High-strength thermal-fatigue-resistant lead-free solder alloy and preparation method therefor

Abstract

A high-strength thermal-fatigue-resistant lead-free solder alloy and a preparation method therefor. The high-strength thermal-fatigue-resistant lead-free solder alloy comprises the following components in percentage by mass: 2.5-4% of silver; 0.5-1% of copper; 3-3.5% of bismuth; and 2.5-4% of antimony; and further comprises 0.01-0.05% of nickel and 0.04-0.1% of neodymium, or / and 0.02-0.1% of manganese and 0.01-0.05% of cobalt, and the balance being tin and inevitable impurities. The preparation method for a lead-free solder alloy comprises: according to the proportions, blending raw materials, melting, carrying out heat preservation and stirring to obtain the lead-free solder alloy. Therefore, the high-strength thermal-fatigue-resistant lead-free solder alloy has excellent thermal fatigue resistance.

Description

A high-strength thermal fatigue-resistant lead-free solder alloy and its preparation method Technical Field

[0001] The present application relates to the field of lead-free solder alloys, and more specifically, to a high-strength, thermal fatigue-resistant lead-free solder alloy and a preparation method thereof. Background Art

[0002] Tin alloy solder is widely used in electronic packaging due to its active properties. With the advancement of multifunctionality and high-density integration in the semiconductor industry, the reliability requirements for industrial electronic packaging have become even more stringent. This is particularly true in the aerospace and automotive electronics sectors, where electronic equipment has a long service life and is exposed to harsh environments such as high temperatures and vibration. This requires solder joints to withstand long-term high-temperature and high-load service.

[0003] The current mainstream connection solder is Sn3.0Ag0.5Cu alloy (SAC305). SAC305 alloy has good thermal fatigue resistance, but has reliability limitations under long-term higher temperatures and thermal stress. The strengthening of SAC305 alloy mainly relies on the compound Ag3Sn phase and Cu6Sn5 phase. During power cycling or long-term high-temperature service or vibration, the Ag3Sn phase and Cu6Sn5 phase of the solder joints strengthened by these two phases coarsen and grow, weakening the ability to inhibit dislocation movement and accumulate damage, causing the matrix tin crystals to recrystallize in high-stress areas, and then cracking over time. In particular, due to the interaction of overall structural stress, thermal stress, etc., the interface near the high-strain area becomes a weak link in the interconnection structure, prone to cracking, leading to failure of the entire package structure.

[0004] Therefore, there is an urgent need to develop a solder alloy with high strength, high toughness and excellent thermal fatigue resistance.

[0005] Summary of the Invention

[0006] In order to improve the thermal fatigue resistance of lead-free solder alloys, the present application provides a high-strength thermal fatigue-resistant lead-free solder alloy and a preparation method thereof.

[0007] In a first aspect, the present application provides a high-strength, thermal fatigue-resistant lead-free solder alloy, which adopts the following technical solutions:

[0008] A high-strength, thermal fatigue-resistant lead-free solder alloy comprising the following components in the following mass percentages:

[0009] Silver 2.5-4%; Copper 0.5-1%; Bismuth 3-3.5%; Antimony 2.5-4%; Also includes:

[0010] Nickel 0-0.05% and one or more selected from neodymium 0-0.1%, lanthanum 0-0.1%, plutonium 0-0.1%, yttrium 0-0.1%; or / and manganese 0-0.1% and one or more selected from cobalt 0-0.05% and titanium 0-0.05%;

[0011] The balance is tin and any unavoidable impurities.

[0012] By adopting the above technical solution, metallic silver can enhance the mechanical strength, thermal conductivity and electrical conductivity of the lead-free solder alloy, increase the elongation of the lead-free solder alloy, improve the vibration fracture resistance, and improve the fatigue resistance of the solder alloy under thermal cycling conditions; metallic copper can enhance the wettability and fatigue resistance of the lead-free solder alloy under thermal cycling conditions, and improve the thermal conductivity and electrical conductivity of the lead-free solder alloy; metallic bismuth helps to lower the melting point of the lead-free solder alloy, and is beneficial to improving the hardness, tensile strength and shear strength of the lead-free solder alloy; metallic antimony is beneficial to improving the ductility of the lead-free solder alloy, increasing the elongation, and is beneficial to improving the tensile strength of the lead-free alloy solder.

[0013] In the present application, silver, copper, bismuth, antimony and tin elements cooperate with each other, and by selecting nickel and one or more selected from neodymium, lanthanum, plutonium and yttrium as solder joint / interface control elements, or selecting manganese and one or more selected from cobalt and titanium as solder joint / interface control elements, the lead-free solder alloy controls the interior and interface of the solder joint, which is beneficial to reducing the supercooling of the lead-free solder alloy during the solidification process, making the microstructure of the lead-free solder alloy more delicate and uniform; making the interface compound formed by the lead-free solder alloy and the metal copper base layer more stable at the microscopic level, and not easily transforming from Cu6Sn5 to Cu3Sn during service, reducing the possibility of growth and coarsening during service, and stabilizing the solder joint structure at the macroscopic level; at the same time, it is beneficial to improve the tensile strength of the lead-free solder alloy, enhance the thermal cycle resistance, and thereby reduce the possibility of mechanical property degradation of the solder joint during thermal aging.

