A high fatigue resistance solder based on a snagcu alloy

Abstract

The application relates to a high fatigue-resistant solder based on a SnAgCu alloy and belongs to the technical field of electronic welding. The solder is composed of the following components in percentage by weight: Ag 0.1-5.0%, Cu 0.1-1.0%, In 1-5%, Bi 1-5%, Sb 1-6%, Ti 0.001-0.5%, Nb 0.001-0.3%, Cr 0.005-0.1%, Ni 0.05-0.1%, Mo 0.005-0.2%, Co 0.005-0.1%, B 0.001-0.01%, and the balance of Sn and inevitable impurities; the application adds the components of In, Bi, Sb, Ti, Nb, Cr, Ni, Mo, Co and B on the basis of the SnAgCu alloy, and is supplemented with a specific preparation method, so that a solder alloy with good mechanical fatigue resistance and temperature impact fatigue resistance is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of brazing material, in particular to a high fatigue resistance solder based on SnAgCu alloy. BACKGROUND

[0002] Sn-Ag-Cu lead-free solder alloy has relatively good brazing process performance, and its tensile strength is close to or higher than that of Sn-Pb eutectic solder. Its yield strength, shear strength, impact toughness and creep resistance are also relatively high. This makes it perform well under mechanical stress and can meet the requirements of various complex and harsh working environments. Compared with traditional Sn-Pb solder, Sn-Ag-Cu lead-free solder alloy does not contain lead element, so it is more in line with environmental protection requirements and has less impact on human health and environment

[0003] However, the melting point of Sn-Ag-Cu lead-free solder alloy is relatively high. During welding and service, when the environmental temperature changes, a large thermal stress will be generated inside the solder joint. These thermal stresses can cause cracks or fractures in the solder joint, thereby affecting its temperature impact fatigue resistance. Moreover, there may be a difference in the thermal expansion coefficient between the solder joint and the base material. During temperature impact, due to the difference in thermal expansion coefficient, additional stress will be generated inside the solder joint, further exacerbating its fatigue damage.

[0004] In addition, during welding, intermetallic compounds will be formed between Sn-Ag-Cu lead-free solder alloy and the base material. The thickness of these compounds will increase over time, causing the mechanical properties at the interface to be severely weakened, thereby affecting the mechanical fatigue life of the solder joint. SUMMARY

[0005] The present application aims to overcome the shortcomings of the prior art and provide a high fatigue resistance solder based on SnAgCu alloy with good mechanical fatigue resistance and temperature impact fatigue resistance.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0007] In a first aspect, the present application provides a high fatigue resistance solder based on SnAgCu alloy, characterized by consisting of the following components by weight percentage: Ag 0.1-5.0%, Cu 0.1-1.0%, In 1-5%, Bi 1-5%, Sb 1-6%, Ti 0.001-0.5%, Nb 0.001-0.3%, Cr 0.005-0.1%, Ni 0.05-0.1%, Mo 0.005-0.2%, Co 0.005-0.1%, B 0.001-0.01%, and the balance being Sn and unavoidable impurities.

[0008] The preparation method of the solder comprises the following steps:

[0009] S1, the SnCuCo alloy, SnNi alloy, Ag, Bi, Sb, Ti, Nb, Cr, Mo and B are put into a quartz crucible, the quartz crucible is put into a vacuum induction furnace, and smelting is carried out under an argon environment and at 600-650 DEG C, and after the sample is cooled, the Sn-Cu-Co-Ni-Ag-Bi-Sb-Ti-Nb-Cr-Mo-B alloy is obtained by taking out.

[0010] S2, the Sn-Cu-Co-Ni-Ag-Bi-Sb-Ti-Nb-Cr-Mo-B alloy and In are put into a quartz crucible, smelting is carried out under an argon environment and at a temperature of 300-350 DEG C, and after heat preservation, the furnace is cooled to obtain the high fatigue resistance solder based on the SnAgCu alloy.

