CN116586814A - VOC-free epoxy-based Sn-Bi lead-free solder paste - Google Patents

Abstract

VOC-free epoxy Sn-Bi lead-free welding belongs to the field of welding. The composition of the solder powder comprises 6-18% of curable auxiliary welding system by mass percentage and the balance of Sn-58 Bi. The curable welding-assisting system consists of an epoxy composition, an active agent and an accelerator; the epoxy composition consists of epoxy resin and a curing agent; the active agent is composed of an organic acid and an organic amine. The epoxy Sn-Bi lead-free soldering paste disclosed by the invention does not contain VOC, and meanwhile, the adopted epoxy curing agent is a self-made modified curing agent, so that the epoxy Sn-Bi lead-free soldering paste has the characteristic of latency, and the storage period of the soldering paste can be prolonged. The formulation cost of the VOC-free epoxy Sn-Bi lead-free solder paste is comparable to the commercial Sn-Bi lead-free solder paste products. The selected materials are common materials, and the cost is low. The preparation process has no special requirement and does not cause cost increase.

Description

VOC-free epoxy-based Sn-Bi lead-free solder paste

technical field

The invention relates to a VOC-free epoxy-based Sn-Bi lead-free solder paste, which belongs to metal materials and brazing materials in the field of metallurgy. It is mainly used for the connection of components in the electronic industry and belongs to the field of welding.

Background technique

Modern electronic products continue to develop rapidly in the direction of thinning, miniaturization, and high reliability, which puts forward higher requirements for the strength and thermal conductivity of solder joints. Low melting point Sn-Bi solder paste has the advantages of good yield strength, creep resistance, cost-effectiveness and thermal shock resistance of electronic packaging, etc., and has important applications in low-temperature connection and heat-sensitive device assembly. Bi lead-free solder paste has defects such as poor mechanical strength and low reliability of solder joints, which limit the application of Sn-Bi solder paste. Therefore, improving the mechanical properties of Sn-Bi solder joints has become one of the current concerns.

Relevant research at home and abroad mainly focuses on the following two research directions. One is to prepare Sn-Bi-X solder by adding trace third elements to Sn-Bi alloy to improve the mechanical properties of solder joints through grain refinement and dispersion strengthening mechanism. Although this method has a certain improvement effect, its effect is limited or restricted due to the problems caused by the addition of other elements, and this method has complicated processes and increases production costs. Another method is to prepare a resin-reinforced composite solder paste by changing the composition of the flux, such as adding a curable resin component. Sn-Bi lead-free solder paste containing epoxy resin has certain advantages in improving the mechanical strength and reliability of solder joints. At the solder joint forming temperature, the curable resin component separated from the solder alloy forms a thin and uniform layer of cured resin around the solder joint, thereby enhancing the bond between the solder joint and the substrate. At the same time, there is no sticky residue on the surface of the solder joint, and the post-solder cleaning step is no longer required. In addition, the VOC-free formula can better meet the requirements of green environmental protection. Therefore, the market prospect of VOC-free epoxy-based Sn-Bi lead-free solder paste is better

Contents of the invention

The task of the present invention is to provide a VOC-free epoxy-based Sn-Bi lead-free solder paste that can form a stable resin shell on the surface of the solder joint. This solder paste can improve the shear performance of the brazing joint and has good wetting Humidity and long storage period.

A VOC-free epoxy-based Sn-Bi lead-free solder paste is characterized in that its composition is: 6-18% curable soldering flux system, and the balance is Sn-58Bi solder powder. The above-mentioned curable fluxing system is composed of epoxy composition, activator and accelerator, and the ratio of each component to the mass percentage of the composition is epoxy composition: activator: accelerator=70～75:24～28: 1～3;

Above-mentioned epoxy composition is made up of epoxy resin and curing agent, epoxy resin: curing agent mass ratio=6～10:1; Above-mentioned epoxy resin is NPEL-127H type bisphenol A, E20 type bisphenol A, E44 type Any one of bisphenol A and E51 type bisphenol A or any combination of any two or three in any proportion; the above curing agent is a self-made modified dicyandiamide curing agent, and the preparation method is: polyetheramine and E51 type Mix bisphenol A epoxy resin, heat at 80°C-100°C for 1-2 hours, then add dicyandiamide, heat at 90°C-110°C for 2-3 hours, and obtain modified dicyandiamide curing agent after cooling, wherein Dicyandiamide: E51 type bisphenol A: mass ratio of polyether amine = 80～95:70～80:20～40;

The above active agent is composed of organic acid and organic amine, organic acid:organic amine mass ratio=1:3～5; organic amine is any one of triethanolamine, polyolamine or any combination of any two, and the organic acid is selected from Any one of glutaric acid and maleic anhydride or any combination of any two in any proportion;

The above accelerator is any one of dimethyl-imidazole, 2,4,6-tris(dimethylaminomethyl)phenol and resorcinol, or any combination of any two or three in any proportion.

