A spraying process for a solder wire with a flux coating on the outside

Abstract

The present invention relates to the technical field of soldering tin, and specifically relates to a spraying process for a soldering tin wire with a flux coating on the outside, which specifically includes: 1) soaking and activating the soldering tin wire after cleaning; 2) obtaining nanoparticles through a hydrothermal reaction using indium trichloride, deionized water, sodium dodecyl sulfate, and urea; 3) adding nickel sulfate hexahydrate, nickel chloride hexahydrate, boric acid, nanoparticles, and sodium dodecylbenzenesulfonate into absolute ethanol to prepare a plating solution, using the activated soldering tin wire as the electroplating cathode and a nickel sheet as the anode, and applying intermittent auxiliary ultrasonic waves during the electroplating process to obtain a pretreated soldering tin wire; 4) heating the flux and spraying it on the surface of the pretreated soldering tin wire, and it can be solidified. In the spraying process of the present invention, the interfacial bonding strength between the soldering tin wire and the flux coating is high, and the flux coating can firmly adhere to the surface of the soldering tin wire, thereby reducing the occurrence of defective products such as open soldering and bridging during soldering, and achieving a high yield rate during soldering.

Description

Technical Field

[0001] The present invention relates to the technical field of soldering tin, and specifically to a spraying process for a soldering wire with a flux coating on the outside. Background Art

[0002] In the application of soldering tin in the electronic and electrical industries, rosin flux is required to clean the oxide on the pads of components to be soldered. Rosin has its unique physical and chemical properties. Rosin-based fluxes have been used in the field of electronic packaging for a long time. However, with the advent of the era of green industrialization, lead-containing solders have been gradually phased out, and lead-free solders have become a research hotspot. Rosin itself has disadvantages such as low activity, easy crystallization, and poor thermal stability, which limit its further development in the field of fluxes. However, with the in-depth research on rosin, by modifying rosin to improve its stability, rosin-based fluxes can be better matched with lead-free solders.

[0003] For example, the invention patent with the publication number CN112719694A discloses a flux composition, its preparation method, a gold-tin solder paste for spraying, and its preparation method. By using modified rosin in this flux, the flux has better stability, thus being able to assist and promote soldering in the soldering process. Currently, in soldering, in order to prevent rosin spatter or tin bead spatter, the flux is often sprayed on the surface of the soldering wire, making the outside of the soldering wire have a flux coating. However, when the existing flux is directly sprayed on the surface of the soldering wire, due to the poor interfacial strength between the soldering wire and the flux coating, the adhesion of the coating is poor. Especially in alkaline, hygroscopic and other environments, external substances will erode the coating, resulting in the easy detachment of the flux coating. Moreover, during the transportation of the soldering wire, the collision and extrusion between each other are likely to cause damage to the coating, resulting in the soldering wire being phased out before it is used, leading to a poor utilization rate of the finished product of the soldering wire.

[0004] Aiming at the above related technologies, currently, the soldering wire with a flux coating on the outside has problems of poor adhesion of the coating and easy breakage of the coating. Summary of the Invention

[0005] In order to improve the problems of poor adhesion of the coating and easy breakage of the coating in the soldering wire with a flux coating on the outside, the present invention provides a spraying process for a soldering wire with a flux coating on the outside. By adding a special carbon skeleton powder to the conventional rosin-based flux and cooperating with a special spraying process, the interfacial bonding strength between the soldering wire and the flux coating is high, the flux coating can firmly adhere to the surface of the soldering wire, and the formed flux coating has high strength. Under the action of external forces, the integrity of the coating can be maintained, not only making the coating not easily damaged, but also being able to well block the erosion of external substances to the coating, thereby helping to improve the utilization rate of the finished product of the soldering wire, and thus reducing the occurrence of defective products such as open soldering and bridging during soldering, achieving a high yield rate during soldering.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A spraying process for a solder wire with a flux coating on the outside, specifically including the following steps:

[0008] 1) After cleaning the solder wire with acetone, soak and activate it with dilute hydrochloric acid to obtain activated solder wire;

[0009] 2) Dissolve indium trichloride in deionized water, then add sodium dodecyl sulfate and urea. Transfer the formed suspension to a high-pressure reaction kettle for hydrothermal reaction. Wash and dry the lower-layer precipitate and then perform annealing treatment to obtain nanoparticles;

[0010] 3) Add nickel sulfate hexahydrate, nickel chloride hexahydrate, boric acid, nanoparticles, and sodium dodecylbenzenesulfonate to anhydrous ethanol in sequence to prepare a plating solution. Use the activated solder wire as the electrodeposition cathode and a nickel sheet as the anode. During electrodeposition, apply intermittent auxiliary ultrasonic waves to obtain pretreated solder wire;

[0011] 4) After heating the flux at 95 - 105 °C, spray it on the surface of the pretreated solder wire. After solidification, solder wire with a flux coating on the outside can be obtained.

