High-stability tin-silver-copper soldering paste for micro-pitch welding

Abstract

The invention discloses tin-silver-copper soldering paste for high-stability fine-pitch welding, and belongs to the technical field of soldering flux. On one hand, in the high-temperature forming process of the alloy powder, the 685 modified rosin is added for coating, then the 685 modified rosin is washed away, and the AX-E modified rosin and the antioxidant are coated on the surface of the alloy powder; on the other hand, the film-forming agent and the active agent form a film-forming agent-active agent microcapsule by adopting a microcapsule technology, and the two improvement points are combined, so that good wettability of the tin-silver-copper soldering paste for high-stability micro-pitch welding after high-temperature welding is ensured; and the stability of the tin-silver-copper soldering paste for high-stability micro-pitch welding in the low-temperature storage process is greatly improved, and the interface stability between the superfine solder alloy powder and the soldering flux is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of solder, and in particular relates to a tin-silver-copper solder paste for high-stability micro-pitch welding. Background Art

[0002] With the rapid development of micro-pitch packaging technology, the technical requirements of solder paste have also increased. Micro-pitch packaging usually reduces the solder joint spacing to less than 75 microns, which puts higher requirements on the particle size of solder paste. The particle diameter of ultra-fine powder solder paste must be less than 15 microns to ensure printing accuracy and reliability of solder joint formation. In addition, solder paste needs to have a balance between high activity and stability, improve wettability and fluidity, and prevent performance degradation during storage and use. As the size of solder joints decreases, solder paste must further reduce the solder joint void rate to ensure the reliability of solder joints. In addition, the improvement of environmental awareness has made lead-free and low-halogen solder paste a trend. As the most representative lead-free solder, tin-silver-copper solder will be used on a larger scale in the future. In summary, the evolution of micro-pitch packaging requires tin-silver-copper alloy ultra-fine powder solder paste with higher stability to ensure that it meets higher performance requirements.

[0003] Solder paste is mainly composed of two parts, namely solder alloy powder and solder paste flux. The stability of solder paste mainly refers to the ability to maintain the two performance indicators of fluidity and wettability after long-term storage or repeated printing. Fluidity will affect the discharge stability of solder paste during printing or dispensing, while wettability affects the welding effect and the stability of physical and electrical connections after welding. For ultrafine solder alloy powder, due to its smaller particle size than traditional solder powder, higher specific surface area, higher surface energy, it is more prone to oxidation, and the interface stability between ultrafine solder alloy powder and flux is more difficult to control. Therefore, for the comprehensive performance improvement of tin-silver-copper solder paste for high-stability micro-pitch welding, it is essential to improve the interface stability between ultrafine solder alloy powder and flux. Summary of the invention

[0004] In view of the above-mentioned shortcomings of the prior art, the present invention provides a tin-silver-copper solder paste for high-stability fine-pitch welding.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A tin-silver-copper solder paste for high-stability micro-pitch welding, comprising solder alloy powder and solder paste flux;

[0007] The preparation method of the solder alloy powder comprises the following steps: using emulsification technology to disperse 685 modified rosin on the surface of tin-silver-copper alloy powder, then high-temperature molding to obtain molded alloy powder, putting the molded alloy powder into a cleaning solvent for cleaning and then removing the cleaning solvent, then adding the cleaning solvent, AX-E modified rosin and benzotriazole to the cleaned alloy powder and stirring, centrifuging to remove the cleaning solvent, and drying to obtain the solder alloy powder;

[0008] The solder paste flux comprises a solvent, a film-forming agent, an activator, a thixotropic agent, an antioxidant, a pH regulator and a surfactant.

[0009] The emulsification technology is a conventional emulsification technology, which disperses the immiscible 685 modified rosin and tin-silver-copper alloy powder.

[0010] The present invention removes part of the 685 modified rosin on the surface of the alloy powder after forming by a cleaning solvent. On the one hand, the retained part of the 685 modified rosin can promote the uniform coating of the AX-E modified rosin and benzotriazole on the surface of the alloy powder, and finally the solder alloy powder still has good sphericity after coating; on the other hand, if part of the 685 modified rosin is not removed, the morphology of the AX-E modified rosin and benzotriazole coating layer formed on the surface of the solder alloy powder will be uncontrollable, and the final sphericity of the solder alloy powder after coating cannot be guaranteed, thereby increasing the viscosity of the solder paste and deteriorating the viscosity stability and wettability stability.

[0011] As a preferred embodiment of the present invention, the size of the tin-silver-copper alloy powder is less than 15 microns.

