat resistance of PCB substrates and electronic components is limited, typically requiring the peak soldering temperature to be controlled within the range of 240-245℃ to avoid board delamination, deformation, and thermal damage to components.

[0003] To meet this temperature limitation, traditional technologies generally employ solder alloy systems with high silver content. This lowers the melting point of lead-free solders such as Sn-Ag-Cu, improving their wetting properties and spreading ability at low temperatures. By increasing the silver content, typically around 3%, the soldering temperature can be controlled within the PCB's tolerance range, thus avoiding thermal damage to the PCB substrate. Simultaneously, the addition of silver also improves solder wettability, enhancing the mechanical properties and fatigue life of the solder joint. However, silver, as a precious metal, is far more expensive than base metals like tin and copper. Significantly increasing the silver content leads to a substantial increase in solder costs, which, for large-scale production, severely weakens the product's market competitiveness.

[0004] When the amount of silver in solder is reduced to control costs, the solder melting point increases, leading to a series of technical problems: First, reducing silver usage to lower material costs increases the solder melting point. For every 5-10°C increase in soldering temperature, the risk of PCB thermal damage increases by 15-20%, while solder wettability decreases by more than 30%, resulting in increased rates of defects such as cold solder joints and bridging, and reduced product yield. Second, low-silver solder formulations have increased surface tension and decreased wettability, resulting in insufficient solder spread on the pad surface, easily causing defects such as cold solder joints and bridging. This is especially problematic for fine-pitch leads and via filling scenarios, where insufficient wettability has become a key bottleneck restricting soldering quality.

[0005] Therefore, how to reduce silver content to control costs while maintaining good wetting performance and solder joint reliability under the premise of ensuring low-temperature welding of 240-245℃ has become a technical problem that the electronic packaging industry urgently needs to solve. Summary of the Invention

[0006] To address the problem of increased solder joint height and decreased welding quality due to reduced silver usage, this application provides a low-silver alloy solder material and its preparation method.

[0007] In a first aspect, this application provides a low-silver alloy solder material, which adopts the following technical solution: A low-silver alloy solder material is prepared from the following raw materials by weight percentage: Silver 0.05-1% Copper 0.4-0.8% Bismuth 0.1-3.8% Indium 0.01-0.3% Antimony 0.01-0.2% Titanium 0.01-0.05% Rare earth oxides 0.05-0.1% Wetting agent 0.1-0.5% The remainder is tin.

[0008] By adopting the above technical solution and through multi-element microalloying and functional synergy mechanism, the wettability and solder joint reliability of low-temperature welding at 240-245℃ are synergistically improved under the condition that the silver content is reduced to 0.05-1%, thus realizing low-temperature welding, avoiding PCB thermal damage, reducing material costs, and enhancing market competitiveness.

[0009] This application incorporates low-melting-point alloying elements such as bismuth and indium to synergistically lower the solder's melting point, maintaining the alloy's solidus temperature within the range of 210-225℃ and liquidus temperature within the range of 225-240℃. This ensures that the peak soldering temperature can be controlled within the PCB's tolerance range of 240-245℃, addressing the issue of increased melting point caused by silver reduction. Simultaneously, this application uses a wetting agent to reduce the melt's surface tension, rare earth oxides to improve spreadability through surface purification and interface activation, and titanium to enhance interfacial reactivity. The synergistic effect of these three elements shortens wetting time and increases spreading area at 245℃, achieving wetting performance comparable to silver solder. This solves the defects such as cold solder joints and bridging caused by increased surface tension and insufficient wetting ability in low-silver formulations.

[0010] This application reduces the silver content from approximately 3% to 0.05-1%, a reduction of 70-98%, resulting in lower material costs. Simultaneously, the microalloying of antimony and the formation of Cu6Sn5 intermetallic compounds by copper reinforce the framework. These two factors synergistically improve the creep resistance and fatigue life of the solder joints, achieving mechanical properties at or above the level of traditional high-silver solders. This compensates for the mechanical property losses caused by the reduction in silver content, maintaining solder joint reliability while controlling costs and meeting the long-term reliability requirements of high-density electronic packaging.

[0011] Preferably, the rare earth oxide is one or more of cerium oxide, lanthanum oxide, and yttrium oxide.

