Flux paste, solder paste and welding method

Abstract

The present invention relates to a solder paste, solder paste and welding method, wherein the solder paste comprises, by mass, 25-45 parts of rosin resin, 25-38 parts of solvent, 3-10 parts of active agent, 5-8 parts of thixotropic agent, 1-3 parts of moisturizing agent, 3-7 parts of antioxidant and 1-3 parts of surfactant. The solder paste of the present invention can be used to make solder paste, has a low melting point, good wettability, long moisturizing time and good pasting effect; has moderate viscosity, meets the printing requirements of roller printing, has small viscosity change during printing, has good printing rolling and tin dropping properties, can complete exquisite printing for pads as low as 0.3mm spacing, has uniform tin dropping, does not produce tiny tin balls and collapse, can replace wave soldering process to complete reflow soldering of heat-resistant components, reduces equipment startup time, improves soldering efficiency, avoids oxidation of tin bars in wave soldering process, and reduces consumables cost.

Description

Technical Field

[0001] The invention relates to the technical field of electronic welding, and in particular to a flux paste, a solder paste and a welding method. Background Art

[0002] In order to install various electronic components such as capacitors on the circuit board, surface mount technology (SMT) or through-hole mounting (THT) technology is generally required. Reflow soldering is the most commonly used method to bond components to printed circuit boards using surface mounting technology, with components and solder joints on the same side of the circuit board. Through wave soldering, the molten solder (lead-tin alloy) is sprayed into a solder wave crest as required by the design by an electric pump or electromagnetic pump. It can also be formed by injecting nitrogen into the solder pool, so that the printed circuit board pre-installed with components passes through the solder wave crest, achieving soldering of mechanical and electrical connections between the component solder ends or pins and the printed circuit board pads, with the solder joints and components on both sides of the circuit board.

[0003] However, wave soldering generally uses low-boiling-point flux, has a complex process flow, a long equipment startup time, and needs to be maintained for 24 hours. In addition, the oxidation of the tin bar during the soldering process produces a large amount of tin slag, the consumables cost is high, and it is not conducive to environmental protection. Summary of the invention

[0004] In order to solve the above problems and realize low-temperature reflow soldering of plug-in components, the first object of the present invention is to provide a soldering paste, which comprises, by weight:

[0005] 25-45 parts of rosin resin, 25-38 parts of solvent, 3-10 parts of activator, 5-8 parts of thixotropic agent, 1-3 parts of humectant, 3-7 parts of antioxidant and 1-3 parts of surfactant.

[0006] In one implementation of the present invention, the solvent includes at least two of diethylene glycol hexyl ether, 2-ethyl-1,3-hexanediol, diethylene glycol butyl ether, dipropylene glycol dimethyl ether, and diethylene glycol monooctyl ether;

[0007] The thixotropic agent comprises at least one of polyamide wax anti-settling agent 6500, DISPARLON 6650 and modified hydrogenated castor oil; and / or

[0008] Rosin resins include polymerized rosin resins and fully hydrogenated resins; and / or

[0009] The active agent comprises at least three of adipic acid, glutaric acid, succinic acid, malonic acid, sebacic acid and dibromobutene glycol; and / or

[0010] The moisturizer includes at least one of moisturizer 825, petrolatum, and castor oil; and / or

[0011] The antioxidant comprises at least one of benzotriazole, antioxidant 1076, antioxidant 245, and butylated hydroxytoluene; and / or

[0012] The surfactant includes at least one of the surfactant 3100 and the surfactant 4300 .

[0013] A second object of the present invention is to provide a solder paste comprising the above-mentioned solder paste and lead-free metal alloy powder.

[0014] In one implementation of the present invention, the viscosity of the solder paste is 150 Pa·S to 190 Pa·S.

[0015] In one implementation of the present invention, the weight percentage of the flux paste in the solder paste is 9.5% to 12%, and the weight percentage of the lead-free metal alloy powder in the solder paste is 88% to 90.5%.

[0016] In one implementation of the present invention, the melting point of the lead-free metal alloy powder is 138-227° C.; and / or

[0017] The lead-free metal alloy powder is LF143.

[0018] The third object of the present invention is to provide an electronic product, comprising a circuit board and components, wherein the components and the circuit board are welded using the above-mentioned solder paste.

[0019] In one implementation of the present invention, the component is a plug-in component.

