Halogen-free pre-coating soft soldering flux for nickel plating layer and coating method

Abstract

The halogen-free precoating soft soldering flux for the nickel plating layer comprises the following components in percentage by weight: 10%-50% of modified rosin, 1.0%-10% of an active agent, 0.5%-2.0% of a surfactant, 1.0%-3.0% of an antioxidant, 1.0%-3.0% of a corrosion inhibitor, 1.0%-3.0% of an additive and the balance of a solvent, the coating method comprises the steps that scaling powder is prepared according to the original component materials, the water bath temperature is constant, a soldering lug is flatly laid on a polytetrafluoroethylene plastic plate to be preheated for half a minute at the temperature of 90-100 DEG C, a proper scaling powder solution for constant-temperature pre-coating is dropwise added to the soldering lug, heating and drying are conducted after uniform brushing, cooling is conducted to the room temperature after drying, and then the formed soldering lug pre-coated with the scaling powder is obtained. The problems that when an existing scaling powder is used for pre-coating a soldering lug, halogen such as Cl and Br is contained, coating is difficult, and adhesion occurs due to mutual contact and pressing of scaling powder coatings are solved. The soldering flux is halogen-free, has proper activity, does not stick to hands after being coated and dried, and is short in welding time, good in wettability and easy to clean; and nickel and nickel alloy can be well welded.

Description

Technical Field

[0001] The invention relates to a nickel-plated layer soldering flux, and in particular to a halogen-free pre-coated soldering flux for a nickel-plated layer and a coating method thereof. Background Art

[0002] At present, microelectronic packaging technology has become one of the key core technologies for miniaturization, lightweight, high density and high performance of electronic products. In electronic packaging, solder paste is widely used, but the traditional welding method requires coating solder paste before welding, which is cumbersome and has low precision. Pre-coated solder sheets are new welding materials. Compared with welding wire or solder paste, pre-coated solder sheets have accurate solder volume and quantitative flux, which can ensure welding consistency and stability, simplify the packaging process, and reduce human errors in the welding process.

[0003] In the field of microelectronics, chemically plated nickel alloy layers are often used in UBM production, printed circuit board surface finishing processes and LCR component manufacturing due to their advantages such as low porosity, high hardness and wear resistance. In chemical nickel plating, Ni-P coatings are widely used and have excellent wear resistance and corrosion resistance. However, during the brazing process, the brazing properties of the Ni-P coating decrease as the phosphorus content increases. As the nickel element diffuses into the solder and combines with tin to form Ni3Sn4, a phosphorus enrichment layer is formed at the welding interface, which severely reduces the joint strength. The present invention uses a nickel-plated alloy plate formed by chemically plating nickel on the copper surface as a substrate, and efficiently welds a pre-coated solder sheet coated with flux to the substrate. How to effectively remove the oxide film, improve welding performance, reduce residues and the flux coating process are the key to pre-coating soft soldering flux for nickel plating.

[0004] At present, there are some reports on flux for nickel-plated soft soldering in China. The main components of the flux described in the patent for a nickel-plated alloy soft soldering solder wire core with patent number CN201210250851.2 are: 60-90% resin, 0.1-20% organic acid, 0.1-10% organic amine, 0.1-20% metal salt, 0.1-2.0% activity enhancer, 0.1-2.0% surfactant, 0.1-1.0% corrosion inhibitor and 0.1-1.0% antioxidant. The characteristics of this flux are that rosin resin and organic acid are used as film removers, and metal salts and organic amines are added as active agents. Although this type of flux is highly active, there are still many solder joints and it is not easy to clean. As time goes by, the halogen residues corrode the solder joints very seriously. Moreover, this flux is mainly used for solder wire cores and is solid at room temperature. It is not suitable for preformed solder sheets. The flux can only be used in conjunction with solder. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a halogen-free pre-coated soldering flux for nickel plating and a coating method. The present invention solves the problems that the existing flux used for pre-coating solder sheets contains halogens such as Cl and Br, is difficult to coat, and the flux coatings stick to each other when pressed against each other; the flux is halogen-free, has appropriate activity, does not stick to the hands after coating and drying, has a short welding time, good wettability, and is easy to clean; and can perform good welding on nickel and nickel alloys.

