Soldering paste for improving mini LED soldering quality and preparation method thereof

Abstract

The application provides a soldering paste for improving Mini LED soldering quality and a preparation method thereof, and belongs to the technical field of solders. The soldering paste comprises liquid resin, an interfacial active agent and a multifunctional additive; the liquid resin comprises epoxy resin and polyurethane resin; the interfacial active agent is a blend of polyvinylpyrrolidone and liquid high-molecular alcohol compounds; and the multifunctional additive is carboxylated PAMAM or a mixture of carboxylated PAMAM and dendritic PAMAM. The method comprises the following steps: mixing epoxy resin, polyurethane resin and part of the interfacial active agent in a proportion, heating to 50-70 DEG C and stirring uniformly; synchronously or step by step adding the multifunctional additive and the remaining interfacial active agent, stirring uniformly under the condition of 80-120 DEG C; stopping heating, continuing stirring until the temperature is reduced to 50-70 DEG C, and stopping stirring and cooling to room temperature. The soldering paste prepared by the method has high wettability, low soldering point cavity rate, high stability and strong anti-collapse performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of solder, and particularly relates to a soldering flux for improving the soldering quality of Mini LED and a preparation method thereof. BACKGROUND

[0002] Mini LED is a "sub-millimeter light-emitting diode", which uses LED chips between 50 mu m and 200 mu m, combines a driving circuit, and forms a pixel unit with a spacing of 0.3 mm to 1.5 mm. Since the size of Mini LED is small, there are a large number of chips and soldering points on each circuit board, and therefore the soldering quality directly affects the performance and reliability of the product.

[0003] Soldering paste is an important material in the LED soldering process, which is composed of soldering paste of alloy powder and soldering flux. Among them, the soldering flux is a good carrier of soldering paste, which is used to adjust the viscosity of the soldering paste to improve the comprehensive performance of the soldering paste such as storage and printing. The main functions of the soldering flux are: removing the oxides on the surface of the soldered metal and preventing the re-oxidation of the soldering flux and the soldering surface; reducing the surface tension of the soldering flux, promoting the mutual wetting of the soldering flux and the soldered metal, and ensuring the formation of a stable insulating layer after soldering. As can be seen, as an important material in the soldering process, the quality of the soldering flux has a crucial influence on the soldering effect.

[0004] At present, the common Mini LED soldering flux is a rosin-based soldering flux, which has defects such as too much residue and soldering tin beads. In order to solve this problem, some soldering fluxes use epoxy resin and organic acid composite materials instead of rosin and organic solvents to form a solvent-free and rosin-free resin-based soldering flux. However, there are defects such as poor wettability, easy formation of soldering point cavities, weak stability, and weak anti-collapse performance. SUMMARY

[0005] In view of this, the present application aims to provide a soldering flux for improving the soldering quality of Mini LED and a preparation method thereof, and to solve at least one technical problem in the background art.

[0006] The present application is implemented as follows:

[0007] The first aspect of the present application provides a soldering flux for improving the soldering quality of Mini LED, which comprises liquid resin, surfactant and multifunctional additive;

[0008] According to the weight ratio, liquid resin: surfactant: multifunctional additive = 1: 0.1-0.5: 0.1-0.5;

[0009] The liquid resin comprises epoxy resin and polyurethane resin; according to the weight ratio, epoxy resin: polyurethane resin = 5-20: 1;

[0010] The interfacial active agent is a blend of polyvinylpyrrolidone and liquid high molecular alcohol compound.

[0011] The multifunctional auxiliary agent is carboxylated PAMAM or a mixture of carboxylated PAMAM and dendritic PAMAM.

[0012] Preferably, the soldering paste further comprises a thixotropic agent selected from at least one of hydrogenated castor oil, polyamide wax, and fumed white carbon black.

[0013] Preferably, the thixotropic agent is used in an amount of 0.5wt% to 10wt% of the liquid resin.

[0014] Preferably, the liquid high molecular alcohol compound is selected from at least one of polyethylene glycol, methoxypolyethylene glycol, polypropylene glycol, and polyvinyl alcohol.

[0015] Preferably, in the interfacial active agent, the weight ratio of polyvinylpyrrolidone to liquid high molecular alcohol compound is 1:2 to 2:1.

