1. In PCBA processing, due to the relatively large number of products in the same batch and the longer chip processing cycle, there may be dry solder paste on the stencil, or the template opening and the circuit board may not be aligned, which may lead to Unnecessary solder paste is generated at the bottom of the template or during the processing of PCBA foundry materials, resulting in poor soldering.
2. Defects in SMT chip processing, 75% to 85 percent of defects are caused by solder paste defects
3. For fine templates, if damage occurs between thin pins due to the bending of the template section, it may cause printing defects and short circuits.
Therefore, in the process of SMT processing, it is necessary to strictly implement the requirements of the quality management system to avoid or reduce the appearance of solder paste defects. This requires management and control details from the initial BOM and Gerber data sorting, to component procurement channel management, solder paste storage and access control, solder paste printing, SPI solder paste inspection, reflow soldering and other aspects. During the printing process of the automatic printing machine, the printing cycle is fixed in a specific mode. Make sure that the template is on the pad, so that the solder paste printing process is clean.
After printing the solder paste in the SMT package, the longer the operator has to wait after discovering a printing error, the more difficult it is to remove the solder paste. When a problem is found, the improperly printed board should be immediately put into the soaking solvent, because the solder paste is easily removed before drying.
In order to prevent the residue of solder paste and other contaminants, you can wipe the surface of the circuit board with a clean cloth during production. After soaking, scrub with a gentle spray, and preferably use a hot air blower for drying. If a horizontal stencil cleaner is used, the clean side should be down to allow the solder paste to fall off the board.