A soldering paste, a preparation method and application thereof

Abstract

The application provides a kind of soldering paste, the components of the soldering paste include film-forming substance 45-65%, organic active ingredient 1-4%, corrosion inhibitor 0.1-1%, surfactant 5-10%, amine substance 0.1-0.8%, thixotropic agent 4-7%, solvent supplementing the balance is 100% by total mass.The prepared soldering paste and soldering paste have excellent storage stability, wettability and expansion rate, good reflow soldering performance, and the yield of soldering can reach more than 95%, the soldering point is bright, and the surface residue is soft and easy to clean.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic device welding, B23K35 / 00, and particularly relates to a soldering flux, a preparation method and application thereof. BACKGROUND

[0002] The soldering flux is widely used in the soldering field of electronic industrial products, and mainly plays the roles of assisting heat conduction, removing surface oxides of a soldering area, creating conditions for spreading of a soldering material on a soldering base material, forming a protective film, preventing re-oxidation of the soldering area, interface activity, reducing surface tension of the soldering material, etc. during the soldering process. The soldering flux effect and post-soldering quality have a crucial influence on the entire production process and the final product quality, and directly affect the reliability and service life of the latter. However, the current soldering flux still has many defects, such as a narrow use temperature range, especially that the active ingredients are prone to failure at high temperatures, low ICT test direct-through rate, poor storage stability, easy occurrence of large particles, stratification and settlement after long-term storage, high soldering product failure rate, insufficient wettability and spreading rate, and weak soldering effect, etc.

[0003] Chinese patent CN103008921B discloses a halogen-free soldering flux for lead-free tin paste and a preparation method thereof. By using organic acid and hydroxyl carboxylic acid as active agents, and oil substances, paraffin release agents and other substances as wetting agents, the wettability and printing performance of the soldering flux are improved. However, the spreading rate is only a little higher than the specified standard, 82-85%, and the spreading rate is still relatively low. Chinese patent CN108788537B discloses a preparation method of a soldering flux. By reducing the crystal size of the soldering flux to the size range of 20 μm through ultrasonic method, the soldering property of the soldering flux is improved. However, the soldering effect is still not enough and needs to be improved. SUMMARY

[0004] In order to solve the above technical problems, the present application first provides a soldering flux. The components of the soldering flux include, by total mass, 45-65% of film-forming substances, 1-4% of organic active ingredients, 0.1-1% of corrosion inhibitors, 5-10% of surfactants, 0.1-0.8% of amine substances, 4-7% of thixotropic agents, and the balance of solvents.

[0005] Further, the film-forming substances are selected from at least one of water white rosin, hydrogenated rosin, rosin pentaerythritol ester, acrylic modified rosin, and glycerol rosin ester.

[0006] Preferably, the film-forming material comprises hydrogenated rosin and acrylic modified rosin. The use of rosin in the present application enables the soldering paste to form an organic film with high stability, which protects the soldering sites such as solder joints and soldered substrates, and has corrosion resistance and insulation performance; for the acrylic rosin, the polar groups contained therein can increase the compactness of the organic film, but the stability of the acrylic rosin is poor and it is easy to decompose at high temperatures; the number of polar groups in the hydrogenated rosin is small, so it can be used instead of part of the acrylic rosin resin, but the addition amount should not be too much, because the hydrogenated rosin is easy to crystallize, has a low melting point, and leaves more residues after soldering. Optimizing the ratio of the two can remove oxides together with the acidic active agent and increase the protection performance of the soldering sites.

[0007] Further, the acid value of the acrylic modified rosin is 200-250 mgKOH / g, and the softening point is 110-150°C (ring and ball method).

[0008] Preferably, the acid value of the acrylic modified rosin is 230-245 mgKOH / g, and the softening point is 122-132°C.

[0009] Further, the mass ratio of the acrylic modified rosin to the hydrogenated rosin is (1-2):1.

[0010] Further, the organic active ingredient comprises a halogen-containing organic active ingredient and / or a halogen-free organic acid.

[0011] Preferably, the organic active ingredient is a halogen-containing organic active ingredient and a halogen-free organic acid.

[0012] Further, the halogen-free organic acid comprises at least one of, but is not limited to, hydroxyacetic acid, methylmalonic acid, succinic acid, methylsuccinic acid, glutaric acid, adipic acid, citric acid, itaconic acid, malic acid, and dichloroacetic acid.

