This process coats a very thin coating of an organic material that inhibits copper oxidation. It is so thin that it is nearly impossible to see and measure. The organic material is removed by the assembly flux. Boards that have been OSP coated will have bright copper pad coloration. The most prevalent is ENTEK CU-106A. This is used for assemblies that will go through multiple assembly operations. PCB’s that have multiple surface finishes can use the CU-106A(X) finish.

This process coats a thin layer of tin directly on top of the copper surface. The tin produces an extremely flat surface for mounting of surface mount components with ultra fine-pitch devices. This also provides a thicker, uniform surface that provides lubrication for press-fit pins.

This process plates a thin layer of silver directly on top of the copper surface. As with the other immersion surface finishes, the finished product produces a very flat surface; it is ideal for fine pitch SMD arrays. This surface finish has the ability to maintain high solderability after multiple heat cycles. This can also be used as an aluminum wire bondable surface. It is compatible with no-clean assembly processes. This is becoming popular as a Hot Air Solder Leveling (HASL) replacement for lead-free soldering applications. This surface finish yields a dull tarnished looking surface. There is significant industry data showing that the dullness does not affect solderability or reliability.

Other finishes include hot-air solder leveling and immersion nickel-gold (ImNiAu). Table 1, from a 2003 SMTA paper, summarizes the attributes of each PCB finish.