A coated solder powder, solder paste, and preparation method and application thereof

Abstract

The application provides a coated solder powder, solder paste and a preparation method and application thereof. The coated solder powder comprises a solder powder and an alkyl imidazole-rare earth complex coated on the surface of the solder powder. The mass of the alkyl imidazole-rare earth complex is 0.5%-1.5% of the mass of the solder powder. The solder paste comprises 85-92 parts of the coated solder powder and 8-15 parts of a flux. The coated solder powder, solder paste, preparation method and application thereof have the following advantages: the alkyl imidazole-rare earth complex coated on the surface of the solder powder has the properties of alkyl imidazole and rare earth elements and has a synergistic effect, the wettability of the solder paste is improved, the chemical stability and storage stability of the solder powder are enhanced, the void rate of the solder joint is reduced, and the shear strength and thermal cycle performance of the solder joint are improved.

Description

Technical Field

[0001] This invention relates to the field of welding materials technology, and more specifically, to a coated solder powder, solder paste, its preparation method, and its application. Background Technology

[0002] Solder paste is a soldering material used in surface mount technology in electronics manufacturing. During the soldering process, it melts and bonds with the pads of electronic components and printed circuit boards (PCBs) to form solder joints. Benzotriazole is a commonly used flux component in solder paste. As a corrosion inhibitor, it forms a protective film on the copper surface, preventing excessive oxidation of the copper pads during soldering and improving solder joint quality. However, benzotriazole has a single function and lacks surface-active properties; its thermal stability is insufficient, and it easily decomposes and generates gas during high-temperature lead-free soldering, which may lead to an increased void ratio in the solder joints.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a coated solder powder, solder paste, its preparation method, and its application. The alkylimidazolium-rare earth complex coated on the surface of the solder powder has the properties of alkylimidazolium and rare earth elements, while also exhibiting a synergistic effect. It plays a role in corrosion inhibition, reduces the surface tension of the solder paste, improves the wetting performance of the solder paste, enhances the chemical stability and storage stability of the solder powder, reduces the void rate of the solder joint, and improves the shear strength and thermal cycling performance of the solder joint.

[0005] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: A coated solder powder includes solder powder and an alkylimidazolium-rare earth complex coated on the surface of the solder powder; the mass of the alkylimidazolium-rare earth complex is 0.5% to 1.5% of the mass of the solder powder.

[0006] Furthermore, the solder powder is at least one of SAC305, SAC0307, ​​and SAC105.

[0007] Furthermore, the alkyl group in the alkylimidazolium-rare earth complex is at least one of decaalkyl, undecyl, and dodecyl.

[0008] Furthermore, the rare earth element in the alkylimidazolium-rare earth complex is at least one of La, Nd, and Y.

[0009] Furthermore, the alkylimidazolium-rare earth complex is prepared by a coordination reaction between alkylimidazolium and rare earth halides.

[0010] Furthermore, the coordination reaction between the alkylimidazolium and the rare earth halide is a monodentate coordination reaction with a coordination ratio of 1:3.

[0011] Furthermore, the halogen element of the rare earth halide is at least one of Cl and Br.

[0012] Furthermore, the method for preparing the alkylimidazolium-rare earth complex includes the following steps: a. Prepare rare earth halide solutions and alkyl imidazole solutions; b. Under nitrogen protection, the alkylimidazolium solution and the rare earth halide solution are mixed evenly and heated and stirred to carry out the coordination reaction according to the molar ratio of rare earth element ions to alkylimidazolium of 1:3.1~1:4. c. After the reaction is complete, the mixture is concentrated under reduced pressure and anhydrous diethyl ether is added. After stirring evenly, the mixture is refrigerated and allowed to stand. The precipitate is collected, washed, and dried to obtain the alkylimidazolium-rare earth complex.

[0013] The preparation method of the above-mentioned coated solder powder includes the following steps: A. Clean and dry the solder powder; B. Prepare alkylimidazolium-rare earth complex solution; C. Add solder powder to the alkylimidazolium-rare earth complex solution according to the mass of the alkylimidazolium-rare earth complex being 0.5%~1.5% of the solder powder mass, and disperse and soak the solder powder evenly. D. After soaking and drying, coated solder powder with alkyl imidazole-rare earth complex is obtained.

[0014] A solder paste comprising the following components in parts by weight: 85-92 parts of the above-mentioned coated solder powder and 8-15 parts of flux.

[0015] Further, the flux comprises the following components by weight: 35-50 parts film-forming agent, 3-8 parts activator, 3-8 parts thixotropic agent, 30-50 parts solvent, 0.5-1.5 parts antioxidant, 0.5-1.2 parts pH adjuster, and 0.1-0.8 parts surfactant.

[0016] Furthermore, the film-forming agent is at least one of hydrogenated rosin, disproportionated rosin, polymerized rosin, water-white rosin, and acrylic rosin.

[0017] Furthermore, the activator is at least one of glutaric acid, adipic acid, succinic acid, malic acid, citric acid, and glycolic acid.

[0018] Furthermore, the thixotropic agent is at least one of hydrogenated castor oil, polyamide wax, and ethylene bis-stearamide.

[0019] Further, the solvent is at least one selected from diethylene glycol butyl ether, tripropylene glycol butyl ether, propylene glycol methyl ether, ethylene glycol, glycerol, and tetrahydrofurfuryl alcohol.

[0020] Furthermore, the antioxidant is at least one selected from 2,6-di-tert-butyl-p-cresol, tert-butylhydroquinone, butylated hydroxyanisole, and sodium diethyldithiocarbamate.

