OSP soldering pad special-purpose tin paste with self-corrosion inhibition and application thereof

Abstract

This application provides an OSP pad solder paste with self-inhibiting corrosion function; by total weight, the solder paste comprises 85-90% solder powder and 10-15% flux; by total weight, the flux components comprise: 30-50% modified rosin, 10-20% polysaccharide anhydride, 1.5-5% activator, 8-13% thixotropic agent, and organic solvent supplemented to make up the balance of 100%; the solder paste has excellent soldering performance, high adhesion to the soldering metal substrate, excellent lubricity and thixotropy, does not corrode the soldered metal and effectively improves its oxidation resistance, has stable printing performance, and has excellent compatibility with OSP pads.

Description

Technical Field

[0001] This invention relates to the field of B23K35 / 24, and more specifically to a special solder paste for OSP pads with self-etching properties and its application. Background Technology

[0002] In reflow soldering, solder paste is a commonly used bonding material. Solder paste consists of two parts: solder powder and flux. At the high temperature of soldering, the organic solvents in the solder paste evaporate, and the activator preheats and releases active ingredients, removing the oxide layer on the substrate surface and improving the wetting performance between the solder paste and the metal substrate being soldered. Rosin and its derivatives are often used in solder paste as effective film-forming agents to protect the metal substrate from oxidation and corrosion. However, rosin residue can significantly reduce the electrical performance of electronic devices, and the decomposition of rosin at high temperatures makes its protective performance for the metal substrate far from sufficient. Furthermore, to effectively remove the oxide layer on the substrate surface and improve the soldering performance between the solder powder and the substrate, strong acids are often used, but this inevitably causes excessive corrosion to the metal substrate. Therefore, how to improve high-temperature protection of the metal substrate, possess suitable activity without causing corrosion, and improve the soldering and electrical performance of the pads remains a problem that needs to be solved in the field of SMT technology.

[0003] Chinese patent CN102581523A discloses a halogen-free flux paste, the components of which include: 30-60% rosin and / or rosin derivatives, 5-20% activator, 5-12% thixotropic agent, 0.3-2% surfactant, 0.1-1.5% corrosion inhibitor, and 30-60% solvent by total weight. In its embodiment, the rosin and / or rosin derivatives are maleic acid-modified rosin and polymerized rosin, and the activator is phthalic acid. The high acid value of the rosin and the high content of phthalic acid give the flux paste high activity, but it may corrode the metal substrate, resulting in a decrease in the quality of the solder pads. Chinese patent CN114986016A discloses a low-residue no-clean flux paste, solder paste, and a method for preparing the flux paste. In this method, the content of rosin, petroleum resin, or terpene resin is controlled to be below 5 wt.% to reduce residue. However, these substances mainly play a film-forming role, and if the content is too low, it will reduce the protection of the soldered metal by the flux paste, resulting in a decrease in soldering performance. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention first provides a solder paste specifically for OSP pads with self-etching properties.

[0005] The solder paste comprises 85-90% solder powder and 10-15% flux by total weight.

[0006] Furthermore, the tin powder includes, but is not limited to, any one of Sn3Ag0.5Cu, Sn0.3Ag0.7Cu, Sn0.3Ag0.5Cu, Sn1Ag0.5Cu, Sn-30Bi-0.5Cu, Sn-40Bi-2Zn-0.3Cu, etc.

[0007] Furthermore, based on the total weight of the flux paste, the flux paste components include: 30-50% modified rosin, 10-20% polysaccharide anhydride, 1.5-5% activator, 8-13% thixotropic agent, and the organic solvent supplement is 100%.

