High-reliability halogen-free soldering paste and preparation method thereof

Abstract

The invention discloses high-reliability halogen-free soldering paste and a preparation method thereof. The high-reliability halogen-free soldering paste is composed of 85-88.5 wt% of coated soldering powder, 3-6 wt% of a film-forming agent, 2-5 wt% of a coated active agent, 0.1-0.3 wt% of a surfactant, 2-5 wt% of a thixotropic agent, 0.1-0.5 wt% of an antioxidant and the balance of a solvent. The coated active agent can well coat and isolate the polybasic acid to inhibit the diffusion of the polybasic acid due to the steric hindrance effect of resin charges and long carbon chains. The weak carboxyl contained in the EAA resin can enable the resin to be firmly adsorbed on the surface of the tin powder, meanwhile, the EAA is a semi-crystalline polymer, and nonpolar and crystallization of an ethylene chain segment can well prevent polybasic acid from diffusing and contacting the surface of the tin powder to corrode the tin powder. According to the invention, the polybasic acid and the tin powder are respectively coated, so that the performance reduction caused by corrosion of the tin powder due to diffusion of the dibasic acid during the room-temperature storage period of the soldering paste is avoided, and the storage stability of the soldering paste is improved.

Description

Technical Field

[0001] The present invention relates to the field of electronic solder paste, and particularly to a high-reliability halogen-free solder paste and a preparation method thereof. Background Art

[0002] As an essential key material in the electronic manufacturing industry, the technological development of solder paste has always received extensive attention. In recent years, with the increasingly strict environmental protection regulations and the evolution of electronic devices towards high density and high reliability, the environmental friendliness, stability and process performance of solder paste have become the focus of industry innovation. The stability of traditional solder paste during storage and use directly affects its performance. Solder paste contains a relatively large amount of organic acids, which will slowly corrode the solder powder when in direct contact with the solder powder at room temperature, thus affecting the performance of the solder paste. Therefore, the vast majority of solder paste on the market needs to be stored and transported at low temperature, increasing the cost and difficulty of use.

[0003] How to improve its environmental friendliness and room-temperature storage stability while maintaining the wettability, adhesion and welding strength of the solder paste to meet the increasingly complex electronic manufacturing requirements is the key technical problem that needs to be overcome by the solder paste today. Summary of the Invention

[0004] In view of the problems in the above technical background, the present invention proposes a high-reliability halogen-free solder paste and a preparation method thereof. Without using chlorine-containing activators, the solder paste not only has excellent wettability and welding effect, but also can be stored at room temperature for a long time without changing the performance of the solder paste, improving the storage stability of the solder paste.

[0005] To achieve the above object, the present invention adopts the following technical solutions.

[0006] A high-reliability halogen-free solder paste is composed of the following components: 85 - 88.5 wt% of coated solder powder, 3 - 6 wt% of film-forming agent, 2 - 5 wt% of coated activator, 0.1 - 0.3 wt% of surfactant, 2 - 5 wt% of thixotropic agent, 0.1 - 0.5 wt% of antioxidant, and the balance is solvent.

[0007] Further, the coated activator is composed of an acrylate resin with a special structure and a polybasic acid, and its preparation process is as follows:

[0008] a) Preparation of acrylate resin solution with special structure: Styrene, acrylate monomer with special structure, acidic monomer, and amino-containing monomer are polymerized by free radical polymerization in xylene solution under the action of a free radical initiator as follows: After the monomers and the initiator are stirred and dissolved evenly, they are used as the dropping phase of the mixed monomer solution. Xylene equal in weight to the total monomers is added to the reaction kettle, heated to 110 °C, and kept under reflux. Then, the dropping phase of the mixed monomer solution is added dropwise. The addition is completed in 4 hours. After keeping warm for 1 hour, it is cooled and reserved to obtain the acrylate resin solution with special structure. The resin solid content in the acrylate resin solution after polymerization is 50 wt%. The molar ratio of styrene, acrylate monomer with special structure, acidic monomer, amino-containing monomer, and free radical initiator is (30 - 50):(5 - 10):(1.5 - 3):1:(0.1 - 0.3);

[0009] b) Preparation of coated active agent: 1 - 2 parts of acrylate resin solution and 57 - 58 parts of xylene are taken, 1 part of non-ionic surfactant with HLB less than 8 is added, and then 40 parts of aqueous solution of polybasic acid is added and stirred and emulsified to obtain a water-in-oil emulsion. After spray drying to prepare powder, the coated active agent is obtained, where the mass fraction of the aqueous solution of polybasic acid is 5 wt%.