[0014] Preferably, the following components are included in percentage by weight:

[0015] Silver 2.5-4%; Copper 0.5-1%; Bismuth 3-3.5%; Antimony 2.5-4%; Nickel 0-0.05%; and one or more selected from Neodymium 0-0.1%, Lanthanum 0-0.1%, Plutonium 0-0.1%, Yttrium 0-0.1%; the balance being Tin and any unavoidable impurities.

[0016] By adopting the above technical solution, the nickel element is combined with one or more rare earth elements selected from neodymium, lanthanum, plutonium, and yttrium, which can effectively inhibit the formation of coarse bismuth phases in the solder alloy during the cooling process, thereby refining the grains and improving the mechanical properties and aging resistance of the lead-free solder alloy; at the same time, the rare earth elements can refine the grains of the lead-free solder alloy and improve the strength and ductility of the lead-free solder alloy.

[0017] Preferably, the following mass percentages of the components are included: silver 2.5-4%; copper 0.5-1%; bismuth 3-3.5%; antimony 2.5-4%; nickel 0-0.05%; neodymium 0-0.1%; the balance being tin and any unavoidable impurities.

[0018] Preferably, the mass percentage of the nickel is 0-0.02%, and the mass percentage of the neodymium is 0.04-0.06%.

[0019] By adopting the above technical solutions, the lead-free solder alloy exhibits a high melting point, better thermal fatigue resistance, better high-temperature mechanical reliability and solder joint strength.

[0020] Preferably, the following components are included in mass percentage: silver 2.5-4%; copper 0.5-1%; bismuth 3-3.5%; antimony 2.5-4%; manganese 0-0.1%; and one or more selected from cobalt 0-0.05% and titanium 0-0.05%; the balance is tin and any unavoidable impurities.

[0021] By adopting the above technical solution, the manganese element is combined with one or more elements selected from cobalt and titanium, which can effectively improve the toughness and tensile strength of the lead-free solder alloy and increase the thermal fatigue life. At the same time, it can effectively inhibit the formation of coarse bismuth phase in the solder alloy during the cooling process, refine the grains, and improve the mechanical properties of the lead-free solder alloy.

[0022] Preferably, the following mass percentages of the components are included: silver 2.5-4%; copper 0.5-1%; bismuth 3-3.5%; antimony 2.5-4%; manganese 0-0.1%; cobalt 0-0.05%; the balance being tin and any unavoidable impurities.

[0023] Preferably, the mass percentage of manganese is 0.02-0.04%; the mass percentage of cobalt is 0-0.02%.

[0024] By adopting the above technical solutions, the lead-free solder alloy exhibits a high melting point, better thermal fatigue resistance, better high-temperature mechanical reliability and solder joint strength.

[0025] By adopting the above technical solution, the mass ratio of each alloy element is further optimized, so that the lead-free solder alloy has better thermal fatigue resistance and high-temperature mechanical reliability.

[0026] Preferably, the lead-free solder alloy has an alloy melting point of 200-250°C.

[0027] Preferably, the lead-free solder alloy has a tensile strength of not less than 80 MPa at 25° C. and a tensile strength of not less than 50 MPa at 125° C.

[0028] By adopting the above technical solution, the lead-free solder alloy of the present application has better mechanical strength at high temperatures, good high-temperature mechanical reliability, and better thermal fatigue resistance, and can be used in high operating temperature scenarios.

[0029] In a second aspect, the present application provides a method for preparing a lead-free solder alloy, which adopts the following technical solution:

[0030] A method for preparing a lead-free solder alloy comprises the following steps:

[0031] The raw materials are mixed according to a ratio, melted, kept warm and stirred to obtain a lead-free solder alloy.

[0032] In summary, this application has the following beneficial effects:

[0033] 1. Since the present application adopts silver, copper, bismuth, antimony and tin elements to cooperate with each other, and selects nickel and one or more selected from neodymium, lanthanum, plutonium and yttrium as the solder joint / interface control elements, or selects manganese and one or more selected from cobalt and titanium as the solder joint / interface control elements, the lead-free solder alloy controls the interior and interface of the solder joint, which is beneficial to reducing the supercooling of the lead-free solder alloy during the solidification process, making the microstructure of the lead-free solder alloy more delicate and uniform; making the interface compound formed by the lead-free solder alloy and the metal copper base more stable at the microscopic level, and not easily changing from Cu6Sn5 to Cu3Sn during service, reducing the possibility of growth and coarsening during service, and stabilizing the solder joint structure at the macroscopic level; at the same time, it is beneficial to improve the tensile strength of the lead-free solder alloy, enhance the thermal cycle resistance, and thus reduce the possibility of mechanical property degradation of the solder joint during thermal aging;

[0034] 2. In this application, nickel and neodymium are preferably used in combination as solder joint / interface control elements, or manganese and cobalt are selected as solder joint / interface control elements, so that the lead-free solder alloy exhibits a high melting point, better thermal fatigue resistance, better high-temperature mechanical reliability and solder joint strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG1 is an electron microscope image of the microstructure of the lead-free solder alloy of Example 6 of the present application;

[0036] FIG2 is a DSC differential thermal analysis curve of the lead-free solder alloy of Example 6 of the present application;

[0037] FIG3 is an electron microscope image of the microstructure of the lead-free solder alloy of Example 16 of the present application;

[0038] FIG4 is a DSC differential thermal analysis curve of the lead-free solder alloy of Example 16 of the present application. DETAILED DESCRIPTION

[0039] The present application is further described in detail below with reference to the accompanying drawings and examples.

