Laser solder paste and its preparation method

Abstract

Laser solder paste and its preparation method, by mass percentage, include 80-95% tin powder and 5-20% flux; the flux includes flux A and flux B; the weight ratio of flux A to flux B is 1:1 to 1:2. Weigh the tin powder, flux A, and flux B; mix the tin powder and flux A at a stirring speed of 10-40 rpm for 20-30 minutes to obtain a uniform intermediate solder paste; mix the intermediate solder paste obtained in step D with flux B at a stirring speed of 30-100 rpm for 10-20 minutes, and then place under vacuum and stir at a stirring speed of 30-100 rpm for degassing for 10-20 minutes to complete the solder paste preparation. The prepared laser solder paste has both excellent anti-spatter properties and excellent wetting properties, making it very suitable for laser soldering.

Description

Technical Field

[0001] This invention belongs to the field of electronic component welding materials technology, specifically relating to a solder paste for laser welding of electronic components and its preparation method. Background Technology

[0002] In the existing technology, solder paste is mainly used in the manufacture of electronic circuits. Conventional mainstream soldering adopts the overall heating method, in which the circuit board and its electronic components and chips are heated to above the melting point of the solder alloy to complete the soldering process. This method consumes a lot of energy and is not environmentally friendly. Some heat-sensitive devices are also easily damaged during reflow and require special handling.

[0003] Laser welding technology is a non-contact, localized heating welding method with significant advantages, including low energy consumption, environmental friendliness, short welding time, and high efficiency. Compared to traditional reflow soldering, which takes several minutes, laser welding can complete the entire process in just a few seconds or even one second. However, the short time and high energy concentration of a single solder joint in laser welding pose a significant challenge to the design of solder paste formulation, necessitating the development of specialized laser solder pastes to meet the rapid release of flux activity.

[0004] The two most common problems with existing laser solder paste technology are: weak anti-splatter ability and weak wetting ability.

[0005] In existing technologies, some methods address the splattering problem of laser solder paste by using rosin with a high softening point. Increasing the activator ratio can improve the splattering problem, but it may lead to a decrease in the stability of residual insulation. Other existing technologies use high-boiling-point additives to prevent the flux solvent from boiling and splashing out during instantaneous energy concentration at the solder joint, thus preventing the solder balls from being carried out and the solder powder from melting. Summary of the Invention

[0006] To address the shortcomings of existing laser solder pastes in terms of poor anti-spatter and wetting properties, this application presents a laser solder paste and its preparation method. The method involves separating a traditional flux into flux A and flux B, and mixing them twice to prepare a laser solder paste that meets the required performance. Extensive experimental verification by the applicant has shown that this two-mixing process also yields better results in the preparation of traditional solder pastes. By adjusting the composition of flux A and flux B, solder pastes with different performance requirements can be obtained. The solder paste in this application is a laser solder paste.

[0007] The traditional method of mixing solder powder with flux B to form solder paste has evolved into a method where solder powder is first mixed with flux A to obtain an intermediate, and then the intermediate is mixed with flux B. Solder paste is prepared through two mixing processes, representing a technological advancement.

[0008] By combining the formulations and preparation methods of flux A and flux B, the prepared laser solder paste exhibits both excellent anti-spatter properties and excellent wetting properties, making it highly suitable for laser soldering.

[0009] The technical solution of this application to solve the above-mentioned technical problems is a laser solder paste, which, by weight percentage, comprises 80-95% tin powder and 5-20% flux; the flux includes flux A and flux B; the weight ratio of flux A to flux B is 1:1 to 1:2. The preparation process involves first mixing tin powder and flux A to obtain a solder paste intermediate, and then mixing the solder paste intermediate with flux B to obtain the solder paste.

[0010] Yes, the solder paste can be laser solder paste, used for laser soldering.

[0011] It can be that flux A includes: solvent 30-45%; resin content 30-40%; resin softening point below 110℃; thixotropic agent 2-9%; organic acid activator 8-20%; covalent halogen activator 0.1%-3%; surface corrosion inhibitor 5-10%; surfactant 0.1-3%; antioxidant 0.5-2%.

[0012] It can be that the organic acid activator A in flux A includes any one or more of adipic acid, malonic acid, succinic acid, itaconic acid, and methylsuccinic acid.

[0013] It can be that the surface corrosion inhibitor A in flux A includes any one or more of 2-bromo-1-methyl-1H-imidazolium, methylimidazolium, 2-ethylimidazolium, benzimidazole, and benzotriazole.

[0014] It can be that the covalent halogen activator in flux A includes any one or more of dibromobutenediol, 2-bromo-1-methyl-1H-imidazolium, and tris(2,3-dibromopropyl)isocyanurate.

[0015] It can be that the thixotropic agent A in flux A includes any one or more of polyamide-modified hydrogenated castor oil CRAYVALLAC® MT, polyamide CRAYVALLAC® SUPER, and modified hydrogenated castor oil THIXATROLST.

[0016] It can be that solvent A in flux A includes any one or a mixture of more than one of the following: tripropylene glycol butyl ether, diethylene glycol hexyl ether, diethylene glycol octyl ether, white petrolatum, rosin methyl ester, di(2-ethylhexyl) sebacate, and pentaerythritol hexadecanoate.

[0017] It can be that the surfactant A in flux A includes any one or more of the anionic surfactant GE-511 and the nonionic surfactant MF-200A.

