Highly reliable solder paste and use thereof

Abstract

The application provides a high-reliability tin paste, which comprises 80-90% of tin powder and 10-20% of a soldering paste according to the total weight; the soldering paste comprises 20-33% of modified rosin, 4.5-7.5% of tackifying resin, 3-7% of a high-molecular polymer, 3.2-6% of C60-C80 ester with a symmetrical structure and at least 4 ester groups, 7.2-11% of an active agent, 4.5-6.5% of a thixotropic agent, 5-8% of a corrosion inhibitor, 2-4% of a thickening agent, 3-6% of a lubricant, and the solvent makes up the rest to 100% according to the total weight of the soldering paste. The tin paste has good wettability, thixotropy and stability, and the soldering pad is not prone to oxidation discoloration, cavitation and collapse and other adverse phenomena during soldering, and the corrosion resistance and oxidation resistance of the soldering pad in the later period are effectively improved.

Description

Technical Field

[0001] This invention relates to the field of B23K35 / 24, and more specifically to a high-reliability solder paste and its application. Background Technology

[0002] Solder paste, as a key connecting material in the electronics industry, not only enables the connection between electronic devices and circuits, but also meets the physical and electrical performance requirements of electrical components. Solder paste consists of two parts: solder powder and flux. Soldering performance mainly depends on the flux. Currently, the following problems still exist in the field of solder paste technology: 1. Traditional solder paste activators generally use halogenated organic salts, such as diethylamine hydrochloride and cyclohexylamine bromate. Although these activators have high activity and good fluxing effect, halogens are seriously harmful to the human body and the environment, and they are also easy to corrode solder powder, resulting in poor stability of solder paste. The halogen-free activators used in the existing technology have weak activity and insufficient fluxing performance; 2. The flux cannot completely remove the oxide layer of the solder powder and the metal substrate being soldered, resulting in poor wettability during soldering, easy formation of solder balls and poor soldering. The metal being soldered is easily corroded and oxidized during the soldering process; 3. In current semiconductor devices, ultrafine solder paste can achieve electrical and thermal conductivity. The smaller the particle size of the solder powder, the easier it is to extract current. However, ultrafine solder powder contains oxygen, has poor wettability, is easily oxidized, and has unstable storage performance in the later stage.

[0003] Chinese patent CN107931891B discloses a solder paste flux that uses acrylic resin instead of rosin to reduce residue and improve the coating of solder powder, preventing oxidation. The solder paste exhibits good stability. However, the protective structure of the acrylic resin is easily decomposed at high temperatures, causing oxidation and discoloration of the metal substrate during soldering, and its subsequent corrosion and oxidation resistance to the metal substrate is also poor. Chinese patent CN114654129A discloses a highly stable solder paste and its preparation method. By compounding rosin with different softening points and acid values, the dispersibility of the system is improved, preventing solder paste settling. However, rosin produces significant residue, and relying solely on rosin for adhesion to the metal substrate provides insufficient protection. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention first provides a highly reliable solder paste and its applications.

[0005] The solder paste comprises 80-90% solder powder and 10-20% flux by total weight.

[0006] Further, based on the total weight of the flux, the flux comprises: 20-33% modified rosin, 4.5-7.5% tackifying resin, 3-7% polymer, 3.2-6% C60-C80 ester having a symmetrical structure and containing at least 4 ester groups, 7.2%-11% activator, 4.5-6.5% thixotropic agent, 5-8% corrosion inhibitor, 2-4% thickener, 3-6% lubricant, and solvent to make up to 100%.

[0007] Furthermore, the modified rosin is at least one of water-white rosin, hydrogenated rosin, maleic acid modified rosin, fumaric acid modified rosin, and acrylic acid modified rosin.

[0008] Furthermore, the modified rosin is hydrogenated rosin and acrylic acid modified rosin, with a weight ratio of 1:(1-2.5).

[0009] Furthermore, the acrylic acid-modified rosin has a softening point of 120-140℃ (ring and ball method) and an acid value of 220-245 mgKOH / g.

[0010] Furthermore, the tackifying resin is selected from at least one of terpene resin, acrylic resin, polypropylene resin, phenolic resin, C5 or C9 petroleum resin.

[0011] Preferably, the tackifying resin is a terpene resin with a softening point of 100-120℃ (ring and ball method).