[0040] Example

[0041] Example 1

[0042] This embodiment discloses a high-strength, thermal fatigue-resistant lead-free solder alloy, including the following components by mass: 8.97 kg tin, 0.34 kg silver, 0.07 kg copper, 0.32 kg bismuth, and 0.3 kg antimony.

[0043] The preparation method of high-strength thermal fatigue-resistant lead-free solder alloy is as follows:

[0044] The raw materials are pure tin blocks, silver particles, copper particles, bismuth blocks and antimony blocks with a purity greater than 99.9%;

[0045] Take the above mass of copper particles and a pure tin block with a mass 9 times that of the copper particles, put them into a vacuum furnace at 600℃ and smelt them for 2 hours. Repeat the smelting twice to obtain Sn10Cu master alloy.

[0046] Take the above-mentioned mass of antimony block and a pure tin block with a mass 9 times that of the antimony block, put them into a vacuum furnace at 600℃ and melt them for 2 hours, and repeat the melting twice to obtain Sn10Sb master alloy;

[0047] The above-mentioned mass of silver particles, Sn10Cu master alloy, bismuth block, Sn10Sb master alloy and the remaining pure tin block are placed in a resistance furnace at 300°C for heating. After the materials are melted, they are stirred and kept warm for 1 hour to obtain a high-strength, thermal fatigue-resistant lead-free solder alloy.

[0048] The lead-free solder alloy prepared in the present application can be expressed as Sn3.4Ag0.7Cu3.2Bi3.0Sb, where each number represents the mass percentage of different metal elements in the lead-free solder alloy, such as "3.4Ag" means that the mass percentage of silver element is 3.4%, "0.7Cu" means that the mass percentage of copper element is 0.7%, "3.2Bi" means that the mass percentage of bismuth element is 3.2%, and "3.0Sb" means that the mass percentage of antimony element is 3.0%.

[0049] Example 2

[0050] The only difference between this embodiment and embodiment 1 is that the high-strength, thermal fatigue-resistant lead-free solder alloy includes the following components by mass: 8.97 kg tin, 0.36 kg silver, 0.06 kg copper, 0.33 kg bismuth, and 0.28 kg antimony.

[0051] The preparation method of high-strength thermal fatigue-resistant lead-free solder alloy is as follows:

[0052] The raw materials are pure tin blocks, silver particles, copper particles, bismuth blocks and antimony blocks with a purity greater than 99.9%;

[0053] Take the above mass of copper particles and a pure tin block with a mass 9 times that of the copper particles, put them into a vacuum furnace at 600℃ and smelt them for 2 hours. Repeat the smelting twice to obtain Sn10Cu master alloy.

[0054] Take the above-mentioned mass of antimony block and a pure tin block with a mass 9 times that of the antimony block, put them into a vacuum furnace at 600℃ and melt them for 2 hours, and repeat the melting twice to obtain Sn10Sb master alloy;

[0055] The above-mentioned mass of silver particles, Sn10Cu master alloy, bismuth block, Sn10Sb master alloy and the remaining pure tin block are placed in a resistance furnace at 300°C for heating. After the materials are melted, they are stirred and kept warm for 1 hour to obtain a high-strength, thermal fatigue-resistant lead-free solder alloy Sn3.6Ag0.6Cu3.3Bi2.8Sb.

[0056] Example 3

[0057] The only difference between this embodiment and embodiment 1 is that the high-strength, thermal fatigue-resistant lead-free solder alloy includes the following components by mass: 8.99 kg tin, 0.25 kg silver, 0.1 kg copper, 0.35 kg bismuth, and 0.31 kg antimony.

[0058] The preparation method of high-strength thermal fatigue-resistant lead-free solder alloy is as follows:

[0059] The raw materials are pure tin blocks, silver particles, copper particles, bismuth blocks and antimony blocks with a purity greater than 99.9%;

[0060] Take the above mass of copper particles and a pure tin block with a mass 9 times that of the copper particles, put them into a vacuum furnace at 600℃ and smelt them for 2 hours. Repeat the smelting twice to obtain Sn10Cu master alloy.

[0061] Take the above-mentioned mass of antimony block and a pure tin block with a mass 9 times that of the antimony block, put them into a vacuum furnace at 600℃ and melt them for 2 hours, and repeat the melting twice to obtain Sn10Sb master alloy;

[0062] The above-mentioned mass of silver particles, Sn10Cu master alloy, bismuth block, Sn10Sb master alloy and the remaining pure tin block are placed in a resistance furnace at 300°C for heating. After the materials are melted, they are stirred and kept warm for 1 hour to obtain a high-strength, thermal fatigue-resistant lead-free solder alloy Sn2.5Ag1.0Cu3.5Bi3.1Sb.