[0008] The resin acid in modified rosin contains carboxyl groups, which can remove oxides from the surface of the metal being soldered during soldering. The dense hydrophobic film formed after soldering improves the electrical insulation of the solder pads and also enhances their moisture resistance. However, rosin is prone to leaving colored residues after high-temperature soldering, affecting product yield. By using polysaccharide anhydride to replace part of the modified rosin, the density of the film formed in the system is controlled, which also improves the surface insulation resistance of the solder pads. During high-temperature soldering, the dissociation of some polysaccharide anhydride can generate carboxylate ions, which increases the adhesion to the metal surface and the removal of surface oxides. The activator effectively removes solder powder and oxides from the surface of the metal being soldered. By controlling the content of lubricant and solvent, the flow properties and viscosity of the solder paste are balanced, reducing solder ball spatter and the formation of solder holes during soldering.

[0009] Furthermore, the modified rosin is at least one of polymerized rosin, fully hydrogenated rosin, polymerized rosin, disproportionated rosin, maleic acid modified rosin, fumaric acid modified rosin, and acrylic acid modified rosin.

[0010] Furthermore, the modified rosin is at least one of disproportionated rosin, maleic acid modified rosin, and fumaric acid modified rosin.

[0011] Preferably, the modified rosin is disproportionated rosin.

[0012] Furthermore, the softening point of the disproportionated rosin is 70-100℃ (ring and ball method), and the acid value is 145-190mg KOH / g.

[0013] Preferably, the disproportionated rosin has a softening point of 80-90℃ (ring and ball method) and an acid value of 160-180 mg KOH / g.

[0014] Furthermore, the polysaccharide has a molecular weight of 4000-8000 and an acid value of 450-800 mg KOH / g. The interaction between the ester bonds in the polysaccharide and the metal being soldered ensures the firm adhesion of the solder paste to the metal surface. It can also modify rosin to produce intermolecular cross-linking, which not only increases the high-temperature decomposition resistance of the rosin but also improves the density of the protective film formed on the metal surface, further protecting the metal being soldered from high-temperature oxidation. However, when the molecular weight of the polysaccharide is too high, it will hinder its adsorption rate on the metal surface. When the acid value is too high, the interaction with the modified rosin will make the cohesive force of the solder paste too high, and the wettability of the metal being soldered will be poor.

[0015] Furthermore, the polysaccharide has a molecular weight of 5000-8000 and an acid value of 450-650 mg KOH / g.

[0016] Preferably, the polysaccharide has a molecular weight of 5800 and an acid value of 603 mg KOH / g.

[0017] Furthermore, the active agent is selected from one or a combination of several inorganic acids, organic acids, and fatty alcohols.

[0018] Furthermore, the active agent is one or a combination of several of nitrogen-containing heterocyclic organic acids, fatty acids, and fatty alcohols.

[0019] Further, the nitrogen-containing heterocyclic organic acid is selected from at least one of 2-pyridinecarboxylic acid, 2,5-pyridinedicarboxylic acid, 3,5-pyridinedicarboxylic acid, imidazole-1-acetic acid, benzimidazole-1-acetic acid, and benzotriazole-1-acetic acid.

[0020] Furthermore, the nitrogen-containing heterocyclic organic acid is selected from at least one of 2-pyridinecarboxylic acid, benzimidazole-1-acetic acid, and benzotriazole-1-acetic acid.

[0021] Furthermore, the fatty acid is selected from at least one of monocarboxylic fatty acids, dicarboxylic fatty acids, and tricarboxylic fatty acids.

[0022] Further, the fatty acid is selected from at least one of succinic acid, octanoic acid, malonic acid, succinic acid, sebacic acid, maleic acid, and malic acid.

[0023] Furthermore, the fatty acid is selected from at least one of malonic acid, succinic acid, maleic acid, and malic acid.

[0024] Preferably, the fatty acid is selected from malonic acid or succinic acid.

[0025] Furthermore, the fatty alcohol is selected from at least one of ethylene glycol, polyethylene glycol, isopropanol, propylene glycol, glycerol, pentaerythritol, pentapentanol, dibromobutenediol, and cyclohexanediol.