[0010] Furthermore, the acrylate monomer with special structure is an acrylate monomer containing a long-chain monomer with more than 8 carbon atoms in the monomer, including one or more of lauryl methacrylate, lauryl acrylate, isooctyl methacrylate, isooctyl acrylate, vinyl ester of tertiary carboxylic acid (with more than 8 carbon atoms); the acidic monomer is one or more of acrylic acid, methacrylic acid, itaconic acid, maleic anhydride; the amino-containing monomer is one or more of diethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, vinyl pyridine;

[0011] Furthermore, the polybasic acid is one or more of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, malic acid, tartaric acid, citric acid; the initiator is one or a mixture of two of benzoyl peroxide and tert-butyl peroxy-2-ethylhexanoate.

[0012] Furthermore, the preparation process of the coated solder powder is as follows: EAA resin (ethylene - acrylic acid copolymer) is dissolved by heating with xylene and then cooled to obtain an EAA resin solution with a mass concentration of 5% - 10%. After adding solder powder, it is spray-dried under stirring to obtain the coated solder powder, where the mass ratio of solder powder to EAA resin (pure resin) is 80 - 140:1. The melting point of the EAA resin is in the range of 80 - 120 °C, and the acrylic acid monomer content in the composition of the EAA resin is 3 - 15 wt%. Preferably, the melting point of the EAA resin is in the range of 85 - 100 °C, and the acrylic acid monomer content is 5 - 10 wt%. The particle size range of the solder powder is 2 - 40 μm.

[0013] Furthermore, the film-forming agent is one or several compositions selected from polymerized rosin, hydrogenated rosin, disproportionated rosin, and aldehyde-ketone resin.

[0014] Furthermore, the surfactant is one or several compositions selected from Peregal O-3, MOA-3, Span 60, Span 80, and castor oil phosphate EL-10.

[0015] Furthermore, the thixotropic agent is one or several compositions selected from nano-silica, hydrogenated castor oil, stearic acid amide, and 12-hydroxy stearic acid.

[0016] Furthermore, the antioxidant is one or several compositions selected from hindered phenol 1010, hindered phenol antioxidant 1076, and hindered phenol 264.

[0017] Furthermore, the solvent is one or several compositions selected from dipropylene glycol butyl ether, dipropylene glycol methyl ether, dipropylene glycol, diethylene glycol butyl ether, and dimethyl glutarate.

[0018] The present invention also provides a method for preparing the high-reliability halogen-free solder paste, comprising the following steps:

[0019] (1) Heat the film-forming agent and the thixotropic agent to 130 °C with a solvent until the film-forming agent and the thixotropic agent are completely dissolved, keep warm for half an hour for hot filtration, and cool to room temperature to obtain an organic carrier.

[0020] (2) Add the coated solder powder, coated active agent, surfactant, and antioxidant to the organic carrier obtained in step (1), premix with a dispersing machine first, and then use a three-roll mill to make the fineness of the paste less than 100 μm to obtain the halogen-free solder paste.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: The acidic monomers and amino monomers contained in the acrylate resin of the present invention make the resin charged, and at the same time, the hydrophobic long-chain monomers contained make the resin have good surface activity. Combining with a non-ionic surfactant can prepare a stable polybasic acid emulsion. The finally formed coated active agent can well coat and isolate the polybasic acid to inhibit the diffusion of the polybasic acid due to the charge of the resin and the steric hindrance of the long carbon chain. The weak carboxyl group contained in the EAA resin can firmly adsorb the resin on the surface of the tin powder. At the same time, EAA is a semi-crystalline polymer, and the non-polarity and crystallization of the ethylene segment can well block the diffusion of the polybasic acid to contact the surface of the tin powder and corrode the tin powder. By separately coating the polybasic acid and the tin powder, the present invention avoids the performance degradation caused by the corrosion of the tin powder by the dibasic acid due to diffusion during the storage of the solder paste at room temperature, and improves the storage stability of the solder paste. Detailed embodiments

[0022] Next, in combination with the embodiments of the present invention, the technical solutions of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0023] Example 1

[0024] (1) The preparation process of the coated surfactant is as follows:

[0025] Lauryl acrylate, styrene, methacrylic acid, and dimethylaminoethyl methacrylate are polymerized by free radical polymerization in a xylene solution. The molar ratio of styrene, lauryl acrylate, methacrylic acid, dimethylaminoethyl methacrylate, and benzoyl peroxide is 50:10:2:1:0.2. After the monomers and the initiator benzoyl peroxide are stirred and dissolved evenly, they are used as the dropping phase. Xylene equal to the total weight of the monomers is added to the reaction kettle, heated to 110 °C, and kept under reflux. Then, the mixed monomer solution dropping phase is started to be dropped. The dropping is completed in 4 hours. After keeping warm for 1 hour, the temperature is lowered and reserved to obtain a polyacrylate solution with a special structure, and the resin solid content is 50 wt%.

