Zero-halogen low-cavity SnBi series flux paste and preparation method thereof

Abstract

The invention discloses a zero-halogen low-cavity SnBi series flux paste and a preparation method thereof. The flux paste comprises the following components in percentage by mass: 35-40% of rosin, 4% of a stabilizer ke-311, 6-8% of a thixotropic agent, 1-2.5% of an anhydride substance, 3-5.5% of a mixture of imidazole and an imidazole derivative, 10-15% of organic acid and 30-40% of an alcohol ether substance. Solder paste prepared from the flux paste and welding powder has the advantages of being low in welding void rate, good in QFN tin climbing, free of black edges on the surface and the periphery of a welding spot, good in storage stability at normal temperature and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of soldering paste and preparation method thereof, and in particular relates to a zero-halogen low-void SnBi soldering paste and a preparation method thereof. Background Art

[0002] In the field of solder paste technology, SnBi low-temperature solder paste is still in the early stages of development. In 2019, the International Electronic Assembly Production Alliance formally proposed to apply low-temperature solder paste to actual SMT production. However, the current process conditions and formula research and development are still immature, and the application is not as extensive and mature as the traditional lead-free SAC series solder paste. However, based on its advantages of low energy consumption, low cost, and low carbon emissions, SnBi low-temperature solder paste will be the development trend of SMT welding in the future. At present, low-temperature solder paste in the industry is mainly used in heat dissipation modules, inverters, low-voltage electrical appliances, LED displays and other products. Among them, the study of void rate is an important performance indicator for conquering the application of low-temperature solder paste, so its research is very important and necessary. The performance indicators of existing low-temperature solder paste are all immature, which are manifested in poor tinning, large void rate, black edges of welding, and poor storage stability. In order to solve the tinning problem, most manufacturers will add halogens, and the reliability after welding cannot be guaranteed. Summary of the invention

[0003] The purpose of the present invention is to solve the deficiencies of the prior art and provide a zero-halogen low-void SnBi solder paste which has low void rate, good solder creep, no black edges in welding and good stability after being prepared into solder paste with solder powder. The present invention also provides a preparation method of the solder paste.

[0004] The purpose of the present invention is achieved through the following technical solutions: A zero-halogen low-void SnBi soldering paste comprises the following components and mass percentages: 35-40% of rosin, 4% of stabilizer ke-311, 6-8% of thixotropic agent, 1-2.5% of anhydride substances, 3-5.5% of a mixture of imidazole and imidazole derivatives, 10-15% of organic acid, and 30-40% of alcohol ether substances.

[0005] Furthermore, the rosin is a polymerized rosin with a certain acid value and a low softening point, specifically one or two of AXE, fully hydrogenated polymerized rosin, HR-CH, 685, and SBR. The acid value of the rosin is 150-250 mgKOH / g, and the acid value of the rosin has a certain promoting effect on reducing the surface tension of the alloy spreading; the softening point of this type of rosin is 50-100°C, and the low softening point can enhance the flow of the solder paste after heating, increase the spreading, reduce the alloy flow work, improve wetting, and thus reduce voids.

[0006] Furthermore, the thixotropic agent is an amide thixotropic agent, which is one or two of ZHH, 6500, THIXATROL PLUS, and thixotropic agent R. This type of thixotropic agent is relatively sensitive to temperature, and is more conducive to the spreading of solder paste on the surface of the pad after being heated during the reflow soldering process, thereby reducing the flow resistance of the molten tin liquid, thereby improving wetting and reducing voids.

[0007] Furthermore, the acid anhydride substance is one or both of glutaric anhydride and NA anhydride. By adding the acid anhydride substance, its reaction mechanism is: chemical reaction with water to generate polybasic organic acid, and the generated polybasic organic acid continues to participate in the reaction to remove the oxides on the surface of the solder and the metal to be welded, thereby reducing the influence of water on the voids, thereby reducing the voids.

[0008] Furthermore, the mixture of imidazole and imidazole derivatives is a mixture of benzimidazole, imidazole and carbonyldiimidazole in a mass ratio of 1.1:1.35:2.2. A large amount of experimental data shows that this ratio is the minimum ratio for no visible black edges after soldering. If the added ratio is too high, the viscosity of the solder paste is high and it is not easy to print.

[0009] Furthermore, the organic acid is a mixture of two or more of DMBA, amine-O, phenol, tetracosanoic acid, adipic acid, OP10, and hydrogenated dimer acid. The main reason for the drying and sanding of solder paste is the redox reaction between organic carboxylic acid and solder powder, among which short-chain acids (less than six carbon atoms) have a higher reaction activity. This patent adopts long-chain acids for configuration, which can largely ensure the stability of the solder paste system; in addition, according to experiments, by adding surfactants OP10 and phenol, the solder creeping performance can be effectively improved.