[0016] Preferably, the generation number of carboxylated PAMAM or dendritic PAMAM is 1 to 5.

[0017] Preferably, in the mixture of carboxylated PAMAM and dendritic PAMAM, the weight ratio of carboxylated PAMAM to dendritic PAMAM is 1 to 5:1.

[0018] The first aspect of the present application provides a preparation method of the soldering paste for improving the Mini LED welding quality as described above, which comprises the following steps:

[0019] Mix the epoxy resin, polyurethane resin, and part of the interfacial active agent in proportion, heat to 50-70℃, and stir uniformly;

[0020] Synchronously or stepwise add the multifunctional auxiliary agent and the remaining interfacial active agent, and stir uniformly at 80-120℃;

[0021] Stop heating, continue stirring until the temperature drops to 50-70℃, and then stop stirring and cool to room temperature.

[0022] Preferably, the preparation method comprises the following steps:

[0023] Mix the epoxy resin, polyurethane resin, and part of the interfacial active agent in proportion, heat to 50-70℃, and stir uniformly;

[0024] Add the thixotropic agent and stir until there are no particles and no stratification;

[0025] Synchronously or stepwise add the multifunctional auxiliary agent and the remaining interfacial active agent, heat to 80-120℃, and stir uniformly;

[0026] Stop heating, continue stirring until the temperature drops to 50-70 DEG C, stop stirring and cool to room temperature.

[0027] Preferably, the partial interfacial surfactant refers to the amount used in this step is 30wt%-50wt% of the total amount of surfactant.

[0028] Compared with the prior art, the present application includes the following beneficial effects:

[0029] 1、The present application uses epoxy resin and polyurethane resin instead of rosin, uses polyvinylpyrrolidone and liquid high molecular alcohol compound to form an interfacial surfactant, and uses carboxylated PAMAM or a mixture of carboxylated PAMAM and dendritic PAMAM to form a multifunctional auxiliary agent, thereby obtaining a soldering paste with high wettability, low solder void rate, high stability and strong anti-collapse performance.

[0030] 2、The present application uses epoxy resin and polyurethane resin as a composite liquid resin, which has the advantages of high adhesion, anti-cracking, strong weather resistance, etc.

[0031] 3、The multifunctional auxiliary agent of the present application has the functions of resin active agent and curing agent, and can also improve the heat resistance and prevent oxidation of the soldering paste.

[0032] 4、The present application blends polyvinylpyrrolidone and liquid high molecular alcohol compound to play the functions of surface activity, lubrication, solubilization, dispersion, etc., and further enhances the oxidation resistance and stability, avoids the decomposition of the soldering paste due to the reaction with air at high temperature during welding, and thereby inhibits the generation of solder voids. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below in combination with examples. It should be understood that the specific implementation examples described herein are only used to explain the present application, and are not used to limit the present application.

[0034] The preparation method of the soldering paste for improving the Mini LED welding quality comprises S1 to S5.

[0035] S1, weighing raw materials

[0036] The raw materials of the soldering paste include liquid resin, interfacial surfactant and multifunctional auxiliary agent.

[0037] In the present application, liquid resin is used to replace rosin in the conventional soldering paste, and the liquid resin includes epoxy resin and polyurethane resin; the epoxy resin is a high molecular polymer, which is a general term for a class of polymers containing two or more epoxy groups in the molecule, and is a polycondensation product of epichlorohydrin and bisphenol A or polyhydric alcohol. Due to the chemical activity of the epoxy group, it can be ring-opened and cross-linked to form a network structure by using various compounds containing active hydrogen, which is a thermosetting resin; and the epoxy resin has high adhesion, which is very suitable for Mini LED packaging process, ensures the chip size accuracy during soldering process, and improves the yield of chip packaging; in specific implementation, the epoxy resin uses any liquid epoxy resin allowed in the art, and the following examples use bisphenol A type epoxy resin (E-40 type) as an example, but is not limited to this epoxy resin, and other unlisted liquid epoxy resins are also applicable. Although the epoxy resin has high adhesion, it has poor weather resistance and large shrinkage, which makes the surface of the final soldering paste easy to deform, become brittle and even crack, and further has poor stability; in order to solve the technical problem, a small amount of liquid polyurethane resin is added to the epoxy resin to form a composite liquid resin. In specific implementation, according to the weight ratio, epoxy resin: polyurethane resin = 5-20:1, for example, it can be 5:1, 10:1, 15:1, 20:1; but is not limited to the listed values, and other unlisted values within the value range are also applicable, and within the range, the liquid resin has the advantages of high adhesion, anti-cracking, strong weather resistance and the like.

