Voc-free epoxy based sn-bi lead-free solder paste

Abstract

The application discloses a VOC-free epoxy Sn-Bi lead-free solder, which belongs to the field of welding and is composed of 6-18% of a solidifiable soldering system and the rest of Sn-58Bi solder powder; the solidifiable soldering system is composed of an epoxy composition, an active agent and an accelerator; the epoxy composition is composed of an epoxy resin and a curing agent; and the active agent is composed of an organic acid and an organic amine. The epoxy Sn-Bi lead-free solder paste disclosed by the application does not contain VOC, and the epoxy curing agent adopted is a self-made modified curing agent, which has the characteristics of latency and can prolong the storage period of the solder paste. Compared with the commercially available Sn-Bi lead-free solder paste product, the VOC-free epoxy Sn-Bi lead-free solder paste has little difference in formula cost. The selected materials are common materials and have low cost. The preparation process has no special requirement and will not cause cost increase.

Description

TECHNICAL FIELD

[0001] The present application relates to a VOC-free epoxy-based Sn-Bi lead-free solder paste, which belongs to the field of brazing materials of metal materials and metallurgy. It is mainly used for the connection of electronic components in the electronic industry and belongs to the field of welding. BACKGROUND

[0002] Modern electronic products are rapidly developing towards thinness, miniaturization and high reliability, which puts higher requirements on the strength and thermal conductivity of the solder joints. Low-melting-point Sn-Bi solder paste has good yield strength, creep resistance, cost-effectiveness and resistance to thermal shock of electronic packaging, and has important applications in low-temperature connection and assembly of thermal sensitive devices. However, the Sn-Bi lead-free solder paste on the market has defects such as poor mechanical strength and low reliability of solder joints, which limits the application of Sn-Bi solder paste. Therefore, improving the mechanical properties of Sn-Bi solder joints has become one of the current concerns.

[0003] The related researches at home and abroad mainly focus on the following two research directions. One is to prepare Sn-Bi-X solder by adding trace amounts of 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 certain improvement effect, the effect is limited or restricted due to the problems caused by the addition of other elements, and the process is complex, which increases the production cost. The other method is to change the composition of the flux, such as adding a solidifiable resin component to prepare a resin-reinforced composite solder paste. 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 solidifiable resin component separated from the solder alloy forms a thin and uniform solidified resin layer around the solder joint, thereby enhancing the bonding force 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-weld cleaning step is no longer needed. In addition, 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 good SUMMARY

[0004] The task of the present application is to provide a VOC-free epoxy-based Sn-Bi lead-free solder paste which can form a stable resin shell layer on the surface of the solder joint, improve the shear performance of the brazed joint, and has good wettability and long storage period.

[0005] A VOC-free epoxy-based Sn-Bi lead-free solder paste, characterized in that the composition is proportioned by mass percentage as follows: 6-18% of a solidifiable fluxing system, and the balance of Sn-58Bi solder powder. The above-mentioned solidifiable fluxing system is composed of an epoxy composition, an activator and an accelerator, and the mass percentage proportion of each component in the composition is epoxy composition: activator: accelerator = 70-75: 24-28: 1-3.

[0006] The epoxy composition is composed of an epoxy resin and a curing agent, and the mass ratio of the epoxy resin to the curing agent is 6-10:1; the epoxy resin is any one or any two or three of NPEL-127H type bisphenol A, E20 type bisphenol A, E44 type bisphenol A and E51 type bisphenol A in any proportion; the curing agent is a self-made modified dicyandiamide curing agent, and the preparation method is as follows: polyether amine and E51 type bisphenol A epoxy resin are mixed, heated at 80-100 DEG C for 1-2 hours, then dicyandiamide is added, heated at 90-110 DEG C for 2-3 hours, and the modified dicyandiamide curing agent is obtained after cooling, wherein the mass ratio of dicyandiamide to E51 type bisphenol A to polyether amine is 80-95:70-80:20-40;

[0007] The active agent is composed of an organic acid and an organic amine, and the mass ratio of the organic acid to the organic amine is 1:3-5; the organic amine is any one or any two of triethanolamine and polyalcohol amine in any proportion, and the organic acid is any one or any two of glutaric acid and maleic anhydride in any proportion;

[0008] The promoter is any one or any two or three of dimethyl-imidazole, 2,4,6-tris(dimethylaminomethyl)phenol and m-dihydroxybenzene in any proportion.

