Question: We are working with components with leads of tin/lead over nickel. After the manufacturing processes, some of the pins are exhibiting what appears to be flaking plating, leaving behind unsolderable surfaces. They will re-tin with flux, but reappear following steam-aging. Is this something you have encountered before?
Answer: There is a metallurgy issue with soldering to nickel plated surfaces and depending upon the thickness of the final tin/lead coating, the steam aging will penetrate the finish coating and create a problem with the adhesion of the final coating. You don’t mention what type of flux is being used, but this is one place where an aggressive flux can be used to remove the passivation from the nickel coating. I would suggest a strong OAH1 FLUX, for tinning the components, with an appropriate cleaning afterwards to remove any of the ionic residues from the surfaces of the leads and components.