[0006] To achieve the above object, the present invention adopts the following scheme:

[0007] A halogen-free pre-coated soldering flux for nickel plating layer, comprising the following components by weight percentage:

[0008] Modified rosin: 10%~50%, activator: 1.0%~10%;

[0009] Surfactant: 0.5%~2.0%, antioxidant: 1.0%~3.0%;

[0010] Corrosion inhibitor: 1.0%~3.0%, additive 1.0%~3.0%, the rest is solvent;

[0011] The total mass percentage of all components is 100%. Preferably, the additive is 2-pyridinecarboxylic acid, and its molecular structure is:

[0012] It can form catalytically active complexes with metal elements such as nickel and cobalt. The process is as follows:

[0013] Preferably, the modified rosin is any one of AXE, ice white rosin, water white rosin, hydrogenated rosin, or a mixture of two of them in a mass ratio of greater than 0% each;

[0014] Preferably, the activator is a mixture of at least two of succinic acid, sebacic acid, stearic acid, glutaric acid, salicylic acid, DL-malic acid, palmitic acid, azelaic acid, etc., each of which is greater than 0% by mass; the activator is a weak acid, which is used to break the oxide film on the surface of nickel and nickel-plated base material to generate water and other gases;

[0015] Preferably, the surfactant is one or two of octylphenol polyoxyethylene ether, nonylphenol polyoxyethylene ether, and alkylphenol polyoxyethylene ether; the activator is a non-ionic surfactant, which can reduce the surface tension generated when the solder contacts the nickel-plated base material, enhance the surface wetting force, and enhance the penetration of the organic acid activator;

[0016] Preferably, the antioxidant is benzotriazole, which can inhibit or delay the oxidative degradation of the flux and extend the shelf life;

[0017] Preferably, the corrosion inhibitor is triethanolamine, and the addition of the corrosion inhibitor reduces the corrosiveness of the residue after welding;

[0018] Preferably, the additive is picolinic acid;

[0019] Preferably, the solvent is 1,2-propylene glycol or isopropanol.

[0020] The preparation method of the halogen-free pre-coated soldering flux for the nickel plating layer is as follows:

[0021] (1) Weighing the formula components according to the weight percentage, then putting the active agent, antioxidant and additive into a container, and stirring continuously for 5 minutes to 10 minutes to mix them evenly;

[0022] (2) Add modified rosin and solvent to another reactor, heat in a water bath at 75°C to 95°C and stir magnetically for 5 minutes to 10 minutes to completely dissolve the rosin in the solvent. The dissolved solution is a light yellow transparent liquid.

[0023] (3) Slowly add the powdery mixed agent obtained by mixing evenly in the above step (1) to the above solution (2), heat it in a water bath at 75°C to 95°C, stir it magnetically for 5min to 10min, then add the corrosion inhibitor and surfactant and continue stirring for 5min to 10min. After all the raw materials are mixed and dissolved evenly, a halogen-free pre-coated soft soldering flux for nickel plating is obtained.

[0024] The present invention also provides a method for coating the above soldering flux onto a soldering sheet, comprising the following steps:

[0025] Prepare the flux according to the original component materials, and then keep the temperature in a water bath; lay the welding piece flat on the polytetrafluoroethylene plastic plate and preheat it at 90℃~100℃ for half a minute, drop appropriate pre-coating flux solution on the welding piece, apply it evenly, heat and dry it, and cool it to room temperature after drying to obtain the pre-coated flux molded welding piece.

[0026] Preferably, the water bath thermostat temperature is 75°C to 95°C.

[0027] Preferably, the drying temperature is 90° C. to 115° C., and the drying time is 30 min to 60 min.

[0028] Compared with the prior art, the advantages of the present invention are:

[0029] (1) The present invention adds a unique additive 2-pyridinecarboxylic acid, The additive can form a complex with catalytic activity with metal elements such as nickel and cobalt, and the flux is heated in a water bath at low temperature to form a pre-coating liquid flux with stable chemical properties and not prone to self-decarboxylation reaction, so that it can fully react with metal elements such as nickel during welding to form a 2-picolinic acid nickel complex, which promotes the wetting of the preformed solder sheet to the substrate base material during welding and promotes the entire preformed solder sheet welding process.

