PCBA Tech - Common shortcomings of SMT solder paste and solutions

Solder paste printing is a complicated process in SMT patch processing, and it is prone to some shortcomings, which affect the quality of the final product. So in order to avoid some troubles often appearing in printing,

1. Draw the tip, generally the solder paste on the PCBA pad will be hill-shaped after printing.

Cause: It may be caused by the gap of the squeegee or the viscosity of the solder paste.

Avoidance or solution: SMT chip processing properly adjust the gap of the scraper or select a solder paste with suitable viscosity.

2. PCBA solder paste is too thin.

The reasons for are: 1. The template is too thin; 2. The pressure of the squeegee is too large; 3. The flowability of the solder paste is poor.

Avoidance or solution: choose a template with a suitable thickness; choose a solder paste with suitable granularity and viscosity; reduce the pressure of the squeegee.

3. After printing, the thickness of solder paste on the pad is different.

Reasons: 1. The solder paste is not uniformly mixed, so that the particle size is not the same. 2. The template is not parallel to the printed board;

Avoidance or solution: Fully mix the solder paste before printing; adjust the relative position of the template and the printed board.

Fourth, the thickness is not the same, there are burrs on the edges and appearance.

Reasons: It may be that the viscosity of the solder paste is low, and the wall of the template hole is rough.

Avoidance or solution: choose a solder paste with a slightly higher viscosity; check the etching quality of the template opening before printing.

Five, fall. After printing, the solder paste sinks to both ends of the pad.

Reasons: 1. The pressure of the squeegee is too large; 2. The positioning of the printed board is not firm; 3. The viscosity of the solder paste or the metal content is too low.

Avoidance or solution: adjust the pressure; fix the printed board from the beginning; select the solder paste with suitable viscosity.

Six solder paste is not printed on some places on the PCB pads.

The reasons are: 1. The hole is blocked or some solder paste sticks to the bottom of the template; 2. The viscosity of the solder paste is too small; 3. There are large-scale metal powder particles in the solder paste; 4. The scraper is worn.

Avoidance or solution: clean the opening and the bottom of the template; select a solder paste with a suitable viscosity, and make the solder paste printing can effectively cover the entire printing area; select the solder paste with the metal powder particle size corresponding to the opening size; check and replace the squeegee . Timing analysis in high-speed PCB design The placement order and pad placement of PCB design. Therefore, solder paste printing in SMT patch processing is a complicated process under the same conditions, and it is prone to some shortcomings, which affect the quality of the final product. Note that the above problems are to avoid some failures that often occur in printing.