[0012] Furthermore, the polymer is selected from at least one of polypentadiene, polyisobutylene, polybutene, and polystyrene.

[0013] Furthermore, the polymer is polypentadiene and / or polyisobutylene.

[0014] Preferably, the polymer is polyisobutylene; the viscosity-average molecular weight of the polyisobutylene is 500,000-700,000,000. Polyisobutylene does not easily produce residual carbon during high-temperature decomposition, and can effectively replace part of the rosin. When its viscosity-average molecular weight is too low, the ultrafine solder powder is prone to agglomeration, resulting in low viscosity after solder paste application. The dripping will reduce the impedance of the solder paste. Conversely, when its viscosity-average molecular weight is too high, the viscosity is too high, resulting in poor processing fluidity and reduced spreadability.

[0015] Furthermore, the C60-C80 ester with a symmetrical structure and containing at least four ester groups is at least one of pentaerythritol oleate, pentaerythritol stearate, and pentaerythritol 2-hexyldecanoate. This application specifies the ester group content to improve the adsorption performance of the solder paste on the metal to be soldered. At the same time, its symmetrical structure also improves the frictional lubrication of the solder paste, increases the spread rate, and prevents solder voids from appearing during soldering. Its macromolecular chains stabilize the ultrafine tin powder at room temperature and low temperature, avoid agglomeration, and improve the storage stability of the solder paste. Meanwhile, if it is decomposed at high temperature, the resulting macromolecular organic acids enhance the removal of oxide layers from the metal to be soldered and tin powder, and complex with the metal matrix, further enhancing the density of the protective film formed by the corrosion inhibitor.

[0016] Preferably, the C60-C80 ester having a symmetrical structure and containing at least four ester groups is pentaerythritol 2-hexyldecanoate.

[0017] Furthermore, the active agent includes at least one of succinic acid, phthalic acid, glutaric acid, adipic acid, octanoic acid, sebacic acid, and palmitic acid.

[0018] Preferably, the activator includes succinic acid and adipic acid.

[0019] Furthermore, the corrosion inhibitor is selected from at least one of pyrazines, imidazoles, and nitrazoles.

[0020] Furthermore, the corrosion inhibitor is an imidazole or nitrazole, selected from at least one of 2-mercaptobenzimidazole, 1-vinylimidazole, 2-ethylimidazole, 2-methylimidazole, benzotriazole, and methylbenzotriazole.

[0021] Preferably, the corrosion inhibitor is a combination of benzotriazole, methylbenzotriazole, and 2-ethylimidazole in a weight ratio of (0.8-1.2):(0.3-0.7):(4-6.5). During high-temperature soldering, hydrogenated rosin and modified rosin have low softening points and are easily carbonized, causing premature decomposition and significantly reducing the electrical properties of the solder paste. This application provides a slow-release effect on the soldered metal from both anodic and cathodic control perspectives. Benzotriazole and methylbenzotriazole can form a complex ring-shaped polymer protective film with the soldered metal, preventing the metal from being anolyzed. While benzotriazole can coordinate with the metal ions being welded, methylbenzotriazole exhibits stronger activity under acidic conditions, coordinating with metal ions more rapidly. The presence of the methyl group also increases the hydrophobicity of the protective film, resulting in superior corrosion inhibition. However, its adsorption on the metal surface is relatively slow, and excessive addition will slow down the formation of the protective film. 2-Ethylimidazole is a cathodic control-oriented corrosion inhibitor. Compared to the previous two, it has less steric hindrance, leading to faster protective film formation. However, the polymeric network structure in the protective film exhibits poor stability at high temperatures. Therefore, controlling the relative content of these three agents is crucial to ensure that the formed protective film effectively prevents corrosion of the metal by the active agent and protects the metal from oxidation.

[0022] In a preferred embodiment, the weight ratio of benzotriazole, methylbenzotriazole and 2-ethylimidazole is 0.95:0.5:5.91.

