Residue-free soldering flux and soldering paste for formic acid atmosphere welding and preparation method of residue-free soldering flux and soldering paste

Abstract

The invention belongs to the technical field of electronic welding materials, and particularly relates to a residue-free soldering flux and soldering paste for formic acid atmosphere welding and a preparation method of the residue-free soldering flux and soldering paste for formic acid atmosphere welding, and the residue-free soldering flux for formic acid atmosphere welding comprises, by weight, 46-55 parts of solvent, 19-29 parts of thixotropic agent, 12-24 parts of active agent and 6-15 parts of flatting agent. The soldering flux is high in applicability, and at least solves the problems of electronic welding material residues and hole inhibition in the formic acid environment.

Description

Technical Field

[0001] The invention relates to the technical field of electronic welding materials, and in particular to a residue-free soldering flux and solder paste for formic acid atmosphere welding and a preparation method thereof. Background Art

[0002] Solder paste welding is a welding technology widely used in the electronics manufacturing industry, such as computers, communications, consumer electronics, automotive electronics, LED lighting and solar photovoltaics. In these fields, solder paste welding technology provides a strong guarantee for the high performance and high reliability of electronic products. Solder paste is composed of metal alloy powder and flux. It is melted at high temperature through reflow heating and penetrates into the contact points between electronic components and circuit boards, thereby achieving the connection between electronic components and circuit boards. Organic additives play a fixing and supporting role during the melting process, ensuring the stability and reliability of the soldering connection.

[0003] Formic acid reflow soldering is a new application technology. It uses the chemical reaction between formic acid and metal oxides. Hydroxyl replaces oxygen atoms to form formate. Formate decomposes at high temperature to form metal elements. The reaction equations are as follows (1) and (2). The heat generated in this process is used to heat and melt the solder, thereby realizing the welding process and eliminating the adverse effects of metal oxides on solder joints.

[0004] SnO2+4HCOOH=Sn(COOH)4+2H2O Formula (1)

[0005] Sn(COOH)4→4CO2+Sn+2H2 Formula (2)

[0006] However, in actual applications, the existing solder paste often has a lot of residue after welding in a formic acid atmosphere, which not only affects the appearance, but also poses a potential threat to the reliability of the application. In particular, when electronic equipment is exposed to high temperature and humidity for a long time, the accumulation of flux residues can easily cause serious problems such as circuit insulation aging, short circuits and corrosion, making the welding quality unstable and ultimately affecting the long-term stable operation of electronic products. Although there are fluxes with washable residues, it will undoubtedly increase the consumption of cleaning agents and labor costs, which will lead to an increase in overall production costs.

[0007] Therefore, the existing solder paste and soldering flux thereof still need to be improved. Summary of the invention

[0008] The main purpose of the present invention is to provide a residue-free soldering flux and solder paste for formic acid atmosphere welding and a preparation method thereof. The soldering flux has strong applicability and at least solves the problems of residual electronic soldering materials and void suppression in a formic acid environment.

[0009] The first aspect of the present invention provides a residue-free soldering flux for formic acid atmosphere welding, the soldering flux comprising the following components in parts by weight: 46 to 55 parts of a solvent, 19 to 29 parts of a thixotropic agent, 12 to 24 parts of an activator, and 6 to 15 parts of a leveling agent.

[0010] In some embodiments of the present invention, the solvent includes one or more combinations of isopropanol, n-butanol, hexylene glycol, rosin alcohol, tripropylene glycol butyl ether, terpineol, ethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol butyl ether, 2-ethyl-1,3-hexanediol, diethylene glycol hexyl ether, glycerol, propylene glycol, dibasic acid esters, diethyl adipate, butyl formate, pentyl formate, diglycidyl ether, dioctyl phthalate, tetraethylene glycol, isohexadecanol, diethylene glycol butyl ether acetate, and nitroethane mixed solvent.

[0011] In some embodiments of the present invention, the thixotropic agent includes at least one of a wax thixotropic agent and an amide thixotropic agent.

[0012] In some embodiments of the present invention, the wax-based thixotropic agent comprises methyl hydrogenated castor oil.