[0026] Preferably, the activator is a combination of nitrogen-containing heterocyclic organic acid, fatty acid, and fatty alcohol in a weight ratio of (0.3-0.7):(0.01-0.04):(0.9-3.5). During preparation, the nitrogen-containing heterocyclic organic acid, fatty acid, and fatty alcohol form ester bonds. These ester bonds break and decompose at the high temperature of soldering, and the resulting carboxyl and hydroxyl groups remove the metal oxide layer. Regulating the relative content of acid and alcohol ensures oxygen removal activity while effectively mitigating corrosion of the metal matrix. When the acid content is too high, the solder paste poses a greater risk of corrosion to the metal. The nitrogen in the nitrogen-containing heterocyclic organic acid can form a coordination complex with the metal, and its polymer network can increase the protective effect on the metal. However, the nitrogen-containing heterocyclic organic acid has relatively large steric hindrance, resulting in slower activity. Conversely, when the fatty alcohol content is too high, the activity of the solder paste decreases significantly.

[0027] Furthermore, the fatty alcohol is pentaerythritol and / or dibromobutenediol.

[0028] Preferably, the fatty alcohol is dibromobutenediol.

[0029] This application unexpectedly discovered that when the fatty alcohol is dibromobutenediol, and its weight ratio to polysaccharide anhydride is specified as (1-2):(13-17), the system exhibits relatively stable activity. The inventors speculate that the reason is that polysaccharide anhydride undergoes partial decomposition at the high temperature of soldering, and the increased carboxyl content improves the solder paste's activity in removing oxide layers. However, the hydroxyl groups in dibromobutenediol can combine with these active carboxyl groups. When the hydroxyl content is too high, this activity is inhibited, and the combination of its alkenyl groups with polysaccharide anhydride also adversely affects the system's flowability and wettability, resulting in a decrease in solder paste spread. Therefore, controlling the relative content of dibromobutenediol and polysaccharide anhydride improves the system's activity and stability.

[0030] Furthermore, the thixotropic agent is at least one of oleamide, hydrogenated castor oil, modified hydrogenated castor oil, 12-hydroxybis(ethylene)stearamide, and polyamide wax.

[0031] Preferably, the thixotropic agent is 12-hydroxybis(ethylene)stearamide.

[0032] Furthermore, the organic solvent is selected from at least one of terpineol, diethylene glycol, tetraethylene glycol, 2-ethyl-1,3-hexanediol, diethylene glycol monohexyl ether, diethylene glycol octyl ether, diethylene glycol hexyl ether, tripropylene glycol butyl ether, and tetraethylene glycol dimethyl ether.

[0033] Furthermore, the organic solvent is diethylene glycol monoethyl ether.

[0034] Furthermore, the method for preparing the flux is as follows:

[0035] (1) Use a partial organic solvent to mix and dissolve fatty acids and fatty alcohols;

[0036] (2) Mix the crushed rosin with the remaining components and heat at a temperature of 130-160°C. Stir until completely dissolved and then stop heating. Add the components from (1) and stir until well mixed. Cool to room temperature to obtain the flux.

[0037] (3) After sealing the flux, freeze it at -18℃ for 12 hours.

[0038] Furthermore, the solder paste is prepared by mixing solder powder and flux paste and stirring evenly at a stirring speed of 30-50 rpm, followed by vacuum degassing.

[0039] Furthermore, the solder paste is stored at 0-10°C.

[0040] Preferably, the tin powder is Sn0.3Ag0.5Cu.

[0041] Preferably, the average particle diameter of the tin powder is 10-45 μm.

[0042] Furthermore, the solder paste described in this application is used in the soldering process of OSP pads.

[0043] Furthermore, the OSP material type is any one of rosin-based, active resin-based, and azole-based materials; preferably, it is an azole-based material.

[0044] Beneficial effects

[0045] 1. The solder paste of this application leaves virtually no rosin residue on the solder joint surface after soldering, exhibiting excellent soldering performance and high electrical reliability. By controlling the cohesive force of the system and its adhesion to the soldering metal substrate, the system possesses excellent lubricity and thixotropy, making it less prone to defects such as voids, collapse, and bridging during soldering, and ensuring stable printing performance.