[0018] It can be that the antioxidant A in flux A includes any one or more of BHT, antioxidant 1010 and antioxidant 3030; antioxidant 3030 is pentaerythritol tetra(2-cyano-3,3-diphenylacrylate); antioxidant 1010 is tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] pentaerythritol ester.

[0019] It can be that the resin A in flux A includes rosin resin or terpene resin, and resin A includes any one or more of AX-E hydrogenated rosin, KR610 hydrogenated rosin, and hydrogenated terpene resin P105.

[0020] It can be that the flux B includes: 30-45% solvent content; 30-40% modified rosin resin content; softening point of modified rosin resin above 110℃; 2-9% thixotropic agent; 6-17% organic acid activator; 0.1%-2% halogen activator; and 6-10% organic amine activator.

[0021] It can be any one or more of the organic acid activators in flux B, including glutaric acid, sebacic acid, 2-decyltetradecanoic acid, dodecanoic acid, high molecular weight organic acid anhydride activators (IPU-22AH, Okamura Oil, Japan), and maleic anhydride-combined polybutadiene (Ricon131MA20, Total Créville, France).

[0022] It can be that the halogen activator in flux B includes covalent halogen activators or ionic halogen activators; covalent halogen activators include any one or more of dibromobutenediol, 2-bromo-1-methyl-1H-imidazolium, and tris(2,3-dibromopropyl)isocyanurate; ionic halogen activators include any one or more of diphenylguanidine hydrobromide, cyclohexylamine hydrobromide, and diethylamine hydrochloride.

[0023] It can be any one or more of the rosin and its modifiers in flux B, including KE-604 and polymeric rosin Dymerex.

[0024] It can be that the organic amine activator B in flux B includes any one or more of trioctylamine, tribenzylamine, methylimidazole, and 2-ethylimidazole.

[0025] It can be that the solvent B in flux B includes any one or a mixture of more than one of the following: tripropylene glycol butyl ether, diethylene glycol hexyl ether, diethylene glycol octyl ether, white petrolatum, rosin methyl ester, di(2-ethylhexyl) sebacate, and pentaerythritol hexadecanoate.

[0026] It can be that the thixotropic agent B in flux B includes any one or more of polyamide-modified hydrogenated castor oil CRAYVALLAC® MT, polyamide CRAYVALLAC® SUPER, and modified hydrogenated castor oil THIXATROLST.

[0027] The technical solution of this application to solve the above-mentioned technical problems can also be a laser solder paste preparation method, including the following steps: Step C: Weigh 80-95% tin powder and 5-20% flux by mass percentage; the flux includes flux A and flux B; the weight ratio of flux A to flux B is 1:1 to 1:2; Step D: Mix tin powder and flux A at a stirring speed of 5-15 rpm for 20-30 minutes to obtain a uniform solder paste intermediate; Step F: Mix the solder paste intermediate obtained in step D with flux B at a stirring speed of 5-15 rpm for 10-20 minutes, place it under vacuum, and degas at a stirring speed of 5-15 rpm for 5-10 minutes to complete the solder paste preparation.

[0028] It can also include step A, the preparation of flux A. Step A includes the following steps: Step A1: Heat solvent A to 110-130℃; Step A2: Add resin A and stir slowly until completely dissolved; reduce the system temperature to between 70-90℃; Step A3: Add organic acid activator A, halogen activator A, and antioxidant A and stir for 10-30 minutes; Step A4: Cool to 40-60℃, add thixotropic agent A, stir for 25-35 minutes, and then cool to room temperature; Step A5: Add corrosion inhibitor A and surfactant A and stir for 5-10 minutes; Step A6: Grind until the maximum particle size of the flux particles is less than 6 micrometers, place in a refrigerator at 2-10℃, and leave for more than 10 hours for later use.

[0029] It can also include step B of flux preparation: Step B includes the following steps: Step B1: Heat solvent B to 110-130℃; Step B2: Add rosin resin B and stir slowly until completely dissolved, then lower the system temperature to between 70-90℃; Step B3: Add organic acid activator B, halogen activator B and organic amine activator B and stir for 10-30 minutes, then cool to 40-60℃; Step B4: Add thixotropic agent, stir at high speed for 25-35 minutes, then cool to room temperature; Step B5: Grind until the maximum particle size of the flux particles is less than 6 micrometers, then place in a refrigerator at 2-10℃ for more than 10 hours for later use.

[0030] One of the beneficial effects of this application is that the laser solder paste uses flux A and flux B. The two fluxes with different properties are mixed with solder powder according to specific preparation steps, so that the solder paste has both good anti-spatter properties and good wetting properties, which is very suitable for laser soldering.

[0031] One of the beneficial effects of this application is that the formulation of flux A makes its properties very suitable for mixing with tin powder first, resulting in extremely low solubility of organic acid activators, which mainly exist in a crystalline form, forming a core layer coated with flux A on the tin powder. The crystalline form of organic acid reduces its corrosion of the tin powder; the use of corrosion inhibitors also further protects the tin powder.

[0032] One of the beneficial effects of this application is that the formulation of flux B, in which the highly soluble organic acid in solvent B of flux B can increase the adhesion of solder paste to the pads (component leads), thus achieving good wetting performance.

[0033] One of the beneficial effects of this application is that the preparation method of flux A ensures the performance of flux A.

[0034] One of the beneficial effects of this application is that the preparation method of flux B ensures the performance of flux B.