[0013] In some embodiments of the present invention, the amide thixotropic agent includes one or more combinations of polyamide wax, erucamide, octadecyl stearamide, lauric acid amide, fatty acid triglyceride, oleic acid amide, p-toluene methane amide, and fatty acid ester amide.

[0014] In some embodiments of the present invention, the active agent includes one or more combinations of stearic acid, propylenediamine phosphate, 2,2-dihydroxymethylbutyric acid, p-tert-butylbenzoic acid, 4-methyl-2-phenylimidazole, citric acid, dibromosuccinic acid, ethylenebisstearamide, suberic acid, oxalic acid, malic acid, glutaric acid, tetradecanoic acid, octadecanoic acid, dioctyl sebacate, dioctyl caproate, methylsuccinic acid, stearic acid, phthalic acid, glutamic acid, glycine, 2-methylbenzimidazole, 2-undecylimidazole, 2-methylacetic acid, 2-phenylbutyric acid, N-ethylimidazole, and benzimidazole.

[0015] In some embodiments of the present invention, the leveling agent includes one or more of potassium monododecyl phosphate, dodecyltrimethylammonium chloride, fatty alcohol polyoxyethylene ether, trisodium citrate, pentaerythritol hexadecanoate, sodium hypophosphite, nonylphenol polyoxyethylene ether, imidazoline, and alkylphenol polyoxyethylene ether.

[0016] The second aspect of the present invention provides a method for preparing the residue-free flux for formic acid atmosphere welding described in the first aspect, the preparation method comprising: adding the components forming the flux into a reaction container according to the required ratio, and performing a first stirring after each component is added, and performing a second stirring after all components are added to obtain the flux.

[0017] In some embodiments of the present invention, the first stirring is performed at 60° C. to 100° C., and the speed of the first stirring is 8 rpm / min to 12 rpm / min.

[0018] In some embodiments of the present invention, the second stirring speed is 10 rpm / min to 20 rpm / min.

[0019] The third aspect of the present invention provides a residue-free solder paste for formic acid atmosphere welding, the solder paste comprising the following components in mass percentage: 86wt% to 90wt% of alloy powder and 10wt% to 14wt% of flux; wherein the flux is the residue-free flux for formic acid atmosphere welding described in the first aspect or the flux prepared by the preparation method of the residue-free flux for formic acid atmosphere welding described in the second aspect.

[0020] The fourth aspect of the present invention provides a method for preparing the residue-free solder paste for formic acid atmosphere welding described in the third aspect, the preparation method comprising: mixing alloy powder and flux in a required ratio, and vacuuming to obtain the solder paste.

[0021] The invention provides a non-residue soldering flux for formic acid atmosphere welding, the equipment and material costs required for using the soldering flux are low, and the formula and manufacturing process are convenient. In addition, formic acid acts as a reducing agent and soldering flux, can form a protective film on the metal surface, slow down the oxidation rate, help maintain the cleanliness of the metal surface during welding, and improve the welding quality.

[0022] The residue-free soldering flux for formic acid atmosphere welding provided by the invention has a simple formula and a production process and can be applied to a variety of solder alloys.

[0023] The residue-free solder paste for formic acid atmosphere welding provided by the present invention can effectively reduce the generation of voids inside the solder layer and the surface tension of the liquid metal during the welding process, has strong applicability, and improves the wetting performance, so that the liquid metal can be better spread on the solid metal surface and fill the weld.

[0024] The residue-free solder paste for formic acid atmosphere welding provided by the present invention has the advantages of low welding void rate and strong wettability, and also has the advantages of no residue in the post-welding system, and the welding layer can withstand large mechanical stress and thermal stress, thereby ensuring the long-term reliability of the product.

[0025] The residue-free soldering flux and solder paste for formic acid atmosphere welding provided by the present invention provide a new solution to the technical problems of electronic welding material residue and void suppression in a formic acid environment.