VOC-free epoxy-based Sn-Bi lead-free solder paste is used in low-temperature connection and heat-sensitive device assembly. The method of use is: fix the PCB board, then align the steel mesh holes with the pads on the PCB board, and use a scraper to The VOC-free epoxy-based Sn-Bi lead-free solder paste is applied to the stencil, so that the VOC-free epoxy-based Sn-Bi lead-free solder paste is evenly printed on the PCB pad through the stencil, and then passed through a specific thermal processing process A solder joint is formed on the pad to complete the soldering.

The epoxy-based Sn-Bi lead-free solder paste of the present invention does not contain VOC, that is, the solder paste does not contain volatile components. The commercially available solder paste contains organic solvents, and the organic solvents volatilize during the soldering process, which has a certain impact on the environment and the occurrence of solder joint defects. Extends shelf life of solder paste. Compared with commercially available Sn-Bi lead-free solder paste products, the formula cost of VOC-free epoxy-based Sn-Bi lead-free solder paste is not much different. The selected materials are common materials with low cost. There are no special requirements for the preparation process, which will not lead to increased costs.

Description of drawings

Figure 1: DSC curves of VOC-free epoxy-based Sn-Bi lead-free solder paste (Sn-58Bi) and curable flux resin system (EP-FIUX);

Figure 2: The influence of curable fluxing systems with different mass fractions on the wetting and spreading properties of VOC-free epoxy-based Sn-Bi lead-free solder paste;

Figure 3: The effect of curable fluxing systems with different mass fractions on the shear performance of VOC-free epoxy-based Sn-Bi lead-free solder paste solder joints;

Fig. 4: embodiment 1 solder joint structural diagram;

Fig. 5: embodiment 2 solder joint structural diagram;

Detailed ways

1. the epoxy composition is made up of epoxy resin and curing agent, and described epoxy resin is NPEL-127H type bisphenol A, E20 type bisphenol A, E44 type bisphenol A, E51 type bisphenol A wherein Any one or any combination of two or three in any ratio; the self-made modified dicyandiamide curing agent, the preparation method is to dicyandiamide, polyether amine and E51 type bisphenol A epoxy resin according to the E51 type Bisphenol A: polyetheramine mass ratio = 70 ~ 80: 20 ~ 40 mixed, heated at 80 ° C ~ 100 ° C for 1 ~ 2 hours, and then according to dicyandiamide: E51 type bisphenol A: polyether amine mass ratio =80~95:

Add dicyandiamide in the ratio of 70～80:20～40, heat at 90℃～110℃ for 2～3 hours, and obtain modified dicyandiamide curing agent after cooling, according to epoxy resin:curing agent mass ratio=6～ 10:1 pre-proportioned and mixed evenly for later use; the active agent is composed of organic acid and organic amine, the organic amine is any one of triethanolamine, polyolamine or any combination of any two, and the organic acid is selected from Any one of glutaric acid and maleic anhydride or any two arbitrary ratio groups, according to organic acid: organic amine mass ratio = 1:3 ~ 5 after mixing evenly for later use; the accelerator is dimethyl-imidazole , 2,4,6-tris(dimethylaminomethyl)phenol, resorcinol, any one or any combination of two or three in any proportion; the curable soldering flux system is composed of epoxy Composition, active agent and accelerator, epoxy composition, active agent and accelerator are according to epoxy composition: active agent: accelerator mass ratio

=70～75:24～28:1～3 pre-proportioned and mixed evenly for later use; use ethanol to clean the commercially available Sn-58Bi solder powder, and clean it in an ultrasonic cleaning machine to obtain the experimental Sn-58Bi solder powder; Finally, use a high-speed mixer (300r/min to 1200r/min) to mix and stir 6-18% of the curable flux system and the balance of Sn-58Bi solder powder for 20min to 30min to obtain a VOC-free epoxy Sn-Bi lead-free solder paste.