[0021] Further, the pH adjuster is at least one of triethanolamine, 2-amino-2-methyl-1-propanol, ethylenediamine, and dimethylethanolamine.

[0022] Furthermore, the surfactant is at least one of polyethylene glycol monomethyl ether, polyoxyethylene octylphenyl ether, polyethylene glycol fatty acid ester, fatty alcohol polyoxyethylene ether, and octylphenol polyoxyethylene ether.

[0023] The above-mentioned method for preparing solder paste includes the following steps: 1) Heat and stir the film-forming agent and solvent until completely dissolved, then add the thixotropic agent and mix thoroughly; 2) Cool down and add the activator, stirring until completely dissolved; 3) Continue cooling, add antioxidants, pH adjusters, and surfactants, and stir until completely dissolved; 4) Cold grinding to obtain flux; 5) Mix the flux with the coated solder powder evenly to obtain solder paste.

[0024] The application of the above-mentioned coated solder powder, the above-mentioned method for preparing coated solder powder, the above-mentioned solder paste, or the above-mentioned method for preparing solder paste in the preparation of antioxidant and strong wetting soldering materials.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The alkylimidazolium-rare earth complex of the present invention, which is coated on the surface of solder powder, has the properties of alkylimidazolium and rare earth elements and also has a synergistic effect.

[0026] 2. The imidazole ring of the alkyl imidazole-rare earth complex coated on the surface of solder powder in this invention has a corrosion inhibitory effect, and the long chain can improve surface activity. It can form a stable adsorption film with the substrate surface to play a corrosion inhibitory role, and reduce the surface tension of the solder paste to improve the wettability of the solder paste. Rare earth element ions can form stable rare earth element -O bonds with oxygen atoms in the oxide film, assisting the activator to remove the oxide film, which can further improve the wettability of the solder paste.

[0027] 3. This invention coats solder powder with alkylimidazolium-rare earth complexes, isolating it from air and water, reducing oxidation, preventing oxidative corrosion, and enhancing its chemical stability and storage stability. Simultaneously, it reduces the gases generated by the decomposition of the solder powder oxide film at soldering temperatures, thus lowering the void ratio at the solder joint from the source.

[0028] 4. In the solder paste of the present invention, rare earth element ions of alkyl imidazole-rare earth complex are dispersed in the solder joint during the soldering process, which refines the grains, avoids the IMC layer (intermetallic compound layer) being too thick, and improves the shear strength and thermal cycling performance of the solder joint. Detailed Implementation

[0029] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0030] A coated solder powder includes solder powder and an alkylimidazolium-rare earth complex coated on the surface of the solder powder; the mass of the alkylimidazolium-rare earth complex is 0.5% to 1.5% of the mass of the solder powder (including but not limited to 0.5%, 0.8%, 1.0%, 1.2%, and 1.5%).

[0031] Preferably, the solder powder is at least one of SAC305, SAC0307, ​​and SAC105.

[0032] Preferably, the alkyl group in the alkylimidazolium-rare earth complex is at least one selected from decaalkyl, undecyl, and dodecyl.

[0033] Preferably, the rare earth element in the alkylimidazolium-rare earth complex is at least one of La, Nd, and Y.

[0034] Preferably, the alkylimidazolium-rare earth complex is prepared by a coordination reaction between alkylimidazolium and rare earth halides.

[0035] Preferably, the coordination reaction is a monodentate coordination reaction with a coordination ratio of 1:3.

[0036] Preferably, the halogen element of the rare earth halide is at least one of Cl and Br.

[0037] Preferably, the method for preparing the alkylimidazolium-rare earth complex includes the following steps: 1. After drying anhydrous rare earth halides under vacuum at 120°C for 5 hours, dissolve them in anhydrous ethanol. Dissolve alkyl imidazoles in anhydrous ethanol with 5% anhydrous acetonitrile added. 2. According to the molar ratio of rare earth element ions to alkyl imidazole of 1:3.1~1:4 (including but not limited to 1:3.1, 1:3.2, 1:3.3, 1:3.4, 1:3.5, 1:3.6, 1:3.7, 1:3.8, 1:3.9, 1:4.0), with excess ligand, under nitrogen protection, slowly add the alkyl imidazole solution dropwise to the rare earth halide solution to avoid excessively high local concentrations, and stir magnetically at 50~70℃ for 8~14 hours; 3. After the reaction is complete, concentrate the solution under reduced pressure at 40~45℃ (including but not limited to 40℃, 41℃, 42℃, 43℃, 44℃, 45℃) and a vacuum degree of 0.08~0.1MPa (including but not limited to 0.08MPa, 0.09MPa, 0.1MPa) to 20~25% of the original volume (including but not limited to 20%, 21%, 22%, 23%, 24%, 25% or a range between two of these values). Add 3 times the volume of anhydrous diethyl ether to the concentrate, stir well, and let it stand in a refrigerator at 0℃ for 24 hours. Collect the precipitate, wash the precipitate 2~3 times with anhydrous diethyl ether, and dry the precipitate in a vacuum drying oven at 35~55℃ (including but not limited to 35℃, 40℃, 45℃, 50℃, 55℃) for 6~10 hours (including but not limited to 6 hours, 7 hours, 8 hours, 9 hours, 10 hours) to obtain the alkylimidazolium-rare earth complex.

