Halogen-free and lead-free solder paste with high wettability and preparation method thereof

Abstract

The application provides a high-wetting halogen-free lead-free soldering paste, which comprises solder alloy powder and flux, wherein the solder alloy powder comprises tin, silver, copper, zirconium, cerium, scandium and iridium; by adding a small amount of rare earth elements scandium and cerium and a small amount of metal elements zirconium and iridium, signal interference caused by the soldering paste when used for integrated circuit board assembly can be reduced, signal interference caused by material nonlinearity can be reduced, the mutual cooperation of scandium and iridium has good heat conduction, electric conduction and ductility, the storage stability of the soldering paste is improved, the strength, hardness and heat resistance of the alloy are improved, the surface insulation resistance and reliability are improved, and the dielectric loss is reduced. The application further provides a preparation method of the high-wetting halogen-free lead-free soldering paste, wherein the flux and the solder alloy powder are prepared in sequence, the process is simple, the reaction is mild, no harmful gas is generated in the process, and the method is suitable for mass production.

Description

[0001] This application is a divisional application. The original application has the application number 2022101574385 and the application date is February 21, 2022. The invention patent title is: A highly reliable halogen-free and lead-free solder paste and its preparation method. Technical Field

[0002] This invention relates to the field of welding materials technology, specifically to a highly wettable halogen-free and lead-free solder paste and its preparation method. Background Technology

[0003] The electronics industry is one of the fastest-growing sectors today, especially with the advancement of automation and intelligence. As essential consumer goods, the materials used in the assembly of electronic products play a decisive role in their quality. Lead-free solder alloys, as the most fundamental materials in electronic assembly processes, are a key focus in the field of electronic packaging technology. Excellent solderability can effectively reduce problems such as cold solder joints and missing solder joints during the soldering process.

[0004] It is worth noting that during use, the actual temperature is very close to the melting point of the solder, which requires the soldering material to have good creep resistance. Currently, Sn-Ag-Cu solder is the most widely used internationally. However, Sn-Ag-Cu solder has the problem of coarse IMC. Compared with Sn-Pb solder, lead-free solder still has weaknesses such as poor wettability, high surface insulation resistance, and high dielectric loss. It is easy to cause rapid growth of the interface and form welding holes at the welding interface, which reduces the reliability of the solder joint.

[0005] Therefore, there is an urgent need for a highly wettable halogen-free and lead-free solder paste and its preparation method. Summary of the Invention

[0006] To address the weaknesses of halogen-free and lead-free solders, such as poor wettability, high surface insulation resistance, and high dielectric loss, this invention provides a halogen-free and lead-free solder paste with high wettability.

[0007] A second objective of this invention is to provide a method for preparing a highly wettable halogen-free and lead-free solder paste.

[0008] To achieve the first objective mentioned above, the technical solution adopted by the present invention is as follows:

[0009] A highly wettable halogen-free and lead-free solder paste comprising the following components: 83.1-89.6 wt% solder alloy powder and 10.4-18.6 wt% flux;

[0010] The solder alloy powder comprises the following components: 6.1-9.1 wt% silver, 3.1-4.8 wt% copper, 2.5-4.7 wt% zirconium, 1.1-2.2 wt% cerium, 0.11-0.25 wt% iridium, and 0.09-0.19 wt% scandium, with the balance being tin. By adding small amounts of rare earth elements scandium and cerium and small amounts of metallic elements zirconium and iridium, signal interference caused by solder paste during integrated circuit board assembly can be reduced, and signal interference caused by material nonlinearity can be reduced. Furthermore, scandium and iridium have good thermal and electrical conductivity and ductility, which improves the strength, hardness and heat resistance of the alloy, enhances the storage stability of the solder paste, as well as the surface insulation resistance and reliability, and reduces dielectric loss.

[0011] The flux comprises the following components: 35.4-42.6 wt% rosin, 10.4-14.6 wt% activator, 5.0-6.1 wt% thixotropic agent, 3.3-6.8 wt% thermosetting resin, 2.4-3.2 wt% antioxidant, and the balance being an organic solvent; the thermosetting resin consists of 48-56 wt% benzoxazine monomer-modified bismaleimide resin and 44-52 wt% epoxy resin. By using a halogen-free activator, the corrosion of the solder paste on the substrate is reduced. This reduces corrosion and residues after soldering. By adding thermosetting resins, including benzoxazine monomer-modified bismaleimide resin and epoxy resin, the benzoxazine monomer-modified bismaleimide resin exhibits high heat resistance, electrical properties, moisture resistance, abrasion resistance, dimensional stability, and high-temperature mechanical properties. It interacts with the short chains of epoxy resin to form a block polymer of bismaleimide resin and epoxy resin, increasing the molecular chain length and reducing the interaction between its own molecular chains, thereby improving the stability and reliability of solder paste performance.

