A low-melting-point SMT soldering paste formula and a preparation method thereof

Abstract

This invention belongs to the field of solder paste technology and discloses a formulation and preparation method of low-melting-point SMT solder paste, comprising solder alloy powder, a mixed substrate, and flux, wherein the ratio of each component of the solder alloy powder, mixed substrate, and flux is 60:30:10. This invention avoids reducing the mechanical strength of the solder joints, ensures the completion of low-melting-point soldering, and improves the wettability of the solder paste. Simultaneously, by utilizing type A and type B viscosity modifiers to control the viscosity of the mixed substrate and flux respectively, it ensures viscosity quality control during comprehensive mixing. This allows the solder paste to adapt to different process requirements in different application scenarios, improves solder adhesion performance, and provides better flow control, enabling the solder to better adhere to the pad apertures or solder joints during vertical printing or wave soldering. Overall, it improves the soldering performance of low-melting-point SMT solder paste, resulting in good soldering effect and long lifespan.

Description

Technical Field

[0001] This invention belongs to the field of solder paste technology, specifically a low-melting-point SMT solder paste formulation and its preparation method. Background Technology

[0002] SMT solder paste is a material used in the soldering process of surface mount technology. SMT solder paste is usually composed of solder powder, flow agent and flux, etc. It is mainly used to solder SMT components on PCB. Low melting point SMT solder paste refers to solder paste containing solder alloys with relatively low melting points. Low melting point solder alloys usually refer to alloys with melting points below 183℃ (361°F). Using low melting point solder paste can reduce the soldering temperature and reduce component damage and thermal stress on PCB substrate caused by high temperature.

[0003] In existing low-melting-point SMT solder pastes, low-melting-point elements (such as bismuth and indium) are typically used to accommodate low-melting-point soldering. This leads to a decrease in solder joint strength and reliability. The addition of these elements can cause the formation of a non-uniform eutectic structure between the solder joint and the pad, thereby reducing the mechanical strength of the solder joint. Furthermore, low-melting-point elements (such as lead and silver) are prone to oxidation during the soldering process, resulting in an oxide layer on the surface of the solder joint, which hinders good wetting and bonding between the solder joint and the pad. In practice, after the low-melting-point solder paste is prepared, this type of solder paste significantly affects the strength of the solder joint during actual soldering, resulting in poor strength and reliability of the solder joint and poor performance. Summary of the Invention

[0004] The purpose of this invention is to provide a low-melting-point SMT solder paste formulation and its preparation method to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a low-melting-point SMT solder paste formulation and its preparation method, comprising solder alloy powder, a mixed substrate, and a flux, wherein the proportions of the components of the solder alloy powder, the mixed substrate, and the flux are 60:30:10; the solder alloy comprises tin, bismuth silver, and aluminum; the mixed substrate comprises synthetic resin, solvent, and type A viscosity modifier; the flux comprises active flux, type B viscosity modifier, and antioxidant; the components of the solder alloy are 95% tin, 3.5% bismuth silver, and 1.5% aluminum; and the components of the mixed substrate are 40% synthetic resin, 55% solvent, and 5% type A viscosity modifier.

[0006] Preferably, the synthetic resin is any one or more of acrylic resin and polyester resin, the solvent is any one or more of acetone, isopropanol, and methyl ethyl ketone, and the type A viscosity modifier is any one or more of microcrystalline wax and thickener.

[0007] Preferably, the thickener is any one or more of colloidal silica and bentonite.

[0008] Preferably, the active flux includes alcohols, organic acids (such as fatty acids), amines, and other additives, and the antioxidant includes stannous chloride (SnCl2), antioxidant particles (such as antioxidant spheres), and organic compounds (such as benzothiadiazole).

[0009] Preferably, the alcohol auxiliaries are any one or more of ethylene glycol, propylene glycol, and isopropanol; the organic acid auxiliaries are any one or more of fatty acids (such as oleic acid and stearic acid) and hydrated boric acid; and the amine auxiliaries are any one or more of amine salts and amine compounds.

[0010] Preferably, the type B viscosity modifier comprises natural resin and nanoparticles, wherein the natural resin is any one or more of rosin and shikimic acid, and the nanoparticles are any one or more of nano-silica and nano-alumina.

[0011] A method for preparing a low-melting-point SMT solder paste formulation includes the following preparation steps:

[0012] S1: Prepare the required materials: solder alloy powder, mixed base and flux, and weigh them according to the formula ratio. Use an electronic balance to weigh them and place them in a polypropylene container.

[0013] S2: Preparation of mixed solder alloy: Take out tin, bismuth silver and aluminum according to the formula ratio, put them in a container and stir to mix for later use;

[0014] S3: Preparation of mixed substrate: Synthetic resin, solvent and type A viscosity modifier are prepared according to the above ratio and stirred and mixed. Type A viscosity modifier is added last during the mixing process and is added gradually during stirring to achieve the required viscosity.