[0063] Example 4

[0064] The only difference between this embodiment and embodiment 1 is that the high-strength, thermal fatigue-resistant lead-free solder alloy includes the following components by mass: 8.90 kg tin, 0.32 kg silver, 0.08 kg copper, 0.30 kg bismuth, and 0.40 kg antimony.

[0065] The preparation method of high-strength thermal fatigue-resistant lead-free solder alloy is as follows:

[0066] The raw materials are pure tin blocks, silver particles, copper particles, bismuth blocks and antimony blocks with a purity greater than 99.9%;

[0067] Take the above mass of copper particles and a pure tin block with a mass 9 times that of the copper particles, put them into a vacuum furnace at 600℃ and smelt them for 2 hours. Repeat the smelting twice to obtain Sn10Cu master alloy.

[0068] Take the above-mentioned mass of antimony block and a pure tin block with a mass 9 times that of the antimony block, put them into a vacuum furnace at 600℃ and melt them for 2 hours, and repeat the melting twice to obtain Sn10Sb master alloy;

[0069] The above-mentioned mass of silver particles, Sn10Cu master alloy, bismuth block, Sn10Sb master alloy and the remaining pure tin block are placed in a resistance furnace at 300°C for heating. After the materials are melted, they are stirred and kept warm for 1 hour to obtain a high-strength, thermal fatigue-resistant lead-free solder alloy Sn3.2Ag0.8Cu3.0Bi4.0Sb.

[0070] Example 5

[0071] The only difference between this embodiment and embodiment 1 is that the high-strength, thermal fatigue-resistant lead-free solder alloy includes the following components by mass: 8.93 kg tin, 0.4 kg silver, 0.1 kg copper, 0.32 kg bismuth, and 0.25 kg antimony.

[0072] The preparation method of high-strength thermal fatigue-resistant lead-free solder alloy is as follows:

[0073] The raw materials are pure tin blocks, silver particles, copper particles, bismuth blocks and antimony blocks with a purity greater than 99.9%;

[0074] Take the above mass of copper particles and a pure tin block with a mass 9 times that of the copper particles, put them into a vacuum furnace at 600℃ and smelt them for 2 hours. Repeat the smelting twice to obtain Sn10Cu master alloy.

[0075] Take the above-mentioned mass of antimony block and a pure tin block with a mass 9 times that of the antimony block, put them into a vacuum furnace at 600℃ and melt them for 2 hours, and repeat the melting twice to obtain Sn10Sb master alloy;

[0076] The above-mentioned mass of silver particles, Sn10Cu master alloy, bismuth block, Sn10Sb master alloy and the remaining pure tin block are placed in a resistance furnace at 300°C for heating. After the materials are melted, they are stirred and kept warm for 1 hour to obtain a high-strength, thermal fatigue-resistant lead-free solder alloy Sn4.0Ag1.0Cu3.2Bi2.5Sb.

[0077] Example 6

[0078] The only difference between this embodiment and embodiment 1 is that the high-strength, thermal fatigue-resistant lead-free solder alloy includes the following components by mass: 8.964 kg tin, 0.34 kg silver, 0.07 kg copper, 0.32 kg bismuth, 0.3 kg antimony, 0.001 kg nickel, and 0.005 kg neodymium.

[0079] The preparation method of high-strength thermal fatigue-resistant lead-free solder alloy is as follows:

[0080] The raw materials are pure tin blocks, silver particles, copper particles, bismuth blocks, antimony blocks, nickel blocks and neodymium blocks with a purity greater than 99.9%;

[0081] Take the above mass of copper particles and a pure tin block with a mass 9 times that of the copper particles, put them into a vacuum furnace at 600℃ and smelt them for 2 hours. Repeat the smelting twice to obtain Sn10Cu master alloy.

[0082] Take the above-mentioned mass of antimony block and pure tin block with a mass 9 times that of copper particles, put them into a vacuum furnace at 600℃ and smelt them for 2 hours. Repeat the smelting twice to obtain Sn10Sb master alloy.

[0083] Take the above-mentioned nickel block and a pure tin block with a mass 5 times that of the nickel block, put them into a vacuum furnace at 600℃ and melt them for 2 hours, and repeat the melting twice to obtain Sn5Ni master alloy;

[0084] The aforementioned mass of silver particles, Sn10Cu master alloy, bismuth block, Sn10Sb master alloy, Sn5Ni master alloy, neodymium block, and the remaining pure tin block were placed in a resistance furnace and heated to 300°C. After the materials were melted, they were stirred and kept warm for 1 hour to obtain a high-strength, thermal fatigue-resistant lead-free solder alloy. The lead-free solder alloy in this application can be represented as Sn3.4Ag0.7Cu3.2Bi3.0Sb0.05Nd0.01Ni.

[0085] Example 7

[0086] The only difference between this embodiment and embodiment 6 is that the high-strength, thermal fatigue-resistant lead-free solder alloy includes the following components by mass: 8.964 kg tin, 0.34 kg silver, 0.07 kg copper, 0.32 kg bismuth, 0.3 kg antimony, 0.001 kg nickel, and 0.005 kg lanthanum.