[0030] (2) The polyoxyethylene ether of alkylphenol added to the pre-coating flux of the present invention can reduce the surface tension generated when the solder contacts the nickel-plated base material, enhance the surface wetting force, and enhance the penetration force of the organic acid activator. The polyoxyethylene ether of alkylphenol added to the pre-coating flux of the present invention can reduce the surface tension generated when the solder contacts the nickel-plated base material, enhance the surface wetting force, and enhance the penetration force of the organic acid activator.

[0031] (3) The pre-coating flux of the present invention has a clever active design, which can meet the coating requirements while maintaining sufficient activity. When welding on a nickel or nickel-plated substrate, it maintains high wettability and spreadability between the solder and the substrate, and makes the pre-coating flux welding piece non-sticky when pressed, and has good non-stickiness. After the pre-coating welding piece is welded, the solder joint is full and shiny, the flux is evenly coated, there is less smoke, the wettability and spreadability are good, the soldering effect is stable, and the pre-coating flux does not contain halogens and halides, does not produce irritating odors, is non-toxic, meets environmental protection requirements, has low cost, and has a simple preparation method. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of a pre-coated formed solder sheet;

[0033] Figure 2 Comparison of solder joint morphology of the pre-coated molded solder sheet before (left) and after (right) welding in Example 1;

[0034] Figure 3 Comparison of solder joint morphology of the pre-coated molded solder sheet before (left) and after (right) welding in Example 2;

[0035] Figure 4 Comparison of the solder joint morphology of the pre-coated molded solder sheet before (left) and after (right) welding in Example 3;

[0036] Figure 5 Comparison of the solder joint morphology of the pre-coated molded solder sheet before (left) and after (right) welding in Example 4;

[0037] Figure 6 Comparison of the solder joint morphology of the pre-coated molded solder sheet before (left) and after (right) welding in Example 5;

[0038] In the attached Figure 1Middle: 1. Flux coating; 2. Preformed solder sheet; DETAILED DESCRIPTION

[0039] The present invention is further described in detail below in conjunction with specific embodiments.

[0040] Example 1

[0041] A halogen-free pre-coated soldering flux for nickel plating is composed of the following components:

[0042] The modified rosin is AXE, accounting for 15% by mass, the active agent is a mixture of succinic acid and palmitic acid, with a mass ratio of 7%, succinic acid: palmitic acid = 2:5, the surfactant is octylphenol polyoxyethylene ether, with a mass ratio of 1%, the antioxidant is benzotriazole, with a mass ratio of 1%, the corrosion inhibitor is triethanolamine, with a mass ratio of 3%, the additive is picolinic acid, with a mass ratio of 2%, and the balance is 1,2-propylene glycol solution.

[0043] The preparation method and coating method thereof include the following steps:

[0044] 1) Weigh an appropriate amount of 1,2-propylene glycol solution according to the weight percentage into a reactor and heat it in a water bath at 75° C.;

[0045] 2) After the temperature rises to 75° C., weigh AXE according to the formula and add it to the reactor in (1). After magnetic stirring for 10 minutes, AXE is completely dissolved in 1,2-propylene glycol, and the solution becomes light yellow and transparent;

[0046] 3) According to the formula, weigh powdered succinic acid, palmitic acid, benzotriazole, and picolinic acid, mix them evenly, and add them to the solution in (2), and stir them magnetically for 10 minutes to completely dissolve the powdered reagents in the solution;

[0047] 4) weighing triethanolamine and octylphenol polyoxyethylene ether according to the formula and adding them to the solution in (3), and stirring magnetically for 10 minutes to obtain a pre-coating flux for nickel-plated alloy soldering;

[0048] 5) Lay the solder sheet flat on the plastic board, preheat at 100℃ for 30s, use a dropper to add flux to the solder sheet, evenly apply flux on the solder sheet, heat and bake at 100℃ for about 30min, dry and cool to obtain the pre-flux-coated solder sheet.