[0026] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented according to the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only used for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. In the accompanying drawings:

[0028] Figure 1 The wetting and residue diagrams of the solder pastes prepared in the examples and comparative examples are shown in FIG. Figure 1 (a)~ Figure 1 (d) are the wetting and residue diagrams of the solder pastes prepared in Examples 1 to 4; Figure 1 (e)~ Figure 1 (f) are the wetting and residue diagrams of the solder pastes prepared in Comparative Examples 1 and 2;

[0029] Figure 2 is the void ratio of the solder paste obtained in the embodiment and the comparative example; wherein, Figure 2 (a)~ Figure 2 (d) are the void ratios of the solder pastes prepared in Examples 1 to 4, respectively; Figure 2 (e)~ Figure 2 (f) are the void ratios of the solder pastes prepared in Comparative Examples 1 and 2, respectively. DETAILED DESCRIPTION

[0030] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of the concept of the present invention.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which the present invention belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention; the terms "including" and "having" in the specification and claims of the present invention and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0032] In the description of the embodiments of the present invention, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present invention, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0033] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0034] In the description of the embodiments of the present invention, the term "and / or" is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0035] In the description of the embodiments of the present invention, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0036] The first aspect of the present invention provides a residue-free soldering flux for formic acid atmosphere welding, which comprises the following components in parts by weight: 46 to 55 parts of a solvent, 19 to 29 parts of a thixotropic agent, 12 to 24 parts of an activator, and 6 to 15 parts of a leveling agent.

[0037] In the embodiments of the present invention, the formula of the residue-free soldering flux for formic acid atmosphere soldering is simple, and through component design, the content of each component is precisely controlled, and the interaction relationship between each component is optimized, so as to achieve excellent compatibility with the formic acid reflow soldering process, not only the system after soldering presents a residue-free state, but also the generation of voids inside the solder layer and the surface tension of the liquid metal during the soldering process can be effectively reduced, the wettability is significantly improved, the oxidation rate is slowed down, and the solder joint is fully filled. In addition, the soldering flux provided by the present invention has strong applicability, and provides a new solution to the technical problems of residual electronic soldering materials and void suppression in formic acid environments.

[0038] In an embodiment of the present invention, the weight fraction of the solvent is 46 to 55 parts. For example, the weight fraction of the solvent can be one of 46 parts, 47 parts, 48 ​​parts, 49 parts, 50 parts, 51 parts, 52 parts, 53 parts, 54 parts, 55 parts, or any value satisfying the above range.

[0039] In an embodiment of the present invention, the solvent includes one or more combinations of isopropanol, n-butanol, hexylene glycol, rosin alcohol, tripropylene glycol butyl ether, pinene alcohol, ethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol butyl ether, 2-ethyl-1,3-hexanediol, diethylene glycol hexyl ether, glycerol, propylene glycol, dibasic acid esters, diethyl adipate, butyl formate, pentyl formate, diglycidyl ether, dioctyl phthalate, tetraethylene glycol, isohexadecanol, diethylene glycol butyl ether acetate, and nitroethane mixed solvent.

[0040] In an embodiment of the present invention, the weight percentage of the thixotropic agent is 19 to 29 parts. For example, the weight percentage of the thixotropic agent can be one of 19 parts, 20 parts, 21 parts, 22 parts, 23 parts, 24 parts, 25 parts, 26 parts, 27 parts, 28 parts, 29 parts, or any value satisfying the above range.

[0041] In an embodiment of the present invention, the thixotropic agent includes at least one of a wax thixotropic agent and an amide thixotropic agent.

[0042] In some embodiments of the present invention, the wax-based thixotropic agent may be, but is not limited to, methyl hydrogenated castor oil.

[0043] In some embodiments of the present invention, the amide thixotropic agent includes one or more combinations of polyamide wax, erucamide, octadecyl stearamide, lauric acid amide, fatty acid triglyceride, oleic acid amide, p-toluene methane amide, and fatty acid ester amide.

[0044] In an embodiment of the present invention, the weight percentage of the active agent is 12 to 24. For example, the weight percentage of the active agent can be 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 or any value satisfying the above range.

[0045] In an embodiment of the present invention, the active agent includes one or more combinations of stearic acid, propylenediamine phosphate, 2,2-dihydroxymethylbutyric acid, p-tert-butylbenzoic acid, 4-methyl-2-phenylimidazole, citric acid, dibromosuccinic acid, ethylenebisstearamide, suberic acid, oxalic acid, malic acid, glutaric acid, tetradecanoic acid, octadecanoic acid, dioctyl sebacate, dioctyl caproate, methylsuccinic acid, stearic acid, phthalic acid, glutamic acid, glycine, 2-methylbenzimidazole, 2-undecylimidazole, 2-methylacetic acid, 2-phenylbutyric acid, N-ethylimidazole, and benzimidazole.