[0011] The present application adds the components of In, Bi, Sb, Ti, Nb, Cr, Ni, Mo, Co and B on the basis of the SnAgCu alloy. Adding Bi, Sb, Ti and other elements can affect the microstructure of the solder joint, increase the types and quantity of intermetallic compounds (IMCs), thereby improving the strength and toughness of the solder joint, and indirectly improving the impact fatigue resistance of the solder joint.

[0012] Adding Ni, Co and Cr elements can improve the thermal fatigue resistance of the alloy, slow down the growth rate of the IMC, reduce the thermal fatigue crack propagation rate when serving at high temperature, and improve the thermal stability of the solder joint. Ni and Co elements can also form a solid solution to increase the hardness of the alloy, and Mo, Nb and Ti can form dispersed particles or compounds to hinder crack propagation.

[0013] It should be noted that although the addition of Bi can significantly reduce the growth rate of the LASAC / Cu interface IMC, thereby improving the anti-aging performance of the solder joint, the formation of InBi phase may cause the embrittlement of the solder joint interface, affecting the reliability of the solder joint. This is because the InBi phase may form at the solder joint interface, increasing the brittleness of the interface, thereby easily causing the fracture of the solder joint during mechanical fatigue or temperature impact fatigue.

[0014] The following is the role of each element:

[0015] The solid solution strengthening effect of Bi in the solder alloy can improve its tensile strength and positively affect the fatigue resistance.

[0016] The addition of In can inhibit the growth of interfacial intermetallic compounds (IMC), helping to maintain interfacial stability and thus improve the fatigue resistance of the solder alloy. If the In content is too low, it will not achieve the effect of refining the organization and improving the wettability, thereby affecting the mechanical fatigue resistance and temperature impact fatigue resistance of the solder joint. When the addition of In exceeds 5.0%, a large number of blocky IMC appears in the matrix after high-temperature aging, which leads to a decrease in the plasticity of the material, thereby affecting its fatigue resistance. At the same time, too high In content may cause the oxidation resistance of the solder to decrease, affecting the stability and reliability of the solder joint in a high-temperature environment. Therefore, an appropriate amount of In can improve the tensile strength and shear strength of the solder alloy, thereby enhancing its fatigue resistance.

[0017] The addition of Sb can refine the β-Sn grains in the solder alloy and make the Ag3Sn phase develop from coarse needles to small spherical particles, with more uniform distribution. This refinement and uniform distribution helps to improve the fatigue resistance of the solder alloy, as smaller grain size can provide more grain boundaries, hindering the movement of dislocations and improving the fatigue resistance of the material. The addition of Sb can reduce the undercooling of the solder, which helps to form a finer and more uniform microstructure during solidification of the solder alloy, thereby improving its fatigue resistance. The addition of Sb can improve the wettability of the solder alloy, reduce the contact angle, and increase the spreading area, thereby helping to form better solder joints. In addition, the addition of Sb can also improve the melting characteristics of the alloy, reducing the melting range, which helps to reduce the porosity and hot tearing tendency during welding.

[0018] Ti, as a micro-alloying element, can refine the austenite grains by precipitating Ti(C, N) phase, thereby obtaining fine martensite laths, which helps to improve the strength of the solder alloy.

[0019] Nb, as a micro-alloying element, can refine the grains in the solder alloy by precipitating phase, thereby improving the strength of the solder alloy. At the same time, the addition of Nb increases the content of MC-type precipitated phase and optimizes the size distribution of the precipitated phase, thereby improving the strength of the material. The addition of Nb improves the tensile strength and hardness of the solder alloy, helping the solder alloy to resist crack initiation and propagation under cyclic loading, thereby improving its fatigue resistance. The addition of Nb helps to inhibit the growth of Cu grains, thereby refining the microstructure of the alloy. If the Nb content is too low, it cannot effectively inhibit the growth of grains, leading to a decrease in the mechanical properties of the alloy, thereby affecting its fatigue resistance. If the addition of Nb is too much, it may increase the brittleness of the solder alloy, thereby reducing its fatigue resistance. Therefore, the appropriate addition of Nb helps to improve the mechanical properties of the solder alloy, including strength and toughness, thereby enhancing its fatigue resistance.

