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Shelflife of platings wrt solderability

I know that I am kicking open an open door. But is there something like a shelf life on SnPb platings as used in terminals the electrotechnical industry? What effects the shelf life the most if we look at solderability (temperature, moist or what...?)

Jim Tjon
- Tilburg, Brabant, Holland

This is tough question, as a lot will affect solderability. The surface oxide that forms on the plating will affect solderability but can be addressed with a good flux. Thin plating will allow oxidation of the base metal is if the plating has a course grain structure, but with the lead it should be grain refined. The biggest affect on shelf life is the base metal. Forget the lead it does not enter into the chemical equation, but the tin will continue to form intermetallics with the base metal over time. If memory serves me right the intermetallic growth is faster on copper than nickel, but nickel is more sensitive per thickness of intermetallic growth than copper. Nickel is preferred over copper for long shelf life. Also plate to the high end of the spec. For nickel I use to use just a dull Watts bath (very low chloride) but if I were to do it again I would use a sulfamate nickel.(better ductility) Is possible to use a steric acid post dip to "seal" parts this also has flux like abilities

Jon Quirt
- Minneapolis, Minnesota

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