Fatigue-resistant high-reliability solder paste and preparation method thereof

Abstract

The application relates to a high-reliability tin paste with fatigue resistance and a preparation method thereof. The tin paste is mainly prepared from the following raw materials in percentage by mass: 85-90% of alloy solder powder and 10-15% of paste soldering agent; wherein the alloy solder powder comprises main body solder powder, alloy powder A and alloy powder B; the paste soldering agent comprises the following raw materials in parts by weight: 5-10 parts of an activating agent, 1-5 parts of a rheological agent, 20-30 parts of an organic solvent, 20-30 parts of a paste-forming agent, 0.1-0.5 parts of a modified filler and 0.1-0.5 parts of a corrosion inhibitor. The tin paste has the advantages of good welding strength, fatigue resistance, low cavity and high insulation impedance.

Description

Technical Field

[0001] This invention relates to the technical field of solder paste, specifically to a fatigue-resistant and highly reliable solder paste and its preparation method. Background Technology

[0002] Traditional solder paste is generally oil-based. Due to the extensive use of rosin and resins as flux components, post-soldering residue becomes viscous and difficult to remove completely using conventional cleaning methods, resulting in significant residue buildup and corrosion of the substrate. The grease components in oil-based solder paste affect the quality of solder joint formation, causing defects such as bubbles and voids. These defects accelerate solder joint fatigue failure and reduce solder joint strength, making them more prone to breakage or deformation under external forces, thus reducing the solder joint's fatigue resistance. Grease and other non-polar contaminants in oil-based solder paste may coat the solder joints or circuit board, forming a conductive film that reduces insulation resistance. Reduced insulation resistance increases the risk of leakage, especially under high humidity or high voltage conditions, where leakage may be more severe, threatening the performance and safety of the circuit board. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a fatigue-resistant and highly reliable solder paste with advantages such as good soldering strength, fatigue resistance, low voids and high insulation resistance, as well as its preparation method.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] In a first aspect, the present invention provides a fatigue-resistant and highly reliable solder paste, which is made from the following raw materials by weight percentage: 85-90% alloy solder powder and 10-15% paste flux, wherein the alloy solder powder includes a main solder powder, alloy powder A and alloy powder B, the main solder powder includes Sn, Ag, Cu and Sb, the alloy powder A includes Bi and / or In, and the alloy powder B includes at least one of Co, Ni, Ti, Nb, Cr, Mo and B;

[0006] The paste flux comprises the following raw materials in parts by weight: 5-10 parts activator, 1-5 parts rheology modifier, 20-30 parts organic solvent, 20-30 parts paste-forming agent, 0.1-0.5 parts modified filler and 0.1-0.5 parts corrosion inhibitor;

[0007] The activator is succinic acid and adipic acid in a mass ratio of 1:(1.5-3), the rheology modifier is a polyamide rheology modifier, the organic solvent is a composition of a low-boiling-point solvent and a high-boiling-point solvent in a mass ratio of (1-2):1, the low-boiling-point solvent includes dipropylene glycol methyl ether and / or ethylene glycol monobutyl ether, the high-boiling-point solvent includes at least one of tripropylene glycol butyl ether, diethylene glycol butyl ether, hexanediol, 2-ethyl-1,3-hexanediol and pentanediol, and the paste-forming agent is polyethylene glycol;

[0008] The method for preparing the modified filler includes the following steps:

[0009] S1. Mix nickel powder, alumina and co-solvent, stir evenly to obtain a precursor dispersion, wherein the co-solvent is a mixed solvent of ethanol, hydrochloric acid and acetic acid, and the mass ratio of co-solvent, nickel powder and alumina is (5-6):1:(1.5-3).

[0010] S2. Add polyvinylpyrrolidone to the precursor dispersion and stir until homogeneous to obtain the precursor dispersion, wherein the mass ratio of polyvinylpyrrolidone to the precursor dispersion is (0.1-0.2):1.

[0011] S3. Electrospin the precursor dispersion to obtain composite fiber paper, dry it, and sinter it in an oxygen-free environment at 1000-1500℃.

[0012] S4. The sintered composite fiber paper is immersed in an epoxy resin mixture for curing, then removed and crushed to obtain a modified filler. The epoxy resin mixture includes a mixture of epoxy resin, curing agent and catalyst in a mass ratio of 1:1:(0.01-0.03); the mass ratio of epoxy resin to sintered composite fiber paper is (2-3):1.

[0013] The solder paste of this invention does not contain large amounts of rosin and resin components as flux; instead, it uses polyethylene glycol as the paste-forming agent, offering advantages such as less post-soldering residue, less corrosiveness to the substrate, and no need for cleaning. The modified filler of this invention is prepared by first using electrospinning and high-temperature sintering techniques to obtain a composite fiber paper of alumina and nickel, which is then impregnated in epoxy resin and cured to obtain the modified filler. This modified filler has a fibrous mesh structure, forming a flexible, bendable, and independent mesh. Its characteristic feature is that nanoscale voids exist between individual fiber meshes, allowing air between the mesh voids to effectively prevent electron flow, thereby improving the insulation performance of the material. In contrast, directly mixing alumina, nickel powder, and epoxy resin results in increased contact between the filler and the matrix, leading to an increased electron conduction path and thus reduced insulation performance.