[0020] The addition of Cr can effectively improve the oxidation resistance of the solder. On the surface of the molten solder, Cr is prone to form Cr203, and this oxide layer can improve the oxidation resistance of the solder, thereby indirectly improving the fatigue resistance of the solder at high temperatures. After adding Cr to the solder alloy, through room temperature tensile test and high temperature aging treatment, it is found that the addition of Cr improves the plasticity of the alloy. This shows that the addition of Cr can improve the high temperature reliability of the solder alloy, thereby improving its fatigue resistance.

[0021] Ni as an alloying element can refine the grain size of the solder alloy and improve the strength of the solder alloy through solid solution strengthening and precipitation strengthening mechanisms. Sb, In and Ni can make intermetallic compounds (IMCs) more uniformly distributed in the Sn matrix, thereby refining the microstructure and improving the tensile strength of the solder alloy.

[0022] Mo is a commonly used alloying element that can improve the high temperature strength of the alloy without significantly reducing its plasticity. This is beneficial for the fatigue resistance of the solder alloy in high temperature environments, as the solder joint needs to maintain certain strength and stability during thermal cycling. The addition of Mo can improve the resistance of the solder alloy to hot corrosion, especially in oxygen-containing environments. This helps the solder joint to maintain its performance in environments where high temperatures and corrosive media coexist, reducing fatigue failure caused by corrosion.

[0023] The addition of Co can inhibit the excessive growth of intermetallic compounds (IMC) in the solder alloy matrix, refine the alloy structure and improve the fatigue resistance of the solder joint. Tests have shown that the addition of trace amounts of Co can improve the thermal fatigue stability of the solder joint. Moreover, the reaction with Sn promotes the rapid melting of Co, which can optimize the distribution of alloying elements and refine the grain structure, further improving the fatigue resistance.

[0024] Boron has a very low solubility in alloys, so it tends to segregate at grain boundaries. This segregation can change the local chemical environment of the grain boundaries, affecting their stability and strength. It is because of the addition of B that the strength of the grain boundaries is improved, thereby improving the fatigue life of the solder alloy under cyclic loading. At the same time, the segregation of boron can reduce the segregation of harmful impurity elements at the grain boundaries, thereby purifying the grain boundaries. At high temperatures, boron can form stable carbides or borides, which have good thermal stability and can improve the performance of the alloy in high temperature environments.

[0025] In the preparation process of the solder alloy of the present application, Sn-Cu-Co-Ni-Ag-Bi-Sb-Ti-Nb-Cr-Mo-B alloy is prepared first, and then In is added after cooling to avoid the formation of brittle InBi phase, avoid being easily affected by external force to produce cracks or fractures. Moreover, it can also reduce the growth rate of intermetallic compounds at the SnBiIn / Cu interface to maintain the stability of the organization at the interface, thereby enhancing the interface bonding force, slowing down the creep deformation, improving the creep resistance of the solder alloy, and thus improving its fatigue resistance. When In (indium) is added to the SnAgCu alloy, it needs to be added at a reduced temperature, mainly because the melting point of indium is relatively low, only 156.61℃. Cooling can avoid excessive volatilization or oxidation of indium at high temperature, and also helps to control the solidification process of the alloy to ensure that copper can be uniformly distributed in the alloy.

[0026] Preferably, the high fatigue resistance solder based on SnAgCu alloy is composed of the following components by weight percentage: Ag 0.5-2.0%, Cu 0.8-1.0%, In 1-3%, Bi 1-2%, Sb 2-4%, Ti 0.1-0.3%, Nb 0.1-0.3%, Cr 0.005-0.008%, Ni 0.08-0.1%, Mo 0.005-0.1%, Co 0.005-0.008%, B 0.005-0.01%, the balance being Sn and unavoidable impurities.