[0026] Take 2 parts of the above polyacrylate resin solution, add 57 parts of xylene, and 1 part of the non-ionic surfactant Span 80, stir and dissolve evenly, add 40 parts of a 5 wt% aqueous solution of polybasic acid (the mass ratio of succinic acid to glutaric acid is 1:4), stir and emulsify to obtain a water-in-oil emulsion, and then spray dry to prepare a powder, which is the coated surfactant.

[0027] (2) The process of the coated solder powder is as follows:

[0028] Dissolve Dow Chemical PRIMACOR 3002 EAA resin (ethylene-acrylic acid copolymer, the acrylic acid monomer content in the copolymer is 8%, and the resin melting point is 100 °C) with xylene by heating and then cool to obtain a 10% EAA resin solution. Add solder powder (the mass ratio of T4 solder powder with a diameter of 20 - 38 μm, T5 solder powder with a diameter of 15 - 25 μm, and T6 solder powder with a diameter of 10 - 20 μm is 1:7:2), stir evenly. The weight ratio of the solder powder to the EAA resin (pure resin) is 120:1, and spray drying is carried out under stirring to obtain the coated solder powder.

[0029] (3) The preparation steps of the solder paste are as follows:

[0030] ① Dissolve 0.8 wt% dipropylene glycol butyl ether, 3.0 wt% dimethyl glutarate, 5 wt% hydrogenated rosin, 1 wt% polymerized rosin, 3 wt% hydrogenated castor oil, 0.1 wt% surfactant MOA-3, and 0.1 wt% antioxidant 1010 at 130 °C, then perform hot filtration and let it stand and cool to obtain an organic carrier.

[0031] ② Add 85 wt% coated solder powder and 2 wt% coated active agent to the organic carrier obtained in ①, premix with a dispersing machine first, and then use a three-roll mill to make the paste fineness less than 100 μm to obtain the sample of Example 1.

[0032] Example 2

[0033] (1) The preparation process of the coated active agent is as follows:

[0034] Vinyl neodecanoate, styrene, acrylic acid, and dimethylaminoethyl methacrylate are polymerized by free radical polymerization in xylene solution (solid content 50%), and the molar ratio of styrene, vinyl neodecanoate, methacrylic acid, dimethylaminoethyl methacrylate, and benzoyl peroxide is 40:5:3:1:0.2. After the monomers and initiator are stirred and dissolved evenly, they are used as the dropping phase. Xylene equal to the total amount of monomers is added to the reaction kettle, heated to 110 °C, kept warm and refluxed, and then the mixed monomer solution is dropped. The dropping is completed in 4 hours, and after keeping warm for 1 hour, the temperature is lowered and reserved to obtain an acrylate solution with a special structure.

[0035] Take 1 part of the above acrylate resin solution, add 58 parts of xylene, add 1 part of non-ionic surfactant Span 60 and stir to dissolve evenly. Add 40 parts of a 5 wt% aqueous solution of polybasic acid (mass ratio of succinic acid to malic acid is 2:1), stir and emulsify to obtain a water-in-oil emulsion, and then spray dry to prepare a powder, which is the coated active agent.

[0036] (2) The process of the coated solder powder is as follows:

[0037] Heat and dissolve ExxonMobil ESCOR 5050EAA resin (ethylene–acrylic acid copolymer, acrylic acid monomer content in the copolymer is 9%, resin melting point is 97 °C) with xylene, then cool to obtain a 5% EAA resin solution. Add solder powder (the mass ratio of T4 solder powder with a diameter of 20 - 38 μm, T5 solder powder with a diameter of 15 - 25 μm, and T6 solder powder with a diameter of 10 - 20 μm is 1:7:2) and stir evenly at a weight ratio of 130:1 with EAA resin (pure resin). Perform spray drying under stirring to obtain the coated solder powder.