[0049] The pre-coated flux-formed solder sheet prepared by the ratio in this case has a solder sheet flux coating that does not stick when touched and has good non-stickiness. There is less volatile smoke during welding, and the solder joints are bright and have a better spreading effect. The added 2-pyridinecarboxylic acid can greatly promote the wetting and spreading of the solder sheet on the substrate, and can enhance the wetting ability and anti-retraction ability of the solder sheet during welding.

[0050] Example 2

[0051] A halogen-free pre-coated soldering flux for nickel plating is composed of the following components:

[0052] The modified rosin is a mixture of AXE and ice white rosin, with a mass ratio of 25%, AXE: ice white rosin = 4:1, the active agent is a mixture of succinic acid and azelaic acid, with a mass ratio of 8%, succinic acid: azelaic acid = 2:6, the surfactant is octylphenol polyoxyethylene ether, with a mass ratio of 1%, the antioxidant is benzotriazole, with a mass ratio of 2%, the corrosion inhibitor is triethanolamine, with a mass ratio of 2%, the additive is picolinic acid, with a mass ratio of 1.5%, and the balance is 1,2-propylene glycol solution.

[0053] The preparation method and coating method thereof include the following steps:

[0054] 1) Weigh an appropriate amount of 1,2-propylene glycol solution according to the weight percentage into a reactor and heat it in a water bath at 75° C.;

[0055] 2) After the temperature rises to 75° C., weigh AXE and ice white rosin according to the formula and add them to the reactor in (1). After magnetic stirring for 10 minutes, AXE is completely dissolved in 1,2-propylene glycol, and the solution is light yellow and transparent;

[0056] 3) According to the formula, weigh powdered succinic acid, azelaic acid, benzotriazole, and picolinic acid, mix them evenly, and add them to the solution in (2), and stir them magnetically for 10 minutes to completely dissolve the powdered reagents in the solution;

[0057] 4) weighing triethanolamine and octylphenol polyoxyethylene ether according to the formula and adding them to the solution in (3), and stirring magnetically for 10 minutes to obtain a pre-coating flux for nickel-plated alloy soldering;

[0058] 5) Lay the solder sheet flat on the plastic board, preheat at 100℃ for 30s, use a dropper to add flux to the solder sheet, evenly apply flux on the solder sheet, heat and bake at 100℃ for about 30min, dry and cool to obtain the pre-flux-coated solder sheet.

[0059] In this case, different rosins were compounded with different organic acids to obtain a pre-coating flux with better performance. The compounding of different rosins enables it to meet the process standards during coating, has good non-stickiness, and is cuttable, that is, the flux coating does not fall off during cutting. In terms of solder wetting performance, the added 2-pyridinecarboxylic acid can react with the surface of the nickel-plated layer under heating conditions to form a complex with catalytic activity, promote the wetting of the solder sheet to the substrate base material, increase the spreading rate, and enhance the wetting ability and anti-retraction ability of the solder sheet during welding.

[0060] Example 3

[0061] A halogen-free pre-coated soldering flux for nickel plating is composed of the following components:

[0062] The modified rosin is a mixture of AXE and ice white rosin, with a mass ratio of 33%, AXE: ice white rosin = 27:6. The active agent is a mixture of succinic acid and sebacic acid, with a mass ratio of 8%, succinic acid: sebacic acid = 2:6. The surfactant is octylphenol polyoxyethylene ether, with a mass ratio of 1%. The antioxidant is benzotriazole, with a mass ratio of 1%. The corrosion inhibitor is triethanolamine, with a mass ratio of 3%. The additive is picolinic acid, with a mass ratio of 2%. The balance is 1,2-propylene glycol solution.