[0046] In an embodiment of the present invention, the weight proportion of the leveling agent is 6 to 15 parts. For example, the weight proportion of the leveling agent can be 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 parts or any value satisfying the above range.

[0047] In an embodiment of the present invention, the leveling agent includes one or more of potassium monododecyl phosphate, dodecyltrimethylammonium chloride, fatty alcohol polyoxyethylene ether, trisodium citrate, pentaerythritol hexadecanoate, sodium hypophosphite, nonylphenol polyoxyethylene ether, imidazoline, and alkylphenol polyoxyethylene ether.

[0048] The second aspect of the present invention provides a method for preparing a residue-free flux for formic acid atmosphere welding. The key lies in that the components forming the flux are added into a reaction container respectively according to the required ratio, and a first stirring is performed after each component is added, and a second stirring is performed after all components are added to obtain the flux.

[0049] In the embodiments of the present invention, the manufacturing process of the flux for formic acid atmosphere welding provided by the present invention is convenient. Not only does the system present a residue-free state after welding, but it can also effectively reduce the generation of voids inside the weld layer and the surface tension of the liquid metal during welding, significantly improve wettability, slow down the oxidation rate, and fully fill the weld.

[0050] In an embodiment of the present invention, the first stirring is performed at 60°C to 100°C, and the speed of the first stirring is 8rpm / min to 12rpm / min. Exemplarily, the temperature of the first stirring may be one of 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, or any value satisfying the above range. The first stirring speed may be one of 8rpm / min, 9rpm / min, 10rpm / min, 11rpm / min, 12rpm / min, or any value satisfying the above range.

[0051] In an embodiment of the present invention, the second stirring speed is 10 rpm / min to 20 rpm / min. Exemplarily, the second stirring speed can be one of 10 rpm / min, 11 rpm / min, 12 rpm / min, 13 rpm / min, 14 rpm / min, 15 rpm / min, 16 rpm / min, 17 rpm / min, 18 rpm / min, 19 rpm / min, 20 rpm / min or any value satisfying the above range.

[0052] In an embodiment of the present invention, a method for preparing a residue-free flux for formic acid atmosphere welding includes: accurately weighing each component and adding them into a reaction container respectively, and stirring at 60°C to 100°C for 8min to 12min after each component is added, and stirring for another 15min to 25min after all components are added to obtain the flux.

[0053] In an embodiment of the present invention, the stirring time after each component is added can be one of 8min, 9min, 10min, 11min, 12min or any value satisfying the above range. The stirring time after all components are added can be one of 15min, 16min, 17min, 18min, 19min, 20min, 21min, 22min, 23min, 24min, 25min or any value satisfying the above range.

[0054] In an embodiment of the present invention, the prepared soldering flux is finely ground and left to stand for 24 hours.

[0055] In an embodiment of the present invention, the reaction container may be a reaction kettle.

[0056] The third aspect of the present invention provides a residue-free solder paste for formic acid atmosphere welding, which comprises the following components in mass percentage: 86wt% to 90wt% of alloy powder and 10wt% to 14wt% of flux; wherein the flux is the residue-free flux for formic acid atmosphere welding described in the first aspect or the flux prepared by the preparation method of the residue-free flux for formic acid atmosphere welding described in the second aspect.

[0057] In an embodiment of the present invention, the alloy powder may be, but is not limited to, one of Sn5Ag2.5Pb92.5 powder, Sn5Ag1.5Pb93.5 powder, Sn5Ag2.2Pb92.8 powder, and Sn2Ag2.5Pb95.5 powder.

[0058] In an embodiment of the present invention, the mass percentage of the alloy powder may be one of 86wt%, 87wt%, 88wt%, 89wt%, 90wt% or any value within the above range. The mass percentage of the flux may be one of 10wt%, 11wt%, 12wt%, 13wt%, 14wt% or any value within the above range.