[0014] The addition of alumina and nickel can improve the mechanical strength and toughness of solder paste, thereby enhancing the fatigue resistance of solder joints. Furthermore, when alumina and nickel are made into fiber paper, their continuous network structure provides better stress distribution and additional mechanical support, resulting in stronger solder joints and further improving the fatigue resistance of solder paste joints. This structure effectively disperses cyclic stress, reducing the generation and propagation of fatigue cracks. Alumina is an excellent electrical insulating material, and its addition can significantly improve the insulation resistance of solder paste. Epoxy resin itself has good insulating properties, which can improve the insulation resistance of solder paste and reduce the risk of leakage and short circuits during electronic device operation. However, the addition of nickel improves the flowability and wettability of solder paste, helping it to better fill pads during printing and reflow, reducing void formation. But because nickel is a conductive material, it can reduce the insulation resistance. However, within the mass ratio of co-solvent, nickel powder, and alumina of (5-6):1:(1.5-3), the insulation resistance and wettability of the solder paste meet the requirements.

[0015] The activator is a combination of succinic acid and adipic acid, whose activation temperatures differ. Succinic acid is active at 180-230℃ and decomposes above 230℃, resulting in no residue after soldering. Adipic acid, on the other hand, is active at 230-260℃, precisely within the soldering zone, effectively reducing solder voids. To improve the compatibility between the solder paste components, this invention incorporates a combination of low-boiling-point and high-boiling-point solvents. The low-boiling-point solvent has a boiling point between 150-200℃, while the high-boiling-point solvent has a boiling point between 210-260℃. The low-boiling-point organic solvent evaporates rapidly during soldering, reducing the risk of solder paste collapse after printing and improving printing accuracy. It also helps reduce the stickiness of the solder paste during printing and soldering, improving printability. Furthermore, the rapid evaporation of the low-boiling-point solvent increases the fluidity of the solder paste during soldering, facilitating solder spread on the pads and improving soldering performance. High-boiling-point organic solvents evaporate more slowly during soldering and are more stable at high temperatures, which helps maintain the performance of the solder paste and affects its printability and slump resistance. Conversely, the addition of more low-boiling-point solvents than high-boiling-point solvents avoids leaving excessive residue, thereby improving the insulation performance and reliability of the solder joints.

[0016] It should be noted that the paste flux of the present invention is suitable for soldering lead-free base solder powder at 180-260°C.

[0017] More preferably, the alloy welding powder, by mass percentage, comprises the following components: Ag 0.1-5.0%, Cu 0.1-1.0%, Sb 1-6%, In 1-5%, Bi 1-5%, Co 0.005-0.1%, Ni 0.05-0.1%, Ti 0.001-0.5%, Nb 0.001-0.3%, Cr 0.005-0.1%, Mo 0.005-0.2%, B 0.001-0.01%, with the balance being Sn and unavoidable impurities.

[0018] Preferably, the corrosion inhibitor is triazole and / or benzotriazole.

[0019] More preferably, in step S1 of the modified filler, the mass ratio of the co-solvent, nickel powder and alumina is 5:1:(2-2.5).

[0020] Preferably, the low-boiling-point solvent is a composition of dipropylene glycol methyl ether and ethylene glycol monobutyl ether in a mass ratio of 1:(0.5-0.7), and the high-boiling-point solvent is a composition of tripropylene glycol butyl ether and diethylene glycol butyl ether in a mass ratio of 1:(0.8-1).

[0021] Preferably, the weight-average molecular weight of the polyethylene glycol is 2000-6000.

[0022] Preferably, the volume ratio of ethanol, hydrochloric acid and acetic acid in the co-solvent is (9-11):1:1.

[0023] Preferably, the curing agent is hexahydrophthalic anhydride; the catalyst is imidazole.

[0024] Preferably, in step S3 of the preparation of the modified filler, the drying temperature is 70-80℃, the drying time is 10-14h, and the sintering time is 1-2h.

[0025] Preferably, in step S4 of the preparation of the modified filler, the curing is a three-stage curing process. The first stage of curing is carried out at a temperature of 65-75°C for 1-2 hours. This low-temperature curing stage facilitates the initial cross-linking of the epoxy resin, forming certain intermolecular connections, but does not result in complete curing. At this stage, the resin begins to cure, but the degree of curing is low, which helps reduce internal thermal stress and volume shrinkage, avoiding cracking or deformation caused by rapid curing. Low-temperature curing also helps the epoxy resin better impregnate the composite fiber paper, enhancing interfacial bonding.

[0026] The second stage of curing involves a temperature of 100-120℃ and a time of 1-2 hours. In this stage, the higher temperature accelerates the cross-linking reaction of the epoxy resin, further increasing the degree of curing. As the degree of curing increases, the mechanical properties of the modified filler, such as strength and toughness, are enhanced, and internal stress caused by volume shrinkage during curing is further reduced.

[0027] The third stage of curing involves a temperature of 140-160℃ and a time of 3-4 hours. This high temperature ensures complete curing of the epoxy resin, forming a stable three-dimensional network structure. Fully cured epoxy resin provides optimal physical and chemical properties, such as high strength, high modulus, and good heat resistance. Prolonged high-temperature curing helps ensure the long-term stability and reliability of the modified filler, especially in applications at high temperatures.

[0028] Secondly, the present invention provides a method for preparing fatigue-resistant and highly reliable solder paste, comprising the following steps:

[0029] (1) Heat and stir the activator, rheology modifier, organic solvent, paste-forming agent and corrosion inhibitor until they are mixed evenly, then heat to 70-80℃ and add the modified filler. After stirring evenly, the paste flux is obtained.

[0030] (2) After the temperature of the paste flux drops to 25±3℃, gradually add alloy solder powder to the paste flux and stir evenly to obtain the fatigue-resistant and highly reliable solder paste.