[0012] As a further preferred solution of the present invention, in step 1), the concentration of the dilute hydrochloric acid is 3 - 5 wt%;

[0013] The soaking and activation time is 20 - 50 s.

[0014] As a further preferred solution of the present invention, in step 2), the dosage ratio of indium trichloride, deionized water, sodium dodecyl sulfate, and urea is (2.0 - 2.6) g : (8 - 12) L : (0.3 - 0.6) g : (3 - 4) g;

[0015] The temperature of the hydrothermal reaction is 120 - 135 °C, and the reaction time is 12 - 16 h;

[0016] The temperature of the annealing treatment is 500 - 550 °C, and the annealing time is 2 - 3 h.

[0017] As a further preferred solution of the present invention, in step 3), in the plating solution, the content of nickel sulfate hexahydrate is 200 - 230 g / L, the content of nickel chloride hexahydrate is 40 - 46 g / L, the content of boric acid is 42 - 49 g / L, the content of nanoparticles is 3 - 10 g / L, and the content of sodium dodecylbenzenesulfonate is 0.2 - 0.6 g / L;

[0018] In the electrodeposition, the distance between the anode and the cathode is 2 - 4 cm. Under the conditions of 5 - 9 V and 46 - 52 °C, electrodeposit for 5 - 15 min;

[0019] The frequency of the intermittent auxiliary ultrasonic wave is 50 - 80 kHz, the ultrasonic auxiliary time is 5 - 10 s, and the interval time between each time is 30 - 50 s.

[0020] As a further preferred embodiment of the present invention, in step 4), the preparation method of the soldering flux is as follows:

[0021] Add rosin into the solvent, stir thoroughly under the condition of a constant temperature water bath at 35 - 38 °C. After the rosin is dissolved, add carbon skeleton powder, active substance and surfactant, and mix evenly.

[0022] As a further preferred embodiment of the present invention, by weight, the rosin is 10 - 15 parts, the solvent is 70 - 80 parts, the active substance is 5 - 8 parts, the surfactant is 1 - 2 parts, and the carbon skeleton powder is 2 - 3 parts;

[0023] The rosin is any one of fumaric rosin and maleic rosin;

[0024] The solvent is composed of ethanol, isopropanol, dipropylene glycol methyl ether, diethylene glycol butyl ether, and glycerol in a volume ratio of 3:3:(2 - 3):(3 - 4):(1 - 2);

[0025] The active substance is composed of suberic acid and succinic acid in a mass ratio of 2:(1 - 2);

[0026] The surfactant is dodecylphenol polyoxyethylene ether.

[0027] Furthermore, the fumaric rosin is obtained by modifying rosin with fumaric acid as a modifier; wherein the fumaric rosin acid ester is 296 ± 2.65 mg / g;

[0028] The maleic rosin is obtained by modifying rosin with maleic anhydride as a modifier; wherein the maleic rosin acid ester is 281 ± 2.36 mg / g.

[0029] As a further preferred embodiment of the present invention, the preparation method of the carbon skeleton powder is as follows:

[0030] 1) Add sodium dodecyl sulfate into deionized water, stir and dissolve it, then add an appropriate amount of divinylbenzene and styrene monomers. After purging the air with sufficient nitrogen, heat it to 75 - 78 °C, add potassium persulfate to the system, keep the temperature constant and react for 3 - 5 h. Then add an appropriate amount of divinylbenzene again, continue to keep the temperature constant and react for 20 - 30 h. After centrifugation, wash it repeatedly with distilled water, and dry it to obtain a polystyrene sphere template;

[0031] 2) Add an aqueous sodium hydroxide solution to phenol, heat to 40 - 45 °C and stir magnetically for 10 - 30 min. Then, dropwise add an appropriate amount of formalin solution, raise the temperature to 75 - 78 °C and react at a constant temperature for 30 - 50 min. After cooling to room temperature, adjust the pH to neutral with dilute hydrochloric acid. After removing water by vacuum distillation, redissolve it in ethanol to obtain a precursor solution;

[0032] 3) Add the nanofiber carbon to the precursor solution. After ultrasonic dispersion, drop it onto a polystyrene sphere template and place it at room temperature and under vacuum for 2 - 5 h. Repeat the above operation 3 - 6 times. After drying the template, perform carbonization under a continuous nitrogen flow. After ultra - fine pulverization, obtain a carbon skeleton powder.

[0033] Furthermore, in step 1), the dosage ratio of sodium dodecyl sulfate, deionized water, divinylbenzene, styrene monomer, and potassium persulfate is (0.2 - 0.4) g : (1000 - 1400) mL : (6.4 - 8.6) mL : (30 - 50) mL : (1.1 - 1.4) g;

[0034] The divinylbenzene is used in two equal portions.