[0038] (3) The preparation steps of the solder paste are as follows:

[0039] ①Dissolve 0.6 wt% dipropylene glycol butyl ether, 3.0 wt% dimethyl glutarate, 4 wt% disproportionated rosin, 1 wt% aldehyde-ketone resin A81, 2 wt% hydrogenated castor oil, 0.2 wt% nano-silica, 0.1 wt% surfactant O-3, and 0.1 wt% antioxidant 1010 by heating to 130 °C, then perform hot filtration and let it stand and cool to obtain an organic carrier.

[0040] ②Add 86 wt% coated solder powder and 3 wt% coated active agent to the organic carrier obtained in ①, first premix with a dispersing machine, and then use a three-roll mill to make the fineness of the paste less than 100 μm to obtain a high-reliability halogen-free solder paste.

[0041] Comparative Example 1

[0042] The preparation process of the coated active agent used in this comparative example is as follows:

[0043] Butyl acrylate, styrene, and methacrylic acid are polymerized by free radical polymerization in a xylene solution, where the molar ratio of styrene, lauryl acrylate, methacrylic acid, and benzoyl peroxide is 50:10:2:0.2. After the monomers and the initiator benzoyl peroxide are stirred and dissolved evenly, they are used as the dropping phase. Add xylene equal to the total weight of the monomers to the reaction kettle, heat to 110 °C and keep it warm and refluxing, then start dropping the mixed monomer solution dropping phase. The dropping is completed in 4 hours. After keeping warm for 1 hour, cool it down for standby to obtain a polyacrylate solution (resin solid content 50%).

[0044] Take 2 parts of polyacrylate resin solution, add 57 parts of xylene, add 1 part of non-ionic surfactant Span 80 and stir to dissolve evenly. Add 40 parts of 5 wt% aqueous solution of polybasic acid (mass ratio of succinic acid to glutaric acid is 1:4), stir and emulsify to obtain a water-in-oil emulsion, and then spray dry to prepare a powder, which is the coated active agent.

[0045] The preparation of the coated solder powder and the solder paste is the same as that in Example 1.

[0046] Comparative Example 2

[0047] The preparation process of the coated active agent used in this comparative example is the same as that in Example 1.

[0048] The preparation process of the coated solder powder used in this comparative example is as follows:

[0049] Dilute the polyacrylate solution prepared in Comparative Example 1 to a solution with a solid content of 10 wt%, add solder powder (the mass ratio of T4 solder powder with a diameter of 20 - 38 μm, T5 solder powder with a diameter of 15 - 25 μm, and T6 solder powder with a diameter of 10 - 20 μm is 1:7:2), stir evenly. The weight ratio of the solder powder to the EAA resin (pure resin) is 120:1, and spray drying is carried out under stirring to obtain the coated solder powder.

[0050] The components and their proportions for preparing the solder paste in this comparative example are the same as those in Example 1.

[0051] Blank example

[0052] The active agent and the solder powder are not coated. The components and their proportions for preparing the solder paste are the same as those in Example 1. That is, the active agent is directly spray-dried with an aqueous solution of 5 wt% polybasic acid (the mass ratio of succinic acid to glutaric acid is 1:4), and the solder powder is composed of T4 solder powder with a diameter of 20 - 38 μm, T5 solder powder with a diameter of 15 - 25 μm, and T6 solder powder with a diameter of 10 - 20 μm in a mass ratio of 1:7:2.

[0053] The performance tests were carried out on the samples of Example 1, Example 2, Comparative Example 1, Comparative Example 2, and the blank example on the day of preparation and after being placed at room temperature for 30 days. The results are shown in Table 1:

[0054] Table 1

[0055]

[0056]

[0057] All parts mentioned in the present invention refer to parts by weight.

[0058] As can be seen from Table 1, the room-temperature storage stability of the solder paste prepared by coating the active agent with a polyacrylate resin having a special structure and coating the solder powder with an EAA resin is significantly improved (the decrease in the welding expansion rate is the smallest).

[0059] The above are only the preferred embodiments of the present invention. For those skilled in the art, modifications, substitutions, or deformations made on the basis of the present invention still fall within the protection scope of the present invention.

Claims

1. A high-reliability halogen-free solder paste, characterized in that It consists of the following components: coated solder powder 85 - 88.5 wt%, film-forming agent 3 - 6 wt%, coated activator 2 - 5 wt%, surfactant 0.1 - 0.3 wt%, thixotropic agent 2 - 5 wt%, antioxidant 0.1 - 0.5 wt%, and the balance is solvent.