[0038] Alkyl imidazoles can undergo coordination reactions with rare earth halides. Rare earth ions have the ability to accept electron pairs, while alkyl imidazoles have the ability to donate electron pairs. The rare earth ion acts as the central ion, and the imidazole ring N3 (not substituted by an alkyl group) of the alkyl imidazole acts as the atomic ligand. The N3 atom provides a lone pair of electrons to form a coordination bond with the empty orbital of the rare earth ion.

[0039] A method for preparing coated solder powder includes the following steps: 1. Clean the solder powder with anhydrous ethanol using ultrasonic cleaning for 10-12 minutes (including but not limited to 10 minutes, 11 minutes, 12 minutes) to remove surface oil stains, filter, and then dry in a vacuum drying oven at 40℃ for 2 hours; 2. Completely dissolve the alkylimidazolium-rare earth complex in anhydrous ethanol; 3. With the alkylimidazolium-rare earth complex at a mass of 0.5%~1.5% of the solder powder mass, add the dried solder powder to the alkylimidazolium-rare earth complex solution and soak at room temperature for 50~60 min (50 min, 52 min, 54 min, 55 min, 56 min, 58 min, 60 min). During this period, ultrasonically stir for 5 min every 15~20 min (including but not limited to 15 min, 16 min, 17 min, 18 min, 19 min, 20 min) to ensure uniform contact between the solder powder and the solution. 4. After soaking, filter and collect the solder powder, and dry it in a vacuum drying oven at 45℃ and 0.08MPa for 7 hours to obtain coated solder powder with alkylimidazolium-rare earth complex.

[0040] Rare earth element ions (in the form of La) in alkyl imidazole-rare earth complexes 3+ (For example) Alkyl imidazoles can form La-O bonds with the oxide layer on the surface of solder powder. The N atom of the imidazole ring in the alkyl imidazole can form coordination bonds with the active metal sites of the oxide layer. The long chains of alkyl imidazoles are hydrophobic and, through van der Waals forces, are arranged in an orderly manner on the surface of the solder powder, forming a dense hydrophobic layer. Furthermore, the long-chain alkyl groups exhibit steric hindrance, which can prevent solder powder agglomeration. When alkyl imidazole-rare earth complexes dissolve in anhydrous ethanol, the anhydrous ethanol can quickly wet the surface of the solder powder, significantly reducing the solid-liquid interfacial tension, allowing the complex molecules to spread uniformly on the solder powder surface.

[0041] A solder paste comprising the following components in parts by weight: 85-92 parts of coated solder powder and 8-15 parts of flux.

[0042] Preferably, the flux comprises the following components by weight: 35-50 parts film-forming agent, 3-8 parts activator, 3-8 parts thixotropic agent, 30-50 parts solvent, 0.5-1.5 parts antioxidant, 0.5-1.2 parts pH adjuster, and 0.1-0.8 parts surfactant.

[0043] Preferably, the film-forming agent is at least one of hydrogenated rosin, disproportionated rosin, polymerized rosin, water-white rosin, and acrylic rosin.

[0044] Preferably, the activator is at least one selected from glutaric acid, adipic acid, succinic acid, malic acid, citric acid, and glycolic acid.

[0045] Preferably, the thixotropic agent is at least one of hydrogenated castor oil, polyamide wax, and ethylene bis-stearamide.

[0046] Preferably, the solvent is at least one selected from diethylene glycol butyl ether, tripropylene glycol butyl ether, propylene glycol methyl ether, ethylene glycol, glycerol, and tetrahydrofurfuryl alcohol.

[0047] Preferably, the antioxidant is at least one selected from 2,6-di-tert-butyl-p-cresol, tert-butylhydroquinone, butylated hydroxyanisole, and sodium diethyldithiocarbamate.

[0048] Preferably, the pH adjuster is at least one selected from triethanolamine, 2-amino-2-methyl-1-propanol, ethylenediamine, and dimethylethanolamine.

[0049] Preferably, the surfactant is at least one of polyethylene glycol monomethyl ether, polyoxyethylene octylphenyl ether, polyethylene glycol fatty acid ester, fatty alcohol polyoxyethylene ether, and octylphenol polyoxyethylene ether.

[0050] A method for preparing solder paste includes the following steps: 1) Add the film-forming agent and solvent to the reaction vessel, heat to 80~95℃ (including but not limited to 80℃, 85℃, 90℃, 95℃), stir until completely dissolved, add the thixotropic agent, and continue stirring for 30~40min (including but not limited to 30min, 32min, 35min, 36min, 38min, 40min). 2) Cool the reactor to 75~80℃ (including but not limited to 75℃, 76℃, 77℃, 78℃, 79℃, 80℃), add the activator, and stir until completely dissolved; 3) Cool the reactor to 65~75℃ (including but not limited to 65℃, 68℃, 70℃, 72℃, 75℃), add antioxidants, pH adjusters, and surfactants, and stir until completely dissolved; 4) Refrigerate at 0~10℃ (including but not limited to 0℃, 3℃, 5℃, 8℃, 10℃) for 48 hours, grind, and obtain flux; 5) Mix the flux with the coated solder powder and stir for 60 minutes to obtain solder paste.

[0051] The application of the above-mentioned coated solder powder, the above-mentioned method for preparing coated solder powder, the above-mentioned solder paste, and the above-mentioned method for preparing solder paste in the preparation of antioxidant and strong wetting soldering materials.