[0013] Further, the halogen-containing organic active ingredient is selected from at least one of dibromobutyrolactone, 2-chloro-4-bromobenzoic acid, and dibromosuccinic acid.

[0014] Further preferably, the organic active ingredient comprises succinic acid and dibromobutyrolactone; the succinic acid accounts for 0.8-2.5% of the total mass of the soldering paste, and the dibromobutyrolactone accounts for 0.2-1.5% of the total mass of the soldering paste.

[0015] Further, the corrosion inhibitor is a nitrogen-containing heterocyclic substance, which comprises at least one of, but is not limited to, benzotriazole, methylbenzotriazole, 2-mercaptobenzimidazole, 1-vinylimidazole, 2-ethyl-4-methylimidazole, 2-ethylimidazole, and 2-methylimidazole.

[0016] Preferably, the corrosion inhibitor is benzotriazole and / or methylbenzotriazole.

[0017] Further, the components of the solder paste further include a lubricant in an amount of 2.0-4.0% by weight of the total weight of the solder paste.

[0018] Further, the lubricant is liquid rosin or paraffin wax.

[0019] In a preferred embodiment, the lubricant is liquid rosin, such as Super Ester A-18.

[0020] Further, the surfactant includes, but is not limited to, at least two of alkyl phenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, polyethylene glycol monostearate, polyethylene glycol monooleate, alkyl amide polyoxyethylene ether, and alkyl amine polyoxyethylene ether.

[0021] Further, the surfactant is a combination of fatty alcohol polyoxyethylene ether and alkyl amide polyoxyethylene ether.

[0022] Preferably, the fatty alcohol polyoxyethylene ether is C8-C16 fatty alcohol polyoxyethylene ether, and the alkyl amide is C10-C18 alkyl amide polyoxyethylene ether.

[0023] Further, the C8-C16 fatty alcohol polyoxyethylene ether is selected from at least one of isooctyl alcohol polyoxyethylene ether, dipropyl heptyl alcohol polyoxyethylene ether, lauryl alcohol polyoxyethylene ether, tridecanol polyoxyethylene ether, myristyl alcohol polyoxyethylene ether, and cetyl alcohol polyoxyethylene ether.

[0024] Further, the C10-C18 alkyl amide polyoxyethylene ether is preferably lauryl amide polyoxyethylene ether.

[0025] In a preferred embodiment, the surfactant is lauryl alcohol polyoxyethylene ether and lauryl amide polyoxyethylene ether, and the mass ratio is (1.5-3.5):1. The surfactant is used to remove tin powder and oxide film on the solder surface, reduce the surface tension of the tin powder after melting, promote the flow and spreading effect, and improve the wetting performance. When lauryl alcohol polyoxyethylene ether and lauryl amide polyoxyethylene ether are selected and the mass ratio is (1.5-3.5):1, the surface wetting performance is best. The storage stability of the solder paste is also improved, and the solder paste does not separate and settle after long-term storage at low temperature, and the particle size changes little. Lauryl alcohol polyoxyethylene ether mainly plays a role in removing acid oil and removing oxides on the surface of tin powder, and lauryl amide polyoxyethylene ether fully emulsifies and encapsulates the surface oil stains. The combination of the two improves the soldering performance of the solder paste. In addition, the encapsulation of the two on the tin powder and the intermolecular interaction generated thereby effectively prevent the granular tin powder from settling and aggregating in the solder paste. However, when the addition amount is too high or too low, the interaction between the molecular chains is destroyed, the emulsification and encapsulation effect of the two on the oil stains and oxides will be weakened, thereby causing the wetting and soldering performance of the solder paste to decrease, and the tin beads to splash seriously.

[0026] More preferably, the mass ratio of lauryl alcohol polyoxyethylene ether and lauryl amide polyoxyethylene ether is 2.5:1.

[0027] Further, the amine substance includes, but is not limited to, any one of N,N'-bis(3-aminopropyl)ethylenediamine, triethanolamine, and triethylamine.

[0028] Preferably, the amine substance includes triethanolamine.

[0029] Further, the thixotropic agent is selected from at least one of 6500, 6650, and 7000.

[0030] Further, the solvent includes at least one of ethylene glycol, isopropyl alcohol, propylene glycol, glycerol, ethylene glycol dimethyl ether, ethylene glycol butyl ether, ethylene glycol hexyl ether, triethylene glycol propyl ether, triethylene glycol monobutyl ether, triethyl carbitol ether, and diethylene glycol hexyl ether.

