A high-spreadability halogen-free and lead-free solder paste and its preparation method

Abstract

This application provides a high spreadability halogen-free and lead-free solder paste, comprising solder alloy powder and flux. The solder alloy powder consists of tin, silver, copper, zirconium, yttrium, rhodium, and palladium. The addition of yttrium significantly improves the strength, hardness, and heat resistance of the tin alloy, increases the melting point of the solder wire, and enhances the oxidation resistance and ductility of the tin alloy. The addition of trace amounts of rare earth elements to the tin alloy improves the solidification and crystallization state of the solder, increases the melting point of the solder wire, and improves the tensile strength and toughness of the solder. The flux includes rosin, thermosetting resin, thixotropic agent, activator, surface activator, and solvent. The copolymer of rosin and thermosetting resin is used as the main component, which not only enhances the soldering ability of the metal surface but also improves the elongation toughness of the solder wire. It can effectively reduce the presence of post-soldering residues, avoid corrosion of the substrate, and prevent the final product from being affected. The method for preparing a high spreadability halogen-free and lead-free solder paste provided by this invention involves the sequential preparation of flux and solder alloy powder. The process is simple, the reaction is mild, and no harmful gases are generated during the process, making it suitable for mass production.

Description

[0001] This application is a divisional application. The original application has the application number 2022101585322 and the application date is February 21, 2022. The invention patent title is: A halogen-free and lead-free solder paste with low residue after soldering and its preparation method. Technical Field

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

[0003] With the rapid development of the electronics industry, the demand for heat-sensitive low-temperature soldering applications such as smart hardware heat sinks, LED lighting component mounting, and solar photovoltaics is growing rapidly. Lead-free solder paste, as a connecting material for electronic components and circuit boards, is widely used. Currently used solder pastes made from lead-free alloys such as SnAgCu and SnAg generally have reflow temperatures above 230℃, which cannot meet the requirements of low-temperature soldering and are unsuitable for soldering heat-sensitive electronic components. Therefore, tin-bismuth-based lead-free solder pastes with lower melting points have become the preferred material in low-temperature soldering. However, existing tin-bismuth-based lead-free solder pastes have low activity, resulting in the inability to remove the surface oxide layer from the solder pads, leading to defects such as cold solder joints, tombstoning, solder balls, and non-wetting. To address these problems, existing technologies mainly use highly corrosive halides (such as ammonium bifluoride and tetrahydroxypropylethylenediamine hydrofluoric acid) as activators to remove the black oxides formed during soldering. This not only corrodes the solder joints and substrate, reducing surface insulation resistance and affecting the electrical performance of the solder joints, but also fails to solve the problem of solder paste storage stability.

[0004] Therefore, there is an urgent need for a halogen-free and lead-free solder paste with high surface insulation resistance, strong wettability, high spreadability, and high spreadability. Summary of the Invention

[0005] In order to solve the problem that the existing technology uses highly corrosive halogen-containing compounds as activators, which corrodes the solder joints and substrates and reduces the surface insulation resistance, the present invention provides a halogen-free and lead-free solder paste with high spreadability.

[0006] The second objective of this invention is to provide a method for preparing a halogen-free and lead-free solder paste with high spreadability.

[0007] To achieve the first objective mentioned above, the technical solution adopted by the present invention is as follows:

[0008] A high spreadability halogen-free and lead-free solder paste comprises the following components: 93.1-96.1 wt% solder alloy powder and 2.4-7.0 wt% flux;

[0009] The solder alloy powder comprises the following components: 1.7-3.1 wt% silver, 2.1-3.6 wt% copper, 6.5-8.7 wt% zirconium, 4.1-5.7 wt% yttrium, 0.11-0.25 wt% rhodium, and 0.09-0.19 wt% palladium, with the balance being tin. The addition of yttrium significantly improves the strength, hardness, and heat resistance of the tin alloy, increases the melting point of the solder wire, and enhances the oxidation resistance and ductility of the tin alloy. The addition of trace amounts of rare earth elements to the tin alloy improves the solidification and crystallization state of the solder, increases the melting point of the solder wire, and improves the tensile strength and toughness of the solder. Since radioactive isotopes such as Bi, Pb, and Co are not added to reduce signal interference caused by decay, and magnetic materials such as Fe, Co, Ni, and Nd are not added to reduce signal interference caused by material nonlinearity.

[0010] The flux comprises the following components: 33-42.5 wt% rosin, 8.5-11.6 wt% activator, 2.7-4.1 wt% thixotropic agent, 11.5-15.2 wt% thermosetting resin, 1.2-3.2 wt% surfactant, and the balance being organic solvent. The thermosetting resin is a compound of cyanate ester resin and melamine resin in a weight ratio of 1-2:3-4, using a copolymer of rosin and thermosetting resin as the main component. This not only enhances the tin-lubricating ability of the metal surface but also improves the elongation and toughness of the solder wire. It can effectively reduce the presence of post-soldering residues, avoid corrosion of the substrate, and prevent affecting the final product performance.

