Just had a problem where the solder paste does not want to stick to the pad, thru the stencil. We have run this board for years with no problem, and this new lot of boards is giving us problems. I know it's a board problem because they look bad. The silver pad looks "different", almost a matte finish compared to what i have seen in the past. Also I can see what looks like a water marks that streak from all the pads. My first question is the silver immersion process. Could these boards have missed a step - or a process run incorrectly?
If I abrade the pads, the paste sticks. I then was able to get them to run by increasing the snap off distance of the screen printer. After that they seem to solder well.
I plan to bring a sample back to the baord house, but thought I'd ask here to see if i could get a leg up on them.