[0020] The fourth object of the present invention is to provide a welding method, which uses a printing process to print the above-mentioned solder paste on a circuit board, places components on the circuit board so that the components and the solder paste are in contact, and performs reflow soldering on the components and the circuit board.

[0021] In one implementation of the present invention, the temperature of the reflow soldering is 143-173° C., and the time of the reflow soldering is 1-2 min.

[0022] In one implementation of the present invention, the printing is scraper printing or roller printing.

[0023] In one implementation of the present invention, printing is secondary printing of the circuit board, specifically, by scraper printing or roller printing, using solder paste with corresponding jigs for secondary printing. Secondary printing generally refers to the completion of the patch printing of the circuit board. The secondary printing has higher requirements on the welding temperature, which must be lower than the welding temperature of the first printing to avoid affecting the first welding temperature.

[0024] The soldering paste of the invention can be used to replace the use of soldering flux in wave soldering, can be used to prepare soldering paste, has low melting point, good wettability, long moisture retention time, which is up to more than 48 hours, and good pasting effect; has moderate viscosity, meets the printing requirements of roller printing, has small viscosity change during printing, has good printing rolling property and tin drop property, and is uniform in tin drop, does not generate tiny tin balls and collapse, and does not deviate patch components; has high welding strength, has very little residue after welding, has large insulation resistance, does not corrode PCB, can meet the requirement of free washing, avoids the use of board washing water, and is beneficial to environmental protection; can realize welding components on circuit boards through low-temperature reflow soldering process, thereby replacing the wave soldering process to complete the reflow soldering of heat-sensitive components, reduces equipment startup time, improves welding efficiency, avoids oxidation of tin bars in the wave soldering process, and reduces consumables cost. DETAILED DESCRIPTION

[0025] References to embodiments of the present invention will now be provided in detail, one or more examples of which are described below. Each example is provided as an explanation rather than a limitation of the present invention. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made to the present invention without departing from the scope or spirit of the present invention. For example, a feature illustrated or described as part of one embodiment may be used in another embodiment to produce a further embodiment.

[0026] Therefore, it is intended that the present invention covers such modifications and variations that fall within the scope of the appended claims and their equivalents. Other objects, features and aspects of the present invention are disclosed in or are obvious from the following detailed description. Those of ordinary skill in the art will appreciate that this discussion is only a description of exemplary embodiments and is not intended to limit the broader aspects of the present invention.

[0027] The traditional wave soldering process includes the following steps: inserting components into corresponding component holes, pre-coating flux, preheating (temperature 90-100°C, length 1-1.2m), wave soldering (220-240°C) cooling, cutting off excess plug-in pins, checking solder joints, and using board washing water to clean residual flux on the circuit board after wave soldering. Therefore, the traditional wave soldering process is complicated and has environmental problems.

[0028] In order to at least partially solve at least one of the above-mentioned technical problems, the first aspect of the present invention provides a soldering paste, which comprises, by mass: 25 to 45 parts of rosin resin, 25 to 38 parts of solvent, 3 to 10 parts of activator, 5 to 8 parts of thixotropic agent, 1 to 3 parts of humectant, 3 to 7 parts of antioxidant and 1 to 3 parts of surfactant.

[0029] The soldering paste of the invention can be used to replace the use of soldering flux in wave soldering, can be used to prepare soldering paste, has a low melting point, good wettability, a long moisturizing time of more than 48 hours, and a good pasting effect; has moderate viscosity, meets the printing requirements of roller printing, has little viscosity change during printing, has good printing rolling property and tin dropping property, and is uniform in tin dropping, does not generate tiny tin balls and collapse, and does not deviate patch components; has high welding strength, has very little residue after welding, has large insulation resistance, does not corrode PCB, can meet the requirement of free washing, avoids the use of board washing water, and is beneficial to environmental protection; can realize welding components on the circuit board through a low-temperature reflow soldering process, thereby replacing the wave soldering process to complete the reflow soldering of heat-sensitive components, reduces the equipment startup time, improves the welding efficiency, avoids the oxidation of tin bars in the wave soldering process, and reduces the cost of consumables.

[0030] In some embodiments, the solvent includes at least two of diethylene glycol hexyl ether, 2-ethyl-1,3-hexanediol, diethylene glycol butyl ether, dipropylene glycol dimethyl ether and diethylene glycol monooctyl ether. The above solvents are all high boiling point solvents with boiling points above 200°C. They can dissolve activators, thixotropic agents and other substances, and mix with melted lead-free metal at high temperature to form a flux paste with a certain viscosity to meet the printing requirements of roller printing, so that the tin under the flux paste is uniform, well-formed, and not brittle.

