Immersion tin: a proven final finish for printed circuit boards providing reliable solderability and marginal formation of tin‐whiskers

This paper describes a state‐of‐the‐art process for immersion tin plating of PCBs which is used to preserve solderability prior to assembly. The process sequence is described and preventive measures for handling the final surface finish is documented. A solderability test method and basic requirements for fluxes and soldering parameters are also described. Quantitative results on the formation of intermetallic tin‐copper phases are shown and their influence on the formation of tin whiskers explained. A problem in production is the precise measurement of the tin thickness, therefore different measuring methods are also detailed. Finally, the mechanism of tin deposition and the formation of tetravalent tin and the relationship with bath age and deposit quality are discussed.