[0087] The preparation method of high-strength thermal fatigue-resistant lead-free solder alloy is as follows:

[0088] The raw materials are pure tin blocks, silver particles, copper particles, bismuth blocks, antimony blocks, nickel blocks, and lanthanum blocks with a purity greater than 99.9%;

[0089] Take the above mass of copper particles and a pure tin block with a mass 9 times that of the copper particles, put them into a vacuum furnace at 600℃ and smelt them for 2 hours. Repeat the smelting twice to obtain Sn10Cu master alloy.

[0090] Take the above-mentioned mass of antimony block and pure tin block with a mass 9 times that of copper particles, put them into a vacuum furnace at 600℃ and smelt them for 2 hours. Repeat the smelting twice to obtain Sn10Sb master alloy.

[0091] Take the above-mentioned nickel block and a pure tin block with a mass 5 times that of the nickel block, put them into a vacuum furnace at 600℃ and melt them for 2 hours, and repeat the melting twice to obtain Sn5Ni master alloy;

[0092] The aforementioned mass of silver particles, Sn10Cu master alloy, bismuth block, Sn10Sb master alloy, Sn5Ni master alloy, lanthanum block, and the remaining pure tin block were placed in a resistance furnace and heated to 300°C. After the materials were melted, they were stirred and kept warm for 1 hour to obtain a high-strength, thermal fatigue-resistant lead-free solder alloy. The lead-free solder alloy in this application can be represented as Sn3.4Ag0.7Cu3.2Bi3.0Sb0.05La0.01Ni.

[0093] Example 8

[0094] The only difference between this embodiment and embodiment 6 is that the high-strength, thermal fatigue-resistant lead-free solder alloy includes the following components by mass: 8.964 kg tin, 0.34 kg silver, 0.07 kg copper, 0.32 kg bismuth, 0.3 kg antimony, 0.001 kg nickel, and 0.005 kg plutonium.

[0095] The preparation method of high-strength thermal fatigue-resistant lead-free solder alloy is as follows:

[0096] Using pure tin blocks, silver particles, copper particles, bismuth blocks, antimony blocks, nickel blocks, and plutonium blocks with a purity greater than 99.9% as raw materials;

[0097] Take the above mass of copper particles and a pure tin block with a mass 9 times that of the copper particles, put them into a vacuum furnace at 600℃ and smelt them for 2 hours. Repeat the smelting twice to obtain Sn10Cu master alloy.

[0098] Take the above-mentioned mass of antimony block and pure tin block with a mass 9 times that of copper particles, put them into a vacuum furnace at 600℃ and smelt them for 2 hours. Repeat the smelting twice to obtain Sn10Sb master alloy.

[0099] Take the above-mentioned nickel block and a pure tin block with a mass 5 times that of the nickel block, put them into a vacuum furnace at 600℃ and melt them for 2 hours, and repeat the melting twice to obtain Sn5Ni master alloy;

[0100] The aforementioned mass of silver particles, Sn10Cu master alloy, bismuth block, Sn10Sb master alloy, Sn5Ni master alloy, plutonium block, and the remaining pure tin block were placed in a resistance furnace and heated to 300°C. After the materials were melted, they were stirred and kept warm for 1 hour to obtain a high-strength, thermal fatigue-resistant lead-free solder alloy. The lead-free solder alloy in this application can be represented as Sn3.4Ag0.7Cu3.2Bi3.0Sb0.05Pu0.01Ni.

[0101] Example 9

[0102] The only difference between this embodiment and embodiment 6 is that the high-strength, thermal fatigue-resistant lead-free solder alloy includes the following components by mass: 8.964 kg tin, 0.34 kg silver, 0.07 kg copper, 0.32 kg bismuth, 0.3 kg antimony, 0.001 kg nickel, and 0.005 kg yttrium.

[0103] The preparation method of high-strength thermal fatigue-resistant lead-free solder alloy is as follows:

[0104] Using pure tin blocks, silver particles, copper particles, bismuth blocks, antimony blocks, nickel blocks, and yttrium blocks with a purity greater than 99.9% as raw materials;

[0105] Take the above mass of copper particles and a pure tin block with a mass 9 times that of the copper particles, put them into a vacuum furnace at 600℃ and smelt them for 2 hours. Repeat the smelting twice to obtain Sn10Cu master alloy.

[0106] Take the above-mentioned mass of antimony block and pure tin block with a mass 9 times that of copper particles, put them into a vacuum furnace at 600℃ and smelt them for 2 hours. Repeat the smelting twice to obtain Sn10Sb master alloy.

[0107] Take the above-mentioned nickel block and a pure tin block with a mass 5 times that of the nickel block, put them into a vacuum furnace at 600℃ and melt them for 2 hours, and repeat the melting twice to obtain Sn5Ni master alloy;

[0108] The aforementioned mass of silver particles, Sn10Cu master alloy, bismuth block, Sn10Sb master alloy, Sn5Ni master alloy, yttrium block, and the remaining pure tin block were placed in a resistance furnace and heated to 300°C. After the materials were melted, they were stirred and kept warm for 1 hour to obtain a high-strength, thermal fatigue-resistant lead-free solder alloy. The lead-free solder alloy in this application can be represented as Sn3.4Ag0.7Cu3.2Bi3.0Sb0.05Y0.01Ni.

