Analysis of reflow soldering defects in the circuit board soldering process
Posted by davidsmithsmile on April 2nd, 2021
Solder Balls: Reason:
1. The screen-printed hole and the pad are not aligned, and the printing is not accurate, which makes the solder paste dirty the PCB.
2. The solder paste is exposed to too much in an oxidizing environment, and there is too much water in the air.
3. Inaccurate heating, too slow and uneven.
4. The heating rate is too fast and the preheating interval is too long.
5. The solder paste dries too fast.
6. Insufficient flux activity.
7. Too many tin powders with small particles.
8. The flux volatility is inappropriate during the reflow process. The process approval standard for solder
balls is: when the distance between the pads or printed wires is 0.13mm, the diameter of the solder balls cannot exceed 0.13mm, or there can be no more than five solder balls within a 600mm square area.
Tin bridge: Generally speaking, the factor that causes the solder bridge is that the solder paste is too thin. SMT patch processing includes low metal or solid content in the solder paste, low thixotropy, easy squeezing of the solder paste, and too large solder paste particles. The pcb prototype surface tension of the flux is too small. Too much solder paste on the pad, too high peak reflow temperature, etc.
Open: Reason:
1. The amount of solder paste is not enough.
2. The coplanarity of component pins is not enough.
3. The tin is not wet enough (not enough to melt, and the fluidity is not good), and the tin paste is too thin to cause tin loss.
4. The pin sucks tin (like rush grass) or there is a connection hole nearby. The coplanarity of the pins is particularly important for fine-pitch and ultra-fine-pitch pin components. One solution is to apply tin on the pads in advance. The pin sucking can be prevented by slowing down the heating speed and heating the bottom surface more and less heating on the top surface. It is also possible to use a flux with a slower wetting speed and a high activation temperature or a solder paste with different ratios of Sn/Pb to retard the melting to reduce the lead absorption.