[0031] Preferably, in step (1), the heating temperature is 50-60℃, the stirring speed is 200-300rpm, and the time is 10-30min. After adding the modified filler, the stirring speed is 500-600rpm and the time is 1-2h.

[0032] Preferably, in step (2), the stirring temperature is 25±3℃, the stirring speed is 30-60rpm, and the time is 20-30min.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] The solder paste of this invention has the advantages of good soldering strength, fatigue resistance, low voids, and high insulation resistance. Because it does not contain large amounts of rosin and resin components as flux, but instead uses polyethylene glycol as the paste-forming agent, it has advantages such as less post-soldering residue, less corrosiveness to the substrate, and no need for cleaning. The modified filler is formed by impregnating composite fiber paper in epoxy resin and curing it. The composite fiber paper has a fibrous mesh structure, and the air between the mesh gaps can effectively prevent the flow of electrons, thereby improving the insulation performance of the material. The addition of alumina and nickel can improve the mechanical strength and toughness of the solder paste, thereby improving the fatigue resistance of the solder joints. Alumina and epoxy resin can improve the insulation resistance of the solder paste. The addition of nickel improves the fluidity and wettability of the solder paste, helping it to better fill the pads during printing and reflow, reducing void formation. The activator is a combination of succinic acid and adipic acid, which have different activation temperatures, both active in the range of 180-260℃, thereby reducing residue and void rate. The organic solvent is a combination of low-boiling-point and high-boiling-point solvents. Low-boiling-point organic solvents evaporate quickly during the soldering process, which can reduce the risk of solder paste collapsing after printing, thereby improving printing accuracy. At the same time, it helps to reduce the stickiness of the solder paste during printing and soldering, improving printability. High-boiling-point organic solvents evaporate more slowly during the soldering process and are more stable at high temperatures, which helps to maintain the performance of the solder paste during the soldering process. Detailed Implementation

[0035] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0036] The reagents used in the following examples and comparative examples were sourced from the following sources:

[0037] Polyamide rheology modifier: Manufacturer is CRAY VALLEY (France), brand name is CRAY VALLEY Super;

[0038] Epoxy resin: Manufacturer: Dow Chemical Company, Grade: DER6510HT;

[0039] Hexahydrophthalic anhydride: Manufacturer: Shanghai Maclean Biochemical Technology Co., Ltd., Grade: C804848;

[0040] Imidazole: Manufacturer is Shanghai Aladdin Biochemical Technology Co., Ltd., brand name is 432539;

[0041] Polyethylene glycol: Polyethylene glycol 2000, polyethylene glycol 4000 and polyethylene glycol 6000 were all purchased from Dow Chemical Company;

[0042] Triazole: Manufacturer is Guangdong Wengjiang Chemical Reagent Co., Ltd., brand name is PB08294;

[0043] Benztriazole: Manufacturer: Guangdong Wengjiang Chemical Reagent Co., Ltd., Brand: PA01680;

[0044] Polyvinylpyrrolidone: Manufacturer is Guangdong Wengjiang Chemical Reagent Co., Ltd., brand name is PA039018.

[0045] The metal materials used in the examples and comparative examples all had a purity greater than 99.9%.

[0046] Other materials and reagents, unless otherwise specified, can be obtained commercially.

[0047] Examples 1-9 and Comparative Examples 1-16

[0048] The alloy solder powder used in the solder pastes of various embodiments and comparative examples includes a base solder powder, alloy powder A, and alloy powder B. The base solder powder includes Sn, Ag, Cu, and Sb; alloy powder A includes Bi and In; and alloy powder B includes Co, Ni, Ti, Nb, Cr, Mo, and B. Specifically, by mass percentage, the alloy solder powder consists of the following components:

[0049]

[0050] The balance is Sn and unavoidable impurities.

[0051] Example 1

[0052] A fatigue-resistant and highly reliable solder paste is made from the following raw materials in weight percentages: 88.5% alloy solder powder and 11.5% paste flux; wherein the paste flux comprises the following raw materials in parts by weight: 8 parts activator, 3 parts rheology modifier, 23 parts organic solvent, 25 parts paste-forming agent, 0.3 parts modified filler and 0.4 parts corrosion inhibitor;

[0053] The activator is succinic acid and adipic acid in a mass ratio of 1:2; the rheology modifier is a polyamide rheology modifier; the organic solvent is a composition of a low-boiling-point solvent and a high-boiling-point solvent in a mass ratio of 1.5:1, wherein the low-boiling-point solvent is a composition of dipropylene glycol methyl ether and ethylene glycol monobutyl ether in a mass ratio of 1:0.7, and the high-boiling-point solvent is a composition of tripropylene glycol butyl ether and diethylene glycol butyl ether in a mass ratio of 1:1; the paste-forming agent is polyethylene glycol 4000; and the corrosion inhibitor is benzotriazole.

[0054] The method for preparing the modified filler includes the following steps:

[0055] S1. Mix nickel powder, alumina and co-solvent, stir evenly to obtain a precursor dispersion, wherein the co-solvent is a mixed solvent of ethanol, hydrochloric acid and acetic acid with a volume ratio of 10:1:1, and the mass ratio of co-solvent, nickel powder and alumina is 5:1:2.5.

[0056] S2. Add polyvinylpyrrolidone to the precursor dispersion and stir until homogeneous to obtain the precursor dispersion, wherein the mass ratio of polyvinylpyrrolidone to the precursor dispersion is 0.15:1.