[0109] Example 10

[0110] The only difference between this embodiment and embodiment 6 is that the high-strength, thermal fatigue-resistant lead-free solder alloy includes the following components by mass: 8.967 kg tin, 0.34 kg silver, 0.07 kg copper, 0.32 kg bismuth, 0.3 kg antimony, 0.001 kg nickel, and 0.002 kg neodymium.

[0111] Example 11

[0112] The only difference between this embodiment and embodiment 6 is that the high-strength, thermal fatigue-resistant lead-free solder alloy includes the following components by mass: 8.965 kg tin, 0.34 kg silver, 0.07 kg copper, 0.32 kg bismuth, 0.3 kg antimony, 0.001 kg nickel, and 0.004 kg neodymium.

[0113] Example 12

[0114] The only difference between this embodiment and embodiment 6 is that the high-strength, thermal fatigue-resistant lead-free solder alloy includes the following components by mass: 8.963 kg tin, 0.34 kg silver, 0.07 kg copper, 0.32 kg bismuth, 0.3 kg antimony, 0.001 kg nickel, and 0.006 kg neodymium.

[0115] Example 13

[0116] The only difference between this embodiment and embodiment 6 is that the high-strength, thermal fatigue-resistant lead-free solder alloy includes the following components by mass: 8.959 kg tin, 0.34 kg silver, 0.07 kg copper, 0.32 kg bismuth, 0.3 kg antimony, 0.001 kg nickel, and 0.01 kg neodymium.

[0117] Example 14

[0118] The only difference between this embodiment and embodiment 6 is that the high-strength, thermal fatigue-resistant lead-free solder alloy includes the following components by mass: 8.945 kg tin, 0.34 kg silver, 0.07 kg copper, 0.32 kg bismuth, 0.3 kg antimony, 0.002 kg nickel, and 0.005 kg neodymium.

[0119] Example 15

[0120] The only difference between this embodiment and embodiment 6 is that the high-strength, thermal fatigue-resistant lead-free solder alloy includes the following components by mass: 8.945 kg tin, 0.34 kg silver, 0.07 kg copper, 0.32 kg bismuth, 0.3 kg antimony, 0.005 kg nickel, and 0.005 kg neodymium.

[0121] Example 16

[0122] The only difference between this embodiment and embodiment 1 is that the high-strength, thermal fatigue-resistant lead-free solder alloy includes the following components by mass: 8.966 kg tin, 0.34 kg silver, 0.07 kg copper, 0.32 kg bismuth, 0.3 kg antimony, 0.003 kg manganese, and 0.001 kg cobalt.

[0123] The preparation method of high-strength thermal fatigue-resistant lead-free solder alloy is as follows:

[0124] The raw materials are pure tin blocks, silver particles, copper particles, bismuth blocks, antimony blocks, manganese blocks and cobalt blocks with a purity greater than 99.9%;

[0125] Take the above mass of copper particles and a pure tin block with a mass 9 times that of the copper particles, put them into a vacuum furnace at 600℃ and smelt them for 2 hours. Repeat the smelting twice to obtain Sn10Cu master alloy.

[0126] Take the above-mentioned mass of antimony block and pure tin block with a mass 9 times that of copper particles, put them into a vacuum furnace at 600℃ and smelt them for 2 hours. Repeat the smelting twice to obtain Sn10Sb master alloy.

[0127] Take the above-mentioned mass of manganese block and pure tin block twice the mass of nickel block, put them into 600℃ vacuum furnace for smelting and keeping warm for 2h, repeat the smelting twice to obtain Sn2Mn master alloy;

[0128] Take the above-mentioned cobalt block and a pure tin block twice the mass of the nickel block, put them into a vacuum furnace at 600℃ and melt them for 2 hours, and repeat the melting twice to obtain Sn2Co master alloy;

[0129] The aforementioned mass of silver particles, Sn10Cu master alloy, bismuth block, Sn10Sb master alloy, Sn2Mn master alloy, Sn2Co master alloy, and the remaining pure tin block were placed in a resistance furnace and heated to 300°C. After the materials were melted, they were stirred and kept warm for 1 hour to obtain a high-strength, thermal fatigue-resistant lead-free solder alloy. The lead-free solder alloy in this application can be represented as Sn3.4Ag0.7Cu3.2Bi3.0Sb0.03Mn0.01Co.

[0130] Example 17

[0131] The only difference between this embodiment and embodiment 16 is that the high-strength, thermal fatigue-resistant lead-free solder alloy includes the following components by mass: 8.966 kg tin, 0.34 kg silver, 0.07 kg copper, 0.32 kg bismuth, 0.3 kg antimony, 0.003 kg manganese, and 0.001 kg titanium.