[0009] The VOC-free epoxy Sn-Bi lead-free solder paste is applied in low-temperature connection and thermal device assembly, and the use method is as follows: the PCB board is fixed, then the solder pad on the PCB board is aligned with the steel mesh hole, the VOC-free epoxy Sn-Bi lead-free solder paste is coated on the steel mesh by using a scraper, the VOC-free epoxy Sn-Bi lead-free solder paste is uniformly printed on the PCB solder pad through the steel mesh, then a solder joint is formed on the solder pad through a specific heat processing process, and the welding is completed.

[0010] The VOC-free epoxy Sn-Bi lead-free solder paste does not contain VOC, that is, the solder paste does not contain volatile components. The commercially available solder paste contains an organic solvent, and the organic solvent volatilizes in the welding process, which has a certain influence on the environment and the generation of solder joint defects. Meanwhile, the epoxy curing agent used is a self-made modified curing agent, which has a latent characteristic and can prolong the storage period of the solder paste. Compared with the commercially available Sn-Bi lead-free solder paste product, the formula cost of the VOC-free epoxy Sn-Bi lead-free solder paste has little difference. The selected materials are common materials, and the cost is low. The preparation process also has no special requirements, and will not cause cost increase. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 DSC curves of the VOC-free epoxy Sn-Bi lead-free solder paste (Sn-58Bi) and the curable soldering resin system (EP-FIUX);

[0012] Figure 2 The influence of different mass fractions of curable flux systems on the wetting and spreading properties of VOC-free epoxy-based Sn-Bi lead-free solder paste;

[0013] Figure 3 The influence of different mass fractions of curable flux systems on the shear properties of solder joints in VOC-free epoxy-based Sn-Bi lead-free solder paste;

[0014] Figure 4 Example 1: Solder joint structure diagram;

[0015] Figure 5 Example 2: Solder joint structure diagram; Detailed Implementation

[0016] 1. The epoxy composition comprises epoxy resin and a curing agent, wherein the epoxy resin is any one, any two, or any three of NPEL-127H type bisphenol A, E20 type bisphenol A, E44 type bisphenol A, and E51 type bisphenol A in any proportion; the self-made modified dicyandiamide curing agent is prepared by mixing dicyandiamide, polyetheramine, and E51 type bisphenol A epoxy resin at a mass ratio of E51 type bisphenol A:polyetheramine = 70-80:20-40, heating at 80℃-100℃ for 1-2 hours, and then mixing at a mass ratio of dicyandiamide:E51 type bisphenol A:polyetheramine = 80-95:

[0017] Dicyandiamide is added at a ratio of 70-80:20-40, heated at 90-110℃ for 2-3 hours, and cooled to obtain a modified dicyandiamide curing agent. This agent is pre-mixed and thoroughly mixed according to a mass ratio of epoxy resin to curing agent of 6-10:1 for later use. The activator is composed of organic acid and organic amine. The organic amine is any one or any combination of two of triethanolamine and polyol amine in any proportion. The organic acid is selected from any one or any combination of two of glutaric acid and maleic anhydride in any proportion. The activator is mixed thoroughly according to a mass ratio of organic acid to organic amine of 1:3-5 for later use. The accelerator is any one or any combination of two or three of dimethylimidazolium, 2,4,6-tris(dimethylaminomethyl)phenol, and resorcinol in any proportion. The curable flux system consists of an epoxy composition, an activator, and an accelerator. The epoxy composition, activator, and accelerator are mixed according to a mass ratio of epoxy composition: activator: accelerator.

[0018] = 70~75: 24~28: 1~3, pre-mixed and mixed evenly for standby; commercially available Sn-58Bi solder powder is cleaned with ethanol and cleaned in an ultrasonic cleaner to obtain experimental Sn-58Bi solder powder; finally, 6-18% of the curable flux system and the rest of the Sn-58Bi solder powder are mixed and stirred for 20-30 min using a high-speed mixer (speed: 300-1200 r / min) to obtain the VOC-free epoxy-based Sn-Bi lead-free solder paste.

[0019] 2. Through a large number of experiments, it is found that the epoxy resin is any one or any two proportion combination of NPEL-127H type bisphenol A, E20 type bisphenol A, and E51 type bisphenol A, and the self-made modified dicyandiamide curing agent is matched, the preparation method is that dicyandiamide, polyether amine and E51 type bisphenol A epoxy resin are mixed according to the mass ratio of E51 type bisphenol A: polyether amine = 77:33, heated at 80°C for 1 hour, then dicyandiamide is added according to the mass ratio of dicyandiamide: E51 type bisphenol A: polyether amine = 90:77:33, heated at 100°C for 2 hours, and the modified dicyandiamide curing agent is obtained after cooling, and the epoxy composition is prepared according to the mass ratio of epoxy resin: curing agent = 6:1, the reaction of the epoxy resin and the curing agent in the epoxy composition is the most sufficient, and the details are shown in Figure 1 , which is the DSC curve of the VOC-free epoxy-based Sn-Bi lead-free solder paste and the curable flux resin system.