[0035] Furthermore, in step 2), the dosage ratio of phenol, aqueous sodium hydroxide solution, and formalin solution is (8 - 12) g : (1.5 - 1.9) g : (14 - 15) g;

[0036] The concentration of the aqueous sodium hydroxide solution is 20 - 23 wt%;

[0037] In the precursor solution, the content of the dissolved substance is 15 - 20 wt%.

[0038] Furthermore, in step 3), the solid - liquid ratio of the nanofiber carbon to the precursor solution is 1 g : (60 - 80) mL;

[0039] The drying is carried out at 90 - 100 °C for 25 - 30 h;

[0040] The carbonization is carried out at 800 - 860 °C for 2 - 4 h;

[0041] The heating rate of the carbonization is 5 - 10 °C / min.

[0042] Compared with the prior art, the beneficial effects of the present invention are:

[0043] In the present invention, after the tin wire is ultrasonically cleaned with acetone, the oil stains and impurities on the surface can be removed. After being activated with dilute hydrochloric acid, the tin dioxide oxide film on the surface can be removed, improving the activity of the tin wire, which is beneficial to the formation of the subsequent coating. By using the hydrothermal method, urea decomposes in deionized water to produce ammonia, which interacts with water to generate hydroxide ions. Indium trichloride decomposes into indium ions in deionized water, and the free sodium dodecyl sulfate aggregates with each other according to the self-assembly effect and gradually forms micelles, while adsorbing the indium ions in the solution. The hydroxide ions in the solution and the indium ions at the micelle sites will spontaneously combine to form indium hydroxide crystal nuclei. The whole reaction centers around the indium hydroxide crystal nuclei and takes the micelle group structure as the skeleton to form indium hydroxide crystals with a three-dimensional morphology structure. After annealing treatment, nano-particles with a flower-like structure are formed. They are formulated into a plating solution with nickel sulfate hexahydrate, nickel chloride hexahydrate, boric acid, and sodium dodecylbenzenesulfonate. Through electroplating treatment, a composite coating is formed on the surface of the tin wire. And because intermittent auxiliary ultrasonic waves are applied during the electroplating process, on the one hand, it can make the nano-nickel grains preferentially orient to the close-packed plane with low surface energy, promoting the uniform and dense deposition of nano-nickel on the surface of the tin wire, improving the density of the nickel layer. At the same time, under the action of ultrasonic waves, the nano-particles can be highly dispersed, reducing the aggregation of nano-particles, so that fewer nano-particles deposit into the nickel layer, and more nano-particles can be exposed on the surface of the nickel layer, thus forming a composite coating with a large number of flower-like nano-particles embedded on the surface. The nano-particles deposited on the surface of the composite coating can, on the one hand, be embedded in the subsequent flux coating, so that a large number of nano-particles are distributed at the interface between the flux coating and the composite coating, which helps to improve the strength of the flux coating, making the flux coating not easy to break. At the same time, the nano-particles distributed at the interface are anchored in the flux coating, increasing the interface bonding strength, which helps to improve the adhesion of the flux coating, so that it can firmly and stably adhere to the surface of the tin wire.

[0044] In the present invention, the precursor solution containing nanofibrous carbon is infiltrated into the interior of the polystyrene sphere array template by vacuum pumping, and fills the gaps between the polystyrene spheres. Through high-temperature carbonization treatment, the polystyrene spheres thermally decompose and volatilize, and the phenolic resin is carbonized. After carbonization, a porous carbon framework material with uniform pore distribution is obtained. At the same time, the incorporated nanofibrous carbon can be embedded in the pores and crosslinked with each other to form a network structure, which can support the pore walls, avoid pore collapse, and thus enable the porous carbon framework material to have a high porosity, improve the loading rate of nanofibrous carbon in the carbon framework powder, increase the contact probability between the nanofibrous carbon and the nanoparticles in the composite coating, and make it easier for the nanofibrous carbon to hook on the nanoparticles. By adding the carbon framework powder to the flux, using the framework support structure formed in the coating, the stress can be better dispersed and transmitted, thereby further improving the strength of the flux coating. Moreover, the network structure formed in the pores of the carbon framework powder is extremely easy to hook with the nanoparticles. Through the connection between the two, the interfacial strength between the flux coating and the composite coating can be further increased, making the flux more firmly attached to the surface of the solder wire.