[0057] S3. The precursor dispersion was electrospun to obtain composite fiber paper, which was dried at 75℃ for 12h and then sintered at 1200℃ in an oxygen-free environment for 1.5h. The electrospinning parameters were as follows: positive voltage 10kV, negative voltage 2kV, and fixed injection speed 0.05mm·min. -1 The rotating collector speed is 100 r / min -1 ;

[0058] S4. The sintered composite fiber paper is immersed in an epoxy resin mixture for curing, then removed and pulverized to obtain the modified filler. The epoxy resin mixture is a mixture of epoxy resin, curing agent, and catalyst in a mass ratio of 1:1:0.02. The curing agent is hexahydrophthalic anhydride, the catalyst is imidazole, and the mass ratio of epoxy resin to sintered composite fiber paper is 2.5:1. The curing is a three-stage curing process: the first stage is cured at 70°C for 2 hours, the second stage is cured at 110°C for 1 hour, and the third stage is cured at 150°C for 3 hours.

[0059] A method for preparing fatigue-resistant and highly reliable solder paste includes the following steps:

[0060] (1) The activator, rheology modifier, organic solvent, paste-forming agent and corrosion inhibitor are heated at 55°C and stirred at 250 rpm for 20 min. After the temperature is raised to 75°C, the modified filler is added and stirred at 550 rpm for 1.5 h. After cooling and grinding, the paste flux is obtained.

[0061] (2) Gradually add alloy solder powder to the paste flux and stir at 40 rpm for 25 min to obtain the fatigue-resistant and highly reliable solder paste.

[0062] Example 2

[0063] A fatigue-resistant and highly reliable solder paste is made from the following raw materials in weight percentages: 85% alloy solder powder and 15% paste flux; wherein the paste flux comprises the following raw materials in parts by weight: 5 parts activator, 1 part rheology modifier, 20 parts organic solvent, 20 parts paste-forming agent, 0.1 part modified filler and 0.1 part corrosion inhibitor;

[0064] The activator is succinic acid and adipic acid in a mass ratio of 1:1.5; the rheology modifier is a polyamide rheology modifier; the organic solvent is a composition of a low-boiling-point solvent and a high-boiling-point solvent in a mass ratio of 1:1; the low-boiling-point solvent is a composition of dipropylene glycol methyl ether and ethylene glycol monobutyl ether in a mass ratio of 1:0.5; the high-boiling-point solvent is a composition of tripropylene glycol butyl ether and diethylene glycol butyl ether in a mass ratio of 1:0.8; the paste-forming agent is polyethylene glycol 2000; and the corrosion inhibitor is triazole.

[0065] The method for preparing the modified filler includes the following steps:

[0066] S1. Nickel powder, alumina and co-solvent are mixed and stirred evenly to obtain a precursor dispersion; wherein the co-solvent is a mixture of ethanol, hydrochloric acid and acetic acid in a volume ratio of 9:1:1, and the mass ratio of co-solvent, nickel powder and alumina is 5:1:1.5.

[0067] S2. Add polyvinylpyrrolidone to the precursor dispersion and stir until homogeneous to obtain the precursor dispersion; wherein the mass ratio of polyvinylpyrrolidone to the precursor dispersion is 0.1:1.

[0068] S3. The precursor dispersion was electrospun to obtain composite fiber paper, which was dried at 70℃ for 14 hours and then sintered at 1000℃ in an oxygen-free environment for 2 hours. The electrospinning parameters were as follows: positive voltage 10kV, negative voltage 2kV, and fixed injection speed 0.05mm·min. -1 The rotating collector speed is 100 r / min -1 .

[0069] S4. The sintered composite fiber paper is immersed in an epoxy resin mixture for curing, then removed and pulverized to obtain a modified filler. The epoxy resin mixture comprises a mixture of epoxy resin, curing agent, and catalyst in a mass ratio of 1:1:0.01. The curing agent is hexahydrophthalic anhydride, the catalyst is imidazole, and the mass ratio of epoxy resin to composite fiber paper is 2:1. The curing is a three-stage curing process: the first stage is cured at 65°C for 2 hours, the second stage is cured at 100°C for 2 hours, and the third stage is cured at 140°C for 3 hours.

[0070] A method for preparing fatigue-resistant and highly reliable solder paste includes the following steps:

[0071] (1) The activator, rheology modifier, organic solvent, paste-forming agent and corrosion inhibitor are heated at 50°C and stirred at 200 rpm for 30 min. After the temperature is raised to 70°C, the modified filler is added and stirred at 500 rpm for 1 h. After cooling and grinding, the paste flux is obtained.

[0072] (2) Gradually add alloy solder powder to the paste flux and stir for 30 minutes at a speed of 30 rpm to obtain the fatigue-resistant and highly reliable solder paste.

[0073] Example 3

[0074] A fatigue-resistant and highly reliable solder paste is made from the following raw materials in weight percentages: 90% alloy solder powder and 10% paste flux; wherein the paste flux comprises the following raw materials in parts by weight: 10 parts activator, 5 parts rheology modifier, 30 parts organic solvent, 30 parts paste-forming agent, 0.5 parts modified filler and 0.5 parts corrosion inhibitor;

[0075] The activator is succinic acid and adipic acid in a mass ratio of 1:3; the rheology modifier is a polyamide rheology modifier; the organic solvent is a composition of a low-boiling-point solvent and a high-boiling-point solvent in a mass ratio of 2:1, wherein the low-boiling-point solvent is dipropylene glycol methyl ether, and the high-boiling-point solvent is a composition of hexanediol, 2-ethyl-1,3-hexanediol, and pentanediol in a mass ratio of 1:1:1; the paste-forming agent is polyethylene glycol 6000; and the corrosion inhibitor is a composition of triazole and benzotriazole in a mass ratio of 1:1.