[0023] Furthermore, the activator also includes salicylic acid. This application unexpectedly discovered that when salicylic acid is added, and its dosage is specified as 30-50% of the weight of benzotriazole and methylbenzotriazole, the welded metal exhibits stronger oxidation resistance and acid corrosion resistance. The speculated reason is that benzotriazole and methylbenzotriazole have boiling points of 204℃ and 160℃, respectively. Under the high-temperature environment during welding, some components of the protective film will volatilize, forming voids, and the complex structure of benzotriazole will decompose at high temperatures, significantly reducing the overall protective effect. However, with the addition of salicylic acid, the complex structure formed by salicylic acid and the metal is more stable at high temperatures, and salicylic acid is less volatile. Combined with the cross-linked polymer chains of benzotriazole and methylbenzotriazole, the resulting protective film is denser and provides superior protection for the metal. However, when the dosage is excessive, its acidity will corrode the metal beyond its protective effect, making the metal more susceptible to the effects of acidic substances and oxygen.

[0024] Furthermore, the thixotropic agent is at least one of hydrogenated castor oil, modified hydrogenated castor oil, polyethylene wax, polyamide, fatty acid amide, and icosicosicoic acid; preferably icosicosicoic acid.

[0025] Furthermore, the thickener is selected from at least one of fatty acid monoglycerides, fatty acid triglycerides, polyethylene wax, ethylene bis-stearamide, and polyamide wax.

[0026] Furthermore, the wetting agent is monooctyl phosphate or white petrolatum; preferably white petrolatum.

[0027] Furthermore, the solvent is selected from at least one of terpineol, diethylene glycol, 2-ethyl-1,3-hexanediol, diethylene glycol monohexyl ether, diethylene glycol hexyl ether, tripropylene glycol butyl ether, and tetraethylene glycol dimethyl ether.

[0028] Furthermore, the solvent is tripropylene glycol butyl ether.

[0029] Furthermore, the method for preparing the flux is as follows:

[0030] (1) Pre-crush the rosin, add all the materials to the dissolving kettle, heat and dissolve while stirring, and the heating temperature shall not exceed 130℃;

[0031] (2) After complete dissolution, cool to 90-105℃ with stirring, and degas under vacuum for 5-8 minutes;

[0032] (3) After sealing the product and storing it at room temperature for 24 hours, grind it with a grinder until the average particle diameter is less than 20μm.

[0033] (4) Store the ointment in a sealed container at 0-10℃ until use.

[0034] Furthermore, the high-reliability solder paste is prepared by mixing solder powder and flux, stirring evenly at a stirring speed of 30-50 rpm, and then degassing under vacuum.

[0035] Furthermore, the tin powder includes, but is not limited to, any one of SAC305 (Sn3Ag0.5Cu), SAC0307 (Sn0.3Ag0.7Cu), and SAC105 (Sn1Ag0.5Cu).

[0036] Furthermore, the average particle diameter of the tin powder is 2-10 μm.

[0037] Furthermore, the solder paste needs to be stored at 0-10°C.

[0038] This application also provides the application of high-reliability solder paste in pad SMT process, wherein the pad is any one of ENIG pad, nickel-plated pad, or copper-plated pad.

[0039] Preferably, the pad is an ENIG pad or a nickel-plated pad.

[0040] Beneficial effects

[0041] 1. The high-reliability solder paste of this application reduces the colored residue of rosin after soldering by compounding different modified rosin and using tackifying resin; by compounding different activators in the system, the solder powder and oxide layer of the metal substrate being soldered can be effectively removed, thus improving the soldering performance; by controlling the cross-linking effect of the system, the system has excellent lubricity and thixotropy, and the solder paste is less prone to defects such as voids and collapse during soldering, thus effectively improving the electrical reliability of the solder pads.

[0042] 2. By controlling the type and amount of corrosion inhibitor, this application enables the solder paste of the present invention to simultaneously control the oxidation of the metal being soldered from both the anode and cathode control surfaces, thereby enhancing the protective film between the corrosion inhibitor and the soldering metal and effectively inhibiting the oxidation and corrosion of the substrate of the soldering metal in the later stage.

[0043] 3. By using salicylic acid and controlling its content with benzotriazole and methylbenzotriazole, this application makes the structure of the protective film more compact, which not only improves the activity of the solder paste, but also further enhances the protective effect on the soldering metal substrate.

[0044] 4. The solder paste of this application is halogen-free and environmentally friendly; the system has good stability and is not prone to layering and agglomeration when using ultrafine solder powder. Detailed Implementation

[0045] Example

[0046] Example 1

[0047] This embodiment provides a highly reliable solder paste; by total weight, the solder paste comprises 85% solder powder and 15% flux, wherein the solder powder is SAC305 and the average particle diameter is 5μm.