[0020] 3. Details are shown in Figure 2 , which shows the influence law of different mass fractions of the curable flux system (containing epoxy composition, active agent, and accelerator, and the mass percentage of each component in the composition is epoxy composition: active agent: accelerator = 73:25.5:1.5) on the wetting and spreading performance of the VOC-free epoxy-based Sn-Bi lead-free solder paste, and the corresponding welding conditions are: heating at 120°C for 30 s; heating to 150°C, holding at 150°C for 60 s; heating to 180°C, holding at 180°C for 60 s.

[0021] Figure 2 It is shown that under the conditions of peak temperature 180°C and holding time 1 min, the wetting angle of the VOC-free epoxy-based Sn-Bi lead-free solder paste of the application on the TU1 oxygen-free copper plate decreases with the increase of the addition amount of the curable flux system (containing epoxy composition, active agent, and accelerator) in the solder paste, and the spreading area increases, which indicates that the addition of the curable flux system (containing epoxy composition, active agent, and accelerator) has no negative effect on the wetting and spreading performance of the Sn-Bi lead-free solder paste, and has an improvement effect.

[0022] 4. Details are shown in Figure 3 ​Figure 3 shows the influence of different mass fractions of the solidifiable fluxing system (comprising an epoxy composition, an active agent, and an accelerator, each component accounting for the mass percentage of the composition in the ratio of epoxy composition: active agent: accelerator = 73:25.5:1.5) on the shear performance of the Sn-Bi lead-free solder paste joint, and the corresponding welding conditions are as follows: heating at 120°C for 30 s; heating to 150°C, holding at 150°C for 60 s; heating to 180°C, holding at 180°C for 60 s.

[0023] Figure 3 As shown, the 50N without the addition of the epoxy resin is increased by 20% to 26%, and the optimal addition amount is 14%, which is increased to 63N (the total addition amount of the epoxy composition, the active agent, and the accelerator is 14%), fully indicating that the addition of the solidifiable fluxing system can significantly improve the shear strength of the Sn-Bi lead-free solder paste joint.

[0024] Compared with the prior art, the creativity of the present application lies in

[0025] (1) The Sn-Bi lead-free solder paste does not contain volatile components. Commercially available solder paste contains organic solvents, and the volatilization of the organic solvents during the welding process has certain influences on the environment and the generation of joint defects.

[0026] Through a large number of tests, screening and optimization are performed, especially in the screening and optimization of the synergistic effect of the curing agent and the accelerator. It is found that the epoxy composition is composed of an epoxy resin and a curing agent, the epoxy resin is any one or any two or three of NPEL-127H type bisphenol A, E20 type bisphenol A, E44 type bisphenol A, and E51 type bisphenol A in any proportion, the self-made modified dicyandiamide curing agent is matched, and the epoxy resin: solid agent mass ratio is 6-10:1; the active agent is composed of an organic acid and an organic amine, the organic amine is any one or any two of triethanolamine and polyol amine in any proportion, the organic acid is selected from any one or any two of glutaric acid and maleic anhydride in any proportion, and the organic acid: organic amine mass ratio is 1:3-5; the active agent is pre-mixed and uniformly mixed for standby use;

[0027] The accelerator is selected from any one or any two or three of dimethyl-imidazole, 2,4,6-tris(dimethylaminomethyl)phenol, and m-dihydroxybenzene in any proportion; the solidifiable fluxing system is composed of the epoxy composition, the active agent, and the accelerator, the epoxy composition, the active agent, and the accelerator are pre-mixed and uniformly mixed in the mass ratio of epoxy composition: active agent: accelerator = 70-75:24-28:1-3 for standby use; the solidifiable fluxing system can be completely solidified within 1 minute at a temperature of 170°C to 190°C, meeting the process requirements of the reflow solder production line batch production.​

[0028] (2). The epoxy curing agent used in the present application is a self-made modified curing agent, which has a latent characteristic and can prolong the storage period of the solder paste.

[0029] The curing agent of the present application is a modified dicyandiamide curing agent, and the epoxy resin selected is any one or any two or three of NPEL-127H type bisphenol A, E20 type bisphenol A, E44 type bisphenol A, and E51 type bisphenol A in any proportion; the self-made modified dicyandiamide curing agent is matched, and the mass ratio of epoxy resin to curing agent is 6-10:1; the components can remain stable with each other for 16 months, which can effectively prolong the storage period of the solder paste.

