After the SMT patch processing is completed, it is followed by reflow soldering. Usually after reflow soldering, the advantages and disadvantages of solder paste selection will be exposed. Tombstones, empty soldering, short circuits, incomplete print,which are all troublesome process problems. PCB and components that are within the normal process range, but defective after reflow soldering, the following methods can be used to find solutions:

1. Select the appropriate alloy composition. The alloy is the material that forms the solder joint, and the alloy composition also determines the welding temperature, so it is important to determine a reasonable alloy composition.

2. Select the appropriate solder paste viscosity. Solder paste printing should be considered to evaluate its mold release, thixotropy, viscosity and solder joint defects before choosing a suitable solder paste.

3. According to the size of the PCB , the size of the components in the patch processing, the pin spacing, the thickness of the PCB , and the pad coating, select the appropriate matching solder paste composition.

4. Determine the ratio of alloy components and flux in the solder paste. The ratio of alloy composition and flux directly affects the printability and viscosity of solder paste, and the proportion of flux is generally 10%-15%.

When choosing to use solder paste, we can determine the appropriate solder paste as long as the composition ratio of the solder paste alloy is combined with the comprehensive consideration of PCB and components. Solder paste should be stored in a low temperature environment of 2-10°C. Too high or too low temperature will cause the solder paste to deteriorate and oxidize.