2. Through a large number of tests for screening and optimization, it is found that the epoxy resin selected is any one of NPEL-127H type bisphenol A, E20 type bisphenol A, and E51 type bisphenol A, or any combination of two ratios , matching self-made modified dicyandiamide curing agent, the preparation method is to mix dicyandiamide, polyether amine and E51 type bisphenol A epoxy resin according to the ratio of E51 type bisphenol A: polyether amine mass ratio = 77:33 , heated at 80°C for 1 hour, then added dicyandiamide according to the ratio of dicyandiamide: E51 type bisphenol A: polyetheramine mass ratio = 90:77:33, heated at 100°C for 2 hours, and changed after cooling Permanent dicyandiamide curing agent, according to epoxy resin: curing agent mass ratio=6:1 ratio preparation, epoxy resin and curing agent reaction are the most sufficient in this epoxy composition, specifically see Fig. 1, and this figure is without DSC curves of VOC epoxy-based Sn-Bi lead-free solder paste and curable flux resin system.

3. See Figure 2 for details, which shows curable fluxing systems with different mass fractions (containing epoxy composition, active agent, and accelerator, and the proportion of each component in the mass percentage of the composition is epoxy composition : activator: accelerator=73:25.5:1.5) on the wetting and spreading properties of VOC-free epoxy-based Sn-Bi lead-free solder paste. 150°C, 150°C

Keep warm for 60s; heat up to 180°C and keep warm at 180°C for 60s. Figure 2 shows that the VOC-free epoxy-based Sn-Bi lead-free solder paste of this invention can be solidified with the solder paste when the TU1 oxygen-free copper is used as the test board, and the thermal processing is carried out under the conditions of peak temperature of 180 ° C and heat preservation for 1 min. With the increase of the addition amount of the soldering flux system (containing epoxy composition, activator, and accelerator), the wetting angle on the TU1 oxygen-free copper plate showed a downward trend, and the spreading area showed an increasing trend, indicating that the curable soldering flux system (containing The addition of epoxy composition, active agent and accelerator) has no negative impact on the wetting and spreading properties of the Sn-Bi lead-free solder paste, and has an improvement effect.

4. See Figure 3 for details, which shows curable fluxing systems with different mass fractions (containing epoxy composition, active agent, and accelerator, and the proportion of each component in the mass percentage of the composition is epoxy composition : Activator: Accelerator=73:25.5:1.5) on the law of influence on the shear performance of VOC-free epoxy-based Sn-Bi lead-free solder paste solder joints, the soldering conditions corresponding to this figure are: heating at 120°C for 30s; heating up to 150°C, 150°C

Keep warm for 60s; heat up to 180°C and keep warm at 180°C for 60s. Fig. 3 shows, the 50N that has never added epoxy resin, the range of improvement is 20%～26%, improves to 63N (the total addition amount of epoxy composition+activator+accelerator is 14% when optimum addition amount is 14%) %), which fully demonstrates that the addition of curable flux system can significantly improve the shear strength of Sn-Bi lead-free solder paste solder joints.

Compared with previous studies, the inventiveness of the present invention lies in

(1). VOC-free epoxy-based Sn-Bi lead-free solder paste does not contain volatile components. Commercially available solder paste contains organic solvents, which volatilize during the soldering process, which has a certain impact on the environment and the generation of solder joint defects.

Screening and optimization through a large number of tests, especially in the screening and optimization of the synergistic effect of curing agent and accelerator, a large number of tests have been carried out. It is found that the epoxy composition is selected. The epoxy composition is composed of epoxy resin and curing agent. The epoxy resin is NPEL-127H type bisphenol A, E20 type bisphenol A, E44 type bisphenol A, E51 type bisphenol A Any one of them or any combination of any two or three in any ratio; match the self-made modified dicyandiamide curing agent, according to the mass ratio of epoxy resin: curing agent = 6 ~ 10: 1 in advance and mix it evenly for backup Use; The selected active agent is composed of organic acid and organic amine. The organic amine is any one of triethanolamine, polyolamine or any combination of any two. The organic acid is selected from any one of glutaric acid and maleic anhydride. Or any two arbitrary ratio groups, according to the organic acid:organic amine mass ratio=1:3～5 pre-proportioned and mixed evenly for later use;

The selected accelerator is any one of dimethyl-imidazole, 2,4,6-tris(dimethylaminomethyl)phenol, resorcinol or any combination of any two or three; curable The welding flux system is composed of an epoxy composition, an activator and an accelerator, and the epoxy composition, the activator and the accelerator are used according to the mass ratio of the epoxy composition:activator:accelerator=70～75:24～28:1 ～3 Pre-proportioned and mixed evenly for later use; this curable flux system can be completely cured within 1 minute at a temperature of 170°C-190°C, which meets the process requirements for mass production of reflow soldering production lines.

(2). The epoxy curing agent used in the present invention is a self-made modified curing agent, which has latent characteristics and can prolong the storage period of solder paste.