[0059] The fourth aspect of the present invention provides a method for preparing a residue-free solder paste for formic acid atmosphere welding, the key of which is to mix and stir the alloy powder and the flux in a required ratio, and evacuate to obtain the solder paste.

[0060] In an embodiment of the present invention, the flux is first stirred evenly, and the stirring speed is 8rpm / min to 12rpm / min. For example, the stirring speed can be one of 8rpm / min, 9rpm / min, 10rpm / min, 11rpm / min, 12rpm / min or any value satisfying the above range of values; the stirring time is 8min to 10min. For example, the stirring time can be one of 8min, 9min, 10min or any value satisfying the above range of values.

[0061] Then, the powder is added to the flux under stirring, and the stirring speed is 6 rpm / min to 10 rpm / min, for example, the stirring speed can be one of 6 rpm / min, 7 rpm / min, 8 rpm / min, 9 rpm / min, 10 rpm / min or any value satisfying the above range; the stirring time is 1 min to 3 min, for example, the stirring time can be one of 1 min, 2 min, 3 min or any value satisfying the above range, to obtain solder paste.

[0062] Then, the solder paste is stirred at a speed of 6 rpm / min to 10 rpm / min, for example, the stirring speed may be one of 6 rpm / min, 7 rpm / min, 8 rpm / min, 9 rpm / min, 10 rpm / min or any value satisfying the above range; the stirring time is 1 min to 3 min, for example, the stirring time may be one of 1 min, 2 min, 3 min or any value satisfying the above range; then, vacuum stirring is performed at a stirring speed of 16 rpm / min to 20 rpm / min, for example, the stirring speed may be 16 rpm / min. m / min, 17rpm / min, 18rpm / min, 19rpm / min, 20rpm / min or any value satisfying the above range; the stirring time is 8min~12min, for example, the stirring time can be 8min, 9min, 10min, 11min, 12min or any value satisfying the above range, and the vacuum degree is evacuated to -0.08Mpa~-0.1Mpa, for example, it is evacuated to one of -0.08Mpa, -0.09Mpa, -0.1Mpa or any value satisfying the above range, to obtain solder paste.

[0063] Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. The experimental reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the raw materials, instruments and equipment used in the following examples, etc., can all be purchased on the market or can be obtained by existing methods; the amounts of the experimental reagents, unless otherwise specified, are the amounts of reagents used in conventional experimental operations; the experimental methods, unless otherwise specified, are all conventional methods.

[0064] Example 1

[0065] A residue-free soldering flux for formic acid atmosphere welding comprises the following components in parts by weight: 9 parts of isopropyl alcohol, 41 parts of 2-ethyl-1,3-hexanediol, 14 parts of methyl hydrogenated castor oil, 10 parts of p-toluene methane amide, 6 parts of p-tert-butylbenzoic acid, 4 parts of phthalic acid, 7 parts of 2-methylbenzimidazole, 2 parts of dodecyltrimethylammonium chloride, 6 parts of trisodium citrate and 1 part of nonylphenol polyoxyethylene ether.

[0066] The preparation method of the residue-free soldering flux for formic acid atmosphere welding is as follows: the above components are added into a reaction kettle respectively, and after each component is added, they are stirred at 80°C for 10 minutes at a stirring speed of 10 rpm / min. After all the components are added, they are stirred for another 15 minutes at a stirring speed of 15 rpm / min. Thereafter, they are finely ground and placed for 24 hours to return to room temperature to obtain the residue-free soldering flux.

[0067] A residue-free solder paste for formic acid atmosphere welding comprises the following components in percentage by mass: 88% of Sn5Ag2.5Pb92.5 powder and 12% of soldering flux.

[0068] The preparation method of solder paste for formic acid atmosphere welding is as follows: the flux is put into a reaction kettle, the stirring speed is 12 rpm / min, and the stirring time is 10 min; then the powder is added while stirring for 1 min, and the stirring speed is 8 rpm / min; then the obtained solder paste is stirred for 1 min, and the stirring speed is 8 rpm / min; then vacuum stirring is performed for 10 min, and the stirring speed is 18 rpm / min, and the vacuum degree is evacuated to -0.08 Mpa to obtain the solder paste prepared by the above flux.