[0031] Preferably, the solvent includes ethylene glycol butyl ether and ethylene glycol hexyl ether; the ethylene glycol butyl ether accounts for 5-9% of the total mass of the soldering flux, and the ethylene glycol hexyl ether accounts for 13-22% of the total mass of the soldering flux.

[0032] Further, the solvent also includes an ester substance, which can be selected from at least one of propylene glycol phenyl ether acetate, diethylene glycol butyl ether acetate, tributyl citrate, and trimethylolpropane trioleate.

[0033] Preferably, the solvent further comprises trimethylolpropane trioleate. The present application dissolves and disperses other raw material components of the soldering paste by compounding different solvents, prevents splashing during soldering of the solder paste, thereby causing virtual welding, soldering beads and other adverse phenomena, widens the soldering temperature range of the solder paste by compounding solvents with different boiling points, prevents the problem that the local temperature of the welding area is much higher than the set value due to the instability of the welding process, thereby causing the performance of the welding point to decrease, but the range of the soldering temperature is still not wide enough, and the highest temperature can only reach about 180℃; on this problem, the present inventors break through the limitation that the commonly used solvents in the art are alcohols and ethers, and use trimethylolpropane trioleate with a higher boiling point as a compounded solvent component, so that the highest soldering temperature can reach about 270℃, and the soldering still has excellent reliability; in addition, the use of trimethylolpropane trioleate also significantly improves the spreading rate of the soldering paste, and the reason may be that: trimethylolpropane trioleate contains a large number of polar groups, these polar groups are connected to each other and exhibit excellent hydrophilicity, and the alkyl chain at the other end exhibits lipophilic hydrophobicity, this asymmetric structure can effectively remove the oil stains on the welding surface, so that the addition of lauryl alcohol polyoxyethylene ether and lauryl amide polyoxyethylene ether in the system can enhance the wetting effect of the soldering paste on the welding surface, and effectively improve the spreading rate of the soldering paste.

[0034] More preferably, the trimethylolpropane trioleate accounts for 2-5% of the total mass of the soldering paste.

[0035] Secondly, the present application provides a preparation method of the soldering paste, comprising the following steps:

[0036] (1) The film-forming material, the halogen-free organic acid, the corrosion inhibitor, the fatty alcohol polyoxyethylene ether and the solvent are weighed and mixed and placed in a container, the container is heated and continuously stirred to completely dissolve the mixture;

[0037] (2) After dissolving, the temperature is reduced to 80-90℃, the halogen-containing organic active ingredient and the fatty amide polyoxyethylene ether are added in turn, and the material is cooled to 50-55℃ after stirring;

[0038] (3) The amine material and the thixotropic agent are added and stirred;

[0039] (4) The material is dispersed at high speed and heated to 60-65℃ for 60-100 minutes for emulsification.

[0040] Preferably, in the step (1), the halogen-free organic acid is dissolved in a certain amount of ethylene glycol hexyl ether in the solvent first, and then added. The amount of this part of ethylene glycol hexyl ether accounts for 2-20% of the total mass of the soldering paste, preferably 2-10%; the remaining amount of ethylene glycol hexyl ether is mixed with the film-forming material, the corrosion inhibitor and the fatty alcohol polyoxyethylene ether in step (1) and added.

[0041] Further, a lubricant is added in step (1).

[0042] Further, the heating temperature in step (1) is not more than 175℃, preferably 160-175℃.

[0043] Further, the high-speed dispersion speed in step (4) is 2500-3500rpm.

[0044] Finally, the application also provides the application of the soldering paste in SMT lead-free soldering paste.

[0045] Further, the mass content of the soldering paste in SMT lead-free soldering paste is 10-15%, and the rest is tin powder.

[0046] Further, the application does not strictly regulate the tin powder, which can be preferably sac305 tin powder.