[0052] Alkyl imidazole-rare earth complexes possess long-chain alkyl groups, which, while acting as corrosion inhibitors, can reduce the surface tension of solder paste and improve its wettability. Alkyl imidazole-rare earth complexes exhibit excellent compatibility with film-forming agents and solvents in fluxes. The rare earth element ions (with La as the main component) in alkyl imidazole-rare earth complexes... 3+ For example, it can form a stable La-O bond with oxygen atoms in the oxide film, assisting the activator in removing the oxide film. Compared with alkylimidazolium, the synergistic effect of alkylimidazolium and rare earth elements in alkylimidazolium-rare earth complex can better improve the wetting performance of solder paste.

[0053] Alkylimidazolium-rare earth complexes coat solder powder, isolating it from air and water, thus reducing oxidation. Compared to benzotriazole and alkylimidazolium, alkylimidazolium-rare earth complexes prevent oxidative corrosion, enhance the chemical and storage stability of the solder powder, and reduce the gases generated by the decomposition of the solder powder oxide film at soldering temperatures, thereby reducing the void ratio of the solder joint from the source. During soldering, rare earth ions from the alkylimidazolium-rare earth complex are dispersed throughout the solder joint, refining the grain size, preventing excessively thick IMC layers, and improving the shear strength and thermal cycling performance of the solder joint.

[0054] Example 1 Anhydrous lanthanum chloride was dried under vacuum at 120°C for 5 hours and then dissolved in anhydrous ethanol. Undecylimidazole (referring to 1-undecylimidazole) was dissolved in anhydrous ethanol with 5% anhydrous acetonitrile added. 3+ The undecylimidazole solution was slowly added dropwise to the lanthanum chloride solution under nitrogen protection at a molar ratio of 1:3.2. The mixture was magnetically stirred at 55°C for 11 h. After the reaction was completed, the solution was concentrated under reduced pressure at 40°C and 0.1 MPa to 20-25% of its original volume. Three volumes of anhydrous diethyl ether were added to the concentrate, and the mixture was stirred until homogeneous. The solution was then allowed to stand at 0°C for 24 h. The precipitate was collected, washed three times with anhydrous diethyl ether, and dried in a vacuum drying oven at 45°C for 8 h to obtain the undecylimidazole-lanthanum complex.

[0055] Undecylimidazole can undergo a coordination reaction with lanthanum chloride, La 3+ 1-Undecylimidazole possesses the ability to accept electron pairs, while La... 3+ As the central ion, the imidazole ring N3 (unsubstituted with undecyl) of 1-undecylimidazolium acts as an atomic ligand, with the N3 atom donating a lone pair of electrons, interacting with La. 3+ Empty orbitals form coordinate bonds. The coordination reaction of 1-undecylimidazole with lanthanum chloride is a undentate coordination reaction with a coordination ratio of 1:3, as shown in the following equation: .

[0056] The undecylimidazolium-lanthanum complex has the following structural formula: .

[0057] Undecylimidazol-lanthanum complexes possess the properties of undecylimidazol and rare earth element La, while also exhibiting synergistic effects.

[0058] Example 2 Anhydrous neodymium chloride was dried under vacuum at 120°C for 5 hours and then dissolved in anhydrous ethanol. Undecylimidazole was dissolved in anhydrous ethanol with 5% anhydrous acetonitrile added. Nd 3+The undecylimidazole solution was slowly added dropwise to the neodymium chloride solution under nitrogen protection at a molar ratio of 1:3.5. The mixture was magnetically stirred at 400 rpm for 12 h at 55 °C. After the reaction was completed, the solution was concentrated under reduced pressure at 40 °C and 0.1 MPa to 20-25% of its original volume. Three volumes of anhydrous diethyl ether were added to the concentrate, and the mixture was stirred until homogeneous. The solution was then allowed to stand in a refrigerator at 0 °C for 24 h. The precipitate was collected, washed three times with anhydrous diethyl ether, and dried in a vacuum drying oven at 50 °C for 8 h to obtain the undecylimidazole-neodymium complex.

[0059] Example 3 Anhydrous yttrium chloride was dried under vacuum at 120°C for 5 hours and then dissolved in anhydrous ethanol. Undecylimidazole was dissolved in anhydrous ethanol with 5% anhydrous acetonitrile added. 3+ The undecylimidazole solution was slowly added dropwise to the yttrium chloride solution under nitrogen protection at a molar ratio of 1:3.1 with undecylimidazole. The mixture was magnetically stirred at 380 rpm for 10 h at 70 °C. After the reaction was completed, the solution was concentrated under reduced pressure at 40 °C and 0.1 MPa to 20-25% of its original volume. Three times the volume of anhydrous diethyl ether was added to the concentrate, and the mixture was stirred until homogeneous. The solution was then allowed to stand at 0 °C for 24 h. The precipitate was collected, washed three times with anhydrous diethyl ether, and dried in a vacuum drying oven at 48 °C for 8 h to obtain the undecylimidazole-yttrium complex.

[0060] Example 4 Anhydrous lanthanum chloride was dried under vacuum at 120°C for 5 hours and then dissolved in anhydrous ethanol. Dodecyl imidazole was dissolved in anhydrous ethanol with 5% anhydrous acetonitrile added. 3+ The dodecyl imidazole solution was slowly added dropwise to the lanthanum chloride solution under nitrogen protection at a molar ratio of 1:3.5. The mixture was magnetically stirred at 50°C for 14 hours. After the reaction was completed, the solution was concentrated under reduced pressure at 40°C and a vacuum of 0.08 MPa to 20-25% of its original volume. Three times the volume of anhydrous diethyl ether was added to the concentrate, and the mixture was stirred until homogeneous. The solution was then allowed to stand at 0°C for 24 hours. The precipitate was collected, washed three times with anhydrous diethyl ether, and dried in a vacuum drying oven at 50°C for 6 hours to obtain the dodecyl imidazole-lanthanum complex.