[0012] By employing the above technical solution, the strong chemical activity of the alloy preferentially adsorbs and removes impurities such as oxygen from the melt, purifying the solder melt, reducing the solid-liquid interfacial tension, shortening the wetting time at 245℃, increasing the spreading area, and improving defects such as cold solder joints and bridging caused by insufficient wettability of low-silver solder. Simultaneously, rare earth oxides act as heterogeneous nucleation cores to refine the solder joint grains, inhibiting excessive growth of intermetallic compounds, thereby improving the shear strength of the solder joint and extending its fatigue life. This ensures solder joint reliability even with a 70-98% reduction in silver content.

[0013] Preferably, the average particle size of the rare earth oxide is 50-200 nm.

[0014] By adopting the above technical solution, the average particle size of rare earth oxides is optimized, and the specific surface area and reactivity are significantly improved by utilizing the nano-size effect. This allows for high dispersion in the melt and full adsorption of oxygen impurities, improving interface purification efficiency and further shortening the wetting time at 245℃. Nanoparticles, acting as heterogeneous nucleation cores, can refine the grain size of the solder joint, reducing the size of intermetallic compounds and improving the creep resistance of the solder joint.

[0015] Preferably, the wetting agent is composed of zinc, magnesium and manganese in a weight ratio of 1:(2-3):(0.1-0.5).

[0016] By adopting the above technical solution and optimizing the type and dosage of wetting agent, magnesium's strong chemical activity breaks down the oxide film on the solder pad surface, zinc reduces the surface tension of the melt, and manganese refines the grains. The synergistic effect of these three agents shortens the wetting time at 245℃ and increases the spreading area, resulting in superior wetting performance compared to traditional organic wetting agents. Furthermore, this metallic wetting agent melts into the alloy matrix during welding, leaving no residual contaminants. It also improves the shear strength of the solder joint, significantly increasing the welding yield while reducing the silver content by 70-98%, thus solving the problem of insufficient wettability in low-silver solders.

[0017] Preferably, the silver content is 0.1-0.8 wt%.

[0018] By adopting the above technical solution, the amount of silver used is further limited, reducing material costs by 70-95%. This range, in conjunction with bismuth and indium, controls the liquidus temperature at 225-240℃, ensuring a shorter wetting time and a larger spreading area during peak welding at 245℃. This reduces costs while maintaining welding quality comparable to high-silver systems, thus improving product yield.

[0019] Preferably, the silver content is 0.2-0.6 wt%.

[0020] By adopting the above technical solution, the amount of silver used is further limited, the cost is reduced by 80-93%, and the liquidus temperature is 227-235℃.

[0021] Preferably, the bismuth content is 0.5-3.5 wt%.

[0022] By adopting the above technical solution, the lower limit of bismuth content is increased. Each 1% bismuth content can lower the melting point by approximately 8-12℃, ensuring that the liquidus temperature of the low-silver formulation remains stable at 225-240℃. This range effectively inhibits β-Sn grain coarsening and brittle Bi phase aggregation, improving the impact toughness of the solder joint, enhancing its spreading performance, and solving the problem of insufficient wettability in low-silver solders.

[0023] Preferably, the bismuth content is 1.0-3.0 wt%.

[0024] By adopting the above technical solution, the bismuth content is further narrowed, forming an optimal melting point reduction synergy with 0.2-0.6% silver, which lowers the solidus temperature of the solder to 210-220℃ and stabilizes the liquidus temperature at 225-235℃. This formulation results in the most uniform solder joint microstructure.

[0025] Preferably, the indium content is 0.05-0.2 wt%.

[0026] By adopting the above technical solution and optimizing the indium dosage, the surface tension reduction effect of indium is improved, and the wetting time at 245℃ is shortened to ≤1.8s. Indium and bismuth synergistically suppress Bi segregation and improve solder joint ductility. Excessive indium will lead to a surge in cost and precipitation of the brittle InSn4 phase. This preferred range achieves a balance between performance and cost.

[0027] Preferably, it is prepared from the following raw materials by weight percentage: Silver 0.3-0.6%, copper 0.5-0.7%, bismuth 1.5-3.0%, indium 0.08-0.15%, antimony 0.05-0.12%, titanium 0.02-0.04%, rare earth oxides 0.06-0.08%, wetting agent 0.2-0.4%, with the remainder being tin.