[0012] As a preferred embodiment of the present invention, the temperature of the high temperature molding is 220-260° C. and the time is 1-2 hours.

[0013] As a preferred embodiment of the present invention, the cleaning solvent is a mixed solvent of short-chain alkanes and short-chain olefins having a carbon atomic weight of less than 7, and the short-chain alkanes and short-chain olefins are mixed in any volume ratio.

[0014] As a preferred embodiment of the present invention, the mass of the 685 modified rosin is 0.1%-1% of the mass of the alloy powder, the mass of the AX-E modified rosin is 0.1%-1% of the mass of the alloy powder, and the mass of the benzotriazole is 0.1%-1% of the mass of the alloy powder.

[0015] As a preferred embodiment of the present invention, the mass of the alloy powder after molding used for each cleaning by the cleaning solvent is twice the mass of the alloy powder after molding; and the cleaning solvent is used to clean the alloy powder after molding for no more than 2 times.

[0016] As a preferred embodiment of the present invention, the film-forming agent is used to microencapsulate the active agent using microencapsulation technology to obtain film-forming agent-active agent microcapsules.

[0017] As a preferred embodiment of the present invention, the microcapsule technology specifically comprises the following steps: mixing the film-forming agent and the active agent, heating and melting them, cooling them to room temperature, and then crushing them to obtain film-forming agent-active agent microcapsules.

[0018] As a preferred embodiment of the present invention, the solvent is propylene glycol phenyl ether, tributyl citrate or tetraethylene glycol dimethyl ether, the film-forming agent is 685 modified rosin, HM604 modified rosin or KE604 modified rosin, the activator is malic acid, adipic acid or dodecanedioic acid, the thixotropic agent is hydrogenated castor oil, polyamide wax or castor oil, the antioxidant is benzotriazole, hydroquinone or butylated hydroxytoluene, and the pH adjuster is triethanolamine.

[0019] As a preferred embodiment of the present invention, the solder paste flux includes the following raw materials in percentage by mass: 35% to 45% solvent, 30% to 40% film former, 10% to 15% activator, 5% to 8% thixotropic agent, 1% to 6% antioxidant and 1% to 3% pH adjuster.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: on the one hand, during the high-temperature forming process of the alloy powder, the present invention adds 685 modified rosin for coating, then washes off part of the 685 modified rosin, and coats the surface of the alloy powder with AX-E modified rosin and an antioxidant; on the other hand, the film-forming agent and the activator are formed into film-forming agent-activator microcapsules by adopting microencapsulation technology, and the combination of the two improvements greatly improves the stability of the tin-silver-copper solder paste for high-stability micro-pitch welding during low-temperature storage, further ensures the long-term stability of the wettability of the tin-silver-copper solder paste for micro-pitch welding after high-temperature welding, and significantly improves the interface stability between the ultrafine solder alloy powder and the flux. DETAILED DESCRIPTION

[0021] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0022] In the present invention, 685 modified rosin, AX-E modified rosin, benzotriazole, propylene glycol phenyl ether, tributyl citrate, tetraethylene glycol dimethyl ether, HM604 modified rosin, KE604 modified rosin, malic acid, adipic acid, dodecanedioic acid, hydrogenated castor oil, polyamide wax, castor oil, hydroquinone, butylated hydroxytoluene, and triethanolamine are all commercially available products. 685 modified rosin is esterified rosin 685, AX-E modified rosin is AX-E fully hydrogenated rosin, HM604 modified rosin is HM-604 acidic hydrogenated modified rosin, and KE604 modified rosin is a KE604 hydrogenated rosin derivative.

[0023] Examples 1-3

[0024] A method for preparing a tin-silver-copper solder paste for high-stability fine-pitch welding comprises the following steps:

[0025] (1) Preparation of solder alloy powder (the coating material composition of the solder alloy powder and the mass percentage of the coating material in the alloy powder are shown in Table 1): 685 modified rosin is dispersed and coated on the surface of tin-silver-copper alloy powder with a particle size of less than 15 μm by emulsification technology, and then formed at 220° C. to obtain formed tin-silver-copper alloy powder. The formed tin-silver-copper alloy powder is placed in a mixed solvent of n-hexane and trichloroethylene and the cleaning solvent is removed. Then, a new cleaning solvent is used and AX-E modified rosin and benzotriazole are added, and the washed tin-silver-copper alloy powder is mixed and stirred. After removing the mixed solvent, the solder alloy powder is obtained.