[0061] Example 5 Anhydrous lanthanum chloride was dried under vacuum at 120°C for 5 hours and then dissolved in anhydrous ethanol. Decylimidazole was dissolved in anhydrous ethanol with 5% anhydrous acetonitrile added. 3+Under nitrogen protection, the decaalkylimidazolium solution was slowly added dropwise to the lanthanum chloride solution at a molar ratio of 1:3.1. The mixture was magnetically stirred at 50°C for 9 hours. After the reaction was completed, the solution was concentrated under reduced pressure at 40°C and a vacuum of 0.08 MPa to 20-25% of its original volume. Three times the volume of anhydrous diethyl ether was added to the concentrate, and the mixture was stirred until homogeneous. The solution was then allowed to stand at 0°C for 24 hours. The precipitate was collected, washed three times with anhydrous diethyl ether, and dried in a vacuum drying oven at 43°C for 8 hours to obtain the decaalkylimidazolium-lanthanum complex.

[0062] Example 6 Anhydrous lanthanum bromide was dried under vacuum at 120°C for 5 hours and then dissolved in anhydrous ethanol. Undecylimidazole was dissolved in anhydrous ethanol with 5% anhydrous acetonitrile added. 3+ The undecylimidazole solution was slowly added dropwise to the lanthanum bromide solution under nitrogen protection at a molar ratio of 1:3.1. The mixture was magnetically stirred at 50°C for 8 hours. After the reaction was completed, the solution was concentrated under reduced pressure at 45°C and a vacuum of 0.09 MPa to 20-25% of its original volume. Three times the volume of anhydrous diethyl ether was added to the concentrate, and the mixture was stirred until homogeneous. The solution was then allowed to stand at 0°C for 24 hours. The precipitate was collected, washed three times with anhydrous diethyl ether, and dried in a vacuum drying oven at 35°C for 10 hours to obtain the undecylimidazole-lanthanum complex.

[0063] Example 7 Solder powder SAC305 was ultrasonically cleaned with anhydrous ethanol for 10 min to remove surface oil, filtered, and then dried in a vacuum drying oven at 40℃ for 2 h. The undecylimidazole-lanthanum complex prepared in Example 1 was completely dissolved in anhydrous ethanol, with the mass of the undecylimidazole-lanthanum complex being 1% of the mass of the solder powder. The dried solder powder was added to the complex solution and soaked at room temperature for 50 min, with ultrasonic stirring for 5 min every 20 min to ensure uniform contact between the solder powder and the solution. After soaking, the solder powder was collected by filtration and dried in a vacuum drying oven at 45℃ and 0.08 MPa for 7 h to obtain coated solder powder coated with the undecylimidazole-lanthanum complex.

[0064] La in undecylimidazolium-lanthanum complex 3+ Undecylimidazole can form La-O bonds with the oxide layer on the surface of solder powder, and the N atom of the imidazole ring in undecylimidazole can form coordinate bonds with the active metal sites of the oxide layer. The long undecylimidazole chain is hydrophobic and, through van der Waals forces, arranges itself in an orderly manner on the solder powder surface, forming a dense hydrophobic layer. Furthermore, the long-chain alkyl group exhibits steric hindrance, which prevents solder powder agglomeration. The undecylimidazole-lanthanum complex dissolves in anhydrous ethanol, which rapidly wets the solder powder surface, significantly reducing the solid-liquid interfacial tension and allowing the complex molecules to spread uniformly on the solder powder surface.

[0065] The imidazole ring of the undecylimidazolium-lanthanum complex exhibits corrosion inhibition, and the long chain enhances surface activity. It can form a stable adsorption film on the substrate surface to inhibit corrosion, and also reduce the surface tension of the solder paste, improving its wettability. The central ion La... 3+ It can form stable La-O bonds with oxygen atoms in the oxide film, assisting the activator in removing the oxide film and further improving the wetting performance of the solder paste.

[0066] The flux contains 46 parts film-forming agent (hydrogenated rosin), 5.2 parts activator (3.6 parts adipic acid and 1.6 parts citric acid), 5 parts thixotropic agent (hydrogenated castor oil), 42 parts solvent (22 parts diethylene glycol butyl ether and 20 parts propylene glycol methyl ether), 0.8 parts antioxidant (2,6-di-tert-butyl-p-cresol), 0.8 parts pH adjuster (triethanolamine), and 0.2 parts surfactant (polyethylene glycol monomethyl ether).

[0067] Solder paste preparation method: 1. Add film-forming agent and solvent to reaction vessel, heat to 82℃, stir until completely dissolved, add thixotropic agent, and continue stirring for 40 min; 2. Cool reaction vessel to 76℃, add activator, and stir until completely dissolved; 3. Cool reaction vessel to 72℃, add antioxidant, pH adjuster, and surfactant, and stir until completely dissolved; 4. Refrigerate at 6℃ for 48 h, grind, and obtain flux; 5. Mix 10.5 parts of flux with 89.5 parts of undecylimidazolium-lanthanum complex-coated solder powder, stir for 60 min, and obtain solder paste.