[0048] Based on the total weight of the flux, the flux comprises: 11% hydrogenated rosin, 16% acrylic-modified rosin (KE604), 5% terpene resin (T-110, Yoshida Chemical), 6.2% polyisobutylene (Polybutene-300R, viscosity-average molecular weight approximately 600,000), 4.75% pentaerythritol 2-hexyldecanoate (ISOCARB ESTER 1605), 5.98% adipic acid, 2.61% succinic acid, 0.58% salicylic acid, 5.5% icosanoic acid, 0.95% benzotriazole, 0.5% methylbenzotriazole, 5.91% 2-ethylimidazole, 3.4% ethylene bis-stearamide, 5% white petrolatum, and tripropylene glycol butyl ether to make up the balance to 100%.

[0049] The preparation method of the flux is as follows: (1) Rosin is pre-crushed, all materials are added to a dissolving vessel, and heated to dissolve under stirring at a temperature of 120°C.

[0050] (2) After complete dissolution, cool to 100°C with stirring, and degas under vacuum for 5 minutes;

[0051] (3) After sealing the product and storing it at room temperature for 24 hours, grind it with a grinder until the average particle diameter is less than 20μm.

[0052] (4) Store the ointment in a sealed container at 6°C until use.

[0053] The solder paste is prepared by mixing solder powder and flux in a certain proportion and stirring evenly at a stirring speed of 40 rpm, followed by vacuum degassing.

[0054] Example 2

[0055] This embodiment provides a highly reliable solder paste; by total weight, the solder paste comprises 80% solder powder and 20% flux, wherein the solder powder is SAC0307 and the average particle diameter is 2μm.

[0056] Based on the total weight of the flux, the flux comprises: 8% hydrogenated rosin, 12% acrylic-modified rosin (KE604), 7.5% terpene resin (T-100, Yoshida Chemical), 7% polyisobutylene (Polybutene-300R, viscosity-average molecular weight approximately 600,000), 3.2% pentaerythritol 2-hexyldecanoate (ISOCARB ESTER 1605), 4.8% adipic acid, 3% succinic acid, 0.75% salicylic acid, 6.5% icosanoic acid, 0.8% benzotriazole, 0.7% methylbenzotriazole, 4% 2-ethylimidazole, 2% ethylene bis-stearamide, 5% white petrolatum, and tripropylene glycol butyl ether to make up the balance to 100%.

[0057] The preparation method of the flux paste is the same as in Example 1.

[0058] The preparation method of the solder paste is the same as in Example 1.

[0059] Example 3

[0060] This embodiment provides a highly reliable solder paste; by total weight, the solder paste comprises 90% solder powder and 10% flux, wherein the solder powder is SAC305 and the average particle diameter is 8μm.

[0061] Based on the total weight of the flux, the flux comprises: 15% hydrogenated rosin, 18% acrylic-modified rosin (KE604), 4.5% terpene resin (T-120, Yoshida Chemical), 3% polyisobutylene (Polybutene-300R, viscosity-average molecular weight approximately 600,000), 6% pentaerythritol 2-hexyldecanoate (ISOCARB ESTER 1605), 6.5% adipic acid, 2.2% succinic acid, 0.45% salicylic acid, 4.5% icosicosuccinic acid, 1.2% benzotriazole, 0.3% methylbenzotriazole, 6.5% 2-ethylimidazole, 4% ethylene bis-stearamide, 6% white petrolatum, and tripropylene glycol butyl ether to make up the balance to 100%.

[0062] The preparation method of the flux paste is the same as in Example 1.

[0063] The preparation method of the solder paste is the same as in Example 1.

[0064] Example 4

[0065] This is basically the same as Example 1, except that the polyisobutylene is BASF Oppanol N100 (viscosity-average molecular weight of 2,600,000).

[0066] Example 5

[0067] The method is basically the same as in Example 1, except that, based on the total weight of the flux, the flux includes: 11% hydrogenated rosin, 16% acrylic-modified rosin (KE 604), 5% terpene resin (T-110, Yoshida Chemical), 6.2% polyisobutylene (Polybutene-300R), 4.75% pentaerythritol 2-hexyldecanoate (ISOCARB ESTER 1605), 5.98% adipic acid, 2.61% succinic acid, 0.58% salicylic acid, 5.5% icosanoic acid, 0.25% benzotriazole, 1.2% methylbenzotriazole, 5.91% 2-ethylimidazole, 3.4% ethylene bis-stearamide, 5% white petrolatum, and tripropylene glycol butyl ether to make up the balance to 100%.