[0027] More preferably, the high fatigue resistance solder based on SnAgCu alloy is composed of the following components by weight percentage: Ag 1-1.7%, Cu 0.9-1.0%, In 1-2%, Bi 1-1.5%, Sb 2-3%, Ti 0.1-0.2%, Nb 0.2-0.3%, Cr 0.005-0.006%, Ni 0.08-0.09%, Mo 0.007-0.1%, Co 0.005-0.006%, B 0.006-0.01%, the balance being Sn and unavoidable impurities.

[0028] Most preferably, the high fatigue resistance solder based on SnAgCu alloy is composed of the following components by weight percentage: Ag 1.5%, Cu 0.92%, In 1.2%, Bi 1.2%, Sb 2.6%, Ti 0.18%, Nb 0.21%, Cr 0.005%, Ni 0.08%, Mo 0.009%, Co 0.005%, B 0.007%, the balance being Sn and unavoidable impurities.

[0029] Preferably, the preparation method of the SnCuCo alloy comprises the following steps:

[0030] The Sn element, Cu element and Co element are respectively placed in a quartz crucible, the quartz crucible is placed in a vacuum induction furnace, and smelting is carried out at 990-1000 DEG C under an argon atmosphere; after the sample is cooled, the SnCuCo alloy is obtained. At 990-1000 DEG C high-temperature smelting, Sn can promote the melting of high-melting-point Cu and Co as quickly as possible, so that Cu and Co can be more uniformly distributed in the SnCuCo alloy. This uniform distribution helps to reduce the composition segregation and local stress concentration in the alloy, thereby improving the overall mechanical properties and fatigue resistance of the solder alloy.

[0031] Preferably, the preparation method of the SnNi alloy comprises the following steps: smelting nickel metal blocks and tin metal blocks at 800-900 DEG C under an argon atmosphere, stirring during smelting until the smelting is completed, and then pouring the alloy liquid into a mold to obtain a SnNi alloy ingot.

[0032] Preferably, in the preparation step S2 of the SnAgCu alloy-based high fatigue resistance solder, the holding time is 40-60 min.

[0033] Preferably, the mass ratio of Sn in the SnCuCo alloy and Sn in the SnNi alloy is (1.5-2):1.

[0034] Compared with the prior art, the beneficial effects of the present application are:

[0035] (1) The present application adds In, Bi, Sb, Ti, Nb, Cr, Ni, Mo, Co and B components to the SnAgCu alloy, which can significantly improve the mechanical fatigue resistance and temperature impact fatigue resistance of the SnAgCu alloy. By adding Bi, Sb, Ti and other elements to synergistically affect the microstructure of the solder joint, the types and quantities of intermetallic compounds (IMCs) are increased, thereby improving the strength and toughness of the solder joint. Sb, In, Ni and Bi and other elements can synergistically improve the tensile strength and plasticity of the Sn-Ag-Cu solder, and the addition of these elements helps to form more uniformly distributed IMCs, thereby bringing a combined strengthening mechanism of solid solution strengthening and precipitation strengthening. The addition of Ni, Co and Cr synergistically improves the heat fatigue resistance of the alloy, slows down the growth rate of the IMC, reduces the thermal fatigue crack propagation rate during high-temperature service, and thus improves the thermal stability of the solder joint.

[0036] (2) In order to avoid adding In and Bi single elements directly to form the brittle InBi phase, in the preparation process of the solder alloy of the present application, the Sn-Cu-Co-Ni-Ag-Bi-Sb-Ti-Nb-Cr-Mo-B alloy is prepared first, and then In single element is added after cooling, so as to avoid forming the brittle InBi phase and being easily affected by external force to produce cracks or breakage. Moreover, the growth rate of intermetallic compounds at the SnBiIn / Cu interface can be reduced, so as to maintain the stability of the structure at the interface, and then the interface bonding force is enhanced, the creep deformation can be slowed down, the creep resistance of the solder alloy is improved, and then the fatigue resistance is improved. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 High-power microscope photo of the solder alloy of Example 1 under 500 times;

[0038] Figure 2 High-power microscope photo of the solder alloy of Comparative Example 13 under 500 times;

[0039] Figure 3 High-power microscope photo of the solder alloy of Comparative Example 14 under 500 times;

[0040] Figure 4 High-power microscope photo of the solder alloy of Comparative Example 16 under 500 times. DETAILED DESCRIPTION

[0041] In order to better illustrate the purpose, technical scheme and advantages of the present application, the present application will be further described below in combination with specific examples.