[0047] Advantages

[0048] 1. The application uses different types of film-forming substances and optimizes the mass ratio, improves the protection performance of the soldering layer on the substrate and the solder joint, and improves the reflow soldering yield;

[0049] 2. The application optimizes the type and relative amount of surfactant, so that the tin paste has excellent wettability and spreading rate, and the storage stability of the tin paste at low temperature is also obviously improved. The prepared tin paste does not separate and the particles do not agglomerate after being placed at low temperature for 12 months;

[0050] 3. The application optimizes the type of solvent. When a specific ester solvent is used, not only can the soldering temperature range of the soldering paste be widened, but also the effect of the surfactant can be played, increasing the wettability and spreading rate of the soldering paste and the soldering paste thereof;

[0051] 4. The application adopts a specific preparation process for the components of the soldering paste. On the basis of fully mixing each raw material component, it also ensures that it will not decompose and fail, further optimizes the addition sequence of the components, so that the prepared soldering paste has excellent processability;

[0052] 5. The soldering paste prepared by the application has excellent reflow soldering performance, and the soldering yield can reach more than 95%, and the solder joint is bright, and the surface residue is soft and easy to clean. DETAILED DESCRIPTION

[0053] EMBODIMENT

[0054] EMBODIMENT 1

[0055] The embodiment provides a soldering paste, ingredients of the soldering paste include film forming substance 53%, succinic acid 1.1%, dibromo butene diol 1%, benzotriazole 0.4%, lubricant 3%, surfactant 7%, triethanolamine 0.4%, thixotropic agent 5.7%, ethylene glycol butyl ether 7.6%, ethylene glycol hexyl ether 17.8%, trimethylolpropane trioleate 3% by total mass.

[0056] The film forming substance is acrylic modified rosin ke604 (acid value is 230-245 KOH / g, softening point is 122-132 DEG C) and hydrogenated rosin (model is: isman foralax-e), and the mass ratio is 1.21:1; the lubricant is Super Ester A-18 liquid rosin; the surfactant is lauryl alcohol polyoxyethylene ether and lauryl amide polyoxyethylene ether, and the mass ratio of the two is 2.5:1; the thixotropic agent is polyamide wax 6650;

[0057] The preparation method of the soldering paste comprises the following steps:

[0058] (1) the dibromo butene diol and 4% of ethylene glycol hexyl ether in total mass of the soldering paste are mixed and heated after stirring, the heating temperature is 58 DEG C, after complete dissolution and clarification, natural cooling is carried out, and a dibromo butene diol solution is prepared;

[0059] (2) the film forming substance, succinic acid, benzotriazole, lauryl alcohol polyoxyethylene ether, lubricant, ethylene glycol butyl ether, the rest of ethylene glycol hexyl ether and trimethylolpropane trioleate are weighed and mixed and placed in a container, the container is heated and continuously stirred, the temperature is controlled to be 170 DEG C, and the mixture is completely dissolved;

[0060] (3) after dissolution, the temperature is reduced to 88 DEG C, the dibromo butene diol solution is added and stirred, then lauryl amide polyoxyethylene ether is added, and after stirring, the material is cooled to 53 DEG C;

[0061] (4) triethanolamine and thixotropic agent are added and stirred;

[0062] (5) the material is dispersed at high speed under 3000 rpm and emulsified for 80 minutes after being heated to 63 DEG C.

[0063] Embodiment 2

[0064] The embodiment provides a soldering paste, ingredients of the soldering paste include film forming substance 63.7%, succinic acid 2.2%, dibromo butene diol 0.2%, benzotriazole 0.1%, lubricant 4.0%, surfactant 5%, triethanolamine 0.8%, thixotropic agent 4%, ethylene glycol butyl ether 5%, ethylene glycol hexyl ether 13%, trimethylolpropane trioleate 2% by total mass.

[0065] The film-forming material is acrylic modified rosin ke604 (acid value 230-245 KOH / g, softening point 122-132°C) and hydrogenated rosin (model: Eastman foralax-e), mass ratio 2:1; the lubricant is Super Ester A-18 liquid rosin; the surfactant is lauryl alcohol polyoxyethylene ether and lauryl amide polyoxyethylene ether, mass ratio 1.5:1; the thixotropic agent is polyamide wax 6650;

[0066] The preparation method of the soldering paste comprises the following steps:

[0067] (1) Mix and stir the dibromobutene diol and 3% of the total amount of the soldering paste to obtain a dibromobutene diol solution after heating at 55°C until completely dissolved and cooled naturally;

[0068] (2) Weigh and mix the film-forming material, succinic acid, benzotriazole, lauryl alcohol polyoxyethylene ether, lubricant, ethylene glycol butyl ether, the remaining ethylene glycol hexyl ether and trimethylolpropane trioleate in a container, heat the container and continuously stir to control the temperature at 160°C to completely dissolve the mixture;

[0069] (3) After dissolving, reduce the temperature to 80°C, add the dibromobutene diol solution, stir, then add lauryl amide polyoxyethylene ether, and cool the material to 50°C after stirring;

[0070] (4) Add triethanolamine and thixotropic agent and stir;

[0071] (5) Disperse the material at 2500 rpm and emulsify for 100 minutes after heating to 65°C.