[0069] Finally, the solder paste prepared in Example 1 was soldered in a formic acid atmosphere, and the residual condition was observed by microscope and the existence of internal voids was observed by X-Ray.

[0070] Example 2

[0071] The remaining operations are the same as those in Example 1, except that the residue-free soldering flux used for formic acid atmosphere welding in Example 2 includes the following components in parts by weight: 8 parts of isopropyl alcohol, 43 parts of 2-ethyl-1,3-hexanediol, 12 parts of methyl hydrogenated castor oil, 12 parts of p-toluene methane amide, 8 parts of p-tert-butyl benzoic acid, 2 parts of phthalic acid, 5 parts of 2-methylbenzimidazole, 4 parts of dodecyltrimethylammonium chloride, 3 parts of trisodium citrate, and 3 parts of nonylphenol polyoxyethylene ether.

[0072] The residue-free solder paste used for formic acid atmosphere welding in Example 2 includes the following components in percentage by mass: 88% Sn5Ag1.5Pb93.5 powder and 12% soldering flux.

[0073] Example 3

[0074] The remaining operations are the same as those in Example 1, except that the residue-free soldering flux used for formic acid atmosphere welding in Example 3 includes the following components in parts by weight: 10 parts of isopropyl alcohol, 38 parts of 2-ethyl-1,3-hexanediol, 16 parts of methyl hydrogenated castor oil, 7 parts of p-toluene methane amide, 7 parts of p-tert-butylbenzoic acid, 5 parts of phthalic acid, 4 parts of 2-methylbenzimidazole, 5 parts of dodecyltrimethylammonium chloride, 7 parts of trisodium citrate, and 1 part of nonylphenol polyoxyethylene ether.

[0075] The residue-free solder paste used for formic acid atmosphere welding in Example 3 includes the following components in percentage by mass: 88% Sn5Ag2.2Pb92.8 powder and 12% soldering flux.

[0076] Example 4

[0077] The remaining operations are the same as those in Example 1, except that the residue-free soldering flux used for formic acid atmosphere welding in Example 4 includes the following components in parts by weight: 9 parts of isopropyl alcohol, 45 parts of 2-ethyl-1,3-hexanediol, 12 parts of methyl hydrogenated castor oil, 13 parts of p-toluene methane amide, 8 parts of p-tert-butyl benzoic acid, 3 parts of phthalic acid, 9 parts of 2-methylbenzimidazole, 3 parts of dodecyltrimethylammonium chloride, 5 parts of trisodium citrate, and 2 parts of nonylphenol polyoxyethylene ether.

[0078] The residue-free solder paste used for formic acid atmosphere welding in Example 4 includes the following components in percentage by mass: 88% Sn2Ag2.5Pb95.5 powder and 12% soldering flux.

[0079] Comparative Example 1

[0080] Comparative Example 1 uses commercially available soldering flux 1 of the same specification, and the remaining operations are the same as those of Example 1.

[0081] Comparative Example 2

[0082] Example 2 uses commercially available soldering flux 2 of the same specification, and the remaining operations are the same as Example 1.

[0083] In the present invention, the solder pastes prepared in the embodiments and comparative examples were subjected to relevant performance tests, and the test results are shown in Table 1.

[0084] Table 1 Summary of performance tests of solder pastes obtained in Examples and Comparative Examples

[0085]

[0086]

[0087] Combined with Figure 1-2 As shown in Table 1, multiple groups of solder pastes were prepared by using the flux of the present invention in combination with different alloy powders. After welding in a formic acid atmosphere, not only was there almost no residue after welding, but the solder joints were bright and showed an ultra-low void rate of less than 5%. Among them, the solder paste prepared using Sn5Ag2.5Pb92.5-T4 powder had the lowest void rate of 1.78%.

[0088] At the same time, by using commercially available flux as a comparative example, it can be seen that the flux for formic acid atmosphere welding provided by the present invention has a convenient formula and production process, not only the system is in a residue-free state after welding, but also the generation of voids inside the weld layer and the surface tension of the liquid metal during welding can be effectively reduced, the wettability can be significantly improved, the oxidation rate can be slowed down, and the weld can be fully filled.

