In the process of Pcb manufacturing, there are many defect factors which cause quality problems . Among them, solder paste printing defects are one of the common quality problems in PCB manufacturing. There are many kinds of defects in solder paste printing. The main defects are uneven pcb printing, missing printing, solder paste slumping, solder balls, dirt, offset and incomplete cleaning. These defects are nearly related to solder paste, printing equipment, etc.
Some of the components printing have requirement for printing specification of solder paste. The printing effect of Chip components, MELF components, SOT, SOIC, QFP, PLCC, LCCC, BGA, CSP, FC and other components are generally based on IPC standards. Table 1 lists the chip 1608, 2125, 3216 solder paste printing specifications separately, the printing effects of specific components can refer to the IPC standard.
1. Solder paste has no offset
2. The amount of solder paste, uniform thickness of 8.31mil
3. Solder paste is well formed without collapse
4.Solder paste covers more than 90% of the pad
1. The opening of the steel stencil has shrinkage holes, but the solder paste still has 85% coverage pads.
2. Even amount of solder paste3.Solder paste thickness is within specification
1. Insufficient amount of solder paste
2. Uneven amount of solder paste between two points3.Over 20% pad Print offset
Solder paste printing specification demonstration
1. Solder paste covers the pad completely
2. The amount of solder paste is even, thickness of 8-12mil
When analyzing solder paste printing defects, the analysis is generally performed in a predetermined order, and the steps are as follows.
1. Observe the quality of the solder paste itself.
2. Observe the quality of the printed stencil.
3. Observe the quality of the PCB pads.
4 .Performance and accuracy of printing equipment.
5.Pcb manufacturer's production environment.
6.Technical analysis of defects.
The above 6 steps must be organically combined, combined analysis, and only by abandoning the traditional one-way thinking habits can we solve the pcba .