[0011] The high spreadability halogen-free and lead-free solder paste described above uses a cyanate ester resin that is one or more combinations of bisphenol A cyanate ester, bisphenol F cyanate ester, bisphenol M cyanate ester, and phenolic cyanate ester. By using the cyanate ester, the triazine network formed after curing exhibits excellent mechanical properties and a high glass transition temperature (T0). g =260℃), by adding a cyanate ester / melamine resin system to the flux, the cyanate ester resin is copolymerized and modified by melamine resin, and the melting point of the system is increased after modification, which can effectively reduce post-soldering residues.

[0012] The high spreadability halogen-free and lead-free solder paste described above uses a melamine resin that is a polymer of 1,3,5-triazine-2,4,6-triamine and formaldehyde. The polymer has a solid content of 30-70% in the melamine resin emulsion. By using it as a crosslinking agent for cyanate ester resin under slightly acidic conditions, the fluidity and stability of the solder paste system during application can be effectively increased.

[0013] The high spreadability halogen-free and lead-free solder paste described above uses an activator that is one or more combinations of succinic acid, glutaric acid, pimelic acid, and malic acid. By using a halogen-free activator, the corrosiveness of the solder paste to the substrate is reduced, post-soldering residues are reduced, excessive corrosion after soldering is avoided, which affects the use of the product, and cleaning costs are saved.

[0014] The high spreadability halogen-free and lead-free solder paste described above uses a thixotropic agent that is a combination of two or more of hydroquinone, dodecyl stearic acid, hydrogenated castor oil, modified hydrogenated castor oil, and fatty acid amides. By adding the thixotropic agent, the viscosity and printing performance of the solder paste are adjusted, and its viscosity is increased under no stress to maintain its inherent shape and prevent the solder paste from collapsing. This helps to prevent phenomena such as tailing, sticking, and collapse during printing.

[0015] The high spreadability halogen-free and lead-free solder paste described above uses rosin, which is any one of aqueous white rosin, fully hydrogenated rosin, or disproportionated rosin. At room temperature, it acts as a protective film and is not active, but its activity is activated at the high temperature of reflow soldering. It quickly removes the oxide film on the surface of the solder and the base material in a very short time, and at the same time forms a protective film on the surface of the solder to prevent metal re-oxidation. This helps to inhibit the formation of oxide film on the surface of the solder during reflow soldering heating, so that the solder paste can maintain good soldering activity under continuous high temperature baking.

[0016] The high spreadability halogen-free and lead-free solder paste described above uses a surface activator composed of halogen-free activator ST-200 and polyethylene glycol 400 in a weight ratio of 1:1-3.

[0017] The high spreadability 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.

[0018] To achieve the second objective mentioned above, the technical solution adopted by the present invention is as follows:

[0019] The method for preparing the high spreadability halogen-free and lead-free solder paste as described in any of the preceding claims includes the following steps:

[0020] S1. Weigh the above components according to the stated weight percentages and set aside.

[0021] 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.

[0022] S3. Keep the temperature at 120-140℃, add the thixotropic agent and stir until completely dissolved;

[0023] S4. Lower the temperature to 60-80℃, add antioxidants and activators, and stir for 40-60 minutes.

[0024] S5. Grind the flux using a grinder at a speed of 4000-5000 r / min until the particle size is less than 20 μm.

[0025] S6. Add flux and solder alloy powder to the mixer and mix for 40-60 minutes to obtain the final product.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] 1. This application provides a high-spreading-rate halogen-free and lead-free solder paste, comprising 93.1-96.6 wt% solder alloy powder and 2.4-7.6 wt% flux. The solder alloy powder consists of tin, silver, copper, zirconium, yttrium, rhodium, and palladium. The addition of yttrium significantly improves the strength, hardness, and heat resistance of the tin alloy, increases the melting point of the solder wire, and enhances the oxidation resistance and ductility of the tin alloy. The addition of trace amounts of rare earth elements to the tin alloy improves the solidification and crystallization state of the solder, increases the melting point of the solder wire, and improves the tensile strength and toughness of the solder. Because no radioactive isotopes such as Bi, Pb, and Co are added, the risk of radioactive contamination is reduced. Since no magnetic materials such as Fe, Co, Ni, and Nd are added to reduce signal interference caused by decay, the flux in this application includes rosin, thermosetting resin, thixotropic agent, activator, surface activator, and solvent. It uses a copolymer of rosin and thermosetting resin as the main component, which not only enhances the soldering ability of the metal surface but also improves the elongation and toughness of the solder wire. This effectively reduces the presence of post-soldering residues, avoids substrate corrosion, and prevents impact on the final product performance. By using cyanate ester, the triazine network formed after curing exhibits excellent mechanical properties and a high glass transition temperature (T0). g =260℃), by adding a cyanate ester / melamine resin system to the flux, the cyanate ester resin is copolymerized and modified by melamine resin, and the melting point of the system is increased after modification, which can effectively reduce post-soldering residues.