[0035] One of the beneficial effects of this application is that the laser solder paste preparation method ensures that flux A is mixed with tin powder first, and then flux B is mixed. The combination of the formula and preparation method allows the oxide film on the surface of the solder joint to be quickly dissolved by the activator in the flux during laser soldering. The heated and molten tin powder can then successfully agglomerate to form a large liquid solder ball, effectively suppressing the generation of spatter. Attached Figure Description

[0036] Figure 1 It is solder paste before laser irradiation;

[0037] Figure 2 It is solder paste used in the laser irradiation process;

[0038] Figure 3 These are photomicrographs of Additive A before laser irradiation;

[0039] Figure 4 These are micrographs of additive A after laser irradiation;

[0040] Figure 5 These are the formulations of various embodiments of additive A;

[0041] Figure 6 These are the formulations of various embodiments of additive B;

[0042] Figure 7 These are the formulations for each embodiment;

[0043] Figure 8 These are proportioned formulas;

[0044] Figure 9 This is a schematic diagram of PCB copper pads;

[0045] Figure 10 This is a schematic diagram showing the time and temperature for laser welding in constant temperature mode.

[0046] Figure 11 These are photos of solder joints with a splash protection rating of A and a wettability rating of A.

[0047] Figure 12 These are photos of solder joints with a splash protection rating of A and a wetting resistance rating of B.

[0048] Figure 13 These are photos of solder joints with a spatter protection rating of C and a wettability rating of A.

[0049] Figure 14 These are the splash-proof performance test and wetting performance test results of the various embodiments and comparative examples in this application. Detailed Implementation

[0050] The contents of this application will be further described in detail below with reference to the accompanying drawings.

[0051] In this application, the mass percentage is the weight percentage, wt% is equivalent to %. Flux A is also known as flux A; flux B is also known as flux B.

[0052] The purpose of this invention is to provide a laser solder paste with high wetting power that prevents spatter during laser welding and its manufacturing technology.

[0053] There is currently no consensus in academia and industry regarding the mechanism of spatter generation during laser welding.

[0054] The inventors carefully analyzed the laser welding process and, based on the physical interaction mechanism between the laser and the components of the solder paste, proposed a simplified physical model for spatter generation. Based on this, they proposed a corresponding two-component flux solution that effectively suppresses spatter generation while achieving excellent wetting properties. Furthermore, the activator content of the flux is controlled within a suitable range, eliminating residual insulation stability issues.

[0055] Laser wavelengths used for laser welding are generally in the near-infrared region. In China, commonly used laser wavelengths are around 915nm (910-920nm), while Japan typically uses 808nm lasers. Literature indicates that organic molecules in flux do not absorb 915nm laser light, including photons in the near-infrared region.

[0056] The surface of solder powder typically has a tin oxide film several nanometers thick. The inner layer of the tin oxide film is stannous oxide, which is relatively thicker, while the outer layer is tin oxide, which is relatively thinner. The tin oxide on the outer layer of the tin oxide film does not absorb 915nm laser light, while the stannous oxide on the inner layer does partially absorb it. The metallic tin beneath the oxide film has a stronger absorption of 915nm laser light, approaching 10%. It can be inferred that the 915nm laser light, after several reflections between the solder powder particles, can be completely absorbed by the solder powder. It can be deduced that when the laser irradiates the solder paste, the solder powder is first heated. Between room temperature and 100°C, the coefficient of thermal expansion of metallic tin is 22.0 × 10⁻⁶. The coefficient of thermal expansion of tin oxide is 5.0–7.0 × 10⁻⁶. The coefficient of thermal expansion of tin oxide is 7.0–9.0 × 10⁻⁶. Significant differences in thermal expansion coefficients cause rapidly heating tin powder to break through the oxide film on its surface under thermal stress. These broken oxide films still partially adhere to the tin powder surface. If they can be quickly dissolved by the activator in the flux, the molten tin powder that is further heated can successfully coalesce to form a large liquid solder ball, effectively suppressing the generation of spatter.

[0057] Conversely, if the oxide film on the surface of these solder powders that has already cracked is not reacted off by the activator in time, the solder powder that cannot be aggregated, or only partially aggregated solder balls, will flow out of the pad area with the flowing flux, forming spatter.

[0058] The aforementioned spatter can be called the first type of spatter, and the metal particles formed by this type of spatter are generally close to the solder joint.

[0059] The second type of spatter refers to solder particles that are far from the solder joint. It is also caused by the fact that the oxides on the surface of the tin powder were not removed by the activator in time and were heated to a high temperature by the laser (tin oxide absorbs 915nm laser and has a melting point of 1080℃), resulting in boiling when it comes into contact with the solvent in the flux.

[0060] Therefore, quickly removing oxides from the surface of solder powder is key to eliminating splattering. However, excessive amounts of activator can also cause other problems, such as residual corrosion. The amount of activator used in this application is appropriate. It effectively prevents splattering and inhibits solder balls while also preventing the presence of highly corrosive residues.

[0061] In this application, flux A is characterized by:

[0062] A. Activator mainly uses activators with poor solubility in flux solvents, such as any one or more of adipic acid, malonic acid, succinic acid, itaconic acid, and methylsuccinic acid.

[0063] A corrosion inhibitor, such as any one or more of 2-bromo-1-methyl-1H-imidazole, methylimidazole, 2-ethylimidazole, benzimidazole, and benzotriazole.