[0031] In some embodiments, at least one of polyamide wax anti-settling agent 6500, DISPARLON 6650, and modified hydrogenated castor oil is used to adjust the viscosity of the flux paste.

[0032] In some embodiments, the rosin resin includes polymerized rosin resin and fully hydrogenated rosin resin. Among them, rosin resin is a light-colored, highly polymerized (dimerized) resin with a high softening point, high viscosity, and better oxidation resistance, and is completely resistant to crystallization in a liquid state or in a solution. It has flux properties, can improve insulation resistance, and prevent leakage. Specifically, polymerized rosin resin is mainly dimer, containing a mixture of rosin and rosin hydrocarbons, etc. It does not crystallize and has a higher softening point than rosin. The dimer accounts for about 20% to 50%, which is relatively stable and not easily oxidized. The molecular formula is C 40 H 60 O4, softening point 90℃~120℃, acid value about 150mgKOH / g. Due to the increase of relative molecular mass and partial elimination of double bonds, polymerized rosin has the characteristics of light color, low acid value, high viscosity, no crystallization, high softening point, good compatibility, excellent antioxidant and strong durability. Rosin that is completely saturated with hydrogen is called tetrahydrorosin, also known as fully hydrogenated rosin, with a structural formula of C 19 H 33 COOH, molecular weight 306.47. The color of hydrogenated rosin becomes lighter, it has higher antioxidant properties and will not oxidize in the air.

[0033] In some embodiments, the active agent includes at least two of adipic acid, succinic acid, malonic acid, sebacic acid, glutaric acid, dibromosuccinic acid, etc., to remove oxides on the metal surface.

[0034] In some embodiments, the moisturizer includes at least one of vaseline, moisturizer 825 and castor oil to prevent the solvent in the flux paste from volatilizing and thus affecting the welding effect of the solder paste.

[0035] Antioxidants include benzotriazole, antioxidant 1076, BHT, antioxidant 245, etc., which are used to prevent the metal in the solder paste from oxidizing at high temperatures.

[0036] The surfactants include surfactant 3100 and surfactant 4300, which are used to increase the wettability of the solder paste and facilitate the solder paste to adhere to the surface of the circuit board.

[0037] It should be noted that the chemical products used in the preparation of the solder paste used in the present invention are all purchased from Shenzhen Jintenglong Industrial Co., Ltd. The numbers in the names of the above solder paste ingredients, for example, polyamide wax anti-settling agent 6500, DISPARLON 6650, antioxidant 1076, humectant 825, antioxidant 245, surfactant 3100 and surfactant 4300 are all product models, and each model of product can be obtained by purchasing the corresponding model of products from Shenzhen Jintenglong Industrial Co., Ltd.

[0038] The second aspect of the present invention provides a solder paste, which contains the above-mentioned flux paste and a lead-free metal alloy. It is understandable that the flux paste containing the above-mentioned formula can form a solder paste with a certain viscosity with the lead-free metal alloy, with a low melting point and good wettability, and a moisture retention time of more than 48 hours, which more effectively guarantees the pasting quality; the printing performance is very stable, the viscosity changes very little during continuous printing, and there will be no tiny solder balls and collapse, and the patch components will not shift, which can be used for the through-hole roller coating (Paste in hole) process to achieve the reflow soldering of the plug-in; good welding performance, which can be used for the hot air reflow process; very little residue after welding, with large insulation resistance, will not corrode the PCB, and can meet the requirements of no-cleaning; the latest demoulding technology is incorporated, the number of screen wiping times is reduced during the operation process, and the work efficiency is improved; the solder joints are bright, full, uniform, and permanently new; the printing rolling and tin-dropping properties are good, thereby realizing low-temperature reflow soldering of components on the circuit board.

[0039] In some implementation schemes, the viscosity of the solder paste is 150Pa·S~190Pa·S, further can be 160Pa·S~190Pa·S, and further can be 180Pa·S~190Pa·S. The viscosity of the solder paste is moderate, the tinning is uniform, the molding is good, and there is no tin bridging. If the viscosity of the solder paste is too small, it will lead to a large amount of tinning, forming cold collapse, and tin bridging, which will lead to excessively high post-furnace labor maintenance costs.