[0063] The preparation method and coating method thereof include the following steps:

[0064] 1) Weigh an appropriate amount of 1,2-propylene glycol solution according to the weight percentage into a reactor and heat it in a water bath at 75° C.;

[0065] 2) After the temperature rises to 75° C., weigh AXE and ice white rosin according to the formula and add them to the reactor in (1). After magnetic stirring for 10 minutes, AXE and ice white rosin are completely dissolved in 1,2-propylene glycol, and the solution is light yellow and transparent;

[0066] 3) According to the formula, weigh powdered succinic acid, sebacic acid, benzotriazole, and picolinic acid, mix them evenly, and add them to the solution in (2), and stir magnetically for 10 minutes to completely dissolve the powdered reagents in the solution;

[0067] 4) weighing triethanolamine and octylphenol polyoxyethylene ether according to the formula and adding them to the solution in (3), and stirring magnetically for 10 minutes to obtain a pre-coating flux for nickel-plated alloy soldering;

[0068] 5) Lay the solder sheet flat on the plastic board, preheat at 100℃ for 30s, use a dropper to add flux to the solder sheet, evenly apply flux on the solder sheet, heat and bake at 100℃ for about 30min, dry and cool to obtain the pre-flux-coated solder sheet.

[0069] The coating flux prepared in this case can greatly promote the bonding of the soldering sheet to the nickel-plated substrate, and the compounding of different rosins makes it non-sticky and cuttable. 2-Pyridinecarboxylic acid can be used as an active agent to break the oxide film of the nickel-plated substrate, and can also bond with Ni 2+ The catalytically active complex is formed to enhance the activity of the flux, promote the wetting of the preformed solder sheet to the substrate base material during welding, and promote the entire preformed solder sheet welding process.

[0070] Example 4

[0071] A halogen-free pre-coated soldering flux for nickel plating is composed of the following components:

[0072] The modified rosin is a mixture of AXE and hydrogenated rosin, with a mass ratio of 33%, AXE: hydrogenated rosin = 27:6, the active agent is a mixture of succinic acid and sebacic acid, with a mass ratio of 8%, succinic acid: sebacic acid = 2:6, the corrosion inhibitor triethanolamine has a mass ratio of 3%, the surfactant alkylphenol polyoxyethylene ether has a mass ratio of 0.7%, the antioxidant is benzotriazole, with a mass ratio of 1%, the additive picolinic acid has a mass ratio of 1.5%, and the balance is 1,2-propylene glycol solution.

[0073] The preparation method and coating method thereof include the following steps:

[0074] 1) Weighing an appropriate amount of 1,2-propylene glycol solution according to the weight percentage and heating it in a water bath at 80° C. in a reactor;

[0075] 2) After the temperature rises to 80° C., weigh AXE and hydrogenated rosin according to the formula and add them to the reactor in (1). After magnetic stirring for 10 minutes, AXE and hydrogenated rosin are completely dissolved in 1,2-propylene glycol, and the solution is light yellow and transparent;

[0076] 3) According to the formula, weigh powdered succinic acid, sebacic acid, benzotriazole, and picolinic acid, mix them evenly, and add them to the solution in (2), and stir magnetically for 10 minutes to completely dissolve the powdered reagents in the solution;

[0077] 4) weighing triethanolamine and alkylphenol polyoxyethylene ether according to the formula and adding them to the solution in (3), and stirring magnetically for 10 minutes to obtain a pre-coating flux for nickel-plated alloy soldering;

[0078] 5) Lay the solder sheet flat on the plastic board, preheat at 110℃ for 30s, use a dropper to add flux to the solder sheet, evenly apply flux on the solder sheet, heat and bake at 110℃ for about 30min, dry and cool to obtain the pre-flux-coated solder sheet.

[0079] The pre-coated flux-formed solder sheet in this case has excellent performance. The compound of organic acids succinic acid and sebacic acid generates cyclic lactones or lactides during brazing. Esters act as good film-forming agents and form films on the surface of the solder during welding, making the solder joint surface full, bright and smooth. The additive 2-pyridinecarboxylic acid has a significant effect on breaking the oxide film of the substrate and wetting the solder during the brazing process. The 2-pyridinecarboxylic acid nickel complex produced by it can enhance the activity of the flux, ensuring that the flux has a certain activity throughout the entire welding process, and the resulting solder joints are bright and smooth.