[0064] A resin with a softening point below 110°C is used, such as any one or more of AX-E hydrogenated rosin, KR610 hydrogenated rosin, and hydrogenated terpene resin P105.

[0065] A covalently bonded halogenated activator, comprising any one or more of dibromobutenediol, 2-bromo-1-methyl-1H-imidazolium, and tris(2,3-dibromopropyl)isocyanurate.

[0066] A thixotropic agent is any one or more of polyamide-modified hydrogenated castor oil CRAYVALLAC® MT, polyamide CRAYVALLAC® SUPER, and modified hydrogenated castor oil THIXATROLST.

[0067] Solvent A is any one or more of tripropylene glycol butyl ether, diethylene glycol hexyl ether, diethylene glycol octyl ether, white petrolatum, rosin methyl ester, di(2-ethylhexyl) sebacate, and pentaerythritol hexadecanoate.

[0068] Surfactant A is any one or more of the following: anionic surfactant GE-511 and nonionic surfactant MF-200A.

[0069] Antioxidant A includes any one or more of BHT, Antioxidant 1010, and Antioxidant 3030; Antioxidant 3030 is pentaerythritol tetra(2-cyano-3,3-diphenylacrylate); Antioxidant 1010 is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid].

[0070] The A resin in flux A includes rosin resin or terpene resin, and A resin includes any one or more of AX-E hydrogenated rosin, KR610 hydrogenated rosin, and hydrogenated terpene resin P105.

[0071] In this application, flux B is characterized by the following:

[0072] The organic acid activator B in flux includes any one or more of the following: glutaric acid, sebacic acid, 2-decyltetradecanoic acid, dodecanoic acid, high molecular weight organic acid anhydride activator (IPU-22AH, Okamura Oil, Japan), and maleic anhydride-combined polybutadiene (Ricon131MA20, Total Créville, France).

[0073] The halogen activator in flux B includes covalent halogen activators or ionic halogen activators; covalent halogen activators include any one or more of dibromobutenediol, 2-bromo-1-methyl-1H-imidazolium, and tris(2,3-dibromopropyl)isocyanurate; ionic halogen activators include any one or more of diphenylguanidine hydrobromide, cyclohexylamine hydrobromide, and diethylamine hydrochloride.

[0074] The B rosin resin in flux B includes any one or more of KE-604 and polymeric rosin Dymerex.

[0075] The organic amine activator B in flux includes any one or more of trioctylamine, tribenzylamine, methylimidazole, and 2-ethylimidazole.

[0076] This invention employs a dual flux approach, namely, flux A and flux B working together.

[0077] By adjusting the type and ratio of solvents in flux A, the solubility of the organic acid activator is made extremely low, and it mainly exists in a crystalline form. Furthermore, in the preparation process, flux A is first mixed with tin powder; the crystalline nature of the organic acid reduces its corrosion of the tin powder. The use of corrosion inhibitors further protects the tin powder. The addition of covalently bonded halogen activators further enhances the activity of flux A while maintaining high solder stability.

[0078] The insufficient wetting power of laser solder paste has its own characteristics. This property is related to the cohesive force of the solder paste. Specifically, when a high-energy-density laser strikes the main body of the solder paste, it is undesirable for the solder paste to expand excessively or even split into several parts. For example... Figure 2 As shown, excessively expanded solder paste loses its ability to block lasers, allowing the laser to pass through the expanded solder paste area and directly irradiate the pads or component leads, causing them to heat up and oxidize. At this time, the dispersed solder paste lacks protection for the pads and component leads, resulting in poor wetting. Therefore, the solder paste has sufficient cohesive force and adhesion to the pads and component leads, which are necessary conditions for achieving good wetting.

[0079] Therefore, in this application, the highly soluble organic acid in the solvent B of flux B can increase the adhesion of the solder paste to the pads (component leads); the use of high molecular weight organic acid anhydrides and high softening point rosin can enhance the cohesive force of the solder paste; the organic amine used also has the same characteristics and effects as the organic acid in flux B; flux B uses the same solvent system and thixotropic system as flux A, which is beneficial to the stability of the overall solder paste structure system.

[0080] The technical solution of this application lies in providing a laser solder paste formulation and preparation method with high wetting power to prevent spatter during laser welding. In the laser solder paste formulation, the tin powder content is between 80-95%, and the flux content is between 5-20%. The flux is divided into two parts: flux A and flux B. The weight ratio of flux A to flux B is between 1:1 and 2. The tin powder composition includes Sn 95-99.6%, Ag 0-4%, and Cu 0.4-1%. The particle size of the tin powder conforms to the particle size requirements of #3, #4, #5, #6, and #7 powders specified in the electronic industry standard SJ / T11391-2019 Solder Alloy Powder for Electronic Product Welding or IPCJ-STD-005A-2019.

[0081] The flux composition by weight is as follows: A solvent 30-45%; A resin content 30-40%; A resin softening point below 110℃; A thixotropic agent 2-9%; A organic acid activator 8-20%; A covalent halogen activator 0.1%-3%; A surface corrosion inhibitor 5-10%; A surfactant 0.1-3%; A antioxidant 0.5-2%.

[0082] The organic acid activator in flux A includes any one or more of adipic acid, malonic acid, succinic acid, itaconic acid, and methylsuccinic acid.

[0083] The surface corrosion inhibitor A in flux A includes any one or more of 2-bromo-1-methyl-1H-imidazolium, methylimidazolium, 2-ethylimidazolium, benzimidazole, and benzotriazole.