The curing agent of the present invention is a modified dicyandiamide curing agent, and the epoxy resin is selected as any one of NPEL-127H type bisphenol A, E20 type bisphenol A, E44 type bisphenol A, E51 type bisphenol A or Any combination of any two or three in any ratio; matching self-made modified dicyandiamide curing agent, according to epoxy resin: curing agent mass ratio = 6 ~ 10:1 ratio, each component can be used within 16 months They are stable with each other for a long time, which can effectively improve the storage period of solder paste.

The present invention will be described in detail below through several embodiments.

Example 1

A VOC-free epoxy-based Sn-Bi lead-free solder paste, characterized in that its composition is a curable soldering flux system with a ratio of 14% by mass percentage, and the balance is Sn-58Bi solder powder, by mass percentage, The Bi element accounts for 58% of the alloy powder, and the balance is Sn; the particle diameter of the alloy powder is 10-80um. The above-mentioned curable soldering flux system is composed of an epoxy composition and an active agent, and the ratio of each component to the mass percentage of the composition is epoxy composition:activator=74:26; the above-mentioned epoxy composition is composed of epoxy resin and The composition of the curing agent, each component accounts for the mass percentage ratio of the composition is epoxy resin: curing agent=6:1, the above-mentioned epoxy resin is E51 type bisphenol A, and the above-mentioned curing agent is self-made modified dicyandiamide curing The preparation method is to mix dicyandiamide, polyether amine and E51 type bisphenol A epoxy resin according to the ratio of E51 type bisphenol A: polyether amine mass ratio = 77:33, heat at 80 ° C for 1 hour, and then Add dicyandiamide according to the ratio of dicyandiamide: E51 type bisphenol A: polyetheramine mass ratio=90:77:33, heat at 100°C for 2 hours, and obtain a modified dicyandiamide curing agent after cooling; the above active agent Prepare triethanolamine and glutaric acid according to organic acid:organic amine mass ratio=1:4.

For the epoxy resin composite Sn-Bi lead-free solder paste obtained by the above ratio, the soldering conditions are as follows: heating at 120°C for 30s; heating to 150°C, and holding at 150°C for 60s; heating to 180°C, holding at 190°C for 60s, and the soldering conditions shown in Figure 4 are obtained. The solder joint structure shown. The shear strength of solder joints increased from 50N without adding epoxy resin to 62N, an increase of 24%.

Example 2

A VOC-free epoxy-based Sn-Bi lead-free solder paste is characterized in that its composition is a curable soldering flux system with a ratio of 14% by mass percentage, and the balance is solder powder of Sn-58Bi, by mass percentage, The Bi element accounts for 58% of the alloy powder, and the balance is Sn; the particle diameter of the alloy powder is 10-80um. The above-mentioned curable soldering flux system is composed of an epoxy composition, an activator and an accelerator, and the ratio of each component to the mass percentage of the composition is epoxy composition:activator:accelerator=73:25.5:1.5; the above-mentioned ring Oxygen composition is made up of epoxy resin and curing agent, and each component accounts for this composition mass percentage ratio and is epoxy resin: curing agent=6:1, and above-mentioned epoxy resin is E51 type bisphenol A, and above-mentioned curing agent For self-modified modified dicyandiamide curing agent, the preparation method is to mix dicyandiamide, polyether amine and E51 type bisphenol A epoxy resin according to the ratio of E51 type bisphenol A: polyether amine mass ratio=77:33, Heat at 80°C for 1 hour, then add dicyandiamide according to the ratio of dicyandiamide: E51 type bisphenol A: polyetheramine mass ratio = 90:77:33, heat at 100°C for 2 hours, and obtain modification after cooling Dicyandiamide curing agent; the above active agent is triethanolamine, glutaric acid according to the organic acid: organic amine mass ratio = 1:4 preparation.

For the epoxy resin composite Sn-Bi lead-free solder paste obtained by the above ratio, the soldering conditions are: heating at 120°C for 30s; heating up to 150°C, and holding at 150°C for 60s; heating up to 180°C, holding at 180°C for 60s, and the soldering conditions shown in Figure 5 are obtained. The solder joint structure shown. The wetting and spreading properties of the epoxy resin composite Sn-Bi lead-free solder paste are improved, and the shear strength of the solder joint is increased from 50N without adding epoxy resin to 63N, with an increase of 26%.

