Solderability of eco-friendly OSP surface finish

In order to enhance the solderability, bare copper on PCBs needs a protection. As an antioxidant, OSP (Organic Solderability Preservatives) has been widely used in PCB surface finishes. The OSP surface finish is a very thin film. It is transparent, colorless and fragile. This makes it difficult to detect the OSP film and indicate the OSP surface solderability. In this work, a chemical reaction is possible for such a characterization. We use scanning electron microscopy to evaluate the reflow behavior of two kinds of high performance OSPs. Microstructural evolution of the OSPs related to the reflow process was investigated. Reflow atmosphere did not affect the OSP films. Reaction product of Ag crystals were found to be dendrite.