With the application of reflow soldering technology,
solder paste has become an important process material in surface mount technology (SMT). In the reflow soldering of surface mount components, solder paste is used to implement the leads or terminals of surface mount components. The connection of the solder pad on the board. Solder paste coating is a key process of surface mount technology, which will directly affect the soldering quality and reliability of surface mount components. Solder paste is used in different processes or processes of surface assembly in PCBA processing, and the performance of solder paste is required to be different. We have collected some information and summarized the following points:
1. The shelf life of solder paste is 6 months, and the solder paste should be kept within 3 to 6 months of validity before printing.
2. The solder paste should have excellent mold release properties during printing; the solder paste is not easy to collapse during and after printing; the viscosity of the solder paste should be moderate.
3. Solder paste printing should have good wetting properties when reflow soldering is heated; a minimum amount of solder balls should be formed, and solder spatter should be less.
4. After solder paste reflow soldering, the lower the solid content in the flux, the better, and it is easy to clean after soldering, that is to say, there is little or no residue after soldering. High strength and firmness after welding.
5. Solder paste should follow four properties in soldering applications: fluidity, stripping, continuous printing, and stability.
Solder paste is a fluid with fluidity. The fluidity of materials can be divided into ideal, plastic, pseudoplastic, expansion and thixotropic, and solder paste is a thixotropic fluid. The ratio of shear stress to shear rate is defined as the viscosity of solder paste, and its unit is Pa.s. The percentage of solder paste alloy, powder particle size, temperature, solder amount and lubricity of thixotropic agent are the factors that affect the viscosity of solder paste. main factor. In practical applications, the viscosity is generally determined according to the type of solder paste printing technology and the thickness printed on the PCB.
In addition, the storage temperature of the solder paste is stored between 2-10°C, the ambient temperature is 20-25°C during use, and the relative humidity is 30%-60%. We have a detailed explanation in the article, which is very important and can be searched for.
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