Searching for a technical document describing how tin plating reacts in a humid environment

January 20, 2009

I am looking for a technical document which will describe how tin plating reacts in a hot, humid environment. Here's my situation.

My company is using an alkaline tin process to barrel plate copper lugs. Some of our product is shipped to an uncontrolled warehouse in Singapore, where conditions can easily reach a temperature of 85F and relative humidity of 85%. I am unsurprised to hear that our tin plated product turns yellowish in this environment, especially since we do not use any post plating antitarnish treatments. This is a purely cosmetic change which does not affect the performance of the lugs. Recently our Asian customers have been rejecting our product based on appearance. I have explained that this is a natural phenomenon when tin is stored in hot, humid conditions. The customers want more reassurance, namely a third party technical document confirming what I said. I am having no luck finding an ASTM, MIL-SPEC, or other technical document confiming something that I know to be true. ASTM B 545 does not address this. Any suggestions would be greatly appreciated.

PS: I am not looking for solutions to the yellowing issue, as I am already investigating several options. I'm just looking for a document which addresses how tin reacts in a humid environment. Thank you in advance for any help.

Linda Corrie
Plating Engineer - Orland Park, IL USA