[0028] 2. The present invention provides a method for preparing a high-spreadability 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

[0029] The technical solution of the present invention will be described below with reference to Examples 1-6.

[0030] Example 1

[0031] A high-spreadability halogen-free and lead-free solder paste comprises the following weight components: 93.10 wt% solder alloy powder and 6.90 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:

[0032] 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 it to 120°C. Then add the rosin and stir until the rosin is completely dissolved. Add the thermosetting resin and keep the temperature at 120°C. Add the thixotropic agent to the container, keep the temperature and stir until it is completely dissolved.

[0033] The temperature was lowered to 70°C, antioxidants and activators were added, the temperature was maintained and the mixture was stirred for 45 minutes; the mixture was then ground in a grinder at 4000 r / min until the particle size was less than 20 micrometers to obtain flux; flux and solder alloy were added to a solder paste mixer, mixed and stirred for 60 minutes, and then refrigerated to obtain the high spreadability halogen-free lead-free solder paste.

[0034] Example 2

[0035] A high-spreadability halogen-free and lead-free solder paste comprises the following weight components: 94.50 wt% solder alloy powder and 5.50 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:

[0036] 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 it to 120°C. Then add the rosin and stir until the rosin is completely dissolved. Add the thermosetting resin and keep the temperature at 120°C. Add the thixotropic agent to the container, keep the temperature and stir until it is completely dissolved.

[0037] The temperature was lowered to 70°C, antioxidants and activators were added, the temperature was maintained and the mixture was stirred for 45 minutes; the mixture was then ground in a grinder at 4000 r / min until the particle size was less than 20 micrometers to obtain flux; flux and solder alloy were added to a solder paste mixer, mixed and stirred for 60 minutes, and then refrigerated to obtain the high spreadability halogen-free lead-free solder paste.

[0038] Example 3

[0039] A high-spreadability halogen-free and lead-free solder paste comprises the following weight components: 95.90 wt% solder alloy powder and 4.10 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 it to 120°C. Then add the rosin and stir until the rosin is completely dissolved. Add the thermosetting resin and keep the temperature at 120°C. Add the thixotropic agent to the container, keep the temperature and stir until it is completely dissolved.

[0041] The temperature was lowered to 70°C, antioxidants and activators were added, the temperature was maintained and the mixture was stirred for 45 minutes; the mixture was then ground in a grinder at 4000 r / min until the particle size was less than 20 micrometers to obtain flux; flux and solder alloy were added to a solder paste mixer, mixed and stirred for 60 minutes, and then refrigerated to obtain the high spreadability halogen-free lead-free solder paste.

[0042] Example 4

[0043] A high-spreadability halogen-free and lead-free solder paste comprises the following weight components: 96.10 wt% solder alloy powder and 3.90 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:

[0044] 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 it to 120°C. Then add the rosin and stir until the rosin is completely dissolved. Add the thermosetting resin and keep the temperature at 120°C. Add the thixotropic agent to the container, keep the temperature and stir until it is completely dissolved.

[0045] The temperature was lowered to 70°C, antioxidants and activators were added, the temperature was maintained and the mixture was stirred for 45 minutes; the mixture was then ground in a grinder at 4000 r / min until the particle size was less than 20 micrometers to obtain flux; flux and solder alloy were added to a solder paste mixer, mixed and stirred for 60 minutes, and then refrigerated to obtain the high spreadability halogen-free lead-free solder paste.

[0046] Example 5

[0047] A high-spreadability halogen-free and lead-free solder paste comprises the following weight components: 94.80 wt% solder alloy powder and 5.20 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:

[0048] 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 it to 120°C. Then add the rosin and stir until the rosin is completely dissolved. Add the thermosetting resin and keep the temperature at 120°C. Add the thixotropic agent to the container, keep the temperature and stir until it is completely dissolved.

[0049] The temperature was lowered to 70°C, antioxidants and activators were added, the temperature was maintained and the mixture was stirred for 45 minutes; the mixture was then ground in a grinder at 4000 r / min until the particle size was less than 20 micrometers to obtain flux; flux and solder alloy were added to a solder paste mixer, mixed and stirred for 60 minutes, and then refrigerated to obtain the high spreadability halogen-free lead-free solder paste.