[0045] In the present invention, by adding a special carbon framework powder to the conventional rosin-based flux and cooperating with a special spraying process, the interfacial bonding strength between the solder wire and the flux coating is high, the flux coating can be firmly attached to the surface of the solder wire, and the formed flux coating has high strength. Under the action of external force, the integrity of the coating can be maintained, which not only makes the coating not easily damaged, but also can well block the erosion of external substances to the coating, thereby helping to improve the finished product utilization rate of the solder wire, and reducing the occurrence of defective products such as open soldering and bridging during soldering, achieving a high yield rate during soldering. Detailed implementation mode

[0046] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0047] Example 1

[0048] A spraying process for a solder wire with a flux coating on the outside, specifically including the following steps:

[0049] 1) Put the solder wire into an acetone solution, then place it in an ultrasonic cleaner and ultrasonically clean for 20 min. After the cleaning is completed, take it out, dry it, and then use the immersion method to soak it in a 3 wt% hydrochloric acid solution for 20 s. After taking it out, rinse it repeatedly with distilled water and dry it to obtain an activated solder wire;

[0050] 2) Dissolve 2.0 g of indium trichloride in 8 L of deionized water. Subsequently, add 0.3 g of sodium dodecyl sulfate and 3 g of urea, and stir magnetically for 30 min to form a suspension. Then transfer it to a high-pressure reaction kettle and carry out hydrothermal reaction at 120 °C for 12 h. After the reaction is completed, repeatedly wash the lower-layer precipitate with deionized water and ethanol, dry it, and then put it into a muffle furnace and anneal at 500 °C for 2 h to obtain nanoparticles;

[0051] 3) Sequentially add appropriate amounts of nickel sulfate hexahydrate, nickel chloride hexahydrate, boric acid, nanoparticles, and sodium dodecylbenzenesulfonate to absolute ethanol, mix well to obtain a plating solution. Use activated tin wire as the electrodeposition cathode and a nickel sheet as the anode. The distance between the anode and cathode is 2 cm. Under the conditions of 5 V and 46 °C, carry out electrodeposition for 5 min. During the electrodeposition process, apply intermittent auxiliary ultrasonic waves at 50 kHz, with the ultrasonic assistance time being 5 s and the interval time between each time being 30 s to obtain pretreated tin wire;

[0052] Among them, in the plating solution, the content of nickel sulfate hexahydrate is 200 g / L, the content of nickel chloride hexahydrate is 40 g / L, the content of boric acid is 42 g / L, the content of nanoparticles is 3 g / L, and the content of sodium dodecylbenzenesulfonate is 0.2 g / L;

[0053] 4) After heating the soldering flux at 95 °C, spray it on the surface of the pretreated tin wire, and it can be obtained as tin wire with a soldering flux coating on the outside after solidification.

[0054] Among them, the preparation method of the above-mentioned soldering flux is as follows:

[0055] Add fumaric rosin (acid value 297.38 mg / g) to the solvent, stir thoroughly under the condition of a 35 °C constant-temperature water bath. After the rosin is dissolved, add carbon skeleton powder, active substance, and surfactant, and mix well;

[0056] Among them, by weight, fumaric rosin is 10 parts, solvent is 70 parts, active substance is 5 parts, surfactant is 1 part, and carbon skeleton powder is 2 parts;

[0057] The solvent is composed of ethanol, isopropanol, dipropylene glycol methyl ether, diethylene glycol butyl ether, and glycerol in a volume ratio of 3:3:2:3:1;

[0058] The active substance is composed of suberic acid and succinic acid in a mass ratio of 2:1;

[0059] The surfactant is dodecylphenol polyoxyethylene ether;

[0060] The preparation method of the carbon skeleton powder is as follows:

[0061] 1) Add 0.2 g of sodium dodecyl sulfate to 1000 mL of deionized water. After stirring and dissolving, add 3.2 mL of divinylbenzene and 30 mL of styrene monomer. After introducing sufficient nitrogen to exhaust air, heat to 75 °C, add 1.1 g of potassium persulfate to the system, react at a constant temperature for 3 h, add another equal amount of 3.2 mL of divinylbenzene, continue to react at a constant temperature for 20 h, centrifuge, wash repeatedly with distilled water, and dry to obtain a polystyrene sphere template;

[0062] 2) Add 1.5 g of an aqueous sodium hydroxide solution with a concentration of 20 wt% to 8 g of phenol. Heat to 40 °C and stir magnetically for 10 min. Then, dropwise add 14 g of formalin solution and raise the temperature to 75 °C for a constant-temperature reaction for 30 min. After cooling to room temperature, adjust the pH to neutral with dilute hydrochloric acid, then remove water by vacuum distillation at 50 °C, and then redissolve in ethanol to obtain a precursor solution with a dissolved content of 15 wt%;

[0063] 3) According to a solid-liquid ratio of 1 g:60 mL, add nanofibrous carbon to the precursor solution. After ultrasonic dispersion, drop it on the polystyrene sphere template, place it at room temperature and under vacuum for 2 h, repeat the above operation 3 times, dry the template at 90 °C for 25 h, carbonize it at 800 °C for 2 h under a continuous nitrogen flow, with a heating rate of 5 °C / min, and obtain carbon skeleton powder after ultrafine pulverization.