[0046] 2. The solder paste of this application has excellent activity at high temperature through optimization of the types and amounts of modified rosin, polysaccharide anhydride, activator, etc. While having a high removal ability of oxide layer, it has basically no corrosive effect on the metal substrate being soldered.

[0047] 3. The solder paste composition of this application has good compatibility with OSP pads, good compatibility with OSP pads made of imidazole, fast bonding speed, bright solder joints, and strong corrosion resistance and oxidation resistance of the pads. Detailed Implementation

[0048] Example

[0049] Example 1

[0050] This embodiment provides a self-etching resistant solder paste for OSP pads; by total weight, the solder paste comprises 88% tin powder and 12% flux; the tin powder is Sn0.3Ag0.5Cu with an average particle diameter of 35μm.

[0051] Based on the total weight of the flux, the flux components include: 40% disproportionated rosin (KR610), 15% polysaccharide anhydride (molecular weight 5800, acid value 603 mg KOH / g, purchased from Wenzhou Qingming Chemical), 0.5% 2-pyridinecarboxylic acid, 0.02% malonic acid, 1.5% dibromobutenediol, 11% 12-hydroxybis(ethylene)stearamide, and diethylene glycol monoethyl ether, with the balance being 100%.

[0052] Example 2

[0053] This embodiment provides a special solder paste for OSP pads with self-etching effect; by total weight, the solder paste includes 85% solder powder and 15% flux; the solder powder is Sn0.3Ag0.5Cu with an average particle diameter of 45μm.

[0054] Based on the total weight of the flux, the flux components include: 50% disproportionated rosin (KR610), 10% polysaccharide anhydride (molecular weight 5800, acid value 603 mg KOH / g, purchased from Wenzhou Qingming Chemical), 0.83% 2-pyridinecarboxylic acid, 0.012% malonic acid, 4.13% dibromobutenediol, 8% 12-hydroxybis(ethylene)stearamide, and diethylene glycol monoethyl ether, with the balance being 100%.

[0055] Example 3

[0056] This embodiment provides a special solder paste for OSP pads with self-etching effect; by total weight, the solder paste comprises 90% solder powder and 10% flux; the solder powder is Sn0.3Ag0.5Cu with an average particle diameter of 10μm.

[0057] Based on the total weight of the flux, the flux components include: 30% disproportionated rosin (KR610), 20% polysaccharide anhydride (molecular weight 5800, acid value 603 mg KOH / g, purchased from Wenzhou Qingming Chemical), 0.16% 2-pyridinecarboxylic acid, 0.02% malonic acid, 1.32% dibromobutenediol, 13% 12-hydroxybis(ethylene)stearamide, and diethylene glycol monoethyl ether, with the balance being 100%.

[0058] Example 4

[0059] It is basically the same as Example 1, except that the polysediment has a molecular weight of 8000 and an acid value of 815 mgKOH / g, and was purchased from Wenzhou Qingming Chemical.

[0060] Example 5

[0061] The method is basically the same as in Example 1, except that, based on the total weight of the flux, the flux components include: 40% disproportionated rosin (KR610), 15% polysaccharide anhydride (molecular weight 5800, acid value 603 mg KOH / g, purchased from Wenzhou Qingming Chemical), 0.5% 2-pyridinecarboxylic acid, 0.02% malonic acid, 11% 12-hydroxybis(ethylene)stearamide, and diethylene glycol monoethyl ether to make up the balance of 100%.

[0062] Example 6

[0063] The method is basically the same as in Example 1, except that, based on the total weight of the flux, the flux components include: 40% disproportionated rosin (KR610), 15% polysaccharide anhydride (molecular weight 5800, acid value 603 mg KOH / g, purchased from Wenzhou Qingming Chemical), 0.5% 2-pyridinecarboxylic acid, 0.02% malonic acid, 5% dibromobutenediol, 11% 12-hydroxybis(ethylene)stearamide, and diethylene glycol monoethyl ether to make up the balance of 100%.