[0038] Since the soldering paste should have two main functions of removing oxides and reducing the surface tension of the soldering paste, the present application adds an interfacial active agent and a multifunctional additive, and in specific implementation, according to the weight ratio, liquid resin: interfacial active agent: multifunctional additive = 1:0.1-0.5:0.1-0.5.

[0039] The interface active agent is a blend of polyvinylpyrrolidone and liquid high molecular alcohol compound. The main function of polyvinylpyrrolidone is surfactant, which has excellent dispersibility and film-forming property. Based on its dispersibility, it plays a role of steric hindrance to the resin, thereby playing the function of surfactant. The liquid high molecular alcohol compound is selected from at least one of polyethylene glycol, methoxypolyethylene glycol, polypropylene glycol and polyvinyl alcohol, and has the functions of surfactant, lubricant, cosolvent, stabilizer and dispersant. The molecular weight of polyethylene glycol is selected from 1400 to 3500, and the molecular weight of methoxypolyethylene glycol is selected from 1000 to 2000. The molecular weight of polypropylene glycol is selected from 500 to 1000. The polyvinyl alcohol has a low degree of polymerization, and the molecular weight is generally 25,000 to 35,000, preferably 35,000. In specific implementation, the weight ratio of polyvinylpyrrolidone to high molecular alcohol compound is 1:2 to 2:1. The polyvinylpyrrolidone powder can be dispersed uniformly with the liquid high molecular alcohol compound under mechanical stirring or ultrasonic dispersion. In addition, the blending of polyvinylpyrrolidone and liquid high molecular alcohol compound can enhance the antioxidant stability of the high molecular alcohol compound to a certain extent, avoid the decomposition of the high molecular alcohol compound due to reaction with air at high temperature during welding, and thereby inhibit the voids in the welding points.

[0040] The multifunctional additive is carboxylated PAMAM or a mixture of carboxylated PAMAM and dendritic PAMAM. The multifunctional additive has the functions of resin activator and resin curing agent, and can also improve the heat resistance and prevent oxidation of the soldering paste.

[0041] Carboxylated PAMAM (PAMAM-COOH) refers to the substitution of the amino group at the end of the PAMAM molecule by carboxyl group, thereby introducing more hydrophilic groups. PAMAM is a polyamide-amine dendrimer, which is a three-dimensional structure of a high molecular compound. Its branched structure provides a large number of active groups, which can load various functional molecules. PAMAM contains a large number of tertiary amines in its molecular structure, which can promote the crosslinking reaction between the hydroxyl group and the epoxy group inside the resin at high temperature, and the reaction between the amino group of PAMAM and the epoxy group molecule, thereby forming a larger crosslinking density and improving the stability, mechanical properties and heat resistance of the soldering paste. In specific implementation, PAMAM-COOH is obtained by hydrolysis and condensation reaction of PAMAM and aldehyde acid, and the amino group in PAMAM is converted into carboxyl group, thereby introducing carboxyl group.

[0042] PAMAM-COOH can further improve the lubricity of the soldering paste. Good wettability helps the soldering paste to better cover and adhere to the substrate, thereby improving the welding quality. PAMAM-COOH makes the residue after welding easier to be washed away by water, which helps to remove the residue of the soldering paste, thereby improving the cleanliness. In addition, the carboxyl group can react with oxides to some extent. For example, the carboxyl group and metal ions can remove the oxide film on the solder pad and the soldering paste in the form of metal soap. In the mixture of carboxylated PAMAM and dendritic PAMAM, the content of carboxylated PAMAM is not less than that of dendritic PAMAM. Preferably, the weight ratio of carboxylated PAMAM to dendritic PAMAM is 1-5:1. The generation number of carboxylated PAMAM or dendritic PAMAM is 1-5. The reason is that low-generation PAMAM is in the form of liquid, which is more uniformly mixed with the resin liquid. High-generation PAMAM usually has a higher surface charge density and a larger hydrophobic cavity, and it is difficult to clean the residue after welding.