[0012] The highly wettable halogen-free lead-free solder paste described above, wherein the benzoxazine monomer includes one or more of bisphenol A type benzoxazine, DCPD type benzoxazine, and phenolphthalein type benzoxazine, which can significantly improve the overall dielectric properties of the solder paste, reduce dielectric loss, and provide good heat resistance when used to modify bismaleimide resin.

[0013] The highly wettable halogen-free lead-free solder paste described above uses an epoxy resin that is one or a combination of alicyclic epoxy resin, bisphenol A type epoxy resin, phenol-aralkyl epoxy resin, and glycidylamine type epoxy resin. The bismaleimide resin is copolymerized and modified with epoxy resin. The modified resin has excellent dielectric properties, resulting in low dielectric loss after the solder paste is cured. At the same time, it can isolate air, reduce the surface tension of the solder, improve the wettability and diffusion ability of the metal surface, and prevent re-oxidation during heating.

[0014] The highly wettable halogen-free and lead-free solder paste described above uses an activator that is one or more combinations of glutaric acid, itaconic acid, o-hydroxybenzoic acid, pimelic acid, and malic acid. By using halogen-free and amino-free activators, excessive corrosion after soldering is avoided, which affects the use and saves cleaning costs.

[0015] The highly wettable halogen-free and lead-free solder paste described above uses a combination of two or more of the following thixotropic agents: hydroquinone, dodecyl stearic acid, hydrogenated castor oil, modified hydrogenated castor oil, and fatty acid amides. By using multiple thixotropic agents in combination, the solder paste is prevented from collapsing, thus preventing phenomena such as tailing, sticking, and collapse during printing.

[0016] The rosin in the highly wettable halogen-free and lead-free solder paste described above is a compound of hydrogenated rosin and disproportionated rosin. By compounding hydrogenated rosin and disproportionated rosin, the spread rate of the solder paste on the substrate can be improved, giving the solder paste better wetting properties, and the solder joints are full, the surface is bright, and the forming effect is better.

[0017] In the highly wettable halogen-free and lead-free solder paste described above, the ratio of disproportionated rosin to hydrogenated rosin is 3-4:6-7.

[0018] The highly wettable halogen-free and lead-free solder paste described above uses one or more combinations of ethoxyquinoline, 2-ethyl ether azole, and methylbenzotriazole as antioxidants, which can improve the antioxidant properties of the solder paste, inhibit the oxidation of solder, and help reduce the occurrence of the pillow effect.

[0019] The highly wettable halogen-free and lead-free solder paste described above, wherein the organic solvent is one or more combinations of tripropylene glycol butyl ether, toluene isobutyl ketone, ethyl acetate, and butyl acetate.

[0020] To achieve the second objective mentioned above, the technical solution adopted by the present invention is as follows:

[0021] The method for preparing a highly wettable halogen-free and lead-free solder paste as described in any of the preceding claims includes the following steps:

[0022] S1. Weigh the above components according to the stated weight percentages and set aside.

[0023] S2. Add the organic solvent to the container, heat to 120-140℃, then add rosin. After it dissolves, add the thermosetting resin and stir until completely dissolved.

[0024] S3. Keep the temperature at 120-140℃, add the thixotropic agent and stir until completely dissolved;

[0025] S4. Lower the temperature to 60-80℃, add antioxidants and activators, and stir for 40-60 minutes.

[0026] S5. Grind the flux using a grinder at a speed of 4000-5000 r / min until the particle size is less than 20 μm.