[0076] The method for preparing the modified filler includes the following steps:

[0077] S1. Nickel powder, alumina and co-solvent are mixed and stirred evenly to obtain a precursor dispersion; wherein, the co-solvent is a mixed solvent of ethanol, hydrochloric acid and acetic acid with a volume ratio of 11:1:1, and the mass ratio of co-solvent, nickel powder and alumina is 6:1:3.

[0078] S2. Add polyvinylpyrrolidone to the precursor dispersion and stir until homogeneous to obtain the precursor dispersion; wherein the mass ratio of polyvinylpyrrolidone to the precursor dispersion is 0.2:1.

[0079] S3. The precursor dispersion was electrospun to obtain composite fiber paper, which was dried at 80℃ for 10 h and then sintered at 1500℃ in an oxygen-free environment for 1 h. The electrospinning parameters were as follows: positive voltage 10 kV, negative voltage 2 kV, and fixed injection speed 0.05 mm·min. -1 The rotating collector speed is 100 r / min -1 ;

[0080] S4. The sintered composite fiber paper is soaked in an epoxy resin mixture for curing, then removed and pulverized to obtain the modified filler. The epoxy resin mixture comprises an epoxy resin, curing agent, and catalyst in a mass ratio of 1:1:0.03. The curing agent is hexahydrophthalic anhydride, and the catalyst is imidazole. The mass ratio of epoxy resin to composite fiber paper is 3:1. The curing is a three-stage process: the first stage is cured at 75°C for 1 hour, the second stage at 120°C for 1 hour, and the third stage at 160°C for 3 hours.

[0081] A method for preparing fatigue-resistant and highly reliable solder paste includes the following steps:

[0082] (1) The activator, rheology modifier, organic solvent, paste-forming agent and corrosion inhibitor are heated at 60°C and stirred at 300 rpm for 30 min. After the temperature is raised to 80°C, the modified filler is added and stirred at 600 rpm for 1 h. After cooling and grinding, the paste flux is obtained.

[0083] (2) Gradually add alloy solder powder to the paste flux and stir at 50 rpm for 20 min to obtain the fatigue-resistant and highly reliable solder paste.

[0084] Example 4

[0085] The difference between Example 4 and Example 1 is that the mass ratio of nickel powder to alumina in the modified filler is 1:1.5.

[0086] Example 5

[0087] The difference between Example 5 and Example 1 is that the mass ratio of nickel powder to alumina in the modified filler is 1:2.

[0088] Example 6

[0089] The difference between Example 6 and Example 1 is that the mass ratio of nickel powder to alumina in the modified filler is 1:3.

[0090] Example 7

[0091] The difference between Example 7 and Example 1 is that the total amount of organic solvent and the mass ratio of high-boiling-point solvent to low-boiling-point solvent remain unchanged. The low-boiling-point solvent is dipropylene glycol methyl ether, and the high-boiling-point solvent is a composition of tripropylene glycol butyl ether and diethylene glycol butyl ether in a mass ratio of 1:1.

[0092] Example 8

[0093] The difference between Example 8 and Example 1 is that the total amount of organic solvent and the mass ratio of high-boiling-point solvent to low-boiling-point solvent remain unchanged. The low-boiling-point solvent is a composition of dipropylene glycol methyl ether and ethylene glycol monobutyl ether with a mass ratio of 1:0.7. The high-boiling-point solvent is tripropylene glycol butyl ether with a mass ratio of 1:0.7.

[0094] Example 9

[0095] The difference between Example 9 and Example 1 is that the total amount of organic solvent and the mass ratio of high-boiling-point solvent to low-boiling-point solvent remain unchanged. The low-boiling-point solvent is dipropylene glycol methyl ether, and the high-boiling-point solvent is tripropylene glycol butyl ether.

[0096] Comparative Example 1

[0097] The difference between Comparative Example 1 and Example 1 is that the modified filler was not added.

[0098] Comparative Example 2

[0099] The difference between Comparative Example 2 and Example 1 is that no alumina is added to the modified filler, and the missing alumina is made up with an equal amount of nickel powder.

[0100] Comparative Example 3

[0101] The difference between Comparative Example 3 and Example 1 is that no nickel powder is added to the modified filler, and the missing nickel powder is made up with an equal amount of alumina.

[0102] Comparative Example 4

[0103] The difference between Comparative Example 4 and Example 1 is that in step S3 of the preparation of the modified filler, the composite fiber paper is not sintered after it is obtained.

[0104] Comparative Example 5

[0105] The difference between Comparative Example 5 and Example 1 is that the modified filler preparation step S4 involves directly crushing the sintered composite fiber paper to obtain the modified filler.

[0106] Comparative Example 6

[0107] The difference between Comparative Example 6 and Example 1 is that the preparation method of the modified filler does not include steps S2-S4. Instead, the precursor dispersion is directly added to the epoxy resin mixture, stirred evenly, and the mixture is subjected to negative pressure suction and dried to obtain the modified filler. The composition and amount of epoxy resin mixture added are the same as those in Example 1.

[0108] Comparative Example 7

[0109] The difference between Comparative Example 7 and Example 1 is that the total amount of nickel powder and alumina remains unchanged, and the mass ratio of nickel powder to alumina in the modified filler is 1:1.