[0089] In summary, the soldering flux for formic acid atmosphere welding provided by the present invention has strong applicability and provides a new solution to the technical problems of electronic welding material residue and void suppression in a formic acid environment.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention. In particular, as long as there is no structural conflict, the various technical features mentioned in each embodiment can be combined in any way. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A residue-free soldering flux for formic acid atmosphere welding, characterized in that: The soldering flux comprises the following components in parts by weight: 46 to 55 parts of solvent, 19 to 29 parts of thixotropic agent, 12 to 24 parts of activator, and 6 to 15 parts of leveling agent.

2. The residue-free soldering flux for formic acid atmosphere welding according to claim 1, characterized in that: The solvent includes one or more combinations of isopropanol, n-butanol, hexylene glycol, rosin alcohol, tripropylene glycol butyl ether, terpineol, ethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol butyl ether, 2-ethyl-1,3-hexanediol, diethylene glycol hexyl ether, glycerol, propylene glycol, dibasic acid esters, diethyl adipate, butyl formate, pentyl formate, diglycidyl ether, dioctyl phthalate, tetraethylene glycol, isohexadecanol, diethylene glycol butyl ether acetate, and nitroethane mixed solvent.

3. The residue-free soldering flux for formic acid atmosphere welding according to claim 1, characterized in that: The thixotropic agent includes at least one of a wax thixotropic agent and an amide thixotropic agent.

4. The residue-free soldering flux for formic acid atmosphere welding according to claim 3, characterized in that: The wax thixotropic agent comprises methyl hydrogenated castor oil; Preferably, the amide thixotropic agent includes one or more combinations of polyamide wax, erucamide, octadecyl stearamide, lauric acid amide, fatty acid triglyceride, oleic acid amide, p-toluene methane amide, and fatty acid ester amide.

5. The residue-free soldering flux for formic acid atmosphere welding according to claim 1, characterized in that: The active agent includes one or more combinations of stearic acid, propylene diamine phosphate, 2,2-dihydroxymethylbutyric acid, p-tert-butylbenzoic acid, 4-methyl-2-phenylimidazole, citric acid, dibromosuccinic acid, ethylene bisstearic acid amide, suberic acid, oxalic acid, malic acid, glutaric acid, tetradic acid, octadecanoic acid, dioctyl sebacate, dioctyl caproate, methylsuccinic acid, stearic acid, phthalic acid, glutamic acid, glycine, 2-methylbenzimidazole, 2-undecylimidazole, 2-methylacetic acid, 2-phenylbutyric acid, N-ethylimidazole, and benzimidazole.

6. The residue-free soldering flux for formic acid atmosphere welding according to claim 1, characterized in that: The leveling agent comprises one or more of potassium monododecyl phosphate, dodecyl trimethyl ammonium chloride, fatty alcohol polyoxyethylene ether, trisodium citrate, pentaerythritol hexadecanoate, sodium hypophosphite, nonylphenol polyoxyethylene ether, imidazoline, and alkylphenol polyoxyethylene ether.

7. A method for preparing a residue-free soldering flux for formic acid atmosphere welding according to any one of claims 1 to 6, characterized in that: The preparation method comprises: The components for forming the soldering flux are added into a reaction container respectively according to the required ratio, and a first stirring is performed after each component is added, and a second stirring is performed after all the components are added, so as to obtain the soldering flux.

8. The method for preparing a residue-free soldering flux for formic acid atmosphere welding according to claim 7, characterized in that: The first stirring is performed at 60° C. to 100° C., and the speed of the first stirring is 8 rpm / min to 12 rpm / min; Preferably, the second stirring speed is 10 rpm / min to 20 rpm / min.

9. A residue-free solder paste for formic acid atmosphere welding, characterized in that: The solder paste comprises the following components by mass percentage: Alloy powder 86wt%~90wt%, flux 10wt%~14wt%; Wherein, the flux is the residue-free flux for formic acid atmosphere welding as described in any one of claims 1-6 or the flux prepared by the preparation method of the residue-free flux for formic acid atmosphere welding as described in any one of claims 7-8.

10. A method for preparing a residue-free solder paste for formic acid atmosphere welding according to claim 9, characterized in that: The preparation method comprises: The alloy powder and the flux are mixed and stirred according to the required ratio, and vacuumized to obtain the solder paste.

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