Water-soluble laser solder paste and method of making same

Abstract

The application discloses a water-soluble laser soldering tin paste, which is prepared from 75% of lead-free solder powder and 25% of water-soluble soldering paste in percentage by mass; wherein the water-soluble soldering paste comprises the following components in parts by weight: 55-70 parts of polyethylene glycol, 10-15 parts of a water-soluble thixotropic agent, 3-10 parts of a water-soluble active agent, 3-5 parts of an organic amine, 10-15 parts of a fatty alcohol polyoxyethylene ether and 0.1-0.5 parts of a defoaming agent. The raw materials can be used to prepare the soldering paste at normal temperature, so that the active performance of the active material can be prevented from being attenuated at high temperature, and the activity of the soldering paste is retained to the maximum extent; compared with the prior art, the water-soluble laser soldering tin paste has the performances of no splashing and tin explosion, strong wetting capacity and the like when soldering, the post-soldering residue can be directly cleaned with water, the use of organic solvents is reduced, the production cost of enterprises is reduced, the physical harm to employees is reduced, and the environment is protected.

Description

Technical Field

[0001] This invention relates to welding technology, and in particular to a water-soluble laser solder paste and its preparation method. Background Technology

[0002] With the popularization of the era of intelligent manufacturing, the components used in the electronics industry are developing towards miniaturization and micro-miniaturization. Traditional surface-mount soldering technology is prone to problems such as desoldering, low solder joint strength, and damage to electronic components when soldering photosensitive components, thermal components, PCB boards, and flexible circuit boards. However, the use of laser welding technology can significantly improve the welding quality. Laser welding is increasingly widely used in the field of microelectronics due to its characteristics of large penetration depth, small deformation, high efficiency, small heat-affected zone, and no solder joint contamination.

[0003] Laser solder paste was developed specifically for laser soldering technology. It's a soldering technique that uses a laser as a heat source to melt solder paste. Laser solder paste is applied to the pads using a dispensing machine or other methods, and then melted and solidified by the laser to form solder joints. The process is simple. However, unlike conventional surface mount solder paste, laser solder paste is composed of small solder powder particles (typically 2-25µm in diameter). At the edges of the laser spot, where the heat is lower, some solder beads may not completely melt, leaving residue that poses a risk of short circuits on the circuit board. Because laser solder paste is primarily used in microelectronics where the spacing between solder joints is small, the risk of short circuits is further increased, necessitating the cleaning of residues.

[0004] However, in existing technologies, laser solder pastes mainly use rosin-based materials to prevent solder splattering, solder balls, and insufficient wetting, in order to avoid these problems. For example, patent publication number CN111451669A describes a method for preparing anti-splatter laser solder paste, which uses special high-boiling-point additives to prevent the flux solvent from boiling and splashing out when the instantaneous energy is concentrated at the solder joint, thus preventing the formation of solder balls and unmelted solder powder. The flux is composed of rosin, thixotropic agents, organic acids, organic amines, and high-boiling-point additives. After soldering, this rosin-based solder paste must be cleaned with a specific organic cleaning agent. Long-term use of such cleaning agents is harmful to operators and the environment, and increases production costs. Summary of the Invention

[0005] In view of this, the present invention addresses the deficiencies of the existing technology, and its main objective is to provide a water-soluble laser solder paste and its preparation method. The solder paste prepared by the present invention does not splatter or explode during soldering, has strong wetting ability, and achieves the goal of allowing the residue after laser soldering to be directly cleaned with water.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A water-soluble laser solder paste, by weight percentage, comprises 75% lead-free solder powder and 25% water-soluble flux; wherein the water-soluble flux comprises the following components in parts by weight: 55-70 parts polyethylene glycol, 10-15 parts water-soluble thixotropic agent, 3-10 parts water-soluble activator, 3-5 parts organic amine, 10-15 parts fatty alcohol polyoxyethylene ether, and 0.1-0.5 parts defoamer.

[0008] As a preferred embodiment, the lead-free solder powder is a SnAgCu series alloy with a particle size of 2-25μm.

[0009] As a preferred embodiment, the SnAgCu series alloy is Sn96.5Ag3.0Cu0.5 with a particle size of 2-12μm.

[0010] As a preferred embodiment, the polyethylene glycol is prepared by addition polymerization of polyethylene oxide with water, and its molecular formula is HO(CH2CH2O). n H, the molecular weight of polyethylene glycol is 10,000-20,000.

[0011] As a preferred embodiment, the polyethylene glycol is one or a mixture of two or more of polyethylene glycol 10000, polyethylene glycol 12000, and polyethylene glycol 15000.