[0028] By adopting the above technical solutions, the usage of each raw material is further optimized, reducing costs while stabilizing the liquidus temperature at 225-235℃, making it suitable for 240-245℃ reflow soldering processes. At 245℃, the wetting time is ≤1.5s, the spreading area is ≥85mm², and the soldering yield is ≥99.5%, solving the problem of insufficient wettability in low-silver formulations. The synergistic microalloying of bismuth, indium, antimony, and titanium, combined with melt purification using rare earth oxides, improves the shear strength of the solder joints, enhances creep resistance, and extends fatigue life.

[0029] Secondly, this application provides a method for preparing a low-silver alloy solder material, using the following technical solution: A method for preparing a low-silver alloy solder material includes the following preparation steps: 1) Weigh each raw material according to the ratio, mix tin, silver, copper, bismuth, indium, antimony, titanium, wetting agent and rare earth oxide, and melt them at 450-550℃ under an inert atmosphere to obtain alloy melt. 2) Transfer the molten alloy to an atomization chamber filled with nitrogen for protection, and obtain low-silver alloy solder material through atomization.

[0030] By adopting the above technical solution and using an inert atmosphere for melting, the oxidation of reactive elements such as titanium, zinc, and magnesium is effectively protected, ensuring the activity of the wetting agent components and the purification effect of rare earth oxides. Nitrogen atomization and rapid solidification suppress the segregation of elements such as bismuth and indium, resulting in high sphericity and a smooth surface of the spherical alloy. Simultaneously, the solder powder with a particle size distribution of 20-40μm exhibits excellent flowability, making it suitable for fine-pitch SMT printing processes and improving printing accuracy. The narrow particle size distribution of 20-40μm ensures consistent solder paste printing, reduces small particle agglomeration and large particle clogging, lowers the soldering defect rate to ≤0.5%, and achieves a product yield of ≥99.5%. This enables large-scale stable production while reducing silver content by 80-90%, resulting in a decrease in overall costs.

[0031] In summary, this application has the following beneficial effects: This application achieves a synergistic improvement in wetting performance and solder joint reliability under low-temperature soldering conditions of 240-245℃ by reducing the silver content from the traditional 3% to 0.05-1%. Specifically, the use of low-melting-point elements such as bismuth and indium lowers the solidus / liquidus temperature of the alloy, ensuring that the peak soldering temperature meets the PCB tolerance requirements and solving the problem of increased melting point caused by silver reduction. Furthermore, the use of wetting agents reduces the surface tension of the melt, rare earth oxides purify the surface and activate the interface, and titanium enhances the interfacial reactivity. These three elements work synergistically to achieve wetting time and spreading area at 245℃ comparable to high-silver solders, effectively avoiding defects such as cold solder joints and bridging. Simultaneously, the microalloying of antimony and the formation of a Cu6Sn5 reinforcing skeleton by copper work synergistically to improve the solder joint's creep resistance and fatigue life, achieving mechanical properties that are equal to or better than traditional high-silver solders. This significantly reduces material costs while ensuring soldering quality and reliability, thereby enhancing the product's market competitiveness. Attached Figure Description

[0032] Figure 1 This is a morphological image of the low-silver alloy solder material in Example 1 under a 1000 eyepiece. Detailed Implementation Example

[0033] Example 1

[0034] A low-silver alloy solder material is prepared by the following method: 992.5g of tin, 0.5g of silver, 4g of copper, 1g of bismuth, 0.14g of indium, 0.1g of antimony, 0.1g of titanium, 1g of wetting agent and 0.5g of rare earth oxide (cerium oxide) were melted at 450℃ under an inert atmosphere to obtain an alloy melt. The average particle size of rare earth oxides is 50 nm; The wetting agent is composed of zinc, magnesium, and manganese in a weight ratio of 1:2:0.1; 2) The molten alloy is transferred to an atomization chamber filled with nitrogen for protection, and low-silver alloy solder material is obtained through atomization, such as... Figure 1 As shown.

[0035] The difference between Examples 2-3 and Example 1 lies in the types and amounts of raw materials used to prepare the low-silver alloy solder material, as well as the parameters. Specific differences are shown in Table 1. Table 1. Raw material types, dosages, and parameters for preparing low-silver alloy solder materials in Examples 1-3.