2. The high-reliability halogen-free solder paste according to claim 1, wherein The coated activator consists of an acrylate resin with a special structure and a polybasic acid, and its preparation process is as follows: a) Preparation of the acrylate resin solution with a special structure: Styrene, acrylate monomer with a special structure, acidic monomer, and amino-containing monomer are polymerized by free radical polymerization in a xylene solution under the action of a free radical initiator. Specifically: After the monomers and the initiator are stirred and dissolved evenly to form a mixed monomer solution dropping phase, xylene with the same weight as the total monomers is added to the reaction kettle, heated to 110 °C and kept at reflux, then the mixed monomer solution dropping phase is started to be dropped. The dropping is completed in 4 hours, and after keeping warm for 1 hour, it is cooled and reserved to obtain the acrylate resin solution with a special structure. After polymerization, the resin solid content in the acrylate resin solution is 50 wt%, and the molar ratio of styrene, acrylate monomer with a special structure, acidic monomer, amino-containing monomer, and free radical initiator is (30 - 50) : (5 - 10) : (1.5 - 3) : 1 : (0.1 - 0.3). b) Preparation of the coated activator: Take 1 - 2 parts of the acrylate resin solution, 57 - 58 parts of xylene, add 1 part of a non-ionic surfactant with an HLB less than 8, then add 40 parts of the polybasic acid aqueous solution and stir to emulsify to obtain a water-in-oil emulsion, and then spray dry to prepare a powder to obtain the coated activator, where the mass fraction of the polybasic acid aqueous solution is 5 wt%.

3. The high-reliability halogen-free solder paste according to claim 2, wherein The acrylate monomer with a special structure is an acrylate monomer containing a long-chain monomer with more than 8 monomer carbon atoms, including one or more of lauryl methacrylate, lauryl acrylate, isooctyl methacrylate, isooctyl acrylate, and vinyl versatate; the acidic monomer is one or more of acrylic acid, methacrylic acid, itaconic acid, and maleic anhydride; the amino-containing monomer is one or more of diethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, and vinyl pyridine; the polybasic acid is one or more of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, malic acid, tartaric acid, and citric acid; the initiator is one or a mixture of two of benzoyl peroxide and tert-butyl peroxy-2-ethylhexanoate.

4. The high-reliability halogen-free solder paste according to claim 1, wherein The preparation process of the coated solder powder is as follows: EAA resin (ethylene - acrylic acid copolymer) is heated and dissolved in xylene and then cooled to obtain an EAA resin solution with a mass concentration of 5% - 10%. After adding solder powder, it is spray-dried under stirring to obtain the coated solder powder, where the mass ratio of solder powder to EAA resin is 80 - 140 :

1. The melting point of the EAA resin is in the range of 80 - 120 °C, the acrylic monomer content in the EAA resin composition is 3 - 15 wt%, and the particle size range of the solder powder is 2 - 40 μm.

5. The high-reliability halogen-free solder paste according to claim 1, wherein The film-forming agent is one or a combination of polymerized rosin, hydrogenated rosin, disproportionated rosin, and aldehyde-ketone resin.

6. The high-reliability halogen-free solder paste according to claim 1, wherein The surfactant is one or several compositions selected from Peregal O-3, MOA-3, Span 60, Span 80, and castor oil phosphate EL-10.

7. The high-reliability halogen-free solder paste according to claim 1, wherein The thixotropic agent is one or several compositions selected from nano-silica, hydrogenated castor oil, stearic acid amide, and 12-hydroxystearic acid.

8. The high-reliability halogen-free solder paste according to claim 1, wherein, The antioxidant is one or several compositions selected from hindered phenol 1010, hindered phenol antioxidant 1076, and hindered phenol 264.

9. The high-reliability halogen-free solder paste according to claim 1, wherein The solvent is one or several compositions selected from dipropylene glycol butyl ether, dipropylene glycol methyl ether, dipropylene glycol, diethylene glycol butyl ether, and dimethyl glutarate.

10. The preparation method of the high-reliability halogen-free solder paste according to any one of claims 1-9, characterized in that It includes the following steps: (1) Heat the film-forming agent and the thixotropic agent to 130°C with the solvent until the film-forming agent and the thixotropic agent are completely dissolved, keep warm for half an hour, conduct hot filtration, and cool to room temperature to obtain an organic carrier. (2) Add the coated solder powder, coated surfactant, surfactant, and antioxidant to the organic carrier obtained in step (1), premix with a disperser first, and then use a three-roll mill to make the fineness of the paste less than 100 μm to obtain a halogen-free solder paste.

Images