[0064] Example 2

[0065] A spraying process for a soldering flux coating on the outside of a tin wire, specifically including the following steps:

[0066] 1) Put the tin wire into an acetone solution, then place it in an ultrasonic cleaner and ultrasonically clean for 25 min. After the cleaning is completed, take it out, dry it, and use the immersion method to soak it in a 4 wt% hydrochloric acid solution for 35 s. After taking it out, rinse repeatedly with distilled water and dry to obtain activated tin wire;

[0067] 2) Dissolve 2.3 g of indium trichloride in 10 L of deionized water, then add 0.5 g of sodium dodecyl sulfate and 3.6 g of urea, stir magnetically for 30 - 50 min to form a suspension, then transfer it to a high-pressure reaction kettle and perform a hydrothermal reaction at 127 °C for 14 h. After the reaction is completed, repeatedly wash the lower-layer precipitate with deionized water and ethanol and then dry it, and then put it into a muffle furnace and anneal it at 530 °C for 2.5 h to obtain nanoparticles;

[0068] 3) An appropriate amount of nickel sulfate hexahydrate, nickel chloride hexahydrate, boric acid, nanoparticles, and sodium dodecylbenzenesulfonate were successively added to anhydrous ethanol. After mixing evenly, a plating solution was obtained. Using the activated tin wire as the electrodeposition cathode and the nickel sheet as the anode, the distance between the anode and cathode was 3 cm. Under the conditions of 7 V and 50 °C, electrodeposition was carried out for 10 min. During the electrodeposition process, intermittent auxiliary ultrasonic waves of 70 kHz were applied, the ultrasonic assistance time was 8 s, and the interval time for each time was 40 s, obtaining the pretreated tin wire.

[0069] Among them, in the plating solution, the content of nickel sulfate hexahydrate was 215 g / L, the content of nickel chloride hexahydrate was 43 g / L, the content of boric acid was 45 g / L, the content of nanoparticles was 8 g / L, and the content of sodium dodecylbenzenesulfonate was 0.4 g / L.

[0070] 4) After heating the soldering flux at 100 °C, it was sprayed on the surface of the pretreated tin wire. After solidification, the tin wire with a soldering flux coating on the outside could be obtained.

[0071] Among them, the preparation method of the above-mentioned soldering flux is as follows:

[0072] Fumaric rosin (acid value 298.65 mg / g) was added to the solvent, and it was fully stirred under the condition of a constant temperature water bath at 36 °C. After the rosin was dissolved, carbon skeleton powder, active substances, and surfactants were added, and after mixing evenly, it was ready.

[0073] Among them, by weight, 12 parts of fumaric rosin, 75 parts of solvent, 7 parts of active substances, 1.5 parts of surfactants, and 2.5 parts of carbon skeleton powder;

[0074] The solvent was composed of ethanol, isopropanol, dipropylene glycol methyl ether, diethylene glycol butyl ether, and glycerol in a volume ratio of 3:3:2.5:3.5:1.5;

[0075] The active substances were composed of suberic acid and succinic acid in a mass ratio of 2:1.5;

[0076] The surfactant was dodecylphenol polyoxyethylene ether;

[0077] The preparation method of the carbon skeleton powder is as follows:

[0078] 1) 0.3 g of sodium dodecyl sulfate was added to 1200 mL of deionized water. After stirring and dissolving, 3.8 mL of divinylbenzene and 40 mL of styrene monomer were added. After introducing sufficient nitrogen to exhaust the air, it was heated to 76 °C. 1.3 g of potassium persulfate was added to the system, and the reaction was carried out at a constant temperature for 4 h. Then, an equal amount of divinylbenzene was added again, and the reaction was continued at a constant temperature for 25 h. After centrifugation, it was repeatedly washed with distilled water and dried to obtain a polystyrene sphere template.

[0079] 2) Add 1.7 g of an aqueous sodium hydroxide solution with a concentration of 21 wt% to 10 g of phenol, heat to 42 °C and stir magnetically for 20 min. Then, dropwise add 14.5 g of formalin solution and raise the temperature to 76 °C for a constant-temperature reaction for 40 min. After cooling to room temperature, adjust the pH to neutral with dilute hydrochloric acid, then remove water by vacuum distillation at 52 °C, and then redissolve in ethanol to obtain a precursor solution with a dissolved content of 17 wt%.