[0036] Example 4

[0037] A low-silver alloy solder material, the difference between this embodiment and embodiment 1 is that the amount of tin used is 992g and the amount of silver used is 1g.

[0038] Example 5

[0039] A low-silver alloy solder material, the difference between this embodiment and embodiment 1 is that the amount of tin used is 985g and the amount of silver used is 8g.

[0040] Example 6

[0041] A low-silver alloy solder material, the difference between this embodiment and embodiment 1 is that the amount of tin used is 991g and the amount of silver used is 2g.

[0042] Example 7

[0043] A low-silver alloy solder material, the difference between this embodiment and embodiment 1 is that the amount of tin used is 987g and the amount of silver used is 6g.

[0044] Example 8

[0045] A low-silver alloy solder material, the difference between this embodiment and embodiment 1 is that the amount of tin used is 988.5g and the amount of bismuth used is 5g.

[0046] Example 9

[0047] A low-silver alloy solder material, the difference between this embodiment and embodiment 1 is that the amount of tin used is 988.5g and the amount of bismuth used is 35g.

[0048] Example 10

[0049] A low-silver alloy solder material, the difference between this embodiment and embodiment 1 is that the amount of tin used is 983.5g and the amount of bismuth used is 10g.

[0050] Example 11

[0051] A low-silver alloy solder material, the difference between this embodiment and embodiment 1 is that the amount of tin used is 963.5g and the amount of bismuth used is 30g.

[0052] Example 12

[0053] A low-silver alloy solder material, the difference between this embodiment and embodiment 1 is that the amount of tin used is 992.1g and the amount of indium used is 0.5g.

[0054] Example 13

[0055] A low-silver alloy solder material, the difference between this embodiment and embodiment 1 is that the amount of tin used is 990.6g and the amount of indium used is 2g.

[0056] Example 14

[0057] A low-silver alloy solder material, the difference between this embodiment and embodiment 1 is: 3g silver, 5g copper, 15g bismuth, 0.8g indium, 0.5g antimony, 0.2g titanium, 0.6g rare earth oxides, 2g wetting agent, and 954.3g tin.

[0058] Example 15

[0059] A low-silver alloy solder material, the difference between this embodiment and embodiment 1 is: 6g silver, 7g copper, 30g bismuth, 1.5g indium, 1.2g antimony, 0.4g titanium, 0.8g rare earth oxides, 0.2-0.4% wetting agent, and 973.1g tin.

[0060] Example 16

[0061] A low-silver alloy solder material, the difference between this embodiment and embodiment 1 is that the wetting agent is composed of zinc and magnesium in a weight ratio of 1:2. Comparative Example

[0062] Comparative Example 1 A silver alloy solder material, the difference between this comparative example and Example 1 is that the amount of tin used is 963g and the amount of silver used is 30g.

[0063] Comparative Example 2 A low-silver alloy solder material, the difference between this embodiment and embodiment 1 is that the amount of tin used is 993g and the amount of lubricant used is 0g.

[0064] Comparative Example 3 A low-silver alloy solder material, the difference between this embodiment and embodiment 1 is that nickel is used instead of titanium.

[0065] Comparative Example 4 A low-silver alloy solder material, the difference between this embodiment and embodiment 1 is that nickel is used instead of indium. Detection methods / test methods

[0066] Melting point characteristics test: Differential scanning calorimetry was used to determine the solidus temperature and liquidus temperature of the alloy according to IPC-TM-650 2.4.25 standard; Wetting time: Refer to J-STD-002E "Component Solderability Test" and IPC-TM-650 2.4.45 "Wetting Balance Test"; Spread area: Place 0.1g of alloy sample on a standard copper pad, heat to 245℃ until melted and hold for 30 seconds, then measure the spread area after cooling. Creep properties: ASTM E139 "Metallic materials, creep test"; Thermal fatigue reliability: IPC-9701 "Test Methods for Performance of Surface Mount Soldered Components". Experimental data are shown in Table 2: Table 2 Experimental data of Examples 1-16 and Comparative Examples 1-4

[0067] The experimental data above show that, under the premise of reducing the silver content by 70-98%, the wetting performance and solder joint reliability of low-silver solder can reach or approach the level of traditional high-silver solder through bismuth-indium-antimony-titanium synergistic melting reduction, rare earth oxide purification of the interface, and zinc-magnesium-manganese wetting agent to improve spreading, while reducing material costs.