[0043] In a specific implementation, the soldering paste further comprises a thixotropic agent. The thixotropic agent can be any thixotropic agent allowed in the art, such as at least one of hydrogenated castor oil, polyamide wax, and fumed white carbon black. The amount of the thixotropic agent is 0.5wt%-10wt% of the liquid resin. The following examples use 5wt% of fumed white carbon black (based on the liquid resin) as an example, but are not limited to the listed thixotropic agents. Other unlisted thixotropic agents are also applicable.

[0044] S2, high-temperature emulsified resin

[0045] The epoxy resin, the polyurethane resin, and part of the surfactant are mixed in proportion and added to an emulsifier, heated to 50-70°C, and stirred at high speed until uniform. The amount of the surfactant is 30wt%-50wt% of the total amount.

[0046] S3, add the thixotropic agent and stir until there are no particles and no stratification.

[0047] S4, synchronously or stepwise add the multifunctional auxiliary agent and the remaining surfactant, heat and warm up, and stir uniformly at 80-120°C;

[0048] The multifunctional auxiliary agent and the remaining surfactant are simultaneously added to the emulsifier, heated to 80-120°C, and stirred at high speed until the raw materials are completely melted into a liquid.

[0049] Alternatively, first add the remaining surfactant and heat to 80-120°C, stir uniformly at high speed; then add the multifunctional auxiliary agent after keeping warm, and stir at high speed until the raw materials are completely melted into a liquid.

[0050] The temperature in this step is adjusted according to the type of surfactant, and the following examples are exemplified at 100 DEG C, but are not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0051] S5, stop heating, continue stirring until the temperature drops to 50 DEG C to 70 DEG C, stop stirring, and cool to room temperature to obtain the soldering paste.

[0052] In a specific implementation, the soldering paste can also be ground and refined using a grinder to obtain a soldering paste with smaller particle size.

[0053] The soldering paste is prepared by the method of low-temperature heating emulsification followed by high-temperature reaction, has small particle size, and has good fluidity.

[0054] Example 1

[0055] A preparation method of a soldering paste for improving Mini LED welding quality, comprising the following steps:

[0056] S1, raw material preparation

[0057] ① Liquid resin: total amount is 600g, including 500g epoxy resin and 100g polyurethane resin, the ratio of which is 5:1;

[0058] ② Surfactant: total amount is 60g, including 20g polyvinylpyrrolidone and 40g polyethylene glycol 2000 (PEG-2000), the ratio of which is 1:2;

[0059] ③ Multifunctional additive: total amount is 60g, including 30g G1 PAMAM-COOH and 30g G1 PAMAM;

[0060] S2, the epoxy resin, polyurethane resin, and 50wt% surfactant are mixed in the emulsifier according to the proportion, heated to 50 DEG C, and stirred at high speed until uniform;

[0061] S3, add 30g of fumed white carbon black, and stir until there are no particles and no stratification.

[0062] S4, first add the remaining surfactant and heat to 100 DEG C, stir at high speed until uniform; add the multifunctional additive after holding, and stir at high speed until the raw materials are completely melted into a liquid.

[0063] S5, stop heating, continue stirring until the temperature drops to 50 DEG C, stop stirring, and cool to room temperature to obtain the soldering paste.

[0064] The soldering paste prepared in Example 1 is mixed with solder powder (Sn 96.5 Ag 3.0 Cu 0.5The alloy is mixed into solder paste according to a weight ratio of 12:88, and the performance of the solder paste is tested, and the test method comprises the following steps:

[0065] (1) Viscosity. The viscosity of the solder paste is tested at room temperature by using a viscometer;

[0066] (2) Spreading coefficient. A higher spreading coefficient means that the solder paste has better wettability and flowability. The spreading experiment is performed according to GB / T11364-2008 “Test method for solder wettability”. The spreading coefficient K is calculated according to the following formula (1);

[0067]

[0068] H is the numerical value of the height of the solder paste after spreading on the surface of the base material, in millimeters; D is the numerical value of the diameter of a sphere with a volume equal to that of the solder paste, in millimeters, D = 1.24V 1 / 3 , V is the ratio of the mass of the solder paste used in the test to the density;

