Other platings used are OSP (organic surface protectant), immersion silver (IAg), immersion tin, electroless nickel with immersion gold coating (ENIG), electroless nickel electroless palladium immersion gold (ENEPIG) and direct gold plating (over nickel). Edge connectors, placed along one edge of some boards, are often nickel plated then gold plated. Another coating consideration is rapid diffusion of coating metal into Tin solder. Tin forms intermetallics such as Cu5Sn6 and Ag3Cu that dissolve into the Tin liquidus or solidus(@50C), stripping surface coating or leaving voids. COUNT 5
QSN1 What does OSP stand for? ANS1 organic surface protectant QSN2 What metal is often under the gold plating on edge connectors? ANS2 nickel QSN3 What's the abbreviation for immersion silver plating? ANS3 IAg QSN4 Ag3Cu is one intermetallic that tin forms; what's the other one? ANS4 Cu5Sn6 QSN5 What might the rapid diffusion of coating metal into tin solder leave in the surface coating? ANS5 voids