[0042] The purity of the metal single elements used in the examples and comparative examples is greater than 99.9%.

[0043] Other materials, reagents, etc. can be obtained from commercial channels if no special description is made.

[0044] Examples 1-7 and Comparative Examples 1-14

[0045] The composition components of the solder alloys of Examples 1-7 and Comparative Examples 1-14 are shown in Table 1.

[0046] Table 1 Composition components of the solder alloys of Examples 1-7 and Comparative Examples 1-14

[0047]

[0048]

[0049]

[0050] The preparation method of the solder alloy of examples 1-7 and comparative examples 1-14 comprises the following steps:

[0051] S1, put SnCuCo alloy, SnNi alloy, Ag, Bi, Sb, Ti, Nb, Cr, Mo and B into a quartz crucible, put the quartz crucible into a vacuum induction furnace, and melt under an argon atmosphere at 650℃, and take out the sample after cooling to obtain Sn-Cu-Co-Ni-Ag-Bi-Sb-Ti-Nb-Cr-Mo-B alloy; wherein the mass ratio of Sn in the SnCuCo alloy and Sn in the SnNi alloy is 1.8:1.

[0052] S2, put Sn-Cu-Co-Ni-Ag-Bi-Sb-Ti-Nb-Cr-Mo-B alloy and In single element into a quartz crucible, melt under an argon atmosphere at 350℃, and cool with the furnace after holding for 40min to obtain the high fatigue resistance solder based on SnAgCu alloy.

[0053] The preparation method of the SnCuCo alloy comprises the following steps:

[0054] Put Sn single element, Cu single element and Co single element into a quartz crucible, put the quartz crucible into a vacuum induction furnace, and melt under an argon atmosphere at 1000℃, and take out the sample after cooling to obtain SnCuCo alloy.

[0055] The preparation method of the SnNi alloy comprises the following steps: melt nickel metal block and tin metal block in a vacuum under an argon atmosphere at 900℃, stir while melting until the melt is clear, and pour the alloy liquid into a mold after the melting is completed to obtain SnNi alloy ingot.

[0056] Example 8

[0057] The alloy composition ratio of example 8 is the same as that of example 1, and the preparation method comprises the following steps:

[0058] S1, put SnCuCo alloy, SnNi alloy, Ag, Bi, Sb, Ti, Nb, Cr, Mo and B into a quartz crucible, put the quartz crucible into a vacuum induction furnace, and melt under an argon atmosphere at 600℃, and take out the sample after cooling to obtain Sn-Cu-Co-Ni-Ag-Bi-Sb-Ti-Nb-Cr-Mo-B alloy; wherein the mass ratio of Sn in the SnCuCo alloy and Sn in the SnNi alloy is 1.8:1.

[0059] S2, the Sn-Cu-Co-Ni-Ag-Bi-Sb-Ti-Nb-Cr-Mo-B alloy and In element are put into a quartz crucible, smelting is carried out under an argon atmosphere and at a temperature of 350 DEG C, after holding for 60 min, the furnace is cooled to obtain the high fatigue resistance solder based on the SnAgCu alloy.

[0060] The preparation method of the SnCuCo alloy comprises the following steps:

[0061] The Sn element, Cu element and Co element are respectively put into a quartz crucible, the quartz crucible is put into a vacuum induction furnace, and smelting is carried out under an argon atmosphere and at 990 DEG C, and the SnCuCo alloy is obtained after the sample is cooled and taken out.