[0084] The covalent halogen activator in flux A includes any one or more of dibromobutenediol, 2-bromo-1-methyl-1H-imidazolium, and tris(2,3-dibromopropyl)isocyanurate.

[0085] The thixotropic agent A in flux A includes any one or more of polyamide-modified hydrogenated castor oil CRAYVALLAC® MT, polyamide CRAYVALLAC® SUPER, and modified hydrogenated castor oil THIXATROLST.

[0086] Solvent A in flux A includes any one or a mixture of more than one of the following: tripropylene glycol butyl ether, diethylene glycol hexyl ether, diethylene glycol octyl ether, white petrolatum, methyl rosin, di(2-ethylhexyl) sebacate, and pentaerythritol hexadecanoate.

[0087] The surfactant A in flux A includes any one or more of the following: anionic surfactant GE-511 and nonionic surfactant MF-200A.

[0088] The antioxidant A in flux A includes any one or more of BHT, antioxidant 1010, and antioxidant 3030; antioxidant 3030 is pentaerythritol tetra(2-cyano-3,3-diphenylacrylate); antioxidant 1010 is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] ester.

[0089] The A resin in flux A includes rosin resin or terpene resin, and A resin includes any one or more of AX-E hydrogenated rosin, KR610 hydrogenated rosin, and hydrogenated terpene resin P105.

[0090] The weight ratio of flux B is as follows: solvent B content 30-45%; modified rosin resin B content 30-40%; softening point of modified rosin resin B is higher than 110℃; thixotropic agent B 2-9%; organic acid activator B 6-17%; halogen activator B 0.1%-2%; organic amine activator B 6-10%. The composition and content of solvent B and thixotropic agent B in flux B are consistent with those of solvent A and thixotropic agent A in flux A.

[0091] The organic acid activator B in flux includes any one or more of the following: glutaric acid, sebacic acid, 2-decyltetradecanoic acid, dodecanoic acid, high molecular weight organic acid anhydride activator (IPU-22AH, Okamura Oil, Japan), and maleic anhydride-combined polybutadiene (Ricon131MA20, Total Créville, France).

[0092] The halogen activator in flux B includes covalent halogen activators or ionic halogen activators; covalent halogen activators include any one or more of dibromobutenediol, 2-bromo-1-methyl-1H-imidazolium, and tris(2,3-dibromopropyl)isocyanurate; ionic halogen activators include any one or more of diphenylguanidine hydrobromide, cyclohexylamine hydrobromide, and diethylamine hydrochloride.

[0093] The rosin and its modifiers in flux B include any one or more of KE-604 and polymeric rosin Dymerex.

[0094] The organic amine activator B in flux includes any one or more of trioctylamine, tribenzylamine, methylimidazole, and 2-ethylimidazole.

[0095] The solvent B in flux B includes any one or a mixture of more than one of the following: tripropylene glycol butyl ether, diethylene glycol hexyl ether, diethylene glycol octyl ether, white petrolatum, methyl rosin, di(2-ethylhexyl) sebacate, and pentaerythritol hexadecanoate.

[0096] The thixotropic agent B in flux B includes any one or more of polyamide-modified hydrogenated castor oil CRAYVALLAC® MT, polyamide CRAYVALLAC® SUPER, and modified hydrogenated castor oil THIXATROLST.

[0097] The present invention provides a method for preparing laser solder paste, comprising the following parts: Preparation of flux A: After heating the solvent to a temperature range of 110-130°C, add resin A and stir slowly until completely dissolved. Reduce the system temperature to 70-90°C, add organic acid activator, halogen activator, and antioxidant, and stir for 10-30 minutes. Then, cool to 40-60°C and add thixotropic agent. Stir at high speed for 25-35 minutes. Cool to room temperature, add corrosion inhibitor and surfactant, and stir slowly for 5-10 minutes. Grind until the maximum particle size of the flux particles is less than 6 micrometers. Then, place it in a refrigerator at 2-10°C and leave it for more than 10 hours for later use.

[0098] Preparation of flux B: After heating the solvent to 110-130℃, add rosin resin B and stir slowly until completely dissolved. Then, lower the system temperature to 70-90℃, add organic acid activator, halogen activator and organic amine activator and stir for 10-30 minutes. Then, cool to 40-60℃ and add thixotropic agent. Stir at high speed for 25-35 minutes. After cooling to room temperature, grind until the maximum particle size of the flux particles is less than 6 micrometers. Then, place it in a refrigerator at 2-10℃ and let it stand for more than 10 hours for later use.

[0099] Preparation of solder paste: Weigh appropriate amounts of tin powder (85-92% by weight) and flux (8-15% by weight); the weight ratio of flux A to flux B is 1:1~2. First, mix the tin powder and flux A at a stirring speed of 5-15 rpm until uniform to obtain an intermediate solder paste. Then, mix the intermediate with flux B at a stirring speed of 5-15 rpm until uniform. Vacuum degassing is performed for 5-10 minutes to complete the preparation of the solder paste.

[0100] The flux A described above contains a strong organic acid activator dispersed in a crystal form. Although these organic acid molecules do not absorb 915nm laser light, experiments show that when flux A is irradiated with a 915nm laser, the number of small activator crystal particles in the flux is significantly reduced. This indicates that the organic acid crystals do absorb 915nm laser light, which may be related to crystallization defects within the organic acid crystals. When the solder paste is irradiated by laser light, near the surface of the solder powder, a large amount of laser light is scattered and absorbed by the organic acid crystals, causing the organic acid crystals to heat up and melt rapidly, releasing their activity. This helps to quickly dissolve the oxide film on the surface of the solder powder, thereby preventing spatter.