[0010] Furthermore, the alcohol ether substance is a mixture of hexanediol and EHDG in a mass ratio of 1-2:2-3. Hexanediol and EHDG are special solvents for solder paste, with good solubility and moderate boiling point. When they are configured in this ratio and heated continuously for about 60 seconds at about 200°C during reflow soldering, their volatility is good (greater than 80%), which can effectively reduce voids.

[0011] The preparation method of the zero-halogen low-void SnBi solder paste of the present invention comprises the following steps: adding rosin, a stabilizer, a thixotropic agent and an alcohol ether substance into a container, heating to 165-180°C, stirring until completely dissolved and then stopping heating, then adding anhydride substance, imidazole and its derivative substance, adding organic acid after dissolving, stirring until completely dissolved and then pouring into a container, and freezing treatment to obtain the solder paste.

[0012] Compared with the prior art, the soldering paste of the present invention has at least the following advantages: (1) The soldering paste of the present invention rationally combines rosin, stabilizer, thixotropic agent, activator, acid anhydride, mixture of imidazole and imidazole derivatives, organic acid, and alcohol ether. In particular, the use of imidazole and its derivatives in a precisely matched ratio can ensure that there is no black edge on the surface and periphery of the solder joint after soldering. The added stabilizer ke-311 can be stored at room temperature (about 25°C) for up to more than 6 months with good stability. The soldering paste does not contain halogen and has good reliability after soldering. (2) The preparation method of the solder paste of the present invention is simple and easy to implement and can be easily industrialized.

[0013] (3) The solder paste prepared by the present invention and the solder powder are prepared into a solder paste, which has the advantages of a small soldering void rate (the soldering void rate of an empty pad is less than 8%), good QFN solder creep (>70%), no black edges in soldering, and good stability. DETAILED DESCRIPTION

[0014] The content of the present invention is further described below in conjunction with embodiments. Example 1

[0015] A zero-halogen, low-void SnBi soldering paste, the components and mass percentages of the soldering paste are as follows: HR-CH 38% ke-311 4% 6500 doses 5% ZHH 3% DMBA 3% Adipic acid 2% Phenol 1% Hydrogenated dimer acid 4.5% Benzimidazole 1.1% Imidazole 1.35% Carbonyldiimidazole 2.2% NA anhydride 1.5% EHDG 20.5% Hexanediol 12.85% The method for preparing a zero-halogen low-void SnBi solder paste is as follows: HR-CH, ke-311, 6500 agent, ZHH, hexanediol, and EHDG are added to a container, heated to 180°C, stirred until completely dissolved and then stopped heating, benzimidazole, imidazole, carbonyldiimidazole, and NA anhydride are added, the temperature is maintained at about 150°C, organic acid DMBA, adipic acid, phenol, and hydrogenated dimer acid are added after dissolution, stirred until completely dissolved, poured into a container, sealed, and placed in a freezer for cooling and solidification to obtain the solder paste of the present invention, and the solder paste is prepared into a solder paste with SnBi35Ag1.0 solder powder in a mass ratio of 11.2:88.8. Example 2

[0016] A zero-halogen, low-void SnBi soldering paste, the components and mass percentages of the soldering paste are as follows: Fully hydrogenated polymerized rosin 25% AXE 13% ke-311 4% Thixotropic agent R 4% THIXATROL PLUS 4% Phenol 1.5% Lignoceric acid 4% OP10 2.5% Hydrogenated dimer acid 4.5% Benzimidazole 1.1% Imidazole 1.35% Carbonyldiimidazole 2.2% Glutaric anhydride 1.5% Hexanediol 13% EHDG 18.35% The method for preparing a zero-halogen low-void SnBi solder paste is as follows: fully hydrogenated polymerized rosin, AXE, ke-311, thixotropic agent R, THIXATROL PLUS, hexanediol, and EHDG are added to a container, heated to 165°C, stirred until completely dissolved and then stopped heating, imidazole, benzimidazole, carbonyldiimidazole, and glutaric anhydride are added, the temperature is maintained at about 160°C, organic acid phenol, tetracosanoic acid, OP10, and hydrogenated dimer acid are added after dissolution, stirred until completely dissolved, poured into a container, sealed, and placed in a freezer for cooling and solidification to obtain the solder paste of the present invention, and the solder paste is prepared into a solder paste with SnBi35Ag1.0 solder powder in a mass ratio of 11.2:88.8. Example 3