[0062] The preparation method of the SnNi alloy comprises the following steps: nickel metal blocks and tin metal blocks are smelted and stirred under an argon atmosphere and at 800 DEG C until the smelting is completed, and the alloy liquid is cast into a mold to obtain a SnNi alloy ingot.

[0063] Example 9

[0064] Example 9 differs from example 1 in that the smelting temperature for preparing the SnCuCo alloy in the preparation method of the solder of example 8 is 980 DEG C.

[0065] Example 10

[0066] Example 10 differs from example 1 in that the mass ratio of Sn in the SnCuCo alloy to Sn in the SnNi alloy is 1:1.

[0067] Example 11

[0068] Example 11 differs from example 1 in that the mass ratio of Sn in the SnCuCo alloy to Sn in the SnNi alloy is 1.5:1.

[0069] Example 12

[0070] Example 12 differs from example 1 in that the mass ratio of Sn in the SnCuCo alloy to Sn in the SnNi alloy is 2:1.

[0071] Example 13

[0072] Example 13 differs from example 1 in that the mass ratio of Sn in the SnCuCo alloy to Sn in the SnNi alloy is 2.5:1.

[0073] Comparative example 15

[0074] The alloy composition of Comparative Example 15 is the same as that of Example 1, and the difference between Comparative Example 16 and Example 1 is that the preparation method of Comparative Example 16 comprises the following steps:

[0075] S1, put all the single elements of Sn, Cu, Co, Ni, Ag, Bi, Sb, Ti, Nb, Cr, Mo and B into a quartz crucible, put the quartz crucible into a vacuum induction furnace, and melt at 600-650°C under argon atmosphere, and take out the sample after cooling to obtain Sn-Cu-Co-Ni-Ag-Bi-Sb-Ti-Nb-Cr-Mo-B alloy;

[0076] S2, put the Sn-Cu-Co-Ni-Ag-Bi-Sb-Ti-Nb-Cr-Mo-B alloy and In single element into a quartz crucible, melt under argon atmosphere and at a temperature of 350°C, and cool with the furnace after holding for 40 min to obtain the solder alloy.

[0077] Comparative Example 16

[0078] S1, put SnCuCo alloy, SnNi alloy, Ag, Bi, Sb, Ti, Nb, Cr, Mo, B and In into a quartz crucible, put the quartz crucible into a vacuum induction furnace, and melt at 650°C under argon atmosphere, and take out the sample after cooling to obtain Sn-Cu-Co-Ni-Ag-Bi-Sb-Ti-Nb-Cr-Mo-B alloy; wherein the mass ratio of Sn in the SnCuCo alloy and Sn in the SnNi alloy is 1.8:1.

[0079] S2, melt Sn-Cu-Co-Ni-Ag-Bi-Sb-Ti-Nb-Cr-Mo-B under argon atmosphere and at a temperature of 350°C, and cool with the furnace after holding for 40 min to obtain the solder alloy.

[0080] Performance test

[0081] 1, use a material testing machine to detect the tensile strength of the lead-free solder alloy prepared in each example and each comparative example at 25°C and 125°C, respectively. The solder alloy prepared in each example and each comparative example is subjected to hot air cycle treatment: after welding, cycle 1000 times under the condition of (-40°C)-(+125°C), and each high temperature and low temperature stays for 30 min; detect the tensile strength again. The test results are summarized in Table 2.

[0082] 2, measure the melting point of the solder alloy of each group of examples and comparative examples by differential scanning calorimetry, and analyze the melting temperature, and the process parameters are set according to JIS-Z3198 standard. The test results are summarized in Table 2.

[0083] Table 2 Performance data of each group of solder alloys

[0084]

[0085]

[0086] In combination with Table 1, it can be seen that Examples 1-7 explore the range of different contents of each element, wherein Example 1 is the optimal embodiment.

[0087] The melting temperature of the SnCuCo alloy of Example 9 is too low, affecting the uniformity of the SnCuCo alloy, resulting in a decline in the performance of the solder alloy obtained.