[0110] Comparative Example 8

[0111] The difference between Comparative Example 8 and Example 1 is that the total amount of nickel powder and alumina remains unchanged, and the mass ratio of nickel powder to alumina in the modified filler is 1:3.5.

[0112] Comparative Example 9

[0113] The difference between Comparative Example 9 and Example 1 is that the total amount of activator remains the same, and only succinic acid is added.

[0114] Comparative Example 10

[0115] The difference between Comparative Example 10 and Example 1 is that the total amount of activator remains the same, and only adipic acid is added.

[0116] Comparative Example 11

[0117] The difference between Comparative Example 11 and Example 1 is that the total amount of activator remains the same, which is succinic acid and adipic acid in a mass ratio of 1:1.

[0118] Comparative Example 12

[0119] The difference between Comparative Example 12 and Example 1 is that the total amount of activator remains the same, which is succinic acid and adipic acid in a mass ratio of 1:3.5.

[0120] Comparative Example 13

[0121] The difference between Comparative Example 13 and Example 1 is that the total amount of organic solvent remains the same, and only a low-boiling-point solvent is added.

[0122] Comparative Example 14

[0123] The difference between Comparative Example 14 and Example 1 is that the total amount of organic solvent remains the same, and only a high-boiling-point solvent is added.

[0124] Comparative Example 15

[0125] The difference between Comparative Example 15 and Example 1 is that the total amount of organic solvent remains the same, and it is a composition of a low-boiling-point solvent and a high-boiling-point solvent in a mass ratio of 0.5:1.

[0126] Comparative Example 16

[0127] The difference between Comparative Example 16 and Example 1 is that the total amount of organic solvent remains the same, and it is a composition of a low-boiling-point solvent and a high-boiling-point solvent in a mass ratio of 2.5:1.

[0128] Performance testing

[0129] 1. Surface insulation resistance: The surface resistance of the solder pastes of Examples 1-9 and Comparative Examples 1-16 was tested using an insulation resistance tester. The specific data are shown in Table 1.

[0130] 2. Void rate: The void rate of the weld joints formed by the alloy welding powder and paste flux of each group was measured by the section microscopic observation method. The specific data are shown in Table 1.

[0131] 3. Spread Rate: Standard copper sheets were selected and processed through polishing, pickling, and baking before being used as the test pieces for soldering. The solder wire was prepared from the alloy solder powder used in the various embodiments and comparative examples. The wire diameter of the solder wire was 1.5-1.6 mm, wound into a ring with an inner diameter of 3 mm. The soldering test temperature was 240℃. During the test, the prepared solder ring was placed in the center of the standard copper sheet, and then about 100 ml of paste flux was applied to the ring. The test piece was then placed on the surface of a molten solder furnace with the soldering temperature set. After 20 seconds, it was removed, cooled, and the residue was cleaned with solvent before the solder joint height (h) was measured.

[0132] The expansion rate (S) is calculated as follows: SR = (D - h) / D × 100%

[0133] In the formula, D is the diameter of a solder ball assuming the same volume as the solder ring used, i.e., D = 1.24V1 / 3.

[0134] V = m / ρ, where m is the mass of the solder ring (obtained by weighing) and ρ is the density of the solder ring.

[0135] 4. Residual content: The base material used in the test was a copper substrate of 30mm×30mm×0.1mm. The solder paste of each group was applied to the base material in equal amounts and soldered at 240℃ for 2s. The residual content after soldering was calculated by the mass change before and after soldering. Each solder paste was soldered at least 5 times and the weighing accuracy was ±0.001g. The residual content Δm after soldering was calculated by formula (1) and the average value of the result was taken: Δm=1000×[0.17m1-(m2-m3)],(1);

[0136] Formula (1): m1 is the printing mass of solder paste on the copper substrate, g; m2 is the total mass of solder paste and copper substrate before soldering, g; m3 is the total mass of solder paste and copper substrate after soldering, g.

[0137] 5. Fatigue Resistance: First, solder paste for each group is printed on the PCB board, followed by reflow soldering. The bond strength of the solder joints is tested. Then, each group of samples is sent to a small rapid temperature change test chamber for thermal cycling testing. The thermal cycling cycle is 1000 cycles, with the cycle unit as follows: heating from -40℃ to 125℃ for 15 minutes, holding at 125℃ for 30 minutes, cooling from 125℃ to -40℃ for 15 minutes, and holding at -40℃ for 30 minutes. After removal, the bond strength of the solder joints is tested. The test method for bond strength is to test the shear strength at fracture of each group of solder joints.

[0138] Table 1 Test results of each group of samples

[0139]

[0140]

[0141] As shown in Table 1, since no rosin was added to the solder paste of each group and the amount of epoxy resin added was low, the residual amount of the solder paste after soldering in each group did not exceed 10mg.

[0142] Examples 1 and Comparative Examples 1-3 investigated the effects of the modified filler on the properties of solder paste. Compared with Example 1, Comparative Example 1, without the addition of modified filler, showed a significant decrease in insulation resistance, fatigue resistance, and wettability. Comparative Example 2, without the addition of alumina, showed a significant decrease in insulation resistance and fatigue resistance, indicating that alumina can improve the mechanical strength and toughness of the solder paste, thereby improving the fatigue resistance of the solder joints. Furthermore, as an electrical insulating material, its addition can significantly improve the insulation resistance of the solder paste. Comparative Example 3, without the addition of nickel powder, although the insulation resistance was slightly higher than that of Example 1, showed a significant decrease in fatigue resistance and wettability, indicating that the combined application of alumina and nickel can give the solder paste good insulation resistance, fatigue resistance, and wettability.