[0026] (2) Preparation of solder paste flux (the raw material components and the mass percentage of each raw material in the solder paste flux are shown in Table 1): the film-forming agent and the activator are heated to 150°C to melt respectively, and the two are fully mixed using a homogenizer. After cooling to room temperature, they are crushed and sieved using an ultrafine grinder to retain powder particles below 10 μm to form a film-forming agent-activator microcapsule with a size of 10 μm, and then fully homogenized and mixed with a thixotropic agent, an antioxidant, a pH adjuster, and a solvent at 80-100°C to form a highly stable halogen-free flux.

[0027] (3) Preparation of solder paste: Place solder alloy powder and solder paste flux into a planetary mixer and stir for 1 hour to fully mix them to form a tin-silver-copper solder paste for high-stability fine-pitch welding.

[0028] Comparative Example 1

[0029] A method for preparing a tin-silver-copper solder paste comprises the following steps:

[0030] (1) Preparation of solder alloy powder (the coating material of the solder alloy powder and the mass percentage of the coating material in the alloy powder are shown in Table 1): 685 modified rosin is dispersed on the surface of tin-silver-copper alloy powder with a particle size of less than 15 μm by emulsification technology, and then the powder is formed at a high temperature of 220° C. to obtain formed tin-silver-copper alloy powder. The formed tin-silver-copper alloy powder is placed in a mixed solvent of n-hexane and trichloroethylene for cleaning, and the mixed solvent is removed to obtain solder alloy powder.

[0031] (2) Preparation of solder paste flux (the raw materials and the mass percentage of each raw material in the solder paste flux are shown in Table 1): the film-forming agent and the activator are heated to 150°C to melt respectively, and the two are fully mixed using a homogenizer. After cooling to room temperature, they are crushed and sieved using an ultrafine grinder to retain powder particles below 10 μm to form a film-forming agent-activator microcapsule with a size of 10 μm, and then fully homogenized and mixed with a thixotropic agent, an antioxidant, a pH adjuster, and a solvent at 80-100°C to form a highly stable halogen-free flux.

[0032] (3) Preparation of solder paste: The above solder alloy powder and solder paste flux are placed in a planetary mixer and stirred for 1 hour to fully mix and form a tin-silver-copper solder paste.

[0033] Comparative Example 2

[0034] A method for preparing a tin-silver-copper solder paste comprises the following steps:

[0035] (1) Preparation of solder alloy powder (the coating material of the solder alloy powder and the mass percentage of the coating material in the alloy powder are shown in Table 1): Tin-silver-copper alloy powder is formed at a high temperature of 220° C. The formed tin-silver-copper alloy powder is placed in a mixed solvent of n-hexane and trichloroethylene to which AX-E modified rosin and benzotriazole are added, and stirred. After removing the mixed solvent, the solder alloy powder is obtained.

[0036] (2) Preparation of solder paste flux (the raw materials and the mass percentage of each raw material in the solder paste flux are shown in Table 1): the film-forming agent and the activator are heated to 150°C to melt respectively, and the two are fully mixed using a homogenizer. After cooling to room temperature, they are crushed and sieved using an ultrafine grinder to retain powder particles below 10 μm to form a film-forming agent-activator microcapsule with a size of 10 μm, and then fully homogenized and mixed with a thixotropic agent, an antioxidant, a pH adjuster, and a solvent at 80-100°C to form a highly stable halogen-free flux.

[0037] (3) Preparation of solder paste: The above solder alloy powder and flux are placed in a planetary mixer and stirred for 1 hour to fully mix and form a tin-silver-copper solder paste.

[0038] Comparative Example 3

[0039] A method for preparing a tin-silver-copper solder paste comprises the following steps:

[0040] (1) Preparation of solder alloy powder (the coating material composition of the solder alloy powder and the mass percentage of the coating material in the alloy powder are shown in Table 1): 685 modified rosin is dispersed and coated on the surface of tin-silver-copper alloy powder with a particle size of less than 15 μm by emulsification technology, and then formed at 220° C. to obtain formed tin-silver-copper alloy powder. The formed tin-silver-copper alloy powder is placed in a mixed solvent of n-hexane and trichloroethylene and the cleaning solvent is removed. Then, a new cleaning solvent is used and AX-E modified rosin and benzotriazole are added, and the washed tin-silver-copper alloy powder is mixed and stirred. After removing the mixed solvent, the solder alloy powder is obtained.

[0041] (2) Preparation of solder paste flux (the raw material components and the mass percentage of each raw material in the solder paste flux are shown in Table 1): the film-forming agent and the activating agent are directly mixed with a thixotropic agent, an antioxidant, a pH adjuster, and a solvent at 80 to 100° C. and fully and homogeneously mixed to form a flux.

