Sound like some sort of Nickel oxide to me. Michael Besket Acuson Corp. [log in to unmask] _______________________________________________________________________________ Subject: Ni contamination From: [log in to unmask] at ccUnix Date: 9/3/95 8:37 AM I manage a captive PWB shop that produces 4,000 square feet per week of double sided plated thru hole product from .062 FR-4 copper laminate. Our product is a bit uncommon in that it has about .0004 inch hard nickel plated over the copper traces. Thru testing, we find a VERY thin layer (maybe 150 angstroms) of some contaminate that affects the surface conductivity when it is used as a switch half with a stainless steel snap dome. Using a Scotchbrite pad to burnish the surface provides a solution, but I would like to know the source of the substance and how to prevent it in the original process. Any ideas on the subject?