[0143] Examples 1, 4-6, and Comparative Examples 7-8 investigated the effect of the mass ratio of nickel powder to alumina in the modified filler on the properties of solder paste. Table 1 shows that the addition of both alumina and nickel improves the mechanical properties and fatigue resistance of the solder paste. However, alumina, being an insulating material, significantly improves the insulation resistance of the solder paste, while nickel, as a conductive material, reduces the insulation resistance. The solder paste achieves the required insulation resistance and wetting properties within the mass ratio of co-solvent, nickel powder, and alumina of 5:1:(1.5-3), with a more preferred ratio of 5:1:(2-2.5).

[0144] Examples 1 and Comparative Examples 13-14 investigated the effects of selecting low-boiling-point and high-boiling-point solvents in organic solvents on solder paste performance. Compared to Example 1, the total amount of organic solvent in Comparative Example 13 remained unchanged, with only a low-boiling-point solvent added. However, due to the decomposition of the low-boiling-point solvent during high-temperature soldering, the stability of the solder paste decreased at high temperatures, resulting in a significant reduction in insulation resistance and fatigue resistance. Comparative Example 14, with the addition of only a high-boiling-point solvent, showed a significant decrease in wettability. This is because the rapid evaporation of the low-boiling-point solvent increases the fluidity of the solder paste during soldering, facilitating solder spread on the pads and improving soldering performance. Therefore, this invention selects both low-boiling-point and high-boiling-point solvents as organic solvents to improve the compatibility between the components of the solder paste. The boiling points of the low-boiling-point solvents are between 150-200°C, while those of the high-boiling-point solvents are between 210-260°C. These solvents can be combined with activators of different boiling points to maintain the performance of the solder paste during soldering at 150-230°C.

[0145] Examples 1, 7-9, and Comparative Examples 15-16 investigated the effect of the ratio of low-boiling-point solvent to high-boiling-point solvent in the organic solvent on the performance of solder paste. Table 1 shows that the solder paste performance is optimal when the low-boiling-point solvent is a combination of dipropylene glycol methyl ether and ethylene glycol monobutyl ether in a mass ratio of 1:0.7, and the high-boiling-point solvent is a combination of tripropylene glycol butyl ether and diethylene glycol butyl ether in a mass ratio of 1:1. In Comparative Examples 15 and 16, the addition of low-boiling-point solvent was excessive and insufficient, respectively, resulting in a decrease in solder paste performance. Therefore, this invention limits the organic solvent to a combination of low-boiling-point solvent and high-boiling-point solvent in a mass ratio of (1-2):1, meaning the addition of low-boiling-point solvent is slightly more than high-boiling-point solvent. This avoids leaving excessive residue, thereby improving the insulation performance and reliability of the solder joint.

[0146] Comparative Examples 4-6 investigated the effect of the preparation method of the modified filler on the performance of solder paste. In Comparative Example 4, the performance of the solder paste obtained from the composite fiber paper without sintering was significantly reduced. This is because high-temperature sintering can promote the mutual fusion of alumina and nickel with the fibers, thereby improving the interfacial bonding force between the alumina and nickel fibers and enhancing their mechanical strength and stability. The high temperature during sintering causes the fiber grains to grow and interconnect, thus improving the overall strength of the material. Moreover, sintering can make the composite fibers form a denser structure, reducing porosity and thus improving the overall performance of the material, including mechanical properties and thermal conductivity.

[0147] In Comparative Example 5, without the addition of epoxy resin to the modified filler, all properties of the solder paste were significantly reduced. Epoxy resin is an excellent insulating material with high resistivity and good electrical insulation properties. Furthermore, the epoxy resin coating of nickel powder improves the dispersibility of the modified filler and prevents the formation of conductive paths with the nickel powder, thereby increasing the insulating impedance of the solder paste. Additionally, epoxy resin reduces surface tension, making the solder paste easier to spread on the pads.

[0148] In Comparative Example 6, the modified filler, without electrospinning and sintering steps, resulted in a significant decrease in all properties of the solder paste. Electrospinning and sintering impart a fibrous structure to the alumina and nickel composite, where the internal voids and air between the fibers effectively impede electron flow, thus improving the material's insulation properties. Furthermore, the continuous network structure provides better stress distribution and additional mechanical support, resulting in stronger solder joints and improved fatigue resistance. In contrast, directly mixing alumina, nickel powder, and epoxy resin increases the contact between the filler and the matrix, leading to an increased electron conduction path and consequently reduced insulation performance.

[0149] Examples 1 and Comparative Examples 9-12 investigated the effect of activator selection on solder paste performance. In Comparative Example 9, the activator contained only succinic acid. Because succinic acid is active at 180-230℃ and decomposes above 230℃, the solder paste of Comparative Example 9 had a lower residue after soldering than that of Example 1. However, since there were no active components above 230℃, the fatigue resistance of the solder paste was significantly reduced, and the void ratio was significantly increased. In Comparative Example 10, the activator contained only adipic acid, with an activity temperature range of 230-260℃, resulting in significantly reduced wettability and fatigue resistance. This indicates that the present invention uses succinic acid and adipic acid as activators, and their activity temperatures differ. Succinic acid is active at 180-230℃ and decomposes above 230℃, resulting in no residue after soldering. Adipic acid, active at 230-260℃, is precisely within the soldering zone and can effectively reduce solder voids. By comparing Example 1 and Comparative Examples 11-12, it can be seen that when the activator is succinic acid and adipic acid in a mass ratio of 1:(1.5-3), the solder paste can simultaneously have good wettability and fatigue resistance, and can also reduce the void ratio.