[0027] S6. Add flux and solder alloy powder to the mixer and mix for 40-60 minutes to obtain the final product.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] 1. This invention provides a highly wettable halogen-free and lead-free solder paste, comprising 80.1-89.6 wt% solder alloy powder and 12.4-18.6 wt% flux. The solder alloy powder consists of tin, silver, copper, zirconium, cerium, scandium, and iridium. By adding small amounts of rare earth elements scandium and cerium, and small amounts of metallic elements zirconium and iridium, signal interference caused by the solder paste during integrated circuit board assembly can be reduced, and signal interference caused by material nonlinearity can be mitigated. Furthermore, the synergistic effect of scandium and iridium provides good thermal and electrical conductivity and ductility, improving the storage stability of the solder paste, enhancing the strength, hardness, and heat resistance of the alloy, and increasing the surface insulation resistance and reliability. Reduce dielectric loss; reduce the corrosiveness of solder paste to the substrate and reduce post-soldering residue by using halogen-free activators; add thermosetting resins, including benzoxazine monomer-modified bismaleimide resin and epoxy resin. The benzoxazine monomer-modified bismaleimide resin has high heat resistance, electrical properties, moisture resistance, abrasion resistance, dimensional stability and high-temperature mechanical properties. It is interconnected with the short chains of epoxy resin to form a block polymer of bismaleimide resin and epoxy resin, which increases the molecular chain length and reduces the interaction between its own molecular chains, thereby improving the stability and reliability of solder paste performance.

[0030] 2. The present invention provides a method for preparing a highly wettable halogen-free and lead-free solder paste, which involves preparing flux and solder alloy powder in sequence. The process is simple, the reaction is mild, and no harmful gases are generated during the process, making it suitable for mass production. Detailed Implementation

[0031] The technical solution of the present invention will be described below with reference to Examples 1-6.

[0032] Example 1

[0033] A highly wettable halogen-free and lead-free solder paste comprises the following weight components: 83.10 wt% solder alloy powder and 16.90 wt% flux, wherein the composition of the solder alloy powder is shown in Table 2, and the composition of the flux is shown in Table 3. Its preparation method includes the following steps:

[0034] Weigh each component according to the weight percentages shown in Tables 2 and 3, and set aside. First, add the solvent to the container and heat to 120°C. Then add rosin and stir until the rosin is completely dissolved. Add the thermosetting resin and maintain the temperature at 120°C. Add the thixotropic agent to the container, maintain the temperature and stir until completely dissolved. Reduce the temperature to 70°C, add the antioxidant and activator, maintain the temperature and stir for 45 minutes. Grind the mixture at 4000 r / min using a grinder until the particle size is less than 20 micrometers to obtain the flux. Add the flux and solder alloy components to the solder paste mixer, mix and stir for 60 minutes, and refrigerate to obtain the highly wettable halogen-free and lead-free solder paste.

[0035] Example 2

[0036] A highly wettable halogen-free and lead-free solder paste comprises the following weight components: 84.50 wt% solder alloy powder and 15.50 wt% flux, wherein the composition of the solder alloy powder is shown in Table 2, and the composition of the flux is shown in Table 3. Its preparation method includes the following steps:

[0037] Weigh each component according to the weight percentages shown in Tables 2 and 3, and set aside. First, add the solvent to the container and heat to 120°C. Then add rosin and stir until the rosin is completely dissolved. Add the thermosetting resin and maintain the temperature at 120°C. Add the thixotropic agent to the container, maintain the temperature and stir until completely dissolved. Reduce the temperature to 70°C, add the antioxidant and activator, maintain the temperature and stir for 45 minutes. Grind the mixture at 4000 r / min using a grinder until the particle size is less than 20 micrometers to obtain the flux. Add the flux and solder alloy components to the solder paste mixer, mix and stir for 60 minutes, and refrigerate to obtain the highly wettable halogen-free and lead-free solder paste.

[0038] Example 3

[0039] A highly wettable halogen-free and lead-free solder paste comprises the following weight components: 85.90 wt% solder alloy powder and 14.10 wt% flux, wherein the composition of the solder alloy powder is shown in Table 2, and the composition of the flux is shown in Table 3. Its preparation method includes the following steps:

[0040] Weigh each component according to the weight percentages shown in Tables 2 and 3, and set aside. First, add the solvent to the container and heat to 120°C. Then add rosin and stir until the rosin is completely dissolved. Add the thermosetting resin and maintain the temperature at 120°C. Add the thixotropic agent to the container, maintain the temperature and stir until completely dissolved. Reduce the temperature to 70°C, add the antioxidant and activator, maintain the temperature and stir for 45 minutes. Grind the mixture at 4000 r / min using a grinder until the particle size is less than 20 micrometers to obtain the flux. Add the flux and solder alloy components to the solder paste mixer, mix and stir for 60 minutes, and refrigerate to obtain the highly wettable halogen-free and lead-free solder paste.

