Hi Experts,
I need help here, advice appreciated from all...
Production is running a Lot of flex-circuit PCB, through the SMT line, with 0402 components. The flex-PCB is taped to FR4 support "pallets" when processing thru' the SMT P&P m/c.
We use WS (water soluble flux) process, and so require Aqueous water wash thru' a Electrovert Aquastorm 90 m/c.
Subsequent oven-bake is required to dry off the water residue (on the side facing in contact to the FR4 pallet side) that wasn't dried up by the Electrovert Air dryers.
Problem is production "forgot" instructions to peel off the flex-PCBA from the pallet before oven-bake drying process. Now the side facing down in contact to the FR4 pallet, is "spotty" with water-stain marks. As this affected side is the contact pads for the end-product "reader" unit, my customer says the water stains are not healthy, and require us to clean up the stains...
we already tried prozone/IPA, and this only "cleans" the pads temporary, after the chemicals "dry-up" the pads have darker-yellowish water-stains again...
I think the flex-PCB pads are either gold/copper in primary content, and my thinking is if its predominent copper, then the water-stains are stuck there for life? (Cu has lousy resistance to itchy finger prints and water stains?)
Any suggestions what chemicals can help us out? Anyone else encountered this problem, and what/how did you resolve it?
Help!
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