[0050] Example 6

[0051] A high-spreadability halogen-free and lead-free solder paste comprises the following weight components: 93.60 wt% solder alloy powder and 6.40 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:

[0052] 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 it to 120°C. Then add the rosin and stir until the rosin is completely dissolved. Add the thermosetting resin and keep the temperature at 120°C. Add the thixotropic agent to the container, keep the temperature and stir until it is completely dissolved.

[0053] The temperature was lowered to 70°C, antioxidants and activators were added, the temperature was maintained and the mixture was stirred for 45 minutes; the mixture was then ground in a grinder at 4000 r / min until the particle size was less than 20 micrometers to obtain flux; flux and solder alloy were added to a solder paste mixer, mixed and stirred for 60 minutes, and then refrigerated to obtain the high spreadability halogen-free lead-free solder paste.

[0054] Table 1: Component weight ratios of solder pastes in Examples 1-6

[0055] Components Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Solder alloy powder 93.10％ 94.50％ 95.90％ 96.10％ 94.80％ 93.60％ flux 6.90％ 5.50％ 4.10％ 3.90％ 5.20％ 6.40％

[0056] Table 2: Component weight ratio of solder alloy powder in Examples 1-6

[0057]

[0058]

[0059] Table 3: Component weight ratio of fluxes in Examples 1-6

[0060]

[0061] The high spreadability halogen-free and lead-free solder pastes prepared in Examples 1-6 and the commercially available lead-free solder pastes of the comparative example were subjected to performance tests. The test results are shown in Table 4.

[0062] Table 4: Test Results of Examples 1-6 and Comparative Examples

[0063]

[0064] As can be seen from the table, this application provides a halogen-free and lead-free solder paste with high spreadability. By adding trace amounts of rare earth elements to the tin alloy, the solidification and crystallization state of the solder can be improved, increasing the melting point of the solder wire and enhancing the tensile strength and toughness of the solder. Using a copolymer of rosin and thermosetting resin as the main component not only enhances the wettability of the metal surface but also improves the elongation toughness of the solder wire, effectively reducing the presence of post-soldering residues and preventing corrosion of the substrate, thus affecting the final product performance. Through the use of cyanate ester, the triazine network formed after curing possesses excellent mechanical properties and a high glass transition temperature (T0). g =260℃), by adding a cyanate ester / melamine resin system to the flux, the cyanate ester resin is copolymerized and modified by melamine resin, and the melting point of the system is increased after modification, which can effectively reduce post-soldering residues.

[0065] 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 expansion rate halogen-free lead-free solder paste, characterized by, The solder alloy powder comprises the following components: 94.50wt% of solder alloy powder, 5.50wt% of flux; The solder alloy powder comprises the following components: 2.90wt% of silver, 2.30wt% of copper, 6.80wt% of zirconium, 5.10wt% of yttrium, 0.15wt% of rhodium, 0.12wt% of palladium and 82.63wt% of tin; The flux comprises the following components: 33.00wt% of water white rosin, 11.60wt% of glutaric acid, 3.50wt% of hydroquinone, 0.30wt% of fatty acid amide, 2.30wt% of bisphenol F cyanate, 9.20wt% of melamine resin, 3.20wt% of surfactant and 36.90wt% of organic solvent.

2. The high spreadability halogen-free lead-free solder paste according to claim 1, characterized by: The melamine resin is a high polymer of 1,3,5-triazine-2,4,6-triamine and formaldehyde, and the solid content of the high polymer in the melamine resin emulsion is 30-70%.

3. The high-soldering-expansion halogen-free lead-free solder paste according to claim 1, characterized in that: The surfactant is a compound of halogen-free active agent ST-200 and polyethylene glycol 400 at a weight ratio of 1:1-3.

4. The high-soldering-expansion halogen-free lead-free solder paste according to claim 1, wherein: The organic solvent is one or more of tripropylene glycol butyl ether, toluene isobutyl ketone, ethyl acetate and butyl acetate.

5. The method of producing the high-spread halogen-free lead-free solder paste according to any one of claims 1 to 4, characterized by, The method comprises the following steps: S1, weighing the above components according to the weight percentage, and preparing; S2, adding the organic solvent to a container, heating to 120-140℃, then adding rosin, and after dissolving, adding the thermosetting resin, and stirring until completely dissolved; S3, keeping the temperature at 120-140℃, adding the thixotropic agent and stirring until completely dissolved; S4, reducing the temperature to 60-80℃, adding the surfactant and activator, and stirring for 40-60min; S5, grinding with a grinder at a speed of 4000-5000r / min until the particle size is less than 20μm, to obtain the flux; S6, adding the flux and the solder alloy powder in a stirrer, mixing and stirring for 40-60min, to obtain the product.

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