[0068] Undecylimidazole-lanthanum complexes coat solder powder, preventing oxidation and corrosion, and exhibiting good chemical stability; they also demonstrate excellent compatibility with film-forming agents and solvents. Coating solder powder with undecylimidazole-lanthanum complexes isolates it from air and water, reducing solder powder oxidation and enhancing its storage stability. Simultaneously, it reduces the gases generated by the decomposition of the solder powder oxide film at soldering temperatures, thereby lowering the void ratio of solder joints from the source. During the soldering process, the La... 3+ It is dispersed in the solder joint, refines the grains, avoids excessive IMC layer thickness, and improves the shear strength and thermal cycling performance of the solder joint.

[0069] Example 8 The difference between this embodiment and Example 7 is that the mass of the undecylimidazolium-lanthanum complex is 0.5% of the mass of the solder powder.

[0070] Example 9 The difference between this embodiment and Example 7 is that the mass of the undecylimidazolium-lanthanum complex is 1.5% of the mass of the solder powder.

[0071] Example 10 The difference between this embodiment and Example 7 is that the mass of the undecylimidazolium-lanthanum complex is 1.2% of the mass of the solder powder.

[0072] Example 11 The difference between this embodiment and Embodiment 7 is that solder paste is prepared by mixing 11.5 parts of flux with 88.5 parts of coated solder powder coated with undecylimidazolium-lanthanum complex.

[0073] Example 12 Solder powder SAC0307 was ultrasonically cleaned with anhydrous ethanol for 12 min to remove surface oil, filtered, and then dried in a vacuum drying oven at 40℃ for 2 h. The undecylimidazole-lanthanum complex prepared in Example 1 was completely dissolved in anhydrous ethanol, with the mass of the undecylimidazole-lanthanum complex being 1.2% of the solder powder mass. The dried solder powder was added to the complex solution and soaked at room temperature for 60 min, with ultrasonic stirring for 5 min every 15 min to ensure uniform contact between the solder powder and the solution. After soaking, the solder powder was filtered and collected, then dried in a vacuum drying oven at 45℃ and 0.08 MPa for 7 h to obtain coated solder powder coated with the undecylimidazole-lanthanum complex.

[0074] The flux contains 45 parts film-forming agent (40 parts hydrogenated rosin, 3 parts disproportionated rosin, 2 parts polymerized rosin), 5.9 parts activator (2.5 parts adipic acid, 2.4 parts citric acid, 1.0 part succinic acid), 5 parts thixotropic agent (hydrogenated castor oil), 42 parts solvent (18 parts diethylene glycol butyl ether, 24 parts propylene glycol methyl ether), 1.0 part antioxidant (2,6-di-tert-butyl-p-cresol), 0.8 parts pH adjuster (triethanolamine), and 0.3 parts surfactant (0.15 parts polyethylene glycol monomethyl ether, 0.15 parts polyoxyethylene octylphenyl ether).

[0075] Solder paste preparation method: 1. Add film-forming agent and solvent to reaction vessel, heat to 92℃, stir until completely dissolved, add thixotropic agent, and continue stirring for 30 min; 2. Cool reaction vessel to 75℃, add activator, and stir until completely dissolved; 3. Cool reaction vessel to 68℃, add antioxidant, pH adjuster, and surfactant, and stir until completely dissolved; 4. Refrigerate at 5℃ for 48 h, grind, and obtain flux; 5. Mix 11 parts flux with 89 parts undecylimidazolium-lanthanum complex-coated solder powder, stir for 60 min, and obtain solder paste.

[0076] Example 13 Solder powder SAC105 was ultrasonically cleaned with anhydrous ethanol for 10 min to remove surface oil, filtered, and then dried in a vacuum drying oven at 40℃ for 2 h. The undecylimidazole-lanthanum complex prepared in Example 1 was completely dissolved in anhydrous ethanol, with the mass of the undecylimidazole-lanthanum complex being 1.3% of the solder powder mass. The dried solder powder was added to the complex solution and soaked at room temperature for 55 min, with ultrasonic stirring for 5 min every 15 min to ensure uniform contact between the solder powder and the solution. After soaking, the solder powder was filtered and collected, then dried in a vacuum drying oven at 45℃ and 0.08 MPa for 7 h to obtain undecylimidazole-lanthanum complex-coated solder powder.

[0077] The flux contains 48 parts film-forming agent (38 parts hydrogenated rosin, 8 parts water-white rosin, 2 parts polymerized rosin), 6.9 parts activator (4.9 parts succinic acid, 1.5 parts glutaric acid, 0.5 parts glycolic acid), 4.0 parts thixotropic agent (modified hydrogenated castor oil), 39 parts solvent (17 parts diethylene glycol butyl ether, 22 parts propylene glycol methyl ether), 0.5 parts antioxidant (2,6-di-tert-butyl-p-cresol), 1.2 parts pH adjuster (triethanolamine), and 0.4 parts surfactant (0.2 parts polyethylene glycol monomethyl ether, 0.2 parts polyoxyethylene octylphenyl ether).

[0078] Solder paste preparation method: 1. Add film-forming agent and solvent to reaction vessel, heat to 89℃, stir until completely dissolved, add thixotropic agent, and continue stirring for 40 min; 2. Cool reaction vessel to 76℃, add activator, and stir until completely dissolved; 3. Cool reaction vessel to 67℃, add antioxidant, pH adjuster, and surfactant, and stir until completely dissolved; 4. Refrigerate at 6℃ for 48 h, grind, and obtain flux; 5. Mix 11.5 parts flux with 88.5 parts undecylimidazolium-lanthanum complex-coated solder powder, stir for 60 min, and obtain solder paste.