[0017] A zero-halogen, low-void SnBi soldering paste, the components and mass percentages of the soldering paste are as follows: Fully hydrogenated polymerized rosin 25% HR-CH 13% ke-311 4% Thixotropic agent R 3% 6500 doses 5% Phenol 1.5% DMBA 4% OP10 2.5% Hydrogenated dimer acid 4.5% Benzimidazole 1.1% Imidazole 1.35% Carbonyldiimidazole 2.2% Glutaric anhydride 1.5% Hexanediol 13% EHDG 18.35% The method for preparing a zero-halogen low-void SnBi solder paste is as follows: fully hydrogenated polymerized rosin, HR-CH, ke-311, thixotropic agent R, 6500 agent, hexanediol, and EHDG are added to a container, heated to 175°C, stirred until completely dissolved and then stopped heating, benzimidazole, imidazole, carbonyldiimidazole, and glutaric anhydride are added, the temperature is maintained at about 155°C, organic acid phenol, DMBA, and OP10 are added after dissolution, stirred until completely dissolved, poured into a container and sealed, and placed in a freezer for cooling and solidification to obtain the solder paste of the present invention, and the solder paste is prepared into a solder paste with SnBi35Ag1.0 solder powder in a mass ratio of 11.2:88.8. Example 4

[0018] A zero-halogen, low-void SnBi soldering paste, the components and mass percentages of the soldering paste are as follows: Fully hydrogenated polymerized rosin 25% AXE 13% ke-311 4% Thixotropic agent R 5% ZHH 3% Phenol 1.5% DMBA 4% OP10 2.5% amine-O 4.5% Benzimidazole 1.1% Imidazole 1.35% Carbonyldiimidazole 2.2% NA anhydride 1.5% Hexanediol 13% EHDG 18.35% The method for preparing zero-halogen low-void SnBi solder paste is as follows: fully hydrogenated polymerized rosin, AXE, ZHH, ke-311 , thixotropic agent R, hexylene glycol, and EHDG are added to a container, heated to 170°C, stirred until completely dissolved and then stopped heating, carbonyldiimidazole, imidazole, benzimidazole, and NA anhydride are added, the temperature is maintained at about 160°C, and organic acid phenol, DMBA, OP10, and amine-O are added after dissolution, stirred until completely dissolved, poured into a container and sealed, and placed in a freezer for cooling and solidification to obtain the solder paste of the present invention, and the solder paste is prepared into a solder paste with SnBi35Ag1.0 solder powder in a mass ratio of 11.2:88.8. Example 5

[0019] A zero-halogen, low-void SnBi soldering paste, the components and mass percentages of the soldering paste are as follows: Fully hydrogenated polymerized rosin 13% HR-CH 25% ke-311 4% Thixotropic agent R 2% THIXATROL PLUS 6% Phenol 1.5% DMBA 4% Lignoceric acid 2.5% Adipic acid 4.5% Benzimidazole 1.1% Imidazole 1.35% Carbonyldiimidazole 2.2% Glutaric anhydride 1.5% Hexanediol 13% EHDG 18.35% The method for preparing a zero-halogen low-void SnBi series solder paste is as follows: fully hydrogenated polymerized rosin, HR-CH, ke-311, THIXATROL PLUS, thixotropic agent R, hexylene glycol, and EHDG are added to a container, heated to 175°C, stirred until completely dissolved and then stopped heating, benzimidazole, carbonyldiimidazole, imidazole, and glutaric anhydride are added, the temperature is maintained at about 165°C, organic acid phenol, DMBA, tetracosanoic acid, and adipic acid are added after dissolution, stirred until completely dissolved, poured into a container, sealed, and placed in a freezer for cooling and solidification to obtain the solder paste of the present invention, and the solder paste is prepared into a solder paste with SnBi35Ag1.0 solder powder in a mass ratio of 11.2:88.8. Example 6

[0020] A zero-halogen, low-void SnBi soldering paste, the components and mass percentages of the soldering paste are as follows: HR-CH 25% 685 13% ke-311 4% ZHH 6% THIXATROL PLUS 2% DMBA 3% Adipic acid 2% Phenol 1% OP10 1% amine-O 4.5% Benzimidazole 1.1% Imidazole 1.35% Carbonyldiimidazole 2.2% NA anhydride 1.5% Hexanediol 14.5% EHDG 17.85% The method for preparing a zero-halogen low-void SnBi solder paste is as follows: HR-CH, 685, ke-311, THIXATROLPLUS, ZHH, hexanediol, and EHDG are added to a container, heated to 180°C, stirred until completely dissolved and then stopped heating, imidazole, benzimidazole, carbonyldiimidazole, and NA anhydride are added, the temperature is maintained at about 170°C, organic acids DMBA, adipic acid, phenol, OP10, and amine-O are added after dissolution, stirred until completely dissolved, poured into a container, sealed, and placed in a freezer for cooling and solidification to obtain the solder paste of the present invention, and the solder paste is prepared into a solder paste with SnBi35Ag1.0 solder powder in a mass ratio of 11.4:88.6. Solder paste welding black edge test method

[0021] The solder paste made from the prepared flux paste in a certain proportion was centrifuged for 2 minutes using an automatic centrifugal mixer and then printed on a copper sheet using a 0.12 mm thick steel screen. The soldering time was maintained for 10 seconds on a constant temperature heating platform heated to 220°C. After removal, the surface of the solder joint and the surrounding black edges were observed under a high-definition microscope.

