We all know that more than 60% of smt quality defects are caused by printing. In other words, printing is one of the main causes of poor quality. So, how to improve printing quality and reduce product defects caused by poor printing.

Setting of printing parameters. The first is the printing pressure. The two classic parameters of printing are the squeegee angle of 60 degrees and the printing pressure of 60N. In fact, it is not the case. The squeegee angle of 60 degrees is correct. This is given by the machine and cannot be easily adjusted. The pressure is adjustable and should be adjusted according to the printing effect. The judgment principle is as follows:

①Check the SMT stencil that you have used, and observe whether there are scratches on the printing surface of the laser stencil, and to what extent.

② Observe whether there is bright gold and gold in the solder paste on the SMD stencil during the printing process. If it indicates that the scraper has squeezed the solder balls in the solder paste into tin pieces, the PCB pads may be There is a defective solder paste, because the tin sheet will block the stencil mesh, so the printing pressure should be reduced, and the solder paste must be replaced at the same time;

③ Observe the thickness of the solder paste on the PCB after printing. If there are too many solder pastes after reflow, and the amount of tin on the pins of the device is too small, the tin climbing height cannot meet the requirements. I suggest to start the analysis and solution by reducing the printing pressure; Pressure can increase the thickness of solder paste printing, reduce virtual soldering, extend machine life, save electricity, and extend the use of SMD stencils.

Then, the printing pressure is better. I suggest to start the test from 20N, and use the above requirements as the principle to determine the printing pressure.