[0012] As a preferred embodiment, the water-soluble thixotropic agent is one or a mixture of two or more of hydroxypropyl cellulose, hydroxymethyl cellulose, hydroxypropyl methyl cellulose, and carboxymethyl cellulose; the water-soluble activator is one or a mixture of two or more of malonic acid, glycolic acid, succinic acid, malic acid, and citric acid, and its purity is higher than 99%.

[0013] As a preferred embodiment, the organic amine is one or a mixture of two or more of dodecylamine, tetradecylamine, hexadecylamine, and octadecylamine; the defoamer is an organosilicone defoamer, which is one or a mixture of two or more of AFE-1410, AFE-7610, AFE-3168, and AFE-0050 manufactured by Dow Chemical Company.

[0014] As a preferred embodiment, the fatty alcohol polyoxyethylene ether is formed by the condensation of polyethylene glycol and fatty alcohol, and its molecular formula is RO(CH2CH2O). n H.

[0015] As a preferred embodiment, the fatty alcohol polyoxyethylene ether is one or a mixture of two or more of fatty alcohol polyoxyethylene ether AEO-12, fatty alcohol polyoxyethylene ether AEO-13, and fatty alcohol polyoxyethylene ether AEO-14.

[0016] A method for preparing water-soluble laser solder paste includes the following steps:

[0017] (1) The aforementioned polyethylene glycol, water-soluble thixotropic agent and water-soluble surfactant are put into a pulverizer and pulverized in proportion. After pulverization, they are added to a stirred reaction vessel equipped with a disperser.

[0018] (2) The aforementioned organic amine, fatty alcohol polyoxyethylene ether and defoamer are placed in the stirring reaction vessel described in step (1) and stirred for more than 30 minutes at a speed of 1200 rpm to obtain a mixture;

[0019] (3) Grind the mixture obtained in step (2) using a three-roll mill to make its particle size less than 5μm to obtain water-soluble flux.

[0020] (4) Add Sn96.5Ag3.0Cu0.5 lead-free solder powder and the water-soluble flux obtained in step (3) into a vacuum mixing pot and stir until evenly mixed to obtain water-soluble laser solder paste.

[0021] Compared with the prior art, the present invention has obvious advantages and beneficial effects. Specifically, as can be seen from the above technical solution:

[0022] The difference between the above preparation method and the conventional method of dissolving and stirring at temperatures above 100 degrees Celsius is that the flux paste is prepared and produced at room temperature. This avoids the degradation of the active material's activity at high temperatures and preserves the activity of the flux paste to the maximum extent. Furthermore, compared with existing technologies, the above water-soluble laser solder paste achieves the same performance as conventional laser solder paste in terms of no splattering and solder splattering, strong wetting ability, and the residue after soldering can be directly washed off with water, reducing the use of organic solvents, lowering enterprise production costs, reducing health hazards to employees, and also playing a role in protecting the environment.

[0023] To more clearly illustrate the effects of the present invention, the present invention will be described in detail below with reference to specific embodiments: Detailed Implementation

[0024] This invention discloses a water-soluble laser solder paste, which, by weight percentage, consists of 75% lead-free solder powder and 25% water-soluble flux; wherein the water-soluble flux comprises the following components in parts by weight: 55-70 parts polyethylene glycol, 10-15 parts water-soluble thixotropic agent, 3-10 parts water-soluble activator, 3-5 parts organic amine, 10-15 parts fatty alcohol polyoxyethylene ether, and 0.1-0.5 parts defoamer.

[0025] This lead-free solder powder is a SnAgCu series alloy with a particle size of 2-25μm. Specifically, the SnAgCu series alloy is Sn96.5Ag3.0Cu0.5 with a particle size of 2-12μm.

[0026] This polyethylene glycol is prepared by addition polymerization of polyethylene oxide with water, and its molecular formula is HO(CH2CH2O). n H, the molecular weight of polyethylene glycol is 10,000-20,000; this polyethylene glycol is one or a mixture of two or more of polyethylene glycol 10,000, polyethylene glycol 12,000, and polyethylene glycol 15,000; the function of polyethylene glycol is to replace rosin in conventional laser solder paste, stabilizing the paste dispensing and forming, melting into an oil film during high-temperature soldering, and preventing the molten solder powder from being oxidized again. At the same time, polyethylene glycol is water-soluble and dissolves in water after soldering, facilitating subsequent water rinsing processes.

[0027] The water-soluble thixotropic agent is one or a mixture of two or more of hydroxypropyl cellulose, hydroxymethyl cellulose, hydroxypropyl methyl cellulose, and carboxymethyl cellulose. The addition of this type of thixotropic agent causes the polar groups in its structure to interact, building a three-dimensional network structure, increasing the rheological volume of the solder paste, and restricting the free movement space of the solder paste, thereby increasing the viscosity of the solder paste. When shear force is applied, the three-dimensional network structure is disrupted, the intermolecular hydrogen bonds disappear, and the viscosity decreases. When the shear force is removed, the hydrogen bonds reform, and the three-dimensional network structure is re-established, thus ensuring good rheological properties.