[0080] 3) According to a solid-liquid ratio of 1 g: 70 mL, add nanocarbon fibers to the precursor solution. After ultrasonic dispersion, drop it on a polystyrene sphere template and place it at room temperature and under vacuum conditions for 3 h. Repeat the above operation 5 times. After drying the template at 95 °C for 27 h, carbonize it at 850 °C for 3 h under a continuous nitrogen flow, with a heating rate of 6 °C / min. After ultrafine pulverization, carbon skeleton powder is obtained.

[0081] Example 3

[0082] A spraying process for a soldering flux coating on the outside of a tin wire specifically includes the following steps:

[0083] 1) Put the tin wire into an acetone solution, then place it in an ultrasonic cleaner and ultrasonically clean for 30 min. After cleaning, take it out, dry it, and then use the immersion method to soak it in a 5 wt% hydrochloric acid solution for 50 s. After taking it out, repeatedly rinse with distilled water and dry it to obtain activated tin wire.

[0084] 2) Dissolve 2.6 g of indium trichloride in 12 L of deionized water, then add 0.6 g of sodium dodecyl sulfate and 4 g of urea, stir magnetically for 50 min to form a suspension, and then transfer it to a high-pressure reaction kettle for hydrothermal reaction at 135 °C for 16 h. After the reaction, repeatedly wash the lower-layer precipitate with deionized water and ethanol and then dry it. Then put it into a muffle furnace and anneal it at 550 °C for 3 h to obtain nanoparticles.

[0085] 3) Add appropriate amounts of nickel sulfate hexahydrate, nickel chloride hexahydrate, boric acid, nanoparticles, and sodium dodecylbenzenesulfonate to anhydrous ethanol in sequence, mix well to obtain a plating solution. Use the activated tin wire as the electroplating cathode and a nickel sheet as the anode. The distance between the anode and cathode is 4 cm. Under the conditions of 9 V and 52 °C, electroplate for 15 min. During the electroplating process, apply intermittent auxiliary ultrasonic waves at 80 kHz, with an ultrasonic assistance time of 10 s and an interval time of 50 s each time to obtain pretreated tin wire.

[0086] Among them, in the plating solution, the content of nickel sulfate hexahydrate is 230 g / L, the content of nickel chloride hexahydrate is 46 g / L, the content of boric acid is 49 g / L, the content of nanoparticles is 10 g / L, and the content of sodium dodecylbenzenesulfonate is 0.6 g / L;

[0087] 4) After heating the soldering flux at 105°C, it is sprayed on the surface of the pretreated tin wire. After solidification, the tin wire with a soldering flux coating on the outside can be obtained.

[0088] Among them, the preparation method of the above-mentioned soldering flux is as follows:

[0089] Add fumaric rosin (acid value 293.35 mg / g) to the solvent, stir well under the condition of a constant temperature water bath at 35 - 38°C. After the rosin is dissolved, add carbon skeleton powder, active substance and surfactant, and mix evenly;

[0090] Among them, by weight, 15 parts of fumaric rosin, 80 parts of solvent, 8 parts of active substance, 2 parts of surfactant, 3 parts of carbon skeleton powder;

[0091] The solvent is composed of ethanol, isopropanol, dipropylene glycol methyl ether, diethylene glycol butyl ether, and glycerol in a volume ratio of 3:3:3:4:2;

[0092] The active substance is composed of suberic acid and succinic acid in a mass ratio of 2:1.8;

[0093] The surfactant is dodecylphenol polyoxyethylene ether;

[0094] The preparation method of the carbon skeleton powder is as follows:

[0095] 1) Add 0.4 g of sodium dodecyl sulfate to 1400 mL of deionized water. After stirring and dissolving, add 4.3 mL of divinylbenzene and 50 mL of styrene monomer. After purging the air with sufficient nitrogen, heat to 78°C, add 1.4 g of potassium persulfate to the system, react at a constant temperature for 5 h, add an equal amount of divinylbenzene again, continue to react at a constant temperature for 30 h, after centrifugation, wash repeatedly with distilled water, and dry to obtain a polystyrene sphere template;

[0096] 2) Add 1.9 g of a 23 wt% sodium hydroxide aqueous solution to 12 g of phenol, heat to 45°C and stir magnetically for 30 min, then dropwise add 15 g of formalin solution, and raise the temperature to 78°C and react at a constant temperature for 50 min. After cooling to room temperature, adjust the pH to neutral with dilute hydrochloric acid, then vacuum distill to remove water at 53°C, and then redissolve in ethanol to obtain a precursor solution with a dissolved matter content of 20 wt%;

[0097] 3) According to the solid-liquid ratio of 1 g:80 mL, add the nanofiber carbon to the precursor solution. After ultrasonic dispersion, drop it on the polystyrene sphere template, place it at room temperature and under vacuum for 5 h, repeat the above operation 6 times, dry the template at 100°C for 30 h, then carbonize it at 860°C for 4 h under a continuous nitrogen flow, with a heating rate of 10°C / min. After ultrafine pulverization, the carbon skeleton powder is obtained.