[0040] In some embodiments, the solder paste also includes lead-free metal alloy powder, the melting point of the lead-free metal alloy powder is 138°C to 227°C, further can be 138°C to 200°C, further can be 138°C to 180°C, 138°C to 160°C, the metal alloy in this melting point range can be mixed with the flux paste of the present invention when melted to form a solder paste with a viscosity of 150Pa·S to 190Pa·S, which can be printed on the circuit board by a scraper printing process, so that the patch components are not easily offset, and can also be printed in the through holes on the circuit board, meeting the viscosity requirements of the solder paste for roller printing, and realizing low-temperature reflow soldering of plug-in components, thereby realizing reflow soldering of different types of components on the circuit board.

[0041] In some specific embodiments, the lead-free metal alloy powder includes LF 143 , LF 143 It is a lead-free metal alloy powder with a melting point of 143°C, which can be mixed with the soldering flux of the present invention by heating to form a solder paste with a certain viscosity. 143 Indicates the product model, which can be obtained by purchasing the corresponding model of products from Beijing Compuxiwei Technology Co., Ltd.

[0042] In some embodiments, in order to achieve a viscosity of 150Pa·S to 190Pa·S, the weight percentage of flux paste in the solder paste is 9.5% to 12%, and the weight percentage of lead-free metal alloy powder in the solder paste is 88% to 90.5%, thereby meeting the printing requirements of scraper printing and tube printing, and realizing reflow soldering of different types of components on circuit boards.

[0043] The third aspect of the present invention provides an electronic product, including a circuit board and components, wherein the components and the circuit board are welded by the above-mentioned solder paste. It is understandable that the circuit board can also be called a ceramic circuit board, an alumina ceramic circuit board, an aluminum nitride ceramic circuit board, a circuit board, a PCB board, an aluminum substrate, a high-frequency board, a thick copper board, an impedance board, a PCB, an ultra-thin circuit board, an ultra-thin circuit board, a printed (copper etching technology) circuit board, etc.; the circuit board can be a single-layer circuit board or a double-layer circuit board.

[0044] Components refer to the general term for various electronic components and devices installed on a circuit board. In some specific implementations, components can be resistors, capacitors, electron tubes, connectors, etc.

[0045] In some embodiments, according to different welding methods, the components can be SMD components or plug-in components. The solder paste prepared by the flux paste of the present invention has a low melting point and good printability, and can be used for low-temperature reflow soldering of heat-sensitive components, including low-temperature reflow soldering of SMD components and low-temperature reflow soldering of plug-in components.

[0046] The fourth aspect of the present invention provides a welding method, which uses a printing process to print the above-mentioned solder paste on a circuit board, places components on the circuit board so that the components and the solder paste are in contact, and performs reflow soldering on the components and the circuit board.

[0047] Specifically, the solder paste is printed on a circuit board, and components are surface mounted or plugged in on the solder paste on the circuit board, so that the components are mounted on the surface of the solder paste, or the components are plugged into the socket containing the solder paste, and the components and the circuit board are reflow soldered.

[0048] The solder paste of the present invention can adopt a "heating-keeping" type heating method or a "gradual heating" type heating method. The actual temperature setting of the reflow soldering needs to be comprehensively considered in combination with factors such as the properties of the welded parts, the distribution and characteristics of the components, and the equipment process conditions.

[0049] In some embodiments, the reflow soldering temperature is 143°C to 173°C, further 153°C to 173°C, and further 163°C to 173°C, and the reflow soldering time is 1 to 2 minutes. If the peak temperature is too high or the reflow soldering time is too long, it may cause the solder joints to darken, the flux residues to carbonize and discolor, and the welded parts to be damaged. If the temperature is too low or the reflow soldering time is too short, the wettability of the solder may deteriorate and high-quality solder joints may not be formed. The solder joints of welded parts with large heat capacity may even form cold solder joints.

[0050] In some specific embodiments, the printing is scraper printing or roller printing. It is understood that the solder paste of the present invention can meet the requirements of roller printing process for the viscosity and fluidity of the solder paste, and the soldering is uniform, well-formed, and not bridging. The melting point of the solder paste of the present invention is

[0051] The fourth aspect of the present invention provides a method for preparing solder paste, comprising mixing the above-mentioned solder paste and lead-free metal powder LF 143 Mix and heat to dissolve to obtain solder paste.

[0052] In some embodiments, the temperature of the heating and dissolving is 143°C to 173°C.