[0069] (3) Void rate. The solder paste is reflow soldered on an OSP circuit board by using a reflow soldering machine. The solder paste is printed on the circuit board by using a special steel mesh. After reflow soldering, the void rate of part of the test solder balls is evaluated by using X-Ray observation;

[0070] (4) Stability. The test method is as follows: 100g of the solder paste is placed in a high-speed centrifuge for continuous centrifugation for 30 minutes. The state of the solder paste is observed at room temperature. If the solder paste is still fine and has strong flowability after centrifugation, it is determined to be level 1. If the solder paste has small roughness and good flowability after centrifugation, it is determined to be level 2. If the solder paste has high roughness and poor flowability after centrifugation, it is determined to be level 3. If the solder paste is sand-like or even dried after centrifugation, it is determined to be level 4;

[0071] (5) Anti-collapse property. The anti-collapse property can be represented by the minimum bridge connection distance of the thermal collapse of the solder paste. The smaller the distance, the better the anti-collapse property. The test method is as follows: refer to SJ / T11186-2019 “General specification for solder paste”. Since the size of the MiniLED is small and the pitch is fine, the collapse represents the ability of the solder paste to maintain the printing form during printing. If the collapse performance is too poor, continuous soldering will occur during the soldering process, resulting in short circuit.

[0072] Example 2

[0073] In this embodiment, the proportion of the epoxy resin and the polyurethane resin is adjusted (the total amount of the liquid resin remains unchanged) on the basis of Example 1. Other conditions are the same as those in Example 1. The performance of the solder paste composed of the soldering flux prepared in this embodiment and the solder is tested by using the same method as that in Example 1. The results are shown in Table 1.

[0074] Table 1

[0075]

[0076] From the data in Table 1, in the liquid resin, with the increase of the content of epoxy resin, the viscosity first decreases, then increases and then decreases, and the spreading coefficient first increases and then decreases; the reason is that the viscosity of epoxy resin and polyurethane resin is different, which changes with the change of the ratio of the two, and cross-linking occurs between epoxy resin, polyurethane resin and additives in the subsequent high temperature synthesis process, thereby causing the fluctuation of viscosity and spreading coefficient, when the ratio of epoxy resin: polyurethane resin is 5:1-20:1, the viscosity is maintained above 150 Pa·s, the spreading coefficient is maintained above 84%, the void rate changes insignificantly, and the stability can basically be kept at level 2 or level 1; the minimum bridging distance is not more than 0.05 mm, indicating that the anti-collapse performance is relatively excellent, among which 10-15:1 has no bridging, which can better meet the welding requirements under the condition of Mini LED ultra-fine pitch and improve the welding quality. Therefore, the ratio of epoxy resin: polyurethane resin is 5:1-20:1, preferably 10-15:1.

[0077] Example 3

[0078] In this embodiment, the composition of the interfacial active agent and the type of liquid high molecular alcohol compound are adjusted on the basis of Example 1, other conditions are the same as those of Example 1, and the performance of the solder paste prepared by mixing the soldering paste prepared in this embodiment with solder is tested by the same method as that of Example 1, and the results are shown in Table 2.

[0079] Table 2

[0080]

[0081] From the data in Table 2, it can be seen that the performance of the solder paste prepared by mixing the soldering paste prepared by using single polyvinylpyrrolidone or liquid high molecular alcohol compound as active agent with tin alloy is greatly reduced; the spreading coefficient, void rate, stability and bridging distance of the solder paste prepared by using the composite interfacial active agent composed of polyvinylpyrrolidone and methoxypolyethylene glycol, polyethylene glycol, polypropylene glycol and polyvinyl alcohol meet the requirements, indicating that the soldering paste has excellent lubricity, activity, stability and anti-collapse performance, and the welding quality is high, among which the performance of the soldering paste prepared by compounding methoxypolyethylene glycol as liquid high molecular alcohol compound with polyvinylpyrrolidone is the best.

[0082] Example 4

[0083] This example adjusts the ratio of polyvinylpyrrolidone to liquid high molecular alcohol compound in the interfacial active agent on the basis of Example 1 (the total amount of interfacial active agent is unchanged), other conditions are the same as in Example 1, and the performance of the solder paste composed of the soldering paste prepared in this example and solder is tested by the same method as in Example 1, and the results are shown in Table 3.

