1 Solder on gold fingers comes from:
1a About 70 % of the time it's caused by poor cleaning of screen printer, staging area (table), conveyor, reflow oven chain or belt, and keeping boards separate from cleaning process
1b After loading paste onto the stencil, are operators handling cards right after it without cleaning or removing their gloves??
1c Paste process. Are you pasting anywhere near the gold fingers, are you leaching under the screen and contaminating the bottom side due to poor printer set up? Is your under-wipe frequency proper? Is paste dropping from the squeegee blades onto the stencil? Could the paste near the edge be getting onto the conveyor?
1d Reflow process. Paste can splatter if your heating profile doesn't match your paste, if your board is full of moisture, or if you�re not controlling your environment. Use a slow ramp to a decent dwell then jump up to reflow and back down within a 60 second window. Keep the ramp to under 2�/sec.
1e Check the boards before starting the printing process to try to eliminate some possibilities