[0079] Example 14 Solder powder SAC305 was ultrasonically cleaned with anhydrous ethanol for 10 min to remove surface oil, filtered, and then dried in a vacuum drying oven at 40℃ for 2 h. The undecylimidazole-lanthanum complex prepared in Example 1 was completely dissolved in anhydrous ethanol, with the mass of the undecylimidazole-lanthanum complex being 1% of the mass of the solder powder. The dried solder powder was added to the complex solution and soaked at room temperature for 50 min, with ultrasonic stirring for 5 min every 20 min to ensure uniform contact between the solder powder and the solution. After soaking, the solder powder was collected by filtration and dried in a vacuum drying oven at 45℃ and 0.08 MPa for 7 h to obtain coated solder powder coated with the undecylimidazole-lanthanum complex.

[0080] The flux contains 46 parts film-forming agent (44 parts hydrogenated rosin, 2 parts polymerized rosin), 5.2 parts activator (3.4 parts adipic acid and 1.8 parts citric acid), 5.0 parts thixotropic agent (hydrogenated castor oil), 42 parts solvent (20 parts diethylene glycol butyl ether and 22 parts propylene glycol methyl ether), 0.8 parts antioxidant (2,6-di-tert-butyl-p-cresol), 0.8 parts pH adjuster (triethanolamine), and 0.2 parts surfactant (0.1 parts polyethylene glycol monomethyl ether and 0.1 parts polyoxyethylene octylphenyl ether).

[0081] Solder paste preparation method: 1. Add film-forming agent and solvent to reaction vessel, heat to 83℃, stir until completely dissolved, add thixotropic agent, and continue stirring for 40 min; 2. Cool reaction vessel to 78℃, add activator, and stir until completely dissolved; 3. Cool reaction vessel to 72℃, add antioxidant, pH adjuster, and surfactant, and stir until completely dissolved; 4. Refrigerate at 4℃ for 48 h, grind, and obtain flux; 5. Mix 10.5 parts of flux with 89.5 parts of undecylimidazolium-lanthanum complex-coated solder powder, stir for 60 min, and obtain solder paste.

[0082] Comparative Example 1 The flux contains 46 parts film-forming agent (hydrogenated rosin), 5.2 parts activator (3.6 parts adipic acid and 1.6 parts citric acid), 5 parts thixotropic agent (hydrogenated castor oil), 42 parts solvent (22 parts diethylene glycol butyl ether and 20 parts propylene glycol methyl ether), 0.8 parts antioxidant (2,6-di-tert-butyl-p-cresol), 0.8 parts pH adjuster (triethanolamine), 0.2 parts surfactant (polyethylene glycol monomethyl ether), and 0.5 parts corrosion inhibitor (benzotriazole).

[0083] Solder paste preparation method: 1. Add film-forming agent and solvent to reaction vessel, heat to 82℃, stir until completely dissolved, add thixotropic agent, and continue stirring for 40 min; 2. Cool reaction vessel to 76℃, add activator, and stir until completely dissolved; 3. Cool reaction vessel to 72℃, add antioxidant, pH adjuster, surfactant, and corrosion inhibitor, and stir until completely dissolved; 4. Refrigerate at 6℃ for 48 h, grind, and obtain flux; 5. Mix 10.7 parts flux with 89.3 parts SAC305 solder powder, stir for 60 min, and obtain solder paste.

[0084] Comparative Example 2 The flux contains 46 parts film-forming agent (hydrogenated rosin), 5.2 parts activator (3.6 parts adipic acid and 1.6 parts citric acid), 5 parts thixotropic agent (hydrogenated castor oil), 42 parts solvent (22 parts diethylene glycol butyl ether and 20 parts propylene glycol methyl ether), 0.8 parts antioxidant (2,6-di-tert-butyl-p-cresol), 0.8 parts pH adjuster (triethanolamine), 0.2 parts surfactant (polyethylene glycol monomethyl ether), and 0.5 parts corrosion inhibitor (undecylimidazole).

[0085] Solder paste preparation method: 1. Add film-forming agent and solvent to reaction vessel, heat to 82℃, stir until completely dissolved, add thixotropic agent, and continue stirring for 40 min; 2. Cool reaction vessel to 76℃, add activator, and stir until completely dissolved; 3. Cool reaction vessel to 72℃, add antioxidant, pH adjuster, surfactant, and corrosion inhibitor, and stir until completely dissolved; 4. Refrigerate at 6℃ for 48 h, grind, and obtain flux; 5. Mix 10.7 parts flux with 89.3 parts SAC305 solder powder, stir for 60 min, and obtain solder paste.

[0086] Test case 1. Solder paste wettability test, refer to standard IPC-TM-650 2.4.45.

[0087] 2. Solder paste void rate test: After completing SMT solder paste printing, component placement, and reflow soldering, the void rate is tested.

[0088] III. Solder paste stability test: After storing the solder paste sample at 25℃ for 30 days, test the viscosity value. If the viscosity value increases by less than 10 Pa·s compared with the initial viscosity value, it is recorded as normal. If the viscosity value increases by more than 10 Pa·s, it is recorded as deterioration.

[0089] IV. Solder paste shear strength test: After the solder paste is connected to the Cu substrate and undergoes a reflow process, a shear force parallel to the substrate surface is applied to the solder joint using a universal testing machine until the solder joint fails.

[0090] V. Solder paste thermal cycling test: 3000 thermal cycles at -40-125℃ for 0.5h each.