[0084] Table 3

[0085]

[0086] From the data in Table 3, it can be seen that when the ratio of polyvinylpyrrolidone to liquid high molecular alcohol compound is 2:1 to 1:2, the spreading coefficient, void rate, stability, and bridging distance of the solder paste all meet the requirements, and when the ratio exceeds this range, the performance of the solder paste is significantly reduced.

[0087] Example 5

[0088] This example adjusts the total amount of interfacial active agent (the ratio of polyvinylpyrrolidone to liquid high molecular alcohol compound is unchanged) on the basis of Example 1, other conditions are the same as in Example 1, and the performance of the solder paste composed of the soldering paste prepared in this example and solder is tested by the same method as in Example 1, and the results are shown in Table 4.

[0089] Table 4

[0090]

[0091] From the data in Table 4, it can be seen that when the total amount of interfacial active agent is increased, the viscosity is reduced and the spreading coefficient is increased, and when the total amount of interfacial active agent to the weight ratio of liquid resin is 0.1 to 0.5:1, the void rate, stability, and bridging distance of the solder paste all meet the requirements, and when the ratio exceeds this range, the performance of the solder paste is significantly reduced, especially the stability and void rate and collapse resistance are significantly deteriorated.

[0092] Example 6

[0093] This example adjusts the composition and amount ratio of multifunctional additives (the total amount of multifunctional additives is unchanged) on the basis of Example 1, other conditions are the same as in Example 1, and the performance of the solder paste composed of the soldering paste prepared in this example and solder is tested by the same method as in Example 1, and the results are shown in Table 5.

[0094] Table 5

[0095]

[0096] From the data in Table 5, it can be seen that the use of carboxylated PAMAM or carboxylated PAMAM+PAMAM as multifunctional additives effectively improves the spreading coefficient, reduces the void ratio, and improves the stability and anti-collapse property. Preferably, the ratio of carboxylated PAMAM (PAMAM-COOH) to dendritic PAMAM is 1-5:1.

[0097] Example 7

[0098] In this example, the PAMAM generation number of the multifunctional additive was adjusted based on Example 1 (the amount and composition of the multifunctional additive remained unchanged), and the other conditions were the same as in Example 1. The performance of the solder paste composed of the soldering paste prepared in this example and solder was tested by the same method as in Example 1, and the results are shown in Table 6.

[0099] Table 6

[0100] Group PAMAM generation Viscosity / Pa s Spreading coefficient / % Void fraction / % Stability Bridge distance / mm Example 7-1 G2 155 85.7 4.9 1 No bridge Example 1 G1 161 85.1 5.4 2 0.06 Example 7-2 G3 150 87.3 4.6 1 No bridge Example 7-3 G4 147 88.0 4.1 1 No bridge Example 7-4 G5 142 87.9 4.4 1 0.06 Example 7-5 G6 135 80.7 8.3 4 0.25

[0101] From the data in Table 6, it can be seen that in the multifunctional additive, as the carboxylated PAMAM and PAMAM generation number increases, the spreading coefficient increases, the void ratio decreases, and the stability and anti-collapse property improve. However, when the generation number exceeds 5, the performance is greatly reduced.

[0102] Example 8

[0103] In this example, the total amount of the multifunctional additive was adjusted based on Example 1 (the ratio of PAMAM-COOH to PAMAM remained unchanged), and the other conditions were the same as in Example 1. The performance of the solder paste composed of the soldering paste prepared in this example and solder was tested by the same method as in Example 1, and the results are shown in Table 7.

[0104] Table 7

[0105]

[0106] From the data in Table 7, it can be seen that as the total amount of the multifunctional additive increases, the spreading coefficient increases, the void ratio decreases, and the stability and anti-collapse property improve. However, when the total amount exceeds a certain value, the performance is greatly reduced. The reason is that excessive amount of the multifunctional additive leads to excessive dilution of the resin, a significant decrease in viscosity, a decrease in activity, and a weakening of the soldering performance. Therefore, the amount of the multifunctional additive is 60-300 g, i.e., the weight ratio of the multifunctional additive to the liquid resin is 0.1-0.5:1, preferably 0.2-0.4:1.