[0088] Examples 1 and 10-13 are to explore the effect of the mass ratio of Sn in the SnCuCo alloy and Sn in the SnNi alloy on the performance. In combination with the data, it can be seen that the mass ratio of Sn in the SnCuCo alloy and Sn in the SnNi alloy is preferably (1.5-2):1.

[0089] Comparative Examples 1-12 respectively lack one component of Ag, Cu, In, Bi, Sb, Ti, Nb, Cr, Ni, Mo, Co and B. In combination with the melting point data, it can be seen that Ag, Cu, Ti, Nb, Cr, Ni, Mo and Co will increase the melting point of the alloy, while In, Bi, Sb and B can significantly reduce the melting point. The tensile strength, fatigue resistance and thermal stability of Comparative Examples 1-13 are all significantly lower than those of Example 1, indicating that the components of Ag, Cu, In, Bi, Sb, Ti, Nb, Cr, Ni, Mo, Co, B and Sn synergistically improve the mechanical fatigue resistance and temperature impact fatigue resistance of the SnAgCu alloy.

[0090] In Comparative Example 13, the amount of In added is too high, in combination with Figure 2 It can be seen that Comparative Example 14 has a large amount of blocky IMC, which leads to a decrease in the plasticity of the material, thereby affecting its fatigue resistance. At the same time, too high an In content can cause a decline in the oxidation resistance of the solder, affecting the stability and reliability of the solder joint in a high-temperature environment.

[0091] In Comparative Example 14, the amount of Nb added is too high, in combination with Figure 3 It can be seen that an unstable microstructure is formed in the SnAgCu alloy, i.e., large blocks of intermetallic compounds and uneven distribution of Nb, which can become the source of fatigue cracks, reducing the fatigue resistance of the alloy.

[0092] Comparative Example 15 is a solder alloy obtained by directly mixing and smelting each element, and its performance is significantly reduced compared with Example 1. It is shown that, after pre-alloying SnCuCo alloy and SnNi alloy and then adding other elements, the alloy elements can be more uniformly distributed in the alloy, and the problem of uneven mixing of elements directly mixed can be reduced. Such uniformity can improve the consistency and reliability of the solder alloy, and can also reduce the phase interface in the alloy, reduce the stress concentration caused by the phase interface, thereby improving the fatigue resistance and thermal stability. At the same time, pre-alloying can lead to a finer and more uniform microstructure, which helps to improve the mechanical strength of the alloy. Fine grains can hinder the movement of dislocations, thereby improving the yield strength and tensile strength of the material

[0093] Comparative Example 16 is a solder alloy obtained by directly mixing SnCuCo alloy, SnNi alloy, Ag, Bi, Sb, Ti, Nb, Cr, Mo, B and In, and its performance is significantly reduced. It can be seen from Figure 1 and Figure 4 that the solder alloy of Example 1 is first prepared into a Sn-Cu-Co-Ni-Ag-Bi-Sb-Ti-Nb-Cr-Mo-B alloy and then mixed with In, so that the brittle InBi phase does not appear. However, the SEM image of Comparative Example 16 shows that the InBi phase appears, and the distribution of intermetallic compounds is also uneven. Therefore, the preparation method of the present application can avoid the formation of brittle InBi phase and avoid the generation of cracks or fractures under the influence of external force. Moreover, it can also reduce the growth rate of intermetallic compounds at the SnBiIn / Cu interface to maintain the stability of the structure at the interface, thereby enhancing the interface bonding force, slowing down the creep deformation, improving the creep resistance of the solder alloy, and thereby improving its fatigue resistance.

[0094] In summary, the present application adds In, Bi, Sb, Ti, Nb, Cr, Ni, Mo, Co and B to the SnAgCu alloy, and uses a specific preparation method to obtain a solder alloy with good mechanical fatigue resistance and temperature impact fatigue resistance.