[0101] like Figure 3 and Figure 4 contrast, Figure 3 These are photomicrographs of Additive A before laser irradiation; Figure 4 This is a micrograph of additive A after laser irradiation. Figure 4 The photo shows the result of irradiating flux A with a 3W laser for 4 seconds (spot size 2.54mm). 2 The microscopic images show that the endothermic melting is more pronounced, indicating that the organic acid crystals heat up and melt rapidly, thus releasing their activity and quickly dissolving the oxide film on the surface of the tin powder, thereby preventing spattering. In actual production, the laser irradiation intensity is 1-2 orders of magnitude higher, making the endothermic melting of the organic acid crystals even more significant.

[0102] Although flux A contains a relatively large amount of organic acid, and it is very close to the surface of the solder powder, the organic acid crystals in flux A exist in a dispersed form, so their corrosiveness to the solder powder is not significant. In particular, flux A uses corrosion inhibitors for protection, which allows the solder paste to achieve both stability and anti-spatter capability.

[0103] The use of high-softening-point rosin resin and high-molecular-weight organic acid anhydride activators in flux B greatly increases the cohesiveness of the solder paste, ensuring that the solder paste body is not broken up when the laser hits it, thus preventing a decrease in wetting power. The use of organic acids that are easily soluble in solvents also enhances the adhesion of the flux to the pads and component leads.

[0104] The preparation process of Example 1 is as follows:

[0105] Flux Preparation A: Place 23 parts (by weight) of tripropylene glycol butyl ether, 2 parts of diethylene glycol octyl ether, 3 parts of rosin methyl ester, 7 parts of white petrolatum, and 1.6 parts of di(2-ethylhexyl) sebacic acid into a heating device and heat to 110°C. Then add 24 parts of AX-E hydrogenated rosin and 10 parts of hydrogenated terpene resin P105 and stir slowly until completely melted. Subsequently, lower the system temperature to 80°C and add 8 parts of succinic acid, 3 parts of adipic acid, 1 part of itaconic acid, 2 parts of dibromobutenediol, 1 part of antioxidant 1010, and 1 part of antioxidant 3030. Stir at medium speed for 10- Dissolve in 20 minutes; further reduce the system temperature to 45°C, add 3 parts CRAYVALLACSUPER thixotropic agent and 1 part THIXATROLST modified castor oil, stir at high speed for 20-30 minutes, then cool the system to room temperature of 25°C, add 6 parts 2-ethylimidazole, 1 part 1,2,3-benzotriazole, and 2.4 parts surfactant MF-200A, stir slowly for 5 minutes, then grind until the maximum particle size of the flux particles is less than 6 micrometers, then place in a refrigerator at 2-10°C for more than 10 hours for later use.

[0106] B. Flux Preparation: Place 23 parts (by weight) of tripropylene glycol butyl ether, 2 parts of diethylene glycol octyl ether, 3 parts of rosin methyl ester, 7 parts of white petrolatum, and 1.6 parts of di(2-ethylhexyl) sebacate into a heating device and heat to 110°C. Then add 20 parts of polymerized rosin Dymerex and 15 parts of KE604 rosin. Subsequently, lower the system temperature to 80°C, add 4 parts of glutaric acid, 6 parts of 2-decyltetradecanoic acid, and 4 parts of IPU-22AH, and stir at medium speed for 10-20 minutes until... Dissolve; further reduce the system temperature to 45℃, add 3 parts CRAYVALLACSUPER thixotropic agent and 1 part THIXATROLST modified castor oil, stir at high speed for 20-30 minutes, then cool the system to room temperature of 25℃, add 3 parts trioctylamine, 6 parts tribenzylamine and 0.5 parts methylimidazole, stir slowly for 5 minutes, then grind until the maximum particle size of the flux particles is less than 6 micrometers, then put it in a refrigerator at 2-10℃ and leave it for more than 10 hours for later use.

[0107] Laser solder paste preparation: Weigh flux A and flux B in a 1:1 ratio, and weigh 87% of the total solder paste volume of tin powder. First, mix the tin powder and flux A at a stirring speed of 5-15 rpm until uniform to obtain an intermediate solder paste. Then, mix it with flux B at a stirring speed of 5-15 rpm until uniform. Vacuum degassing is performed for 5-10 minutes to complete the solder paste preparation.

[0108] Example 2. The formula for Example 2 is as follows: Figure 5 The table and Figure 6 As shown in the table, its manufacturing process is the same as in Example 1, except for the weight ratio of flux A to flux B and the ratio of flux to solder powder, as follows. Figure 7 The table is shown.

[0109] Example 3. The formula for Example 3 is as follows: Figure 5 The table and Figure 6 As shown in the table, the manufacturing process is the same as in Example 1. The difference lies in the weight ratio of flux A to flux B and the ratio of flux to solder powder, as shown in the table. Figure 7 The table is shown.

[0110] Example 4. The formula for Example 4 is as follows: Figure 5 The table and Figure 6 As shown in the table, the manufacturing process is the same as in Example 1. The difference lies in the weight ratio of flux A to flux B and the ratio of flux to solder powder, as shown in the table. Figure 7 The table is shown.