[0132] The preparation method of high-strength thermal fatigue-resistant lead-free solder alloy is as follows:

[0133] The raw materials are pure tin blocks, silver particles, copper particles, bismuth blocks, antimony blocks, manganese blocks and titanium blocks with a purity greater than 99.9%;

[0134] Take the above mass of copper particles and a pure tin block with a mass 9 times that of the copper particles, put them into a vacuum furnace at 600℃ and smelt them for 2 hours. Repeat the smelting twice to obtain Sn10Cu master alloy.

[0135] Take the above-mentioned mass of antimony block and pure tin block with a mass 9 times that of copper particles, put them into a vacuum furnace at 600℃ and smelt them for 2 hours. Repeat the smelting twice to obtain Sn10Sb master alloy.

[0136] Take the above-mentioned mass of manganese block and pure tin block twice the mass of nickel block, put them into 600℃ vacuum furnace for smelting and keeping warm for 2h, repeat the smelting twice to obtain Sn2Mn master alloy;

[0137] The aforementioned mass of silver particles, Sn10Cu master alloy, bismuth block, Sn10Sb master alloy, Sn2Mn master alloy, titanium block, and the remaining pure tin block were placed in a resistance furnace and heated to 300°C. After the materials were melted, they were stirred and kept warm for 1 hour to obtain a high-strength, thermal fatigue-resistant lead-free solder alloy. The lead-free solder alloy in this application can be represented as Sn3.4Ag0.7Cu3.2Bi3.0Sb0.03Mn0.01Ti.

[0138] Example 18

[0139] The only difference between this embodiment and embodiment 16 is that the high-strength, thermal fatigue-resistant lead-free solder alloy includes the following components by mass: 8.965 kg tin, 0.34 kg silver, 0.07 kg copper, 0.32 kg bismuth, 0.3 kg antimony, 0.003 kg manganese, and 0.002 kg cobalt.

[0140] Example 19

[0141] The only difference between this embodiment and embodiment 16 is that the high-strength, thermal fatigue-resistant lead-free solder alloy includes the following components by mass: 8.962 kg tin, 0.34 kg silver, 0.07 kg copper, 0.32 kg bismuth, 0.3 kg antimony, 0.003 kg manganese, and 0.005 kg cobalt.

[0142] Example 20

[0143] The only difference between this embodiment and embodiment 16 is that the high-strength, thermal fatigue-resistant lead-free solder alloy includes the following components by mass: 8.968 kg tin, 0.34 kg silver, 0.07 kg copper, 0.32 kg bismuth, 0.3 kg antimony, 0.001 kg manganese, and 0.001 kg cobalt.

[0144] Example 21

[0145] The only difference between this embodiment and embodiment 16 is that the high-strength, thermal fatigue-resistant lead-free solder alloy includes the following components by mass: 8.967 kg tin, 0.34 kg silver, 0.07 kg copper, 0.32 kg bismuth, 0.3 kg antimony, 0.002 kg manganese, and 0.001 kg cobalt.

[0146] Example 22

[0147] The only difference between this embodiment and embodiment 16 is that the high-strength, thermal fatigue-resistant lead-free solder alloy includes the following components by mass: 8.965 kg tin, 0.34 kg silver, 0.07 kg copper, 0.32 kg bismuth, 0.3 kg antimony, 0.004 kg manganese, and 0.001 kg cobalt.

[0148] Example 23

[0149] The only difference between this embodiment and embodiment 16 is that the high-strength, thermal fatigue-resistant lead-free solder alloy includes the following components by mass: 8.959 kg tin, 0.34 kg silver, 0.07 kg copper, 0.32 kg bismuth, 0.3 kg antimony, 0.01 kg manganese, and 0.001 kg cobalt.

[0150] Comparative Example

[0151] Comparative Example 1

[0152] This comparative example provides a lead-free solder alloy comprising 7.5 kg tin, 0.25 kg silver, 0.25 kg copper, and 2.0 kg indium. The preparation method of the lead-free solder alloy is as follows:

[0153] The raw materials are pure tin blocks, silver particles, copper particles and indium blocks with a purity greater than 99.9%;

[0154] Take the above mass of copper particles and a pure tin block with a mass 9 times that of the copper particles, put them into a vacuum furnace at 600℃ and smelt them for 2 hours. Repeat the smelting twice to obtain Sn10Cu master alloy.

[0155] The above-mentioned mass of silver particles, Sn10Cu master alloy, indium block and the remaining pure tin block are placed in a resistance furnace at 300°C and heated. After the materials are melted, they are stirred and kept warm for 1 hour to obtain a lead-free solder alloy.

[0156] Comparative Example 2

[0157] This comparative example discloses a lead-free solder alloy comprising 9.2 kg of tin, 0.3 kg of silver, and 0.5 kg of copper. The preparation method of the lead-free solder alloy is as follows:

[0158] The raw materials are pure tin blocks, silver particles and copper particles with a purity greater than 99.9%;

[0159] Take the above mass of copper particles and a pure tin block with a mass 9 times that of the copper particles, put them into a vacuum furnace at 600℃ and smelt them for 2 hours. Repeat the smelting twice to obtain Sn10Cu master alloy.

