Wave Soldering Defects
Solder Mask Discoloration on a Printed Circuit Board
Normally this is a cosmetic issue but should be investigated for the real cause. When running a thicker board it is probable that the soldering process or dwell times may have changed.
Figure 1: Dark stripes on the solder mask after selective soldering.
The most common reasons for this occurrence include:
- Different flux used, higher temperature, longer dwell time or boards were run twice in pallet
- Solder mask/resist type, thickness or cure cycles have changed
- PCB supplier has been changed, or mixed batches of boards
There is no reference to the board finish, solder alloy being used or flux type - water or alcohol based. These are important when conducting analysis of the process problem.