[0030] The present application will be described in detail below through several embodiments.

[0031] Example 1

[0032] A VOC-free epoxy-based Sn-Bi lead-free solder paste, characterized in that the composition is proportioned by mass percentage as follows: 14% of a curable soldering system, and the balance of Sn-58Bi solder powder, wherein 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 system is composed of an epoxy composition and an active agent, and the mass percentage of each component in the composition is epoxy composition: active agent = 74:26; the above-mentioned epoxy composition is composed of an epoxy resin and a curing agent, and the mass percentage of each component in 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 a self-made modified dicyandiamide curing agent, the preparation method of which is as follows: dicyandiamide, polyether amine and E51 type bisphenol A epoxy resin are mixed in a mass ratio of E51 type bisphenol A: polyether amine = 77:33, heated at 80℃ for 1 hour, then dicyandiamide is added in a mass ratio of dicyandiamide: E51 type bisphenol A: polyether amine = 90:77:33, heated at 100℃ for 2 hours, and the modified dicyandiamide curing agent is obtained after cooling; the above-mentioned active agent is prepared by mixing triethanolamine and glutaric acid in a mass ratio of organic acid: organic amine = 1:4.

[0033] The epoxy resin composite Sn-Bi lead-free solder paste obtained by the above-mentioned proportioning has a welding condition of: heating at 120℃ for 30s; heating to 150℃, holding at 150℃ for 60s; heating to 180℃, holding at 190℃ for 60s, to obtain a solder joint structure as shown in the figure. The shear strength of the solder joint is increased from 50N without adding epoxy resin to 62N, with an increase of 24%. Figure 4

[0034] Example 2

[0035] ​The application discloses a VOC-free epoxy-based Sn-Bi lead-free solder paste, which is characterized by the following components in percentage by mass: 14% of a solidifiable soldering system, and the rest of Sn-58Bi solder powder, wherein the Bi element accounts for 58% of the alloy powder, and the rest is Sn; and the particle diameter of the alloy powder is 10-80 um. The solidifiable soldering system is composed of an epoxy composition, an active agent and an accelerator, and the components in the composition are in the following percentage by mass: epoxy composition: active agent: accelerator = 73:25.5:1.5; the epoxy composition is composed of an epoxy resin and a curing agent, and the components in the composition are in the following percentage by mass: epoxy resin: curing agent = 6:1; the epoxy resin is E51 type bisphenol A; the curing agent is a self-made modified dicyandiamide curing agent; the preparation method comprises the following steps: mixing dicyandiamide, polyether amine and E51 type bisphenol A epoxy resin according to the mass ratio of E51 type bisphenol A: polyether amine = 77:33, heating at 80 DEG C for 1 hour, then adding dicyandiamide according to the mass ratio of dicyandiamide: E51 type bisphenol A: polyether amine = 90:77:33, and heating at 100 DEG C for 2 hours, and then cooling to obtain the modified dicyandiamide curing agent; and the active agent is prepared by mixing triethanolamine and glutaric acid according to the mass ratio of organic acid: organic amine = 1:4.

[0036] The epoxy resin composite Sn-Bi lead-free solder paste prepared according to the above ratio has the solder joint structure shown in the figure. Figure 5 The wetting and spreading performance of the epoxy resin composite Sn-Bi lead-free solder paste is improved, the shear strength of the solder joint is increased from 50N of the solder paste without the epoxy resin to 63N, and the increase amplitude is 26%.

[0037] Example 3

[0038] The application discloses a VOC-free epoxy-based Sn-Bi lead-free solder paste, which is characterized by the following components in percentage by mass: 14% of a solidifiable soldering system, and the rest of Sn-58Bi solder powder, wherein the Bi element accounts for 58% of the alloy powder, and the rest is Sn; and the particle diameter of the alloy powder is 10-80 um. The solidifiable soldering system is composed of an epoxy composition, an active agent and an accelerator, and the components in the composition are in the following percentage by mass: epoxy composition:active agent:accelerator=72:25:3. The epoxy composition is composed of an epoxy resin and a curing agent, and the components in the composition are in the following percentage by mass: epoxy resin:curative=6:1. The epoxy resin is E51 type bisphenol A, and the curing agent is a self-made modified dicyandiamide curing agent. The preparation method comprises the following steps: mixing dicyandiamide, polyether amine and E51 type bisphenol A epoxy resin according to the mass ratio of E51 type bisphenol A to polyether amine=77:33, heating at 80 DEG C for 1 hour, then adding dicyandiamide according to the mass ratio of dicyandiamide to E51 type bisphenol A to polyether amine=90:77:33, and heating at 100 DEG C for 2 hours, and obtaining the modified dicyandiamide curing agent after cooling. The active agent is prepared by mixing triethanolamine and glutaric acid according to the mass ratio of organic acid to organic amine=1:4.