[0028] The water-soluble surfactant is one or a mixture of two or more of malonic acid, glycolic acid, succinic acid, malic acid, and citric acid, and its purity is higher than 99%. This type of surfactant is not only easily soluble in water, but also exhibits stronger acidity due to its short carbon chain segment and the higher the proportion of carboxyl groups in the total molecular mass. It is suitable for short-time laser welding and can quickly remove the oxide film on the tin powder and the surface of the welded surface while the temperature rises.

[0029] The organic amine is one or a mixture of two or more of dodecylamine, tetradecylamine, hexadecylamine, and octadecylamine. The main function of the organic amine is to neutralize the water-soluble surfactant, as the latter exhibits strong activity even at room temperature, which is detrimental to the preservation and use of solder paste. Therefore, the organic amine is added to the flux as an acidity regulator. At room temperature and without a catalyst, the organic amine in the flux reacts with organic acids to form acid amine salts. These acid amine salts are unstable and decompose back into organic acids and organic amines as the laser soldering temperature increases. Utilizing this property, at room temperature, the organic amine can inhibit the activity of carboxyl groups in organic acids, thus mitigating the latter's corrosion of the solder powder. During reflow heating, the carboxyl and amino groups released from the decomposition of the acid amine salt can simultaneously exert their fluxing effect.

[0030] This fatty alcohol polyoxyethylene ether is formed by the condensation of polyethylene glycol and fatty alcohol, and its molecular formula is RO(CH2CH2O). nH; The fatty alcohol polyoxyethylene ether is one or a mixture of two or more of fatty alcohol polyoxyethylene ether AEO-12, fatty alcohol polyoxyethylene ether AEO-13, and fatty alcohol polyoxyethylene ether AEO-14; because organic acids and metal oxide films will produce metal salts during the welding process, these metal salts are difficult to dissolve in water, but the added fatty alcohol polyoxyethylene ether can dissolve in these metal salts, and it is also hydrophilic, so that these metal salts can ultimately be dissolved in water.

[0031] The defoamer is an organosilicon defoamer, and includes, but is not limited to, silicone oil-based defoamers, silicone ether-based defoamers, and modified organosilicon polyether defoamers. The organosilicon defoamer is one or a mixture of two or more of AFE-1410, AFE-7610, AFE-3168, and AFE-0050 produced by Dow Chemical Company. When cleaning post-weld residues with water, a large amount of gas enters the liquid. Due to its low density, it floats and forms bubbles that are not conducive to thoroughly cleaning post-weld residues. The organosilicon defoamer can break up the bubbles, reduce the production of bubbles, and facilitate the completion of the cleaning process.

[0032] This invention also discloses a method for preparing water-soluble laser solder paste, comprising the following steps:

[0033] (1) The aforementioned polyethylene glycol, water-soluble thixotropic agent and water-soluble surfactant are put into a pulverizer and pulverized in proportion. After pulverization, they are added to a stirred reaction vessel equipped with a disperser.

[0034] (2) The aforementioned organic amine, fatty alcohol polyoxyethylene ether and defoamer are placed in the stirring reaction vessel described in step (1) and stirred for more than 30 minutes at a speed of 1200 rpm to obtain a mixture.

[0035] (3) Grind the mixture obtained in step (2) using a three-roll mill to make its particle size less than 5μm to obtain water-soluble flux.

[0036] (4) Add Sn96.5Ag3.0Cu0.5 lead-free solder powder and the water-soluble flux obtained in step (3) into a vacuum mixing pot and stir until evenly mixed to obtain water-soluble laser solder paste.

[0037] The following description is based on specific embodiments and comparative examples. The raw material ratios used in the water-soluble fluxes of Examples 1-6 are shown in Table 1.

[0038]

[0039]

[0040] Table 1

[0041] The water-soluble flux prepared in Examples 1-6 is mixed with Sn96.5Ag3.0Cu0.5 lead-free solder powder in a vacuum mixing pot in a certain proportion and stirred until homogeneous to obtain water-soluble laser solder paste.

[0042] Comparative Example 1:

[0043] Compared to Example 1, no dodecylamine was added, but the other preparation steps were the same as in Example 1.

[0044] Comparative Example 2:

[0045] Compared with Example 2, AFE-1410 and AFE7610 are not added, and the other manufacturing steps are the same as in Example 2.

[0046] Comparative Example 3:

[0047] Compared to Example 3, all raw materials were mixed by heating and dissolving, cooled, and then passed through a three-roll mill. Other production steps were the same as in Example 3.

[0048] The performance of Examples 1-6 and Comparative Examples 1-3 was tested below, and the test results are shown in Table 2.