[0042] (3) Preparation of solder paste: The above solder alloy powder and flux are placed in a planetary mixer and stirred for 1 hour to fully mix and form a tin-silver-copper solder paste.

[0043] Table 1

[0044]

[0045]

[0046] Effect Example 1

[0047] The oxygen content of the solder alloy powders prepared in Examples 1-3 and Comparative Examples 1-3 was monitored during storage in a constant temperature and humidity chamber at a temperature of 25° C. and a humidity of 50%. The results are shown in Table 2.

[0048] Table 2

[0049]

[0050] It can be seen from Table 2 that the oxygen content of the solder alloy powder prepared in the example is significantly lower than that in the comparative examples 1-3.

[0051] Effect Example 2

[0052] The viscosity of the tin-silver-copper solder pastes prepared in Examples 1-3 and Comparative Examples 1-3 during storage in a constant temperature and humidity chamber at a temperature of 25° C. and a humidity of 50% was monitored. The results are shown in Table 3.

[0053] Table 3

[0054]

[0055] Effect Example 3

[0056] The wettability of the tin-silver-copper solder paste prepared in Examples 1-3 and Comparative Examples 1-3 was monitored during storage in a constant temperature and humidity chamber at a temperature of 25°C and a humidity of 50%. The results are shown in Table 4. The wettability test was evaluated using the solder joint expansion rate parameter. The welding material was a copper sheet. A significant decrease in wettability indicated that the solder paste had poor wetting stability.

[0057] Table 4

[0058]

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A tin-silver-copper solder paste for high-stability fine-pitch welding, characterized in that: Includes solder alloy powder and solder paste flux; The preparation method of the solder alloy powder comprises the following steps: using emulsification technology to disperse 685 modified rosin on the surface of tin-silver-copper alloy powder, then high-temperature molding to obtain molded alloy powder, washing and filtering the molded alloy powder in a cleaning solvent, adding a cleaning solvent, AX-E modified rosin and benzotriazole to the washed alloy powder, stirring, centrifuging to remove the cleaning solvent, and drying to obtain the solder alloy powder; The solder paste flux comprises a solvent, a film-forming agent, an activator, a thixotropic agent, an antioxidant, a pH regulator and a surfactant.

2. The tin-silver-copper solder paste for high-stability fine-pitch welding according to claim 1, characterized in that: The size of the tin-silver-copper alloy powder is less than 15 microns.

3. The tin-silver-copper solder paste for high-stability fine-pitch welding according to claim 1, characterized in that: The temperature of the high temperature molding is 220-260° C., and the time is 1-2 hours.

4. The tin-silver-copper solder paste for high-stability fine-pitch welding according to claim 1, characterized in that: The cleaning solvent is a mixed solvent of short-chain alkanes and short-chain olefins having less than 7 carbon atoms.

5. The tin-silver-copper solder paste for high-stability fine pitch welding as claimed in claim 4, characterized in that: The mass of the 685 modified rosin is 0.1%-1% of the mass of the tin-silver-copper alloy powder, the mass of the AX-E modified rosin is 0.1%-1% of the mass of the tin-silver-copper alloy powder, and the mass of the benzotriazole is 0.1%-1% of the mass of the tin-silver-copper alloy powder.

6. The tin-silver-copper solder paste for high-stability fine pitch welding according to claim 1, characterized in that: The film-forming agent-active agent microcapsules are obtained by microencapsulating the active agent with the film-forming agent using microencapsulation technology.

7. The tin-silver-copper solder paste for high-stability fine pitch welding as claimed in claim 6, characterized in that: The microcapsule technology specifically comprises the following steps: mixing the film-forming agent and the active agent, heating and melting them, cooling them to room temperature, and then crushing them to obtain the film-forming agent-active agent microcapsules.

8. The tin-silver-copper solder paste for high-stability fine pitch welding as claimed in claim 1, characterized in that: The solvent is propylene glycol phenyl ether, tributyl citrate or tetraethylene glycol dimethyl ether, the film-forming agent is 685 modified rosin, HM604 modified rosin or KE604 modified rosin, the activator is malic acid, adipic acid or dodecanedioic acid, the thixotropic agent is hydrogenated castor oil, polyamide wax or castor oil, the antioxidant is benzotriazole, hydroquinone or butylated hydroxytoluene, and the pH regulator is triethanolamine.

9. The tin-silver-copper solder paste for high-stability fine pitch welding as claimed in claim 8, characterized in that: The solder paste flux comprises the following raw materials in percentage by mass: 35% to 45% solvent, 30% to 40% film former, 10% to 15% active agent, 5% to 8% thixotropic agent, 1% to 6% antioxidant and 1% to 3% pH regulator.

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