[0080] Example 5

[0081] A halogen-free pre-coated soldering flux for nickel plating is composed of the following components:

[0082] The modified rosin is a mixture of ice white rosin and AXE, with a mass ratio of 30%, ice white rosin: AXE = 2:1, the active agent is a mixture of succinic acid and palmitic acid, with a mass ratio of 8%, succinic acid: palmitic acid = 2:6, the corrosion inhibitor is triethanolamine, with a mass ratio of 3%, the surfactant octylphenol polyoxyethylene ether has a mass ratio of 1%, the corrosion inhibitor benzotriazole has a mass ratio of 1.5%, the additive picolinic acid has a mass ratio of 1.5%, and the balance is 1,2-propylene glycol solution.

[0083] The preparation method and coating method thereof include the following steps:

[0084] 1) Weighing an appropriate amount of 1,2-propylene glycol according to the weight percentage and heating it in a water bath at 85° C. in a reactor;

[0085] 2) After the temperature rises to 85° C., weigh ice white rosin and AXE according to the formula and add them to the reactor in (1). After magnetic stirring for 10 minutes, the ice white rosin and AXE are completely dissolved in 1,2-propylene glycol, and the solution is light yellow and transparent;

[0086] 3) According to the formula, weigh powdered succinic acid, palmitic acid, benzotriazole, and picolinic acid, mix them evenly, and add them to the solution in (2), and stir them magnetically for 10 minutes to completely dissolve the powdered reagents in the solution;

[0087] 4) weighing triethanolamine and octylphenol polyoxyethylene ether according to the formula and adding them to the solution in (3), and stirring magnetically for 10 minutes to obtain a pre-coating flux for nickel-plated alloy soldering;

[0088] 5) Lay the solder sheet flat on the plastic board, preheat at 110℃ for 30s, use a dropper to add flux to the solder sheet, evenly apply flux on the solder sheet, heat and bake at 110℃ for about 30min, dry and cool to obtain the pre-flux-coated solder sheet.

[0089] The coating flux prepared in this case can be used for coating of various solder sheets, such as Sn63Pb37, SAC305 and other solder sheets. The flux is in liquid state before coating, which is convenient for controlling the thickness of the flux coating layer and can evenly distribute the active ingredients of the flux, thus avoiding uneven spreading of the solder sheet during welding and reducing pores. At the same time, the 2-pyridinecarboxylic acid in the flux is evenly coated on the preformed solder sheet in the liquid flux. When welding with the nickel-plated substrate, the contact area is large and the reaction is sufficient, which can effectively increase the solder spreading rate and spreading area.

[0090] Example 6

[0091] A halogen-free pre-coated soldering flux for nickel plating is composed of the following components:

[0092] The modified rosin is a mixture of hydrogenated rosin and ice white rosin, with a mass ratio of 28%, hydrogenated rosin: ice white rosin = 3:1, the activator is a mixture of glutaric acid and stearic acid, with a mass ratio of 9%, succinic acid: palmitic acid = 2:7, the corrosion inhibitor is triethanolamine, with a mass ratio of 3%, the surfactant alkylphenol polyoxyethylene ether has a mass ratio of 1%, the corrosion inhibitor benzotriazole has a mass ratio of 1%, the additive picolinic acid has a mass ratio of 2%, and the balance is 1,2-propylene glycol solution.

[0093] The preparation method and coating method thereof include the following steps:

[0094] 1) Weighing an appropriate amount of 1,2-propylene glycol according to the weight percentage and heating it in a water bath at 85° C. in a reactor;

[0095] 2) After the temperature rises to 85° C., weigh hydrogenated rosin and ice white rosin according to the formula and add them to the reactor in (1). After magnetic stirring for 10 minutes, the hydrogenated rosin and ice white rosin are completely dissolved in 1,2-propylene glycol, and the solution is light yellow and transparent;

[0096] 3) According to the formula, weigh powdered succinic acid, palmitic acid, benzotriazole, and picolinic acid, mix them evenly, and add them to the solution in (2), and stir them magnetically for 10 minutes to completely dissolve the powdered reagents in the solution;

[0097] 4) weighing triethanolamine and alkylphenol polyoxyethylene ether according to the formula and adding them to the solution in (3), and stirring magnetically for 10 minutes to obtain a pre-coating flux for nickel-plated alloy soldering;

[0098] 5) Lay the solder sheet flat on the plastic board, preheat at 110℃ for 30s, use a dropper to add flux to the solder sheet, evenly apply flux on the solder sheet, heat and bake at 110℃ for about 30min, dry and cool to obtain the pre-flux-coated solder sheet.