[0160] The above-mentioned mass of silver particles, Sn10Cu master alloy and the remaining pure tin block are placed in a resistance furnace at 300°C and heated. After the materials are melted, they are stirred and kept warm for 1 hour to obtain a lead-free solder alloy.

[0161] Comparative Example 3

[0162] This comparative example discloses a lead-free solder alloy including 9.5 kg of tin and 0.5 kg of antimony.

[0163] The preparation method of lead-free solder alloy is:

[0164] Using pure tin blocks and antimony blocks with a purity greater than 99.9% as raw materials;

[0165] Take the above-mentioned mass of antimony block and pure tin block with a mass 9 times that of copper particles, put them into a vacuum furnace at 600℃ and smelt them for 2 hours. Repeat the smelting twice to obtain Sn10Sb master alloy.

[0166] The Sn10Sb master alloy and the remaining pure tin block were placed in a resistance furnace at 300°C and heated. After the materials were melted, they were stirred and kept warm for 1 hour to obtain a lead-free solder alloy.

[0167] Performance testing

[0168] The tensile strength of the lead-free solder alloys prepared in each Example and Comparative Example was tested using a material testing machine at 25°C and 125°C. The lead-free solder alloys prepared in each Example and Comparative Example were subjected to a hot air circulation treatment: 1000 cycles of heat treatment from -40°C to +125°C after soldering, with a 30-minute dwell time at both high and low temperatures. The tensile strength was then tested again. The test results are summarized in Table 1.

[0169] Table 1

[0170] 1 and 3 , the microstructures of the lead-free solder alloys prepared in Example 6 and Example 16 were observed using an electron microscope. It can be seen that the microstructures of the high-strength, thermal fatigue-resistant lead-free solder alloys in Example 6 and Example 16 are both relatively fine and uniform.

[0171] Referring to Figures 2 and 4, the melting points of the lead-free solder alloys prepared in Examples 6 and 16 were measured using a DSC2910 differential scanning calorimeter (TA Instrument) for melting temperature analysis. The process parameters were set in accordance with JIS-Z3198. The melting points of the high-strength, thermal fatigue-resistant lead-free solder alloys obtained in Examples 6 and 16 were both 221.8°C.

[0172] It can be seen from Example 1, Comparative Examples 1-3 and Table 1 that the lead-free solder alloy disclosed in this application has excellent tensile strength and thermal fatigue resistance, better tensile strength at high temperature, can be used in high temperature scenarios, and has good thermal stability.

[0173] It can be seen from Examples 1-5 and Table 1 that Sn3.4Ag0.7Cu3.2Bi3.0Sb has better high-temperature mechanical strength stability and thermal fatigue resistance.

[0174] Combining Examples 6-9 with Table 1, it can be seen that selecting nickel and neodymium in combination as solder joint / interface control elements can enable the lead-free solder alloy to have relatively balanced mechanical properties and thermal fatigue resistance.

[0175] From Example 6, Examples 10-15 and Table 1, it can be seen that Sn3.4Ag0.7Cu3.2Bi3.0Sb0.05Nd0.01Ni has better and more balanced high-temperature mechanical reliability and thermal fatigue resistance.

[0176] From Examples 16-17 and Table 1, it can be seen that selecting manganese and cobalt in combination as solder joint / interface control elements can enable the lead-free solder alloy to obtain better tensile strength and thermal fatigue resistance.

[0177] From Example 16, Examples 18-23 and Table 1, it can be seen that Sn3.4Ag0.7Cu3.2Bi3.0Sb0.03Mn0.01Co has better and more balanced high-temperature mechanical reliability and thermal fatigue resistance.

[0178] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A high-strength thermal fatigue-resistant lead-free solder alloy, characterized in that: The following components are included in mass percentage: Silver 2.5-4%; Copper 0.5-1%; Bismuth 3-3.5%; Antimony 2.5-4%; Also includes: Nickel 0.01-0.05% and neodymium 0.04-0.1%; or / and, manganese 0.02-0.1% and cobalt 0.01-0.05%; The balance is tin and any unavoidable impurities.

2. The high-strength thermal fatigue-resistant lead-free solder alloy according to claim 1, characterized in that: The mass percentage of the nickel is 0.01-0.02%, and the mass percentage of the neodymium is 0.04-0.06%.

3. The high-strength thermal fatigue-resistant lead-free solder alloy according to claim 1, characterized in that: The mass percentage of manganese is 0.02-0.04%; the mass percentage of cobalt is 0.01-0.02%.

4. The high-strength thermal fatigue-resistant lead-free solder alloy according to claim 1, characterized in that: The alloy melting point of the lead-free solder alloy is 200-250°C.

5. The high-strength thermal fatigue-resistant lead-free solder alloy according to claim 1, characterized in that: The lead-free solder alloy has a tensile strength of not less than 80 MPa at 25° C., and a tensile strength of not less than 50 MPa at 125° C.

6. A method for preparing a high-strength, thermal fatigue-resistant lead-free solder alloy as claimed in any one of claims 1 to 5, characterized in that: The following steps are involved: The raw materials are mixed according to a proportion, melted, kept warm and stirred to obtain a lead-free solder alloy.

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