[0041] Example 4

[0042] A highly wettable halogen-free and lead-free solder paste comprises the following weight components: 86.80 wt% solder alloy powder and 13.20 wt% flux, wherein the composition of the solder alloy powder is shown in Table 2, and the composition of the flux is shown in Table 3. Its preparation method includes the following steps:

[0043] Weigh each component according to the weight percentages shown in Tables 2 and 3, and set aside. First, add the solvent to the container and heat to 120°C. Then add rosin and stir until the rosin is completely dissolved. Add the thermosetting resin and maintain the temperature at 120°C. Add the thixotropic agent to the container, maintain the temperature and stir until completely dissolved. Reduce the temperature to 70°C, add the antioxidant and activator, maintain the temperature and stir for 45 minutes. Grind the mixture at 4000 r / min using a grinder until the particle size is less than 20 micrometers to obtain the flux. Add the flux and solder alloy components to the solder paste mixer, mix and stir for 60 minutes, and refrigerate to obtain the highly wettable halogen-free and lead-free solder paste.

[0044] Example 5

[0045] A highly wettable halogen-free and lead-free solder paste comprises the following weight components: 87.60 wt% solder alloy powder and 12.40 wt% flux, wherein the composition of the solder alloy powder is shown in Table 2, and the composition of the flux is shown in Table 3. Its preparation method includes the following steps:

[0046] Weigh each component according to the weight percentages shown in Tables 2 and 3, and set aside. First, add the solvent to the container and heat to 120°C. Then add rosin and stir until the rosin is completely dissolved. Add the thermosetting resin and maintain the temperature at 120°C. Add the thixotropic agent to the container, maintain the temperature and stir until completely dissolved. Reduce the temperature to 70°C, add the antioxidant and activator, maintain the temperature and stir for 45 minutes. Grind the mixture at 4000 r / min using a grinder until the particle size is less than 20 micrometers to obtain the flux. Add the flux and solder alloy components to the solder paste mixer, mix and stir for 60 minutes, and refrigerate to obtain the highly wettable halogen-free and lead-free solder paste.

[0047] Example 6

[0048] A highly wettable halogen-free and lead-free solder paste comprises the following weight components: 89.30 wt% solder alloy powder and 10.70 wt% flux, wherein the composition of the solder alloy powder is shown in Table 2, and the composition of the flux is shown in Table 3. Its preparation method includes the following steps:

[0049] Weigh each component according to the weight percentages shown in Tables 2 and 3, and set aside. First, add the solvent to the container and heat to 120°C. Then add rosin and stir until the rosin is completely dissolved. Add the thermosetting resin and maintain the temperature at 120°C. Add the thixotropic agent to the container, maintain the temperature and stir until completely dissolved. Reduce the temperature to 70°C, add the antioxidant and activator, maintain the temperature and stir for 45 minutes. Grind the mixture at 4000 r / min using a grinder until the particle size is less than 20 micrometers to obtain the flux. Add the flux and solder alloy components to the solder paste mixer, mix and stir for 60 minutes, and refrigerate to obtain the highly wettable halogen-free and lead-free solder paste.

[0050] Table 1: Component weight ratios of solder pastes in Examples 1-6

[0051] Components Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Solder alloy powder 83.10％ 84.50％ 85.90％ 86.80％ 87.60％ 89.30％ flux 16.90％ 15.50％ 14.10％ 13.20％ 12.40％ 10.70％

[0052] Table 2: Component weight ratio of solder alloy powder in Examples 1-6

[0053] Components Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 tin 86.00％ 84.63％ 80.90％ 84.44％ 81.48％ 84.00％ silver 6.10％ 6.90％ 7.50％ 7.10％ 8.90％ 9.10％ copper 3.10％ 3.30％ 4.80％ 3.50％ 4.40％ 3.10％ zirconium 3.40％ 2.80％ 4.70％ 3.20％ 2.60％ 2.50％ cerium 1.10％ 2.10％ 1.80％ 1.50％ 2.20％ 1.10％ iridium 0.11％ 0.15％ 0.21％ 0.11％ 0.25％ 0.11％ scandium 0.19％ 0.12％ 0.09％ 0.15％ 0.17％ 0.09％

[0054] Table 3: Component weight ratio of fluxes in Examples 1-6

[0055]

[0056] The high wettability halogen-free and lead-free solder pastes prepared in Examples 1-6 and commercially available lead-free solder pastes as a comparative example were subjected to performance tests. The test results are shown in Table 4.