[0095] Finally, it should be pointed out that the above examples are only used to illustrate the technical solutions of the present application and do not limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A high fatigue resistance solder based on SnAgCu alloy, characterized in that, consists of the following components in weight percentage: Ag 0.1-5.0%, Cu 0.1-1.0%, In 1-5%, Bi 1-5%, Sb 1-6%, Ti 0.001-0.5%, Nb 0.001-0.3%, Cr 0.005-0.1%, Ni 0.05-0.1%, Mo 0.005-0.2%, Co 0.005-0.1%, B 0.001-0.01%, and the balance of Sn and inevitable impurities; The preparation method of the solder comprises the following steps: S1, putting SnCuCo alloy, SnNi alloy, Ag, Bi, Sb, Ti, Nb, Cr, Mo and B into a quartz crucible, putting the quartz crucible into a vacuum induction furnace, and carrying out smelting under an argon atmosphere and at 600-650 DEG C, taking out the sample after cooling to obtain Sn-Cu-Co-Ni-Ag-Bi-Sb-Ti-Nb-Cr-Mo-B alloy; wherein the preparation method of the SnCuCo alloy comprises the following steps: putting Sn element, Cu element and Co element in an argon atmosphere and smelting at 990-1000 DEG C to obtain the SnCuCo alloy, and the mass ratio of Sn in the SnCuCo alloy and Sn in the SnNi alloy is (1.5-2):1; S2, putting Sn-Cu-Co-Ni-Ag-Bi-Sb-Ti-Nb-Cr-Mo-B alloy and In element into a quartz crucible, smelting under an argon atmosphere and at a temperature of 300-350 DEG C, cooling in the furnace after holding to obtain the high fatigue resistance solder based on SnAgCu alloy.

2. The high fatigue resistance SnAgCu alloy-based solder of claim 1, wherein, consists of the following components in weight percentage: Ag 0.5-2.0%, Cu 0.8-1.0%, In 1-3%, Bi 1-2%, Sb 2-4%, Ti 0.1-0.3%, Nb 0.1-0.3%, Cr 0.005-0.008%, Ni 0.08-0.1%, Mo 0.005-0.1%, Co 0.005-0.008%, B 0.005-0.01%, and the balance of Sn and inevitable impurities.

3. The high fatigue resistance SnAgCu alloy-based solder of claim 1, wherein, consists of the following components in weight percentage: Ag 0.5-2.0%, Cu 0.8-1.0%, In 1-3%, Bi 1-2%, Sb 2-4%, Ti 0.1-0.3%, Nb 0.1-0.3%, Cr 0.005-0.008%, Ni 0.08-0.1%, Mo 0.005-0.1%, Co 0.005-0.008%, B 0.005-0.01%, and the balance of Sn and inevitable impurities. consists of the following components in weight percentage: Ag 0.5-2.0%, Cu 0.8-1.0%, In 1-3%, Bi 1-2%, Sb 2-4%, Ti 0.1-0.3%, Nb 0.1-0.3%, Cr 0.005-0.008%, Ni 0.08-0.1%, Mo 0.005-0.1%, Co 0.005-0.008%, B 0.005-0.01%, and the balance of Sn and inevitable impurities.

4. The high fatigue resistance SnAgCu alloy-based solder of claim 1, wherein, Consists of the following weight percentage of components: Ag 1.5%, Cu 0.92%, In 1.2%, Bi 1.2%, Sb 2.6%, Ti 0.18%, Nb 0.21%, Cr 0.005%, Ni 0.08%, Mo 0.009%, Co 0.005%, B 0.007%, the balance is Sn and inevitable impurities.

5. The high fatigue resistance SnAgCu alloy-based solder of claim 1, wherein, The preparation method of the SnNi alloy comprises the following steps: melting nickel metal blocks and tin metal blocks in an argon atmosphere at 800-900 DEG C, stirring while melting until the melting is clear, after the melting is completed, pouring the alloy liquid into a mold to obtain a SnNi alloy ingot.

6. The high fatigue resistance SnAgCu alloy-based solder of claim 1, wherein, The holding time in the step S2 is 40-60 min.

Images