[0098] Comparative Example 1: This comparative example is basically the same as Example 1, except that steps 2)-3) are omitted, and after the solder wire is activated, a soldering flux is directly sprayed on its surface.

[0099] Comparative Example 2: This comparative example is basically the same as Example 1, except that step 2) is omitted, and after the solder wire is activated, electroplating is carried out on its surface, and then a soldering flux is sprayed.

[0100] Comparative Example 3: This comparative example is basically the same as Example 1, except that the intermittent auxiliary ultrasonic wave is omitted in step 3).

[0101] Comparative Example 4: This comparative example is basically the same as Example 1, except that carbon skeleton powder is not added to the soldering flux.

[0102] Test experiment:

[0103] 1. Alkaline resistance: After the solder wires described in Examples 1-3 and Comparative Examples 1-4 are placed in a 0.01 mol / L sodium hydroxide aqueous solution for 1 h, observe whether the soldering flux coating peels off. Each solder wire is tested 100 times, and record the number of times the soldering flux coating peels off. The test results are shown in Table 1.

[0104] 2. Moisture absorption resistance: After the solder wires described in Examples 1-3 and Comparative Examples 1-4 are placed in air with a relative humidity of 90% at 25 °C for 6 months, observe whether the soldering flux coating peels off. Each solder wire is tested 100 times, and record the number of times the soldering flux coating peels off. The test results are shown in Table 1.

[0105] 3. Yield rate: Use an automatic machine welding and an HST-9 type constant temperature and humidity machine (purchased from Shanghai Shiteng Electric Co., Ltd.), and solder 1000 points of the solder wires described in Examples 1-3 and Comparative Examples 1-4 at 400 °C respectively according to the JIS Z 3197 standard. If there is an open circuit or a short circuit, it is recorded as a defective product. Record the number of defective products and calculate the yield rate. The test results are shown in Table 1.

[0106] 4. Finished product utilization rate: Take 100 solder wires each of Examples 1-3 and Comparative Examples 1-4 and stack them in a sealed glass container. Place the glass container in a shaker and vibrate it at 30 rpm for 30 min. Record the number of solder wires with obvious coating damage, and calculate the finished product utilization rate. The test results are shown in Table 1.

[0107] Table 1

[0108] Alkali resistance Moisture absorption resistance Yield rate % Finished product utilization rate % Example 1 1 1 99.6 100 Example 2 0 0 99.9 100 Example 3 1 1 99.3 100 Comparative example 1 9 14 94.2 90 Comparative example 2 5 7 96.3 94 Comparative example 3 4 6 97.3 95 Comparative example 4 8 12 95.1 92

[0109] As can be seen from Table 1, in the spraying process of the present invention, the interfacial bonding strength between the solder wire and the flux coating is high, and the flux coating can firmly adhere to the surface of the solder wire, which not only makes the coating not easily damaged, but also can well block the erosion of external substances on the coating, thus achieving a high yield rate during soldering.

[0110] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principle and practical application of the present invention, so that those skilled in the art can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A spraying process for a solder wire with a flux coating on the outside, characterized in that, Specifically, it includes the following steps: 1) After cleaning the solder wire with acetone, soak it in dilute hydrochloric acid for activation to obtain activated solder wire; 2) Dissolve indium trichloride in deionized water, then add sodium dodecyl sulfate and urea. Transfer the formed suspension to a high-pressure reaction kettle for hydrothermal reaction. Wash and dry the lower-layer precipitate, and then perform annealing treatment to obtain nanoparticles; 3) Add nickel sulfate hexahydrate, nickel chloride hexahydrate, boric acid, nanoparticles, and sodium dodecylbenzenesulfonate to anhydrous ethanol in sequence to prepare a plating solution. Use the activated solder wire as the electro-deposition cathode and a nickel sheet as the anode. During the electro-deposition process, apply intermittent auxiliary ultrasonic waves to obtain pre-treated solder wire; 4) Heat the flux at 95 - 105 °C, then spray it on the surface of the pre-treated solder wire. After solidification, solder wire with a flux coating on the outside can be obtained; In step 4), the preparation method of the flux is as follows: Add rosin to the solvent, stir thoroughly under the condition of a constant temperature water bath at 35 - 38 °C. After the rosin is dissolved, add carbon skeleton powder, active substance, and surfactant, and mix evenly; By weight, the rosin is 10 - 15 parts, the solvent is 70 - 80 parts, the active substance is 5 - 8 parts, the surfactant is 1 - 2 parts, and the carbon skeleton powder is 2 - 3 parts; The rosin is any one of fumaric rosin and maleic rosin; The solvent is composed of ethanol, isopropanol, dipropylene glycol methyl ether, diethylene glycol butyl ether, and glycerol in a volume ratio of 3:3:(2 - 3):(3 - 4):(1 - 2); The active substance is composed of suberic acid and succinic acid in a mass ratio of 2:(1 - 2); The surfactant is dodecylphenol polyoxyethylene ether.