[0064] Example 7

[0065] The method is basically the same as in Example 1, except that, based on the total weight of the flux, the flux components include: 40% disproportionated rosin (KR610), 15% polysaccharide anhydride (molecular weight 5800, acid value 603 mg KOH / g, purchased from Wenzhou Qingming Chemical), 0.5% 2-pyridinecarboxylic acid, 0.02% malonic acid, 1.5% pentaerythritol, 11% 12-hydroxybis(ethylene)stearamide, and diethylene glycol monoethyl ether to make up the balance of 100%.

[0066] Example 8

[0067] The results are basically the same as in Example 1, except that the disproportionated rosin has a softening point of 75°C (ring and ball method), an acid value of 150 mg KOH / g, and was purchased from Xiamen Weier Chemical Co., Ltd., WG Grade.

[0068] In the above embodiments 1-8, the preparation method of the flux paste is as follows:

[0069] (1) Use a partial organic solvent to mix and dissolve fatty acids and fatty alcohols;

[0070] (2) Mix the crushed rosin with the remaining components and heat at 150°C. Stir until completely dissolved and then stop heating. Add the components from (1) and stir until well mixed. Cool to room temperature to obtain the flux.

[0071] (3) After sealing the flux, freeze it at -18℃ for 12 hours.

[0072] The solder paste is prepared by mixing solder powder and flux, stirring evenly at a stirring speed of 45 rpm, and then removing bubbles by vacuuming.

[0073] Performance testing methods:

[0074] Copper plate corrosion resistance: Tested according to IPC-TM-650 2.6.15 standard. Surface insulation resistance (SIR): Tested according to IPC-TM-650 2.6.3.3B standard, using comb-type electrodes as specified in IPC-B-24, with a line width of 0.14 mm and a line spacing of 0.5 mm. The test temperature was 85℃, the humidity was 85%RH, and a 50V DC bias voltage was applied for a 168-hour damp test. The resistance values ​​were measured after 24 hours, 96 hours, and 168 hours, with a test voltage of -100V DC. Spread rate: The spread rate of the solder paste was tested according to JIS-Z-3197 in the example test. Solder ball test: Tested according to IPC-TM-650 2.4.43 standard. The test results of the example are shown in Table 1.

[0075] Performance test results:

[0076] Table 1

[0077]

Claims

1. An OSP solder paste with self-etching inhibition, characterized in that, The solder paste comprises 85-90% solder powder and 10-15% flux by total weight. Based on the total weight of the flux paste, the flux paste components include: 30-50% modified rosin, 10-20% polysaccharide anhydride, 1.5-5% activator, 8-13% thixotropic agent, and the organic solvent balance is 100%. The active agent is a combination of nitrogen-containing heterocyclic organic acids, fatty acids, and dibromobutenediol; The weight ratio of the nitrogen-containing heterocyclic organic acid, fatty acid, and dibromobutenediol is (0.3-0.7):(0.01-0.04):(0.9-3.5). The polysaccharide has a molecular weight of 4000-8000 and an acid value of 450-800 mg KOH / g; The nitrogen-containing heterocyclic organic acid is selected from at least one of 2-pyridinecarboxylic acid, benzimidazole-1-acetic acid, and benzotriazole-1-acetic acid.

2. The OSP solder paste with self-etching inhibition function according to claim 1, characterized in that, The modified rosin is disproportionated rosin.

3. The OSP solder paste with self-etching effect according to claim 2, characterized in that, The softening point of the disproportionated rosin, as determined by the ring and ball method, is 70-100℃, and its acid value is 145-190 mg KOH / g.

4. An OSP solder paste with self-etching inhibition function according to any one of claims 1-3, characterized in that, The average particle diameter of the tin powder is 10-45 μm.

5. An application of the OSP pad solder paste with self-etching inhibition according to any one of claims 1-4, characterized in that, The solder paste is used in the soldering process of OSP pads, and the material type of the OSP is any one of rosin-based, active resin-based, and azole-based.

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