[0053] The soldering paste of the invention can be used to replace the use of soldering flux in wave soldering, can be used to prepare soldering paste, has a low melting point, good wettability, long moisturizing time and good pasting effect; has moderate viscosity, meets the printing requirements of roller printing, has small viscosity change during printing, has good printing rolling property and tin dropping property, and tin dropping is uniform, and will not generate tiny tin balls and collapse, and patch components will not shift; has high welding strength, has very little residue after welding, has large insulation resistance, will not corrode PCB, can meet the requirement of free washing, avoids the use of board washing water, and is beneficial to environmental protection; can realize welding components on circuit boards through low-temperature reflow soldering process, thereby replacing the wave soldering process to complete the reflow soldering of heat-sensitive components, reduces equipment startup time, improves welding efficiency, avoids oxidation of tin bars in the wave soldering process, and reduces consumables cost.

[0054] The embodiments of the present invention will be described in detail below with reference to examples.

[0055] Example 1

[0056] The present embodiment provides a soldering paste, which includes, by mass: 30 parts of rosin (604), 15 parts of fully hydrogenated rosin, 23.5 parts of hexyl ether, 10 parts of hexylene glycol, 5 parts of neopentanoic acid, 5 parts of succinic acid, 1 part of malonic acid, 3 parts of moisturizer (825), 4.5 parts of thixotropic agent (6650), 2 parts of triethanolamine, and 1 part of surfactant (3100).

[0057] This embodiment also provides a solder paste, using the solder paste of this embodiment and the lead-free metal powder LF 143 Mix and heat at 150°C to dissolve to obtain.

[0058] Example 2

[0059] The present embodiment provides a soldering paste, which includes, by mass: 20 parts of rosin (604), 25 parts of fully hydrogenated rosin, 23 parts of hexyl ether, 10 parts of hexylene glycol, 10 parts of neodecanoic acid, 1 part of succinic acid, 0.5 parts of malonic acid, 1 part of dibromobutylene glycol, 8252 parts, 4.5 parts of thixotropic agent (6650), 1 part of surfactant (3100), and 2 parts of triethanolamine.

[0060] This embodiment also provides a solder paste, using the solder paste of this embodiment and the lead-free metal powder LF 143 Mix and heat at 150°C to dissolve to obtain.

[0061] Example 3

[0062] The present embodiment provides a soldering paste, which includes, by mass: 20 parts of rosin (604), 25 parts of fully hydrogenated rosin, 23 parts of hexyl ether, 10 parts of hexylene glycol, 10 parts of neodecanoic acid, 1 part of adipic acid, 0.5 parts of malonic acid, 0.8 parts of dibromobutylene glycol, 0.2 parts of cyclohexylamine hydrochloride, 3 parts of humectant (825), 4.5 parts of thixotropic agent (6650), 1 part of surfactant (3100), and 2 parts of triethanolamine.

[0063] The present embodiment further provides a solder paste, which is obtained by mixing the solder paste of the present embodiment and lead-free metal powder LF143 and heating and dissolving them at 150° C.

[0064] Comparative Example 1

[0065] This comparative example provides a soldering paste, which includes, by mass: 20 parts of rosin (604), 5 parts of fully hydrogenated rosin, 33.5 parts of hexyl ether, 19 parts of hexylene glycol, 5 parts of neopentanoic acid, 5 parts of succinic acid, 1 part of malonic acid, 3 parts of moisturizer (825), 5.5 parts of thixotropic agent (6650), 2 parts of triethanolamine, and 1 part of surfactant (3100).

[0066] This comparative example also provides a solder paste, which is obtained by mixing the flux paste of this comparative example and lead-free metal powder LF143 and heating and dissolving them at 150° C.

[0067] Comparative Example 2

[0068] This comparative example provides a soldering paste, which includes, by mass: 25 parts of rosin (604), 25 parts of fully hydrogenated rosin, 20 parts of hexyl ether, 8 parts of hexylene glycol, 8 parts of neodecanoic acid, 1 part of adipic acid, 0.5 parts of malonic acid, 0.8 parts of dibromobutylene glycol, 0.2 parts of cyclohexylamine hydrochloride, 3 parts of humectant (825), 5.5 parts of thixotropic agent (6650), 2 parts of triethanolamine, and 1 part of surfactant (3100).

[0069] This comparative example also provides a solder paste, using the solder paste and lead-free metal powder LF 143 Mix and heat at 150°C to dissolve to obtain.