[0068] As can be seen from the experimental data of Example 1 and Comparative Examples 1-5, the cost reduction scheme of this technology is feasible. By reducing the amount of silver used and combining it with components such as lubricant, titanium and indium, the low-silver alloy solder material can simultaneously achieve the comprehensive performance of low cost, low temperature soldering and high reliability.

[0069] The experimental data from Examples 1 and 4-7 show that, under the extreme condition of silver content as low as 0.05%, the solder can still maintain excellent performance with a liquidus temperature of 232°C, a wetting time of 1.4s, and a thermal fatigue life of 8200 cycles. Increasing the silver content to 0.8% can shorten the wetting time to 1.0s and extend the life to 9500 cycles, but the performance improvement shows a diminishing marginal effect.

[0070] As can be seen from the experimental data of Examples 1 and 8-11, as the bismuth content increases, the solidus / liquidus temperature decreases, but excessive addition will prolong the wetting time, reduce the spreading area, increase the creep rate, and shorten the thermal fatigue life.

[0071] Experimental data from Examples 1 and 12-13 show that Example 12 reduced the wetting time from 1.4s to 1.2s and increased the spreading area to 102mm², proving that trace amounts of indium can improve wettability. However, Example 13 shows that further increasing the indium content only brings marginal performance improvement; the wetting time is 1.0s, but it leads to a 4-fold increase in cost and a deterioration in creep rate to 2.6, suggesting that excessive indium will precipitate the brittle InSn4 phase. 0.05-0.15% is the optimal cost-performance range, ensuring breakthroughs in wetting efficiency at 245℃ while avoiding a surge in cost and the risk of microstructure embrittlement, achieving a balance between performance, cost, and reliability.

[0072] The experimental data from Examples 1 and 14-15 show that, compared with the baseline formulation of Example 1, the liquidus temperature is lower, the wetting time is shorter, the spreading area is increased, the creep rate is lower, and the thermal fatigue life is extended. This indicates that optimizing the dosage of each component can achieve a balance between low-temperature welding, wetting effect, and long-term reliability.

[0073] The experimental data from Examples 1 and 16 show that removing manganese leads to a longer wetting time and a smaller spreading area, indicating that the grain refinement effect of manganese is beneficial to improving the wetting performance of low-silver alloy solder materials.

[0074] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A low-silver alloy solder material, characterized in that, It is prepared from the following raw materials by weight percentage: Silver 0.05-1% Copper 0.4-0.8% Bismuth 0.1-3.8% Indium 0.01-0.3% Antimony 0.01-0.2% Titanium 0.01-0.05% Rare earth oxides 0.05-0.1% Wetting agent 0.1-0.5% The remainder is tin.

2. The low-silver alloy solder material according to claim 1, characterized in that: The rare earth oxide is one or more of cerium oxide, lanthanum oxide, and yttrium oxide.

3. The low-silver alloy solder material according to claim 2, characterized in that: The average particle size of the rare earth oxide is 50-200 nm.

4. The low-silver alloy solder material according to claim 1, characterized in that: The wetting agent is composed of zinc, magnesium and manganese in a weight ratio of 1:(2-3):(0.1-0.5).

5. The low-silver alloy solder material according to claim 1, characterized in that: The silver content is 0.1-0.8 wt%.

6. The low-silver alloy solder material according to claim 1, characterized in that: The bismuth content is 0.5-3.5 wt%.

7. The low-silver alloy solder material according to claim 1, characterized in that: It is prepared from the following raw materials by weight percentage: Silver 0.3-0.6%, copper 0.5-0.7%, bismuth 1.5-3.0%, indium 0.08-0.15%, antimony 0.05-0.12%, titanium 0.02-0.04%, rare earth oxides 0.06-0.08%, wetting agent 0.2-0.4%, with the remainder being tin.

8. A method for preparing a low-silver alloy solder material as described in any one of claims 1-7, characterized in that, The preparation steps include the following: 1) Weigh each raw material according to the proportion, mix tin, silver, copper, bismuth, indium, antimony, titanium, wetting agent and rare earth oxide, and melt them at 450-550℃ under an inert atmosphere to obtain alloy melt. 2) Transfer the molten alloy to an atomization chamber filled with nitrogen for protection, and obtain low-silver alloy solder material through atomization.

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