[0015] S4: Preparation of flux: Obtain active flux, type B viscosity modifier and antioxidant according to the ratio described. Mix the active flux and type B viscosity modifier and stir evenly to achieve the required viscosity. Gradually add antioxidant while stirring to ensure that all components are fully mixed.

[0016] S5: Solder paste preparation: Mix the base and flux together and stir evenly to form the base of the solder paste. Gradually add the pre-prepared solder alloy powder to the base while stirring and dispersing evenly. Heat and mix until a uniform solder paste is formed.

[0017] The beneficial effects of this invention are as follows:

[0018] This invention improves the formula by selecting a lead-free solder paste alloy and utilizing a ratio of 3.5% bismuth silver and 1.5% aluminum. By using low-melting-point elements, it achieves the preparation of low-melting-point SMT solder paste while reducing the formation of non-uniform eutectic structures between solder joints and pads, thus preventing a decrease in the mechanical strength of the solder joints, ensuring the completion of low-melting-point soldering, and improving the wettability of the solder paste. Simultaneously, by using type A and type B viscosity modifiers to control the viscosity of the mixed substrate and flux respectively, it ensures viscosity quality control during comprehensive mixing. This allows the solder paste to adapt to different process requirements in various application scenarios, improves solder adhesion performance, and provides better flow control, enabling the solder to better adhere to the pad apertures or solder joints during vertical printing or wave soldering. Overall, it improves the soldering performance of low-melting-point SMT solder paste, resulting in better soldering effect and longer lifespan. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the preparation process of the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] like Figure 1 As shown, this embodiment of the invention provides a formulation and preparation method for a low-melting-point SMT solder paste, comprising solder alloy powder, a mixed substrate, and a flux. The component ratios of the solder alloy powder, the mixed substrate, and the flux are 60:30:10. The solder alloy comprises tin, bismuth silver, and aluminum. The mixed substrate comprises synthetic resin, solvent, and type A viscosity modifier. The flux comprises active flux, type B viscosity modifier, and antioxidant. The components of the solder alloy are: 95% tin, 3.5% bismuth silver, and 1.5% aluminum. The components of the mixed substrate are: 40% synthetic resin, 55% solvent, and 5% type A viscosity modifier.

[0022] By eliminating lead during use, the environmental friendliness of the solder alloy can be improved, meeting modern environmental protection requirements. Bismuth-silver alloy has a higher melting point and provides better thermal stability compared to traditional lead-tin alloy, reducing the risk of solder melting and deformation, and improving welding quality and reliability. Adding aluminum can enhance the mechanical properties, hardness, and strength of the solder alloy, thereby improving the durability of the solder joint. The optimized formula of the solder alloy components results in good wettability, which can better wet the welding contact surface and improve the quality and reliability of solder joint formation.

[0023] Wherein, the synthetic resin is any one or more of acrylic resin and polyester resin, the solvent is any one or more of acetone, isopropanol, and methyl ethyl ketone, the type A viscosity modifier is any one or more of microcrystalline wax and thickener, and the thickener is any one or more of colloidal silica and bentonite.

[0024] In use, a mixture of synthetic resin, solvent, and type A viscosity modifier serves as the solvent and carrier for solder paste preparation. The ratio of synthetic resin, solvent, and type A viscosity modifier in the mixed base controls the viscosity of the solder paste, ensuring uniform distribution during coating or printing, facilitating soldering operations. The synthetic resin in the mixed base also possesses adhesive properties, allowing the solder paste to bond well to the circuit board or other coated surfaces, ensuring soldering reliability. Good adhesion reduces soldering cracking or failure during the soldering process. Furthermore, by increasing the stability of the solder paste, including its ability to maintain uniformity and fluidity during use, it avoids issues such as delamination, drying, or condensation, extending the solder paste's lifespan. The mixed base formulation enhances the wetting properties of the solder paste, improving the interaction between the solder paste and the soldering surface during the soldering process. This allows the solder paste to effectively adhere to the solder joint, forming a uniform solder joint and improving soldering quality.

[0025] The active flux includes alcohols, organic acids (such as fatty acids), amines, and other additives. The antioxidants include stannous chloride (SnCl2), antioxidant particles (such as antioxidant spheres), and organic compounds (such as benzothiadiazole). The alcohol additives are any or more of ethylene glycol, propylene glycol, and isopropanol. The organic acid additives are any or more of fatty acids (such as oleic acid and stearic acid) and hydrated boric acid. The amine additives are any or more of amine salts and amine compounds. The type B viscosity modifier includes natural resins and nanoparticles. The natural resins are any or more of rosin and shikimic acid. The nanoparticles are any or more of nano-silica and nano-alumina.