2. The spraying process of a solder wire with a flux coating on the outside according to claim 1, characterized in that, In step 1), the concentration of the dilute hydrochloric acid is 3 - 5 wt%; The soaking activation time is 20 - 50 s.

3. The spraying process of a solder wire with a flux coating on the outside according to claim 2, characterized in that, In step 2), the dosage ratio of indium trichloride, deionized water, sodium dodecyl sulfate, and urea is (2.0 - 2.6) g:(8 - 12) L:(0.3 - 0.6) g:(3 - 4) g; The temperature of the hydrothermal reaction is 120 - 135 °C, and the reaction time is 12 - 16 h; The temperature of the annealing treatment is 500 - 550 °C, and the annealing time is 2 - 3 h.

4. A spraying process for a solder wire with a flux coating on the outside according to claim 2, characterized in that, In step 3), in the plating solution, the content of nickel sulfate hexahydrate is 200 - 230 g / L, the content of nickel chloride hexahydrate is 40 - 46 g / L, the content of boric acid is 42 - 49 g / L, the content of nanoparticles is 3 - 10 g / L, and the content of sodium dodecylbenzenesulfonate is 0.2 - 0.6 g / L; In the electro-deposition, the distance between the anode and the cathode is 2 - 4 cm. Under the conditions of 5 - 9 V and 46 - 52 °C, electro-deposit for 5 - 15 min; The frequency of the intermittent auxiliary ultrasonic wave is 50 - 80 kHz, the ultrasonic assistance time is 5 - 10 s, and the interval time for each time is 30 - 50 s.

5. A spraying process for a solder wire with a flux coating on the outside according to claim 1, characterized in that, The preparation method of the carbon skeleton powder is as follows: 1) Add sodium dodecyl sulfate to deionized water. After stirring and dissolving, add appropriate amounts of divinylbenzene and styrene monomers. After introducing sufficient nitrogen to exhaust air, heat to 75 - 78 °C, add potassium persulfate to the system, react at a constant temperature for 3 - 5 h, add an appropriate amount of divinylbenzene again, continue to react at a constant temperature for 20 - 30 h, centrifuge, and wash repeatedly with distilled water. After drying, obtain a polystyrene sphere template; 2) Add an aqueous sodium hydroxide solution to phenol, heat to 40 - 45 °C and stir magnetically for 10 - 30 min. Then, dropwise add an appropriate amount of formalin solution and raise the temperature to 75 - 78 °C to react at a constant temperature for 30 - 50 min. After cooling to room temperature, adjust the pH to neutral with dilute hydrochloric acid. After removing water by vacuum distillation, redissolve in ethanol to obtain a precursor solution; 3) Add carbon nanofibers to the precursor solution. After ultrasonic dispersion, drop it onto the polystyrene sphere template and place it at room temperature and under vacuum for 2 - 5 h. Repeat the above operation 3 - 6 times. After drying the template, carry out carbonization under a continuous nitrogen flow. After ultra - fine pulverization, obtain carbon skeleton powder.

6. The spraying process of a solder wire with a flux coating on the outside according to claim 5, characterized in that, In step 1), the dosage ratio of sodium dodecyl sulfate, deionized water, divinylbenzene, styrene monomer, and potassium persulfate is (0.2 - 0.4) g : (1000 - 1400) mL : (6.4 - 8.6) mL : (30 - 50) mL : (1.1 - 1.4) g; The divinylbenzene is used in two equal portions.

7. A spraying process for a solder wire with a flux coating on the outside according to claim 5, characterized in that, In step 2), the dosage ratio of phenol, aqueous sodium hydroxide solution, and formalin solution is (8 - 12) g : (1.5 - 1.9) g : (14 - 15) g; The concentration of the aqueous sodium hydroxide solution is 20 - 23 wt%; In the precursor solution, the content of the dissolved substance is 15 - 20 wt%.

8. A spraying process for a solder wire with a flux coating on the outside, according to claim 5, characterized in that, In step 3), the solid - liquid ratio of carbon nanofibers to the precursor solution is 1 g : (60 - 80) mL; The drying is carried out at 90 - 100 °C for 25 - 30 h; The carbonization is carried out at 800 - 860 °C for 2 - 4 h; The heating rate of the carbonization is 5 - 10 °C / min.