[0107] Example 9

[0108] In this example, the amount of the surfactant in steps S2 and S4 was adjusted based on Example 1, and the other conditions were the same as in Example 1. The performance of the solder paste composed of the soldering paste prepared in this example and solder was tested by the same method as in Example 1, and the results are shown in Table 8.

[0109] Table 8

[0110]

[0111]

[0112] From the data in Table 8, it can be seen that, by adding different proportions of surfactants in the first step of emulsification and subsequent high-temperature synthesis, the spreading coefficient is increased, the void ratio is reduced, and the stability and anti-collapse performance are improved. The reason is that in the S2 process, the emulsification efficiency of the resin is improved, and in the S4 process, the activation efficiency is improved; and the preferred amount of surfactant used in the first step of emulsification is 30% to 50% of the total amount, within which range the void ratio is low and the stability and anti-collapse performance are good.

[0113] Example 10

[0114] This example is based on Example 1, with the temperature of heating in step S2 being changed, and other conditions being the same as in Example 1. The performance of the solder paste composed of the soldering flux prepared in this example and solder was tested by the same method as in Example 1, and the results are shown in Table 9.

[0115] Table 9

[0116]

[0117] From the data in Table 9, it can be seen that, as the temperature in step S2 increases, the spreading coefficient is increased, the void ratio is reduced, and the stability and anti-collapse performance are improved, but the performance decreases beyond a certain temperature, because a too high temperature causes the resin to solidify prematurely and not to react sufficiently with the subsequent additives.

[0118] Example 11

[0119] This example is based on Example 1, with the temperature of heating in step S4 being changed, and other conditions being the same as in Example 1. The performance of the solder paste composed of the soldering flux prepared in this example and solder was tested by the same method as in Example 1, and the results are shown in Table 10.

[0120] Table 10

[0121]

[0122] From the data in Table 10, it can be seen that, as the temperature in step S4 increases, the spreading coefficient is increased, the void ratio is reduced, and the stability and anti-collapse performance are improved, because as the temperature increases, the additives react more fully with the resin, and the activity of the soldering flux increases, but the performance decreases beyond a certain temperature, because a too high temperature causes the network structure formed by the resin and additives to be destroyed, and the performance to deteriorate.

[0123] Example 12

[0124] The embodiment is based on the temperature at the end of stirring in step S5 of embodiment 1, and other conditions are the same as embodiment 1. The performance of the soldering paste composed of the soldering paste and solder is tested by the same method as embodiment 1, and the results are shown in Table 11.

[0125] Table 11

[0126]

[0127] From the data in Table 11, it can be seen that as the temperature in step S5 increases, the spreading coefficient increases, the void rate decreases, and the stability and anti-collapse performance improve, but the performance decreases when the temperature exceeds a certain temperature. The reason is that the high temperature leads to over-reaction of the resin and additives, thereby causing poor performance.

[0128] Example 13

[0129] The difference between this embodiment and embodiment 1 is only in step S5, and other conditions are the same as embodiment 1. The S5 of this embodiment is specifically: simultaneously adding the remaining surfactant and multifunctional additive, and stirring at high speed until all the raw materials are melted into liquid. The performance of the soldering paste composed of the soldering paste and solder is tested by the same method as embodiment 1, and the results are shown in Table 12.

[0130] Table 12

[0131]

[0132] From the data in Table 12, it can be seen that the step-by-step addition and simultaneous addition of the remaining surfactant and multifunctional additive in step S5 can enhance the performance of the soldering paste, and the effect of step-by-step addition is better than that of simultaneous addition.

[0133] Comparative Example 1

[0134] The soldering paste is prepared by a conventional high-temperature synthesis method, and the specific steps are as follows:

[0135] S1, same as S1 of embodiment 1;

[0136] S2, the epoxy resin, polyurethane resin, surfactant, thixotropic agent, and multifunctional additive are mixed in a proportion and added to an emulsifier, heated to 150°C, and stirred at high speed until all the raw materials are melted into liquid; the heating is turned off, the temperature is reduced to 100°C while stirring, and then the stirring is stopped after cooling to room temperature to obtain the soldering paste.