[0111] Example 5. The formulation of Example 5 is as follows: Figure 5 The table and Figure 6 As shown in the table, the manufacturing process is the same as in Example 1. The difference lies in the weight ratio of flux A to flux B and the ratio of flux to solder powder, as shown in the table. Figure 7 The table is shown.

[0112] Examples 6-10. The formulations of Examples 6-10 are as follows: Figure 5 The table and Figure 6 As shown in the table, the manufacturing process is the same as in Example 1. The difference lies in the weight ratio of flux A to flux B and the ratio of flux to solder powder, as shown in the table. Figure 7 The table is shown.

[0113] To better illustrate the effectiveness of the technical solution in this application, the following comparative examples are designed for effect comparison.

[0114] Comparative Example 1. The formula for Comparative Example 1 is as follows: Figure 8 As shown in the table, Comparative Example 1 uses only one type of flux, and its formula is calculated based on the 1:1 ratio of flux A and flux B from Example 1. The flux preparation process is the same as that of flux A in Example 1, and the solder paste preparation method is also similar to that of Example 1, except that only one type of flux is mixed with tin powder.

[0115] Comparative Example 2. The formula for Comparative Example 2 is as follows: Figure 8 As shown in the table, Comparative Example 2 uses only one type of flux, and its formula is calculated based on the formulations of flux A and flux B from Example 2 at a ratio of 1:1.2. The flux preparation process is the same as that of flux A in Example 2, and the solder paste manufacturing method is also similar to that of Example 2, except that one type of flux is mixed with tin powder.

[0116] Comparative Example 3. The formula for Comparative Example 3 is as follows: Figure 8 As shown in the table, Comparative Example 3 uses only one type of flux, and its formula is calculated based on the formulations of flux A and flux B from Example 3, in a 1:1.5 ratio. The flux preparation process is the same as that of flux A in Example 3, and the solder paste manufacturing method is also similar to that of Example 3, except that one type of flux is mixed with tin powder.

[0117] Comparative Example 4. The formula for Comparative Example 4 is as follows: Figure 8 As shown in the table, Comparative Example 4 uses only one type of flux, and its formula is calculated based on the formulations of flux A and flux B from Example 4, in a 1:2 ratio. The flux preparation process is the same as that of flux A in Example 4, and the solder paste manufacturing method is also similar to that of Example 4, except that one type of flux is mixed with tin powder.

[0118] Comparative Example 5. The flux used in Comparative Example 4 is a commercially available laser solder paste flux. The manufacturing method of the solder paste is similar to that in Example 5, except that it is a mixture of a commercially available flux and solder powder.

[0119] To demonstrate the comparative effects of the technology, the inventors conducted a splash test.

[0120] Printing laser solder paste on Figure 9 On the PCB copper pads, a laser is used to adjust the spot size so that it completely covers the four pads, according to... Figure 10 The constant temperature mode program shown is used for laser soldering. The strength of the solder paste's anti-splatter ability is judged by observing the amount and size of solder beads around the solder pads after soldering.

[0121] The splash-proof performance test results are divided into three levels:

[0122] Grade A: The number of solder balls (powder) around the pad is 0;

[0123] Grade B: The number of solder balls (powder) around the pad is between 1 and 3;

[0124] Grade C: The number of solder balls (powder) around the pad exceeds 3.

[0125] There are two criteria for judging wettability: first, whether the solder paste is broken up when irradiated by laser; and second, the proportion of the area of ​​the pad covered by solder to the total area after soldering.

[0126] The wetting performance test results are also divided into three levels: A level: the solder paste is not broken up during laser irradiation and the solder coverage is greater than 90%; B level: the solder paste is not broken up during laser irradiation and the solder coverage is between 80% and 90%; C level: the solder paste is broken up during laser irradiation and the solder coverage is less than 80%.

[0127] Figure 11 It is a solder joint with a splash protection rating of A and a wetting strength rating of A. Figure 12 It is a solder joint with a spatter protection rating of A and a wetting strength rating of B. Figure 13 It is a solder joint with anti-spatter rating of C and wetting rating of A.

[0128] like Figure 14 The table summarizes the splash-proof performance test and wetting performance test results of various embodiments and comparative examples in this application. Figure 14 As can be seen from the table, the splash resistance and wetting performance test results of the comparative examples are both at level C, while the embodiments of this application can all achieve level A, proving that the technical solution of this application has good splash resistance and wetting performance.