[0026] During use, alcohol-based fluxes exhibit good wetting and flow properties, helping the solder to wet the circuit board surface. Organic acid fluxes remove oxides and provide surface activity, helping the solder to form a good wetting layer on the metal surface. Amine fluxes have degassing and purifying effects, helping to eliminate bubbles and impurities generated during the soldering process. In addition, oxalate esters, nitrile compounds, transition metal complexes, etc., can be selected, which can include improving solder flow, enhancing wettability, reducing board chipping and desoldering effects. By using a variety of fluxes in combination, after preparing the solder paste, the wetting performance between the solder paste and the soldering surface is improved. At the same time, oxides, dirt, and residues on the soldering surface are removed, ensuring the cleanliness of the solder joints. Under the action of antioxidants, oxidation reactions are prevented or reduced, maintaining the activity of the solder alloy, thereby improving the soldering quality and reliability, as well as the electrical performance and overall use effect.

[0027] A method for preparing a low-melting-point SMT solder paste formulation includes the following preparation steps:

[0028] S1: Prepare the required materials: solder alloy powder, mixed base and flux, and weigh them according to the formula ratio. Use an electronic balance to weigh them and place them in a polypropylene container.

[0029] S2: Preparation of mixed solder alloy: Take out tin, bismuth silver and aluminum according to the formula ratio, put them in a container and stir to mix for later use;

[0030] S3: Preparation of mixed substrate: Synthetic resin, solvent and type A viscosity modifier are prepared according to the above ratio and stirred and mixed. Type A viscosity modifier is added last during the mixing process and is added gradually during stirring to achieve the required viscosity.

[0031] S4: Preparation of flux: Obtain active flux, type B viscosity modifier and antioxidant according to the ratio described. Mix the active flux and type B viscosity modifier and stir evenly to achieve the required viscosity. Gradually add antioxidant while stirring to ensure that all components are fully mixed.

[0032] S5: Solder paste preparation: Mix the base and flux together and stir evenly to form the base of the solder paste. Gradually add the pre-prepared solder alloy powder to the base while stirring and dispersing evenly. Heat and mix until a uniform solder paste is formed.

[0033] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A formulation for a low-melting-point SMT solder paste, characterized in that: The invention comprises solder alloy powder, a mixed substrate, and a flux. The component ratio of the solder alloy powder, mixed substrate, and flux is 60:30:

10. The solder alloy includes tin, bismuth silver, and aluminum. The mixed substrate includes synthetic resin, solvent, and type A viscosity modifier. The flux includes active flux, type B viscosity modifier, and antioxidant. The components of the solder alloy are: 95% tin, 3.5% bismuth silver, and 1.5% aluminum. The components of the mixed substrate are: 40% synthetic resin, 55% solvent, and 5% type A viscosity modifier. The synthetic resin is any one or more of acrylic resin and polyester resin. The solvent is any one or more of acetone, isopropanol, and methyl ethyl ketone. The type A viscosity modifier is any one or more of microcrystalline wax and thickener. The type B viscosity modifier includes natural resin and nanoparticles. The natural resin is any one or more of rosin and shikimic acid. The nanoparticles are any one or more of nano-silica and nano-alumina.

2. The formulation of a low-melting-point SMT solder paste according to claim 1, characterized in that: The thickener is any one or more of colloidal silica and bentonite.

3. The formulation of a low-melting-point SMT solder paste according to claim 1, characterized in that: The active flux includes alcohols, organic acids, and amines, and the antioxidants include stannous chloride, antioxidant particles, and organic compounds.

4. The formulation of a low-melting-point SMT solder paste according to claim 3, characterized in that: The alcohol auxiliaries are any one or more of ethylene glycol, propylene glycol, and isopropanol; the organic acid auxiliaries are any one or more of fatty acids and hydrated boric acid; and the amine auxiliaries are any one or more of amine salts and amine compounds.

5. A method for preparing a low-melting-point SMT solder paste according to any one of claims 1-4, characterized in that: The preparation steps include the following: S1: Prepare the required materials: Prepare the materials required for preparing solder alloy powder, mixed substrate and flux, and weigh them according to the formula ratio. Use an electronic balance to weigh them and place them in a polypropylene container. S2: Preparation of mixed solder alloy: Take out tin, bismuth silver and aluminum according to the formula ratio, put them in a container and stir to mix for later use; S3: Preparation of mixed substrate: Synthetic resin, solvent and type A viscosity modifier are obtained according to the formula ratio and stirred and mixed. During the mixing process, type A viscosity modifier is added last and gradually added during the stirring process to achieve the required viscosity. S4: Preparation of flux: Obtain active flux, type B viscosity modifier and antioxidant according to the formula ratio. Mix the active flux and type B viscosity modifier and stir evenly to achieve the required viscosity. Gradually add antioxidant while stirring to ensure that all components are fully mixed. S5: Solder paste preparation: Mix the base and flux together and stir evenly to form the base of the solder paste. Gradually add the pre-prepared solder alloy powder to the base while stirring and dispersing evenly. Heat and mix until a uniform solder paste is formed.

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