[0137] Comparative Example 2

[0138] The soldering paste is prepared by a conventional high-temperature emulsification method, and the specific steps are as follows:

[0139] S1, same as S1 of embodiment 1;

[0140] S2, epoxy resin, polyurethane resin, surfactant are mixed in proportion into an emulsifier, heated to 70℃, high speed stirring until no obvious solid or liquid layering;

[0141] S3, adding thixotropic agent, multifunctional additives while stirring cooling until emulsion, stop heating and stirring, cooling to room temperature, get soldering paste.

[0142] The soldering paste prepared by the soldering paste of the application and the soldering paste of the comparative example 1 and the comparative example 2 are tested by the same method as the example 1, and the performance of the soldering paste is compared with the example 1, and the results are shown in table 13

[0143] Table 13

[0144]

[0145]

[0146] From the data in table 13, compared with the conventional high temperature emulsification or high temperature synthesis process, the anti-collapse property and the spreading coefficient of the soldering paste prepared by the preparation method of the application are increased, and the void rate is reduced, that is, the performance is more excellent.

[0147] The above described examples only express several embodiments of the application, and the description is more specific and detailed, but it cannot be understood as the limitation of the patent scope of the application. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the application, a number of modifications and improvements can be made, which belong to the protection scope of the application. Therefore, the protection scope of the patent of the application should be subject to the appended claims.

Claims

1. A soldering paste for improving Mini LED soldering quality, characterized by, The soldering paste comprises liquid resin, interface active agent and multifunctional assistant; The liquid resin: interface active agent: multifunctional assistant = 1:0.1-0.5:0.1-0.5 by weight; The liquid resin comprises epoxy resin and polyurethane resin; the epoxy resin: polyurethane resin = 5-20:1 by weight; The interface active agent is a blend of polyvinylpyrrolidone and liquid high molecular alcohol compound; The multifunctional assistant is carboxylated PAMAM or a mixture of carboxylated PAMAM and dendritic PAMAM.

2. The soldering paste for improving Mini LED soldering quality according to claim 1, wherein, The soldering paste further comprises thixotropic agent selected from at least one of hydrogenated castor oil, polyamide wax and fumed white carbon black.

3. The soldering paste for improving Mini LED soldering quality according to claim 2, wherein, The amount of the thixotropic agent is 0.5wt%-10wt% of the liquid resin.

4. The soldering paste for improving Mini LED soldering quality according to claim 1, wherein, The liquid high molecular alcohol compound is selected from at least one of polyethylene glycol, methoxypolyethylene glycol, polypropylene glycol and polyvinyl alcohol.

5. The soldering paste for improving Mini LED soldering quality according to claim 1 or 4, characterized in that, The weight ratio of polyvinylpyrrolidone to liquid high molecular alcohol compound in the interface active agent is 1:2-2:

1.

6. The soldering paste for improving Mini LED soldering quality according to claim 1, wherein, The generation number of carboxylated PAMAM or dendritic PAMAM is 1-5.

7. The soldering paste for improving Mini LED soldering quality according to claim 1 or 6, wherein, In the mixture of carboxylated PAMAM and dendritic PAMAM, the weight ratio of carboxylated PAMAM to dendritic PAMAM is 1-5:

1.

8. The method of claim 1 to 7 for preparing a soldering paste for improving the quality of Mini LED soldering, characterized in that, The preparation method comprises the following steps: Mixing epoxy resin, polyurethane resin and part of interface active agent in proportion, heating to 50-70℃ and stirring uniformly; Synchronously or stepwise adding multifunctional assistant and the rest of interface active agent, and stirring uniformly at 80-120℃; Stopping heating, continuing stirring until the temperature drops to 50-70℃, and cooling to room temperature after stopping stirring.

9. The preparation method of the soldering paste for improving Mini LED soldering quality according to claim 8, characterized in that, The preparation method comprises the following steps: Mixing epoxy resin, polyurethane resin and part of interface active agent in proportion, heating to 50-70℃ and stirring uniformly; Adding thixotropic agent and stirring until no particles and no stratification; Synchronously or stepwise adding multifunctional assistant and the rest of interface active agent, and heating to 80-120℃ and stirring uniformly; Stopping heating, continuing stirring until the temperature drops to 50-70℃, and cooling to room temperature after stopping stirring.

10. The method of claim 8 or 9, wherein the flux is prepared by adding the fluxing agent to the flux core. The part of interface active agent refers to the amount of 30wt%-50wt% of the total amount of interface active agent in this step.

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