[0070] The solder pastes of Examples 1 to 3 and Comparative Examples 1 and 2 were subjected to performance tests and roller printing. The performance test results of the solder pastes of the Examples and Comparative Examples and the roller printing effects are shown in Table 1.

[0071] Table 1

[0072]

[0073] Furthermore, after the solder paste is printed by roller printing, the circuit board is reflowed at a soldering temperature of 163° C. to 173° C. for 1-2 min. The soldering effects of the embodiment and the comparative example are compared, as shown in Table 2.

[0074] Table 2

[0075]

[0076] According to the welding effects of the embodiments and comparative examples in Table 2, the solder paste prepared by the flux paste of the present invention combined with the roller printing process can complete the low-temperature reflow soldering of plug-in components, the solder joints are full, the welding is tight, the solder paste has no bridging phenomenon, the solder paste has moderate viscosity, and does not stick to the roller, while the solder paste in comparative example 1 has bridging phenomenon, and there will be problems such as uneven welding surface, bridging, and incomplete welding. In comparative example 2, the solder paste sticks to the roller, and there will be problems such as incomplete solder joints.

[0077] In summary, the solder paste prepared by the flux paste of the present invention has a low melting point, good wettability, long moisturizing time and good pasting effect; the viscosity is moderate, which meets the printing requirements of roller printing, the viscosity changes little during printing, the printing rolling property and tin dropping property are good, the tin is evenly applied, and there will be no tiny tin balls and collapse, and the patch components will not shift; the welding strength is high, and there is very little residue after welding, and it has a large insulation resistance, will not corrode the PCB, can meet the requirements of no-washing, avoid the use of board washing water, and is beneficial to environmental protection; it can realize the welding of components on the circuit board through the low-temperature reflow soldering process, thereby replacing the wave soldering process to complete the reflow soldering of heat-sensitive components, reducing the equipment startup time, improving the welding efficiency, avoiding the oxidation of the tin bar in the wave soldering process, and reducing the cost of consumables.

[0078] The above embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A solder paste, characterized in that: Contains solder paste and lead-free metal alloy powder; The lead-free metal alloy powder is LF143; The components of the soldering paste, measured by mass, include: 25-45 parts of rosin resin, 25-38 parts of solvent, 3-10 parts of active agent, 5-8 parts of thixotropic agent, 1-3 parts of moisturizing agent, 3-7 parts of antioxidant and 1-3 parts of surfactant; The solvent includes at least two of diethylene glycol hexyl ether, 2-ethyl-1,3-hexanediol, diethylene glycol butyl ether, dipropylene glycol dimethyl ether, and diethylene glycol monooctyl ether; The active agent comprises at least three of adipic acid, glutaric acid, succinic acid, malonic acid, sebacic acid, neodecanoic acid and dibromobutene glycol; The moisturizer includes at least one of moisturizer 825, vaseline and castor oil; The rosin resin includes polymerized rosin resin and fully hydrogenated resin; The thixotropic agent includes at least one of polyamide wax anti-settling agent 6500, DISPARLON 6650 and modified hydrogenated castor oil; The antioxidant includes at least one of benzotriazole, antioxidant 1076, antioxidant 245, and butylated hydroxytoluene; The surfactant includes at least one of the surfactant 3100 and the surfactant 4300; The weight percentage of the flux paste in the solder paste is 9.5% to 12%, and the weight percentage of the lead-free metal alloy powder in the solder paste is 88% to 90.5%; The viscosity of the solder paste is 150Pa·S to 190Pa·S; The solder paste is obtained by mixing the flux paste and the lead-free metal alloy powder LF143 and heating and dissolving them, and the heating and dissolving temperature is 143° C. to 173° C.

2. An electronic product, characterized in that: It comprises a circuit board and components, wherein the components and the circuit board are welded with the solder paste as claimed in claim 1.

3. The electronic product according to claim 2, characterized in that: The components are surface mount components or plug-in components.

4. A welding method, characterized in that: The steps include: Printing the solder paste according to claim 1 on a circuit board; The components to be soldered are placed on the circuit board so that the components are in contact with the solder paste, and reflow soldering is performed on the components and the circuit board.

5. The welding method according to claim 4, characterized in that: The temperature of the reflow soldering is 143-173° C., and the time of the reflow soldering is 1-2 minutes.

6. The welding method according to claim 4 or 5, characterized in that: The printing is doctor blade printing or roller printing.

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