Solution: Adjust the position of the template; adjust the printing machine.

2. Insufficient filling.
Insufficient filling is a phenomenon of insufficient supply of solder paste to PCB Pads. Unfilled, missing solder, less solder, dents, etc. all belong to insufficient filling. Because the insufficient filling amount is related to many factors such as printing pressure, squeegee speed, off-screen conditions, solder paste performance and state, template production method, and poor template cleaning, it is very important to optimize the printing conditions.

3. Penetration.
Penetration refers to the phenomenon that the flux penetrates around the filled pad. The causes of infiltration are excessive pressure of the printing squeegee, too large gap between the template and the PCB, etc. Measures should be taken to adjust the printing parameters and clean the template in time.

4. Bridging.
Bridging is a phenomenon in which solder paste is printed on adjacent pads. Possible reasons include the position deviation of the template and PCB, high printing pressure, large printing gap, and dirty back of the template. The printing parameters should be adjusted reasonably and the template should be cleaned in time.

5. The solder paste pattern has depressions.
Reason: With too much pressure on the squeegee, insufficient hardness of the rubber squeegee; or The template window is too large.
Risk: Insufficient amount of solder, false soldering is easy to occur, and solder joint strength is not enough.
Solution: Adjust the printing pressure; replace with a metal squeegee; improve the design of the template window.

6. Too much solder paste.
Reason: The size of the template window is too large; the gap between the template and the PCB is too large.
Risk: Easy to cause bridging.
Solution: Check the size of the template window; adjust the printing parameters, especially the gap of the PCB template.

7. The amount of solder paste is uneven and there are break points.
Reason: The stencil window wall is not smooth; the printing times are too many and the residual solder paste cannot be wiped off in time; the solder paste is not thixotropic.
Risk: Easy to cause insufficient amount of solder, such as false soldering, defects.
Solution: Wipe the template.

8. Graphic smear.
Reason: The stencil was printed too many times and was not cleaned up in time; the quality of the solder paste was poor; there was jitter when off-screen.
Risk: Easy to cause bridging.
Solution: Scrub template; change solder paste; adjust machine.

In short, when printing solder paste, it should be noted that the parameters of the solder paste will change at any time, such as particle size, shape, thixotropy, flux performance, etc. In addition, the parameters of the printing machine will also cause changes, such as printing pressure, speed, environmental temperature, etc. The quality of solder paste printing has a great influence on the quality of soldering, so every parameter in the printing process should be treated carefully, and relevant data should be observed and recorded frequently.

SMT are easy to have various problems. What we can do is to try our best to control every step and provide the high-quality and high-stability PCBA products to our clients.