[0091] Table 1. Performance test results of solder pastes prepared in Examples 7-14 and Comparative Examples 1-2

[0092] A comparison of the solder paste performance between the examples and Comparative Example 1 shows that benzotriazole only has a corrosion-inhibiting effect, while the undecylimidazole-lanthanum complex, with its long-chain alkyl group, can reduce the surface tension of the solder paste and improve its wettability while also exerting a corrosion-inhibiting effect. The undecylimidazole-lanthanum complex exhibits excellent compatibility with film-forming agents, solvents, and other components in the flux.

[0093] The performance comparison between the solder pastes prepared in Examples 1 and 2 shows that the La in the undecylimidazolium-lanthanum complex... 3+ It can form stable La-O bonds with oxygen atoms in the oxide film, assisting the activator in removing the oxide film. Compared with undecylimidazole, the synergistic effect of undecylimidazole and lanthanum can better improve the wetting performance of solder paste.

[0094] Undecylimidazole-lanthanum complexes coat solder powder, isolating it from air and water, thus reducing oxidation. Compared to benzotriazole and undecylimidazole, this avoids oxidative corrosion, enhances the chemical and storage stability of the solder powder, and reduces the gases generated by the decomposition of the solder powder oxide film at soldering temperatures, thereby lowering the void rate of solder joints from the source. During the soldering process, the La... 3+ It is dispersed in the solder joint, refines the grains, avoids excessive IMC layer thickness, and improves the shear strength and thermal cycling performance of the solder joint.

[0095] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A coated solder powder, characterized in that, It includes solder powder and an alkylimidazolium-rare earth complex coated on the surface of the solder powder; the mass of the alkylimidazolium-rare earth complex is 0.5% to 1.5% of the mass of the solder powder; The alkyl group in the alkylimidazolium-rare earth complex is at least one of decaalkyl, undecyl, and dodecyl.

2. The coated solder powder according to claim 1, characterized in that, Includes at least one of the following technical features: (1) The solder powder is at least one of SAC305, SAC0307, ​​and SAC105; (2) The rare earth element in the alkylimidazolium-rare earth complex is at least one of La, Nd, and Y; (3) The alkylimidazolium-rare earth complex is prepared by alkylimidazolium and rare earth halide through coordination reaction.

3. The coated solder powder according to claim 2, characterized in that, Includes at least one of the following technical features: (1) The coordination reaction between the alkylimidazolium and the rare earth halide is a monodentate coordination reaction with a coordination ratio of 1:3; (2) The halogen element of the rare earth halide is at least one of Cl and Br.

4. The coated solder powder according to claim 3, characterized in that, The method for preparing the alkylimidazol-rare earth complex includes the following steps: a. Prepare rare earth halide solutions and alkyl imidazole solutions; b. Under nitrogen protection, the alkylimidazolium solution and the rare earth halide solution are mixed evenly and heated and stirred to carry out the coordination reaction according to the molar ratio of rare earth element ions to alkylimidazolium of 1:3.1~1:

4. c. After the reaction is complete, the mixture is concentrated under reduced pressure and anhydrous diethyl ether is added. After stirring evenly, the mixture is refrigerated and allowed to stand. The precipitate is collected, washed, and dried to obtain the alkylimidazolium-rare earth complex.

5. The method for preparing coated solder powder according to any one of claims 1 to 4, characterized in that, Includes the following steps: A. Clean and dry the solder powder; B. Prepare alkylimidazolium-rare earth complex solution; C. Add solder powder to the alkylimidazolium-rare earth complex solution according to the mass of the alkylimidazolium-rare earth complex being 0.5%~1.5% of the solder powder mass, and disperse and soak the solder powder evenly. D. After soaking and drying, coated solder powder with alkyl imidazole-rare earth complex is obtained.

6. A solder paste, characterized in that, It comprises the following components by weight: 85-92 parts of the coated solder powder as described in any one of claims 1 to 4, and 8-15 parts of flux.

7. The solder paste according to claim 6, characterized in that, The flux comprises the following components by weight: 35-50 parts film-forming agent, 3-8 parts activator, 3-8 parts thixotropic agent, 30-50 parts solvent, 0.5-1.5 parts antioxidant, 0.5-1.2 parts pH adjuster, and 0.1-0.8 parts surfactant.

8. The solder paste according to claim 7, characterized in that, Includes at least one of the following technical features: (1) The film-forming agent is at least one of hydrogenated rosin, disproportionated rosin, and polymerized rosin; (2) The activator is at least one of glutaric acid, adipic acid, succinic acid, malic acid, citric acid, and glycolic acid; (3) The thixotropic agent is at least one of hydrogenated castor oil, polyamide wax, and ethylene bis-stearamide; (4) The solvent is at least one of diethylene glycol butyl ether, tripropylene glycol butyl ether, propylene glycol methyl ether, ethylene glycol, glycerol, and tetrahydrofurfuryl alcohol; (5) The antioxidant is at least one of 2,6-di-tert-butyl-p-cresol, tert-butylhydroquinone, butylated hydroxyanisole, and sodium diethyldithiocarbamate; (6) The pH adjuster is at least one of triethanolamine, 2-amino-2-methyl-1-propanol, ethylenediamine, and dimethylethanolamine; (7) The surfactant is at least one of polyethylene glycol monomethyl ether, polyoxyethylene octylphenyl ether, polyethylene glycol fatty acid ester, and fatty alcohol polyoxyethylene ether.

9. The application of the coated solder powder according to any one of claims 1 to 4, the method for preparing the coated solder powder according to claim 5, or the solder paste according to any one of claims 6 to 8, characterized in that, Application in the preparation of antioxidant and highly wettable welding materials.

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