[0129] The above are merely embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of the application specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A solder paste for laser soldering, comprising, by mass percentage, 80-95% of tin powder; 5-20% of flux; the flux comprising A flux and B flux; the weight ratio of A flux to B flux ranging from 1:1 to 1:2; a preparation process, wherein the tin powder and the A flux are mixed to obtain a solder paste intermediate, and the solder paste intermediate and the B flux are mixed to obtain the solder paste for laser soldering; the A flux comprising 30-45% of A solvent, 30-40% of A resin, 2-9% of A thixotropic agent, 8-20% of A organic acid activator, 0.1-3% of A covalent halogen activator, 5-10% of A surface corrosion inhibitor, 0.1-3% of A surfactant, and 0.5-2% of A antioxidant; the B flux comprising 30-45% of B solvent, 30-40% of B modified rosin resin, 2-9% of B thixotropic agent, 6-17% of B organic acid activator, 0.1-2% of B halogen activator, and 6-10% of B organic amine activator. 2.The solder paste for laser soldering according to claim 1, comprising any one of the following technical features: TA1: the A organic acid activator in the A flux comprises any one or more of adipic acid, malonic acid, succinic acid, itaconic acid, and methyl succinic acid; TA2: the A surface corrosion inhibitor in the A flux comprises any one or more of 2-bromo-1-methyl-1H-imidazole, methyl imidazole, 2-ethyl imidazole, benzimidazole, and benzotriazole; TA3: the A covalent halogen activator in the A flux comprises any one or more of dibromobutenediol, 2-bromo-1-methyl-1H-imidazole, and tris(2,3-dibromopropyl) isocyanurate; TA4: the A thixotropic agent in the A flux comprises any one or more of polyamide modified hydrogenated castor oil CRAYVALLAC® MT, polyamide CRAYVALLAC® SUPER, and modified hydrogenated castor oil THIXATROL ST; TA5: the A solvent in the A flux comprises a mixture of any one or more of tripropylene glycol butyl ether, diethylene glycol hexyl ether, diethylene glycol octyl ether, white vaseline, methyl abietate, and di(2-ethylhexyl) sebacate; TA6: the A surfactant in the A flux comprises any one or more of anionic surfactant GE-511 and nonionic surfactant MF-200A; TA7: the A resin in the A flux is rosin resin or terpene resin, and the A resin comprises any one or more of AX-E hydrogenated rosin, KR610 hydrogenated rosin, and hydrogenated terpene resin P105; TA8: the A antioxidant in the A flux comprises any one or more of BHT, antioxidant 1010, and antioxidant 3030; the antioxidant 3030 is pentaerythritol tetrakis(2-cyano-3,3-diphenylpropenoate); the antioxidant 1010 is tetra[β-(3.5-di-tert-butyl-4-hydroxyphenyl)propionic acid] pentaerythritol ester. ​ ​ 3. The laser soldering tin paste according to claim 1, wherein, Any one of the following technical features is included: TB1: The B organic acid active agent in the B flux includes any one or more of glutaric acid, sebacic acid, 2-decyltetradecanoic acid, dodecanedioic acid, high molecular organic acid anhydride active agent, maleic anhydride added polybutadiene; TB2: The B halogen active agent in the B flux includes covalent bond halogen active agent or ionic bond halogen active agent; the covalent bond halogen active agent includes any one or more of dibromobutene diol, 2-bromo-1-methyl-1H-imidazole, tris(2,3-dibromopropyl) isocyanurate; the ionic bond halogen active agent includes any one or more of diphenyl guanidine hydrobromide, cyclohexylamine hydrobromide, diethylamine hydrochloride; TB3: The modified rosin resin in the B flux includes any one or more of KE-604, polymeric rosin Dymerex; TB4: The B organic amine active agent in the B flux includes any one or more of trioctylamine, trisbenzylamine, methyl imidazole, 2-ethyl imidazole; TB5: The B solvent in the B flux includes a mixture of any one or more of tripropylene glycol butyl ether, diethylene glycol hexyl ether, diethylene glycol octyl ether, white vaseline, methyl abietate, sebacic acid di(2-ethylhexyl) ester, pentaerythritol hexadecanoate; TB6: The B thixotropic agent in the B flux includes any one or more of polyamide modified hydrogenated castor oil CRAYVALLAC MT, polyamide CRAYVALLAC SUPER, modified hydrogenated castor oil THIXATROL ST.

4. A method for preparing the laser solder paste according to any one of claims 1 to 3, characterized in that The following steps are included, Step C: tin powder 80-95% by mass; flux 5-20%; the flux includes A flux and B flux; the weight ratio of A flux to B flux is in the range of 1:1 to 1:2; Step D: mix the tin powder and A flux at a stirring speed of 5-15 rpm for 20-30 minutes to obtain a uniform tin paste intermediate; Step F: mix the tin paste intermediate obtained in step D with B flux at a stirring speed of 5-15 rpm for 10-20 minutes, degas under vacuum at a stirring speed of 5-15 rpm for 5-10 minutes, and complete the preparation of the tin paste.

5. The laser soldering tin paste preparation method according to claim 4, wherein, The preparation step A of the A flux is further included, and step A includes the following steps, Step A1: heat the A solvent to 110-130°C; Step A2: add the A resin and stir slowly until completely dissolved; reduce the system temperature to between 70-90°C; Step A3: add the A organic acid active agent, A halogen active agent, and A antioxidant and stir for 10-30 minutes; Step A4: cool to 40-60°C, add the A thixotropic agent, stir for 25-35 minutes, and then cool to room temperature; Step A5: add the A corrosion inhibitor and A surfactant and stir for 5-10 minutes; Step A6: grind until the maximum particle size of the particles in the flux is less than 6 microns, place in a 2-10°C refrigerator, and store for more than 10 hours.

6. The method of claim 4, wherein the solder paste is prepared by the steps of: a solder flux preparation step B, wherein the step B comprises the steps of: B1: heating B solvent to 110-130°C; B2: adding B modified rosin resin and stirring slowly until completely dissolved, and reducing the temperature of the system to 70-90°C; B3: adding B organic acid activator, B halogen activator and B organic amine activator, and stirring for 10-30 minutes, and reducing the temperature to 40-60°C; B4: adding thixotropic agent, and stirring at high speed for 25-35 minutes, and cooling to room temperature; B5: grinding until the maximum particle size of the solder flux is less than 6 microns, and then placing in a 2-10°C refrigerator for more than 10 hours, and then ready for use.

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