[0072] Example 3

[0073] The soldering paste provided in this example comprises, by total mass, 45% of film-forming material, 0.8% of succinic acid, 1.5% of dibromobutene diol, 1% of benzotriazole, 2.0% of lubricant, 8% of surfactant, 0.1% of triethanolamine, 7% of thixotropic agent, 9% of ethylene glycol butyl ether, 20.6% of ethylene glycol hexyl ether and 5% of trimethylolpropane trioleate.

[0074] The film-forming material is acrylic modified rosin ke604 (acid value 230-245 KOH / g, softening point 122-132°C) and hydrogenated rosin (model: Eastman foralax-e), mass ratio 1:1; the lubricant is Super Ester A-18 liquid rosin; the surfactant is lauryl alcohol polyoxyethylene ether and lauryl amide polyoxyethylene ether, mass ratio 3.5:1; the thixotropic agent is polyamide wax 6650;

[0075] The preparation method of the soldering paste comprises the following steps:

[0076] (1) Mix and stir the dibromobutene diol and 5% of the total amount of the soldering paste to obtain a dibromobutene diol solution by heating at 60°C until completely dissolved and clear, and then naturally cooling down;

[0077] (2) Weigh and mix the film-forming material, succinic acid, benzotriazole, lauryl alcohol polyoxyethylene ether, lubricant, ethylene glycol butyl ether, the remaining amount of ethylene glycol hexyl ether, and trimethylolpropane trioleate, and then place them in a container, heat the container and continuously stir, control the temperature at 175°C, and make the mixture completely dissolved;

[0078] (3) After dissolving, reduce the temperature to 90°C, add the dibromobutene diol solution, stir, then add lauryl amide polyoxyethylene ether, stir, and then cool the material to 55°C;

[0079] (4) Add triethanolamine and thixotropic agent and stir;

[0080] (5) Disperse the material at 3500 rpm and emulsify for 60 minutes at 60°C, and then it is ready.

[0081] Example 4

[0082] The example is basically the same as example 1, except that the trimethylolpropane trioleate is replaced by tributyl citrate.

[0083] Comparative Example 1

[0084] The example is basically the same as example 1, except that the mass ratio of the acrylic modified rosin ke604 and hydrogenated rosin is 1:2.

[0085] Comparative Example 2

[0086] The example is basically the same as example 1, except that the film-forming material is acrylic modified rosin ke604.

[0087] Comparative Example 3

[0088] The example is basically the same as example 1, except that the acrylic modified rosin ke604 is replaced by soldering rosin JT-90 (softening point 80-90°C, acid value 160 mg LOH / g, purchased from Shenzhen Jitian Chemical Industry).

[0089] Comparative Example 4

[0090] The soldering paste consists of 53% film forming substance, 1.1% succinic acid, 1% dibromo butene diol, 0.4% benzotriazole, 3% lubricant, 7% surfactant, 0.4% triethanolamine, 5.7% thixotropic agent, 7.6% ethylene glycol butyl ether, 20.8% ethylene glycol hexyl ether, by total mass.

[0091] Comparative Example 5

[0092] The soldering paste consists of 53% film forming substance, 1.1% succinic acid, 1% dibromo butene diol, 0.4% benzotriazole, 3% lubricant, 7% surfactant, 0.4% triethanolamine, 5.7% thixotropic agent, 7.6% ethylene glycol butyl ether, 20.8% ethylene glycol hexyl ether, by total mass.

[0093] Comparative Example 6

[0094] The soldering paste consists of 53% film forming substance, 1.1% succinic acid, 1% dibromo butene diol, 0.4% benzotriazole, 3% lubricant, 7% surfactant, 0.4% triethanolamine, 5.7% thixotropic agent, 7.6% ethylene glycol butyl ether, 20.8% ethylene glycol hexyl ether, by total mass.

[0095] Comparative Example 7

[0096] The soldering paste consists of 53% film forming substance, 1.1% succinic acid, 1% dibromo butene diol, 0.4% benzotriazole, 3% lubricant, 7% surfactant, 0.4% triethanolamine, 5.7% thixotropic agent, 7.6% ethylene glycol butyl ether, 20.8% ethylene glycol hexyl ether, by total mass.