[0057] Table 4: Test Results of Examples 1-6 and Comparative Examples

[0058]

[0059]

[0060] As can be seen from the table, this invention provides a highly wettable halogen-free and lead-free solder paste. By adding small amounts of rare earth elements scandium and cerium, and small amounts of metallic elements zirconium and iridium, signal interference caused by the solder paste during integrated circuit board assembly can be reduced, and signal interference caused by material nonlinearity can be mitigated. Furthermore, the combination of scandium and iridium exhibits good thermal and electrical conductivity and ductility, improving the storage stability and performance stability of the solder paste, and enhancing surface insulation resistance and reliability. The surface insulation resistance of all samples is ≤2.0*10⁻⁶. 12 This reduces dielectric loss to below 0.021; by using halogen-free activators, the corrosiveness of the solder paste to the substrate is reduced, and post-soldering residues are minimized; by adding thermosetting resins, including benzoxazine monomer-modified bismaleimide resin and epoxy resin, the benzoxazine monomer-modified bismaleimide resin exhibits high heat resistance, electrical properties, moisture resistance, abrasion resistance, dimensional stability, and high-temperature mechanical properties. It interacts with the short chains of epoxy resin to form a block polymer of bismaleimide resin and epoxy resin, increasing the molecular chain length and reducing the interaction between its own molecular chains, thereby improving the stability and reliability of the solder paste performance.

[0061] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A high wettability halogen-free lead-free solder paste, characterized by, The solder alloy powder comprises the following components: 83.1-89.6wt% of solder alloy powder, 10.4-16.9wt% of flux; The solder alloy powder comprises the following components: 6.1-9.1wt% of silver, 3.1-4.8wt% of copper, 2.5-4.7wt% of zirconium, 1.1-2.2wt% of cerium, 0.11-0.25wt% of iridium, and 0.09-0.19wt% of scandium, and the balance of tin; The flux comprises the following components: 35.4-42.6wt% of rosin, 10.4-14.6wt% of activator, 5.0-6.1wt% of thixotropic agent, 3.3-6.8wt% of thermosetting resin, 2.4-3.2wt% of antioxidant, and the balance of organic solvent; The rosin is a mixture of hydrogenated rosin and disproportionated rosin; The thermosetting resin is composed of 48-56wt% of benzoxazine monomer modified bismaleimide resin and 44-52wt% of epoxy resin.

2. The high wettability halogen-free lead-free solder paste according to claim 1, characterized in that: The ratio of the disproportionated rosin to the hydrogenated rosin is 3-4:6-7.

3. The high wettability halogen-free lead-free solder paste according to claim 1, characterized in that: The activator is one or more combinations of succinic acid, glutaric acid, heptanedioic acid, and malic acid.

4. The high wettability halogen-free lead-free solder paste according to claim 1, characterized in that: The thixotropic agent is two or more combinations of hydroquinone, dodecyl hydroxystearic acid, hydrogenated castor oil, modified hydrogenated castor oil, and fatty acid amide.

5. The high wettability halogen-free lead-free solder paste according to claim 1, characterized in that: The benzoxazine monomer comprises one or more of bisphenol A type benzoxazine, DCPD type benzoxazine, and phenolphthalein type benzoxazine.

6. The high wettability halogen-free lead-free solder paste of claim 1, wherein: The epoxy resin is one or more combinations of alicyclic epoxy resin, bisphenol A type epoxy resin, phenol-aralkyl epoxy resin, and glycidyl amine type epoxy resin.

7. The high wettability halogen-free lead-free solder paste of claim 1, wherein: The antioxidant is one or more combinations of ethoxyquinoline, 2-ethyl etherazole, and methylbenzotriazole.

8. The high wettability halogen-free lead-free solder paste of claim 1, wherein: The organic solvent is one or more combinations of tripropylene glycol butyl ether, toluene isobutyl ketone, ethyl acetate, and butyl acetate.

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