[0022] Solder Paste QFN Solder Creep Test Method

[0023] Take the prepared solder paste and mount the same type of QFN chip on the same test PCB board. Reflow is performed under the same reflow soldering conditions. The soldered PCBA sample is placed under a microscope to measure the side tin creep height at the same angle and record the tin creep height percentage.

[0024] The solder paste in the embodiment was tested under the same test conditions according to the above test method. The performance test results are as follows: Solder Paste Performance Test Comparison Table It can be seen from the above table that under the same test conditions, the solder paste of the present invention has the following characteristics: the solder void rate is <10%, the QFN solder creep rate is >70%, and the solder pastes in the embodiments are all zero-halogen solder pastes, among which the solder paste in Embodiment 3 has the best comprehensive performance.

[0025] Elimination of black edges of solder joints after soldering is a difficult point in soldering of SnBi alloys. No black edges appear after soldering in the solder paste formula of the present invention, and the soldering appearance is good.

[0026] The halogen content affects the storage stability of the solder paste. After being placed at room temperature for a long time (90 days) at 25°C, the solder pastes of the examples were in good condition within the same period of time, with a viscosity change value of <20Pa·s, and good storage stability. Among them, the appearance of the solder paste of Example 4 can be maintained for more than 6 months under room temperature storage, and the viscosity change value is <10Pa·s.

[0027] The stabilizer ke-311 described in the present invention, rosin such as AXE, fully hydrogenated polymerized rosin, HR-CH, 685, SBR, stearic acid amide thixotropic agent such as ZHH, 6500, THIXATROL PLUS, thixotropic agent R, organic acid such as DMBA, amine-O, phenol, tetracosanoic acid, adipic acid, OP10, hydrogenated dimer acid, as well as glutaric anhydride, NA anhydride, benzimidazole, imidazole, carbonyldiimidazole, etc., can all be commercially available.

[0028] The above embodiments are merely descriptions of preferred implementations of the present invention and are not intended to limit the scope of the present invention. Without departing from the technology of the present invention, various modifications and improvements made to the technical solutions of the present invention by those skilled in the art should all fall within the scope of protection determined by the claims of the present invention.

Claims

1. A zero-halogen low-void SnBi soldering paste, characterized in that: The components and mass percentages of the soldering paste are: 35-40% of rosin, 4% of stabilizer ke-311, 6-8% of thixotropic agent, 1-2.5% of anhydride substances, 3-5.5% of a mixture of imidazole and imidazole derivatives, 10-15% of organic acid, and 30-40% of alcohol ether substances.

2. The zero-halogen low-voiding SnBi soldering paste according to claim 1, characterized in that: The rosin is one or two of AXE, fully hydrogenated polymerized rosin, HR-CH, 685, and SBR.

3. The zero-halogen low-voiding SnBi soldering paste according to claim 1, characterized in that: The thixotropic agent is an amide thixotropic agent, which is one or two of ZHH, 6500, THIXATROL PLUS and thixotropic agent R.

4. The zero-halogen low-voiding SnBi soldering paste according to claim 1, characterized in that: The acid anhydride substance is one or both of glutaric anhydride and NA anhydride.

5. The zero-halogen low-voiding SnBi soldering paste according to claim 1, characterized in that: The mixture of imidazole and imidazole derivatives is a mixture of benzimidazole, imidazole and carbonyldiimidazole in a mass ratio of 1.1:1.35:2.

2.

6. The zero-halogen low-voiding SnBi soldering paste according to claim 1, characterized in that: The organic acid is a mixture of two or more of DMBA, amine-O, phenol, tetracosanoic acid, adipic acid, OP10, and hydrogenated dimer acid.

7. The zero-halogen low-voiding SnBi soldering paste according to claim 1, characterized in that: The alcohol ether substance is a mixture of hexylene glycol and EHDG in a mass ratio of 1-2:2-3.

8. A method for preparing a zero-halogen low-void SnBi soldering paste according to any one of claims 1 to 7, characterized in that: The method is as follows: add rosin, stabilizer, thixotropic agent and alcohol ether substances into a container, heat to 165-180°C, stir until completely dissolved and then stop heating, then add acid anhydride substances, imidazole and its derivative substances, add organic acid after dissolving, stir until completely dissolved and then pour into the container, and obtain solder paste after freezing treatment.

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