[0150] In summary, the solder paste of the present invention has the advantages of good soldering strength, fatigue resistance, low voids and high insulation resistance.

[0151] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A fatigue-resistant high-reliability solder paste, characterized by, The alloy welding powder is prepared from the following raw materials in percentage by mass: 85-90% of the alloy welding powder and 10-15% of the paste flux, wherein the alloy welding powder comprises a main body welding powder, an alloy powder A and an alloy powder B, the main body welding powder comprises Sn, Ag, Cu and Sb, the alloy powder A comprises Bi and / or In, and the alloy powder B comprises at least one of Co, Ni, Ti, Nb, Cr, Mo and B. The paste flux comprises the following raw materials in parts by weight: 5-10 parts of an activating agent, 1-5 parts of a rheological agent, 20-30 parts of an organic solvent, 20-30 parts of a paste-forming agent, 0.1-0.5 parts of a modified filler and 0.1-0.5 parts of a corrosion inhibitor; the activating agent is a combination of succinic acid and adipic acid at a mass ratio of 1:(1.5-3); the rheological agent is a polyamide rheological agent; the organic solvent is a combination of a low-boiling-point solvent and a high-boiling-point solvent at a mass ratio of (1-2):1, the low-boiling-point solvent comprises dipropylene glycol methyl ether and / or ethylene glycol monobutyl ether, and the high-boiling-point solvent comprises at least one of tripropylene glycol butyl ether, diethylene glycol butyl ether, hexylene glycol, 2-ethyl-1,3-hexylene glycol and pentylene glycol; and the paste-forming agent is polyethylene glycol. The preparation method of the modified filler comprises the following steps: S1, mixing nickel powder, aluminum oxide and a co-solvent, stirring uniformly to obtain a precursor dispersion, wherein the co-solvent is a mixed solvent of ethanol, hydrochloric acid and acetic acid, and the mass ratio of the co-solvent, the nickel powder and the aluminum oxide is (5-6):1:(1.5-3); S2, adding polyvinylpyrrolidone to the precursor dispersion, stirring uniformly to obtain a precursor dispersion, wherein the mass ratio of polyvinylpyrrolidone to the precursor dispersion is (0.1-0.2):1; S3, electrospinning the precursor dispersion to obtain a composite fiber paper, drying the composite fiber paper, and sintering the composite fiber paper in an oxygen-free environment at 1000-1500℃; S4, soaking the sintered composite fiber paper in an epoxy resin mixed solution for curing, taking out and crushing to obtain the modified filler, wherein the epoxy resin mixed solution comprises epoxy resin, a curing agent and a catalyst at a mass ratio of 1:1:(0.01-0.03), and the mass ratio of the epoxy resin to the sintered composite fiber paper is (2-3):

1.

2. The high-reliability fatigue-resistant solder paste of claim 1, wherein, The alloy welding powder is prepared from the following raw materials in percentage by mass: Ag 0.1-5.0%, Cu 0.1-1.0%, Sb 1-6%, In 1-5%, Bi 1-5%, Co 0.005-0.1%, Ni 0.05-0.1%, Ti 0.001-0.5%, Nb 0.001-0.3%, Cr 0.005-0.1%, Mo 0.005-0.2%, B 0.001-0.01%, and the balance of Sn and inevitable impurities.

3. The high-reliability fatigue-resistant solder paste of claim 1, wherein the solder particles are tin particles. The corrosion inhibitor is triazole and / or benzotriazole.

4. The high-reliability fatigue-resistant solder paste of claim 1, wherein the solder particles are tin particles. The low-boiling point solvent is a combination of dipropylene glycol methyl ether and ethylene glycol monobutyl ether with a mass ratio of 1:(0.5-0.7), and the high-boiling point solvent is a combination of tripropylene glycol butyl ether and diethylene glycol butyl ether with a mass ratio of 1:(0.8-1).

5. The high-reliability fatigue-resistant solder paste of claim 1, wherein the solder particles are tin particles. The volume ratio of ethanol, hydrochloric acid and acetic acid in the co-solvent is (9-11):1:

1.

6. The high-reliability fatigue-resistant solder paste of claim 1, wherein the solder particles are tin particles. The curing agent is hexahydrophthalic anhydride, and the catalyst is imidazole.

7. The high-reliability fatigue-resistant solder paste of claim 1, wherein the solder particles are tin particles. In the preparation step S3 of the modified filler, the drying temperature is 70-80℃, the time is 10-14h, and the sintering time is 1-2h.

8. The high-reliability fatigue-resistant solder paste of claim 1, wherein the solder particles are tin particles. In the preparation step S4 of the modified filler, the curing is three-stage curing, the first-stage curing temperature is 65-75℃, the time is 1-2h, the second-stage curing temperature is 100-120℃, the time is 1-2h, and the third-stage curing temperature is 140-160℃, the time is 3-4h.

9. A method for preparing fatigue-resistant and highly reliable solder paste according to any one of claims 1-8, characterized in that, The method comprises the following steps: (1) heating and stirring the activator, rheological agent, organic solvent, paste-forming agent and corrosion inhibitor until they are uniformly mixed, then adding the modified filler after the temperature is raised to 70-80℃, and obtaining the paste flux after uniform stirring; (2) gradually adding alloy welding powder to the paste flux after the temperature of the paste flux is reduced to 25±3℃, and stirring uniformly to obtain the fatigue-resistant high-reliability tin paste.

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