[0039] The epoxy resin composite Sn-Bi lead-free solder paste prepared according to the above ratio has the following welding conditions: heating at 120 DEG C for 30 s, heating to 150 DEG C, keeping at 150 DEG C for 60 s, heating to 165 DEG C, and keeping at 165 DEG C for 60 s. Since the solidifiable soldering system has a low curing temperature, when the Sn-58Bi solder is melted, the resin has been cured, the fluidity is poor, the welding spot cannot realize complete metallurgical combination with the copper substrate, and the wetting and spreading performance of the epoxy resin composite Sn-Bi lead-free solder paste is adversely affected. Compared with the welding spot shear strength of the solder paste without adding the epoxy resin, the shear strength is reduced.

Claims

1. A VOC-free epoxy based Sn-Bi lead-free solder paste, characterized in that, The composition is proportioned by mass percentage as follows: 6-18% of the solidifiable soldering system, and the balance of Sn-58Bi solder powder; the solidifiable soldering system is composed of an epoxy composition, an active agent and an accelerator, and the mass percentage of each component in the solidifiable soldering system is epoxy composition: active agent: accelerator = 70-75: 24-28: 1-3; The epoxy composition is composed of an epoxy resin and a curing agent, and the mass ratio of the epoxy resin to the curing agent is 6-10:1; the epoxy resin is any one or any two or three of NPEL-127H type bisphenol A, E20 type bisphenol A, E44 type bisphenol A and E51 type bisphenol A in any proportion; the curing agent is a self-made modified dicyandiamide curing agent, and the preparation method is as follows: polyether amine and E51 type bisphenol A epoxy resin are mixed, heated at 80-100 ℃ for 1-2 hours, then dicyandiamide is added, and heated at 90-110 ℃ for 2-3 hours, and the modified dicyandiamide curing agent is obtained after cooling, wherein the mass ratio of dicyandiamide: E51 type bisphenol A: polyether amine is 80-95: 70-80: 20-40; In the Sn-58Bi alloy powder, Bi accounts for 58% of the alloy powder in terms of mass percentage, and the balance is Sn.

2. A VOC-free epoxy based Sn-Bi lead-free solder paste according to claim 1, characterized in that, The active agent is composed of an organic acid and an organic amine, and the mass ratio of the organic acid to the organic amine is 1:3-5; the organic amine is any one or any two of triethanolamine and polyol amine in any proportion, and the organic acid is any one or any two of glutaric acid and maleic anhydride in any proportion.

3. The VOC-free epoxy-based Sn-Bi lead-free solder paste according to claim 1, characterized in that, The accelerator is any one or any two or three of dimethyl-imidazole, 2,4,6-tris(dimethylaminomethyl)phenol and m-dihydroxybenzene in any proportion.

4. A VOC-free epoxy-based Sn-Bi lead-free solder paste according to claim 1, characterized in that, The particle diameter of the alloy powder is 10-80 um.

5. A method of using a VOC-free epoxy based Sn-Bi lead-free solder paste as claimed in claim 1, wherein, The VOC-free epoxy-based Sn-Bi lead-free solder paste is applied in low-temperature connection and thermal device assembly, and the use method is as follows: fix the PCB board, then align the steel mesh hole with the pads on the PCB board, use a scraper to apply the VOC-free epoxy-based Sn-Bi lead-free solder paste to the steel mesh, make the VOC-free epoxy-based Sn-Bi lead-free solder paste uniformly pass through the steel mesh and be printed on the PCB pads, then form solder joints on the pads through a heat processing process, and complete welding; The heat processing process is as follows: the welding condition is 120 ℃ for 30 s; the temperature is raised to 150 ℃, and the temperature is kept at 150 ℃ for 60 s; the temperature is raised to 180 ℃, and the temperature is kept at 190 ℃ for 60 s; Or the welding condition is 120 ℃ for 30 s; the temperature is raised to 150 ℃, and the temperature is kept at 150 ℃ for 60 s; the temperature is raised to 180 ℃, and the temperature is kept at 180 ℃ for 60 s; Or the welding condition is 120 ℃ for 30 s; the temperature is raised to 150 ℃, and the temperature is kept at 150 ℃ for 60 s; the temperature is raised to 165 ℃, and the temperature is kept at 165 ℃ for 60 s.

Images