[0068] Example 6

[0069] It is basically the same as Example 1, except that salicylic acid is not added to the flux.

[0070] Example 7

[0071] The method is basically the same as in Example 1, except that, based on the total weight of the flux, the flux includes: 11% hydrogenated rosin, 16% acrylic-modified rosin (KE 604), 5% terpene resin (T-110, Yoshida Chemical), 6.2% polyisobutylene (Polybutene-300R), 4.75% pentaerythritol 2-hexyldecanoate (ISOCARB ESTER 1605), 5.56% adipic acid, 2.61% succinic acid, 1% salicylic acid, 5.5% icosuccinic acid, 0.95% benzotriazole, 0.5% methylbenzotriazole, 5.91% 2-ethylimidazole, 3.4% ethylene bis-stearamide, 5% white petrolatum, and tripropylene glycol butyl ether to make up the balance to 100%.

[0072] Example 8

[0073] The method is basically the same as in Example 1, except that, based on the total weight of the flux, the flux includes: 11% hydrogenated rosin, 16% acrylic-modified rosin (KE 604), 5% terpene resin (T-110, Yoshida Chemical), 6.2% polyisobutylene (Polybutene-300R), 4.75% pentaerythritol stearate (CAS: 115-83-3), 5.98% adipic acid, 2.61% succinic acid, 0.58% salicylic acid, 5.5% icosanoic acid, 0.95% benzotriazole, 0.5% methylbenzotriazole, 5.91% 2-ethylimidazole, 3.4% ethylene bis-stearamide, 5% white petrolatum, and tripropylene glycol butyl ether to make up the balance to 100%.

[0074] Performance testing methods:

[0075] 1. Copper plate corrosion test: conducted according to IPC-TM-650 2.6.15 test standard.

[0076] 2. Wettability: Tested according to IPC TM-650 2.3.28.1 standard.

[0077] 3. Expansion rate: Tested according to JIS-Z-3197:1999 standard.

[0078] 4. Viscosity change rate: The solder paste of the example was placed in an environment of 25°C, and the viscosity data (Pa·s, rotation speed of 10 rpm) of the solder paste in the example was measured every half hour in accordance with the JIS Z 3284 test standard. The measurement was carried out continuously for 24 hours, and the viscosity change rate was calculated based on the last measurement result.

[0079] The test results of the examples are shown in Table 1.

[0080] Performance test results:

[0081] Table 1

[0082]

Claims

1. A high-reliability solder paste, characterized in that, The solder paste comprises 80-90% solder powder and 10-20% flux by total weight. Based on the total weight of the flux, the flux comprises: 20-33% modified rosin, 4.5-7.5% tackifying resin, 3-7% polymer, and 3.2-6% C44 having a symmetrical structure and containing at least 4 ester groups. 60 -C 80 Ester, 7.2%-11% surfactant, 4.5%-6.5% thixotropic agent, 5-8% corrosion inhibitor, 2-4% thickener, 3-6% lubricant, and solvent to make up to 100%; The polymer is polyisobutylene; the viscosity-average molecular weight of the polyisobutylene is 600,000. The C having a symmetrical structure and containing at least 4 ester groups 60 -C 80 The ester is pentaerythritol 2-hexyldecanoate; The corrosion inhibitor is a combination of benzotriazole, methylbenzotriazole and 2-ethylimidazole, in a weight ratio of (0.8-1.2):(0.3-0.7):(4-6.5). The active agent includes salicylic acid, and the amount of salicylic acid used is 30-50% of the weight of benzotriazole and methylbenzotriazole.

2. The high-reliability solder paste according to claim 1, characterized in that, The modified rosin is hydrogenated rosin and acrylic acid modified rosin.

3. The high-reliability solder paste according to claim 2, characterized in that, The softening point of the acrylic acid-modified rosin, as determined by the ring and ball method, is 120-140℃, and the acid value is 220-245 mg KOH / g.

4. A high-reliability solder paste according to any one of claims 1-3, characterized in that, The average particle diameter of the tin powder is 2-10 μm.

5. The application of a high-reliability solder paste according to any one of claims 1-4 in SMT pad bonding processes, characterized in that, The pad can be any one of ENIG pads, nickel-plated pads, or copper-plated pads.

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