In the different processes or procedures of surface assembly, solder paste is required to have corresponding properties. The specific requirements of SMT process for solder paste characteristics and related factors are as follows:
(1) The solder paste should have good storage stability. After the solder paste is prepared, it should be stored at room temperature or refrigerated conditions for 3 to 6 months before printing without changing its performance.
(2) The properties that the solder paste should have during printing and before reflow heating:
①The solder paste should have excellent mold release during printing.
②The solder paste is not easy to collapse during and after printing.
③The solder paste should have a certain viscosity.
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(3) The properties of solder paste during reflow heating:
①Should have good wetting performance.
②No or minimum solder balls are formed.
③There should be less solder spatter.
(4) The properties that the solder paste should have after reflow soldering:
①The lower the solid content in the flux, the better, and it is easy to clean after welding.
②High welding strength.