[0099] The pre-coated flux-molded solder sheet in this case has excellent performance and can effectively weld metals such as nickel and nickel alloys. The addition of 2-pyridine carboxylate can enhance the activity of the flux, and its metal complex can greatly promote the welding reaction and effectively improve the wetting rate and anti-retraction ability.

[0100] By adding 2-pyridinecarboxylic acid, the spreading rate is improved to different degrees (as shown in Table 1). After adding 2-pyridinecarboxylic acid, the improvement in the above cases is 5.36%, 4.97%, 7.04%, 4.90%, 3.21%, and 5.18%. By adding additives to improve the spreading rate, dewetting and dewetting do not occur during welding.

[0101] Table 1 Comparison of spreading rate before and after adding 2-pyridine carboxylic acid

[0102]

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application rather than to limit the technical solution. Although the applicant has described the present application in detail with reference to the preferred embodiments, ordinary technicians in this field should understand that those modifications or equivalent substitutions of the technical solution of the present application without departing from the purpose and scope of the technical solution of the present application should be included in the scope of the claims of the present application.

Claims

1. A halogen-free pre-coated soldering flux for nickel plating, characterized in that: The components by weight percentage include: Modified rosin 10% to 50%, active agent 1.0% to 10%, surfactant 0.5% to 2.0%, antioxidant 1.0% to 3.0%, corrosion inhibitor 1.0% to 3.0%, additive 1.0% to 3.0%, the rest is solvent, and the total mass percentage of all components is 100%; The modified rosin is any one of AXE, ice white rosin, water white rosin, hydrogenated rosin, or a mixture of two of them with a mass ratio of each greater than 0%; The active agent is a mixture of at least two of succinic acid, sebacic acid, stearic acid, glutaric acid, salicylic acid, DL-malic acid, palmitic acid, azelaic acid, etc., each of which is greater than 0% by mass; The surfactant is one or two of octylphenol polyoxyethylene ether, nonylphenol polyoxyethylene ether and alkylphenol polyoxyethylene ether; The antioxidant is benzotriazole; The corrosion inhibitor is triethanolamine; The additive is picolinic acid; The solvent is either 1,2-propylene glycol or isopropanol.

2. The method for preparing a halogen-free pre-coated soldering flux for nickel plating according to claim 1, characterized in that: It includes the following steps: (1) Weighing the formula components according to the weight percentage, then placing the active agent, antioxidant, and additive into a container in sequence, and stirring continuously for 5 minutes to 10 minutes to mix them evenly; (2) Add modified rosin and solvent to another reactor, heat in a water bath at 75°C to 95°C and stir magnetically for 5 minutes to 10 minutes to completely dissolve the rosin in the solvent. The dissolved solution is a light yellow transparent liquid. (3) Slowly add the powdery mixed agent obtained by mixing evenly in the above step (1) to the above solution (2), heat it in a water bath at 75°C to 95°C, stir it magnetically for 5min to 10min, then add the corrosion inhibitor and surfactant and continue stirring for 5min to 10min. After all the raw materials are mixed and dissolved evenly, a halogen-free pre-coated soft soldering flux for nickel plating is obtained.

3. A method for coating a nickel-plated layer with a halogen-free pre-coated soldering flux according to claim 1, characterized in that: The following steps are involved: Prepare a constant temperature water bath with flux according to the original component materials, lay the soldering sheet flat on a polytetrafluoroethylene plastic plate and preheat it at 90°C to 100°C for half a minute, drop appropriate constant temperature pre-coating flux solution on the soldering sheet, apply it evenly and heat and dry it, and then cool it to room temperature to obtain a pre-coated flux molded soldering sheet.

4. A method for coating a nickel-plated layer with a halogen-free pre-coated soldering flux according to claim 3, characterized in that: The water bath constant temperature is 75° C. to 95° C., the drying temperature is 90° C. to 115° C., and the drying time is 30 min to 60 min.

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