[0049]

[0050] Table 2

[0051] in conclusion

[0052] As shown in Table 2, organic amines can enhance wetting, prevent the solder paste from drying out during use, and increase its service life. The addition of defoamer has a beneficial effect on the cleaning of residues. The room temperature uniform mixing preparation method described in this invention has a beneficial effect on solder paste wetting. As can be seen from the above test results, the water-soluble laser solder paste of this invention achieves the performance of conventional laser solder paste in that it does not splatter or splatter, has strong wetting ability, and the residues after soldering can be directly cleaned with water, making it suitable for laser soldering.

[0053] Test method:

[0054] Referring to the Japanese JIS-Z3284 standard, the solder pastes prepared in Examples 1-6 and Comparative Examples 1-3 were subjected to laser soldering tests for more than 8 hours. The spattering and wetting performance were observed and recorded. The evaluation criteria for spattering and wetting performance are shown in Table 3. At the same time, it was recorded whether the solder paste dried out within 8 hours of continuous use and whether the residue after soldering could be cleaned with water.

[0055] The instructions here specify using a 500W laboratory ultrasonic cleaner and rinsing with clean water for 10 minutes.

[0056]

[0057]

[0058] Table 3

[0059] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A water-soluble solder paste for laser soldering, characterized by: 75% of lead-free solder powder and 25% of water-soluble flux; wherein the water-soluble flux comprises the following components by weight: polyethylene glycol 55-70 parts, water-soluble thixotropic agent 10-15 parts, water-soluble active agent 3-10 parts, organic amine 3-5 parts, fatty alcohol polyoxyethylene ether 10-15 parts, and defoaming agent 0.1-0.5 parts; wherein the polyethylene glycol is prepared by polyaddition of polyethylene oxide and water, and the molecular formula is HO(CH2CH2O) n H, the molecular weight of the polyethylene glycol is 10000-20000; the polyethylene glycol is one or a mixture of two or more of polyethylene glycol 10000, polyethylene glycol 12000, and polyethylene glycol 15000; and the water-soluble thixotropic agent is one or a mixture of two or more of hydroxypropyl cellulose, hydroxymethyl cellulose, hydroxypropyl methyl cellulose, and carboxymethyl cellulose.

2. The water-soluble solder paste for laser soldering according to claim 1, wherein: The lead-free solder powder is SnAgCu series alloy, and the particle size is 2-25 μm.

3. The water-soluble solder paste for laser soldering according to claim 2, wherein: The SnAgCu series alloy is Sn96.5Ag3.0Cu0.5, and the particle size is 2-12 μm.

4. The water-soluble solder paste for laser soldering according to claim 1, wherein: The water-soluble active agent is one or two or more than two kinds of mixture of malonic acid, glycolic acid, succinic acid, malic acid and citric acid, and the purity is higher than 99%.

5. The water-soluble solder paste for laser soldering according to claim 1, wherein: The organic amine is one or two or more than two kinds of mixture of dodecylamine, tetradecylamine, hexadecylamine and octadecylamine; the defoaming agent is silicone defoaming agent, which is one or two or more than two kinds of mixture of AFE-1410, AFE-7610, AFE-3168 and AFE-0050 produced by Dow Chemical Company.

6. The water-soluble solder paste for laser soldering according to claim 1, wherein: The fatty alcohol polyoxyethylene ether is condensed from polyethylene glycol and fatty alcohol, and its molecular formula is RO(CH2CH2O) n H.

7. The water-soluble solder paste for laser soldering according to claim 6, wherein: The fatty alcohol polyoxyethylene ether is one or two or more than two kinds of mixture of fatty alcohol polyoxyethylene ether AEO-12, fatty alcohol polyoxyethylene ether AEO-13 and fatty alcohol polyoxyethylene ether AEO-14.

8. A method of preparing a water-soluble solder paste for laser soldering according to any one of claims 1 to 7, characterized in that: The method comprises the following steps: (1) proportionally putting polyethylene glycol, water-soluble thixotropic agent and water-soluble active agent into a pulverizer for pulverization, and then adding into a stirring reaction kettle with a disperser; (2) proportionally putting organic amine, fatty alcohol polyoxyethylene ether and defoaming agent into the stirring reaction kettle in step (1) for stirring, wherein the stirring time is greater than 30 minutes, and the rotating speed is 1200 r / min, to obtain a mixture; (3) grinding the mixture obtained in step (2) by using a three-roll grinder to make the particle size less than 5 μm, to obtain water-soluble soldering paste; (4) proportionally putting lead-free solder powder and the water-soluble soldering paste obtained in step (3) into a vacuum stirring kettle for stirring, and then obtaining water-soluble laser soldering paste after uniform stirring.

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