Example 3

A VOC-free epoxy-based Sn-Bi lead-free solder paste, characterized in that its composition is a curable soldering flux system with a ratio of 14% by mass percentage, and the balance is Sn-58Bi solder powder, by mass percentage, The Bi element accounts for 58% of the alloy powder, and the balance is Sn; the particle diameter of the alloy powder is 10-80um. The above-mentioned curable flux system is composed of epoxy composition, activator and accelerator, and the ratio of each component to the mass percentage of the composition is epoxy composition:activator:accelerator=72:25:3; the above-mentioned ring Oxygen composition is made up of epoxy resin and curing agent, and each component accounts for this composition mass percentage ratio and is epoxy resin: curing agent=6:1, and above-mentioned epoxy resin is E51 type bisphenol A, and above-mentioned curing agent For self-modified modified dicyandiamide curing agent, the preparation method is to mix dicyandiamide, polyether amine and E51 type bisphenol A epoxy resin according to the ratio of E51 type bisphenol A: polyether amine mass ratio=77:33, Heat at 80°C for 1 hour, then add dicyandiamide according to the ratio of dicyandiamide: E51 type bisphenol A: polyetheramine mass ratio = 90:77:33, heat at 100°C for 2 hours, and obtain modification after cooling Dicyandiamide curing agent; the above active agent is triethanolamine, glutaric acid according to the organic acid: organic amine mass ratio = 1:4 preparation.

The epoxy resin composite Sn-Bi lead-free solder paste obtained by the above ratio is soldered under the following conditions: heat at 120°C for 30s; heat up to 150°C and hold at 150°C for 60s; heat up to 165°C and hold at 165°C for 60s. Due to the low curing temperature of the curable soldering flux system, when the Sn-58Bi solder melts, the resin has solidified, the fluidity becomes poor, and the solder joints have not achieved complete metallurgical bonding with the copper substrate. Lead-free solder paste has adverse effects on wetting and spreading properties. The shear strength is reduced compared to the solder joint shear strength of the solder paste without epoxy added.

Claims (6)

1. The VOC-free epoxy Sn-Bi lead-free soldering paste is characterized by comprising the following components in percentage by mass: 6-18% of a curable fluxing system, the balance being Sn-58Bi solder powder; the curable welding-assisting system consists of an epoxy composition, an active agent and an accelerator, wherein the mass percentage of each component in the composition is that the epoxy composition comprises the active agent and the accelerator=70-75:24-28:1-3.

2. The VOC-free epoxy Sn-Bi lead-free solder paste according to claim 1, wherein the epoxy composition consists of epoxy resin and curing agent, the mass ratio of the epoxy resin to the curing agent is=6-10:1; the epoxy resin is any one or any combination of any two or three of NPEL-127H type bisphenol A, E type bisphenol A, E type bisphenol A, E type bisphenol A; the curing agent is a self-made modified dicyandiamide curing agent, and the preparation method comprises the following steps: mixing polyether amine and E51 bisphenol A epoxy resin, heating at 80-100 ℃ for 1-2 hours, then adding dicyandiamide, heating at 90-110 ℃ for 2-3 hours, and cooling to obtain a modified dicyandiamide curing agent, wherein dicyandiamide is obtained by the steps of: e51 bisphenol A polyether amine mass ratio=80-95: 70-80:20-40.

3. A VOC-free epoxy Sn-Bi lead-free solder paste according to claim 1, wherein the active agent consists of an organic acid and an organic amine, the mass ratio of organic acid to organic amine = 1:3-5; the organic amine is any one or any combination of any two of triethanolamine and polyalcohol amine, and the organic acid is selected from any one or any combination of any two of glutaric acid and maleic anhydride.

4. The VOC-free epoxy Sn-Bi lead-free solder paste according to claim 1, wherein the accelerator is any one or any combination of any two or three of dimethyl-imidazole, 2,4, 6-tris (dimethylaminomethyl) phenol and resorcinol.

5. The VOC-free epoxy Sn-Bi lead-free solder paste of claim 1, wherein the Sn-Bi alloy powder contains 58% by mass of Bi element and the balance Sn; the diameter of the alloy powder particles is 10-80um.

6. The method of using a VOC-free epoxy Sn-Bi lead-free solder paste of claim 1, wherein the VOC-free epoxy Sn-Bi lead-free solder paste is used in low temperature connections and thermal device assembly, the method of using comprising: fixing a PCB, aligning a steel mesh with a bonding pad on the PCB, coating the VOC-free epoxy Sn-Bi lead-free soldering paste on the steel mesh by using a scraper, enabling the VOC-free epoxy Sn-Bi lead-free soldering paste to uniformly penetrate through the steel mesh to be printed on the bonding pad of the PCB, and forming a welding spot on the bonding pad by a specific hot working process to finish welding.