[0097] Comparative Example 8

[0098] The soldering paste consists of 53% film forming substance, 1.1% succinic acid, 1% dibromo butene diol, 0.4% benzotriazole, 3% lubricant, 7% surfactant, 0.4% triethanolamine, 5.7% thixotropic agent, 7.6% ethylene glycol butyl ether, 20.8% ethylene glycol hexyl ether, by total mass.

[0099] Performance test method:

[0100] The soldering paste of the above examples, when prepared into a tin paste, consists of 13wt% soldering paste and 87wt% sac305 tin powder, by total mass of the tin paste. The above tin paste is tested as follows:

[0101] 1. Wettability and tin bead test: according to GB / 31475-2015 standard;

[0102] 2. Copper plate corrosion and spread rate: according to IPC-TM-650 test standard;

[0103] 3. Low temperature storage performance: after the tin paste is well sealed, it is stored in 8-10℃ refrigerator, and taken out every month to observe the tin paste state after being warmed at room temperature (if there are adverse phenomena such as stratification, particle aggregation, etc., the storage is stopped), and then put back into storage;

[0104] 4. Reflow soldering yield: 100 circuit boards of the same model were extracted, and after SMT automatic printing of tin paste, patching, and reflow soldering, the soldering performance of the soldering points was detected, and the yield was calculated according to the results.

[0105] Performance test results:

[0106] The test results are shown in Table 1.

[0107] Table 1

[0108]

[0109]

[0110] The above data analysis: the technical solutions of examples 1-4 can all obtain relatively excellent soldering performance; the expansion rate and reflow soldering yield of comparative examples 1-2 are relatively poor, which may be because the hydrogenated rosin is unstable, and an excessive amount will cause more soldering point residues, but when only using the acrylic modified rosin, the acidity of the soldering paste is relatively large, and the corrosion is also relatively strong, which seriously affects the soldering performance; in comparative example 3, the acid value of the acrylic rosin is relatively low, the surface tension of the soldering paste and the substrate is large, and the film layer formed in the soldering process is not dense enough, so that the soldering high temperature causes the oxidation of the tin powder or the substrate, which seriously affects the reflow soldering yield; the results of comparative examples 4-5 show that only a suitable amount of ester solvent can improve the wettability and expansion rate, and when the ester solvent is excessive, the balance of the system will be broken, and the storage stability of the soldering paste will decrease; in comparative example 6, it may be because the hydrophobic and lipophilic alkyl chain is too long, so that the wettability of the surfactant to the substrate decreases, and the emulsification and wrapping effect on the oil stains also decreases; in comparative example 7, because the cross-linked emulsification state formed by the surfactant is completely changed, the wettability and expansion rate generated are significantly reduced.

Claims

1. A solder paste characterized by, The components of the soldering paste include film forming substance 45-65%, organic active ingredient 1-4%, corrosion inhibitor 0.1-1%, surfactant 5-10%, amine substance 0.1-0.8%, thixotropic agent 4-7%, and solvent supplementing the balance to 100% by total mass; the organic active ingredient includes halogen-containing organic active ingredient and / or halogen-free organic acid; the film forming substance includes hydrogenated rosin and acrylic modified rosin, and the mass ratio of the acrylic modified rosin to the hydrogenated rosin is (1-2):1; the acid value of the acrylic modified rosin is 200-250 mgKOH / g, and the softening point is 110-150 DEG C; the surfactant is lauryl alcohol polyoxyethylene ether and lauryl amide polyoxyethylene ether, and the mass ratio of the two is (1.5-3.5):1; the solvent includes ethylene glycol butyl ether and ethylene glycol hexyl ether; ethylene glycol butyl ether accounts for 5-9% of the total mass of the soldering paste, and ethylene glycol hexyl ether accounts for 13-22% of the total mass of the soldering paste; the solvent is selected from at least one of propylene glycol phenyl ether acetate, diethylene glycol butyl ether acetate, tributyl citrate and trimethylolpropane trioleate; when the solvent is trimethylolpropane trioleate, trimethylolpropane trioleate accounts for 2-5% of the total mass of the soldering paste.

2. Use of the soldering paste according to claim 1 in SMT lead-free soldering paste, characterized in that, The mass content of the soldering paste in the SMT lead-free soldering paste is 10-15%, and the rest is tin powder.

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