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  for Metal Finishing since 1989
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Poor Solderability Problem

I'm researching the detailed reasons why surface oxides (zinc / tin) prevent solder from properly wetting electrical terminals. The brass terminals used in our application are pre-plated tin over copper flash, stamped, then post tin plated on the tip where it's to be soldered later into a circuit. I would appreciate any feedback on this matter.

Tom Horn
- Auburn Hill, Michigan
2003

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Most metal oxides are kissing cousins of ceramics, IE: very non reactive to most chemicals and are a wonderful barrier to prevent proper soldering. Tin plated material has a shelf life of about 1 month if it is in open boxes on the shelf. You might look at nitrogen flush bags of parts and then vacuum evacuate them and seal it. Think of the late night infomercials for household stuff. We had a nice business of tin plating parts for local electronics companies and would give them a one week turn around. We actually stored them for one company and basically gave them a just in time delivery plus a few days.

They will last a lot longer on the shelf if you give them a dip in Xylene ⇦this on eBay or Amazon [affil links] with a small amount of stearic acid ⇦this on eBay or Amazon [affil links] (beef fat derivative). Used to be in the mil spec.

James Watts
- Navarre, Florida
2003

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Tom,

Check thickness of the Tin on the contact (should not be over a few tenths). If the tin is too thick it will not flow or wet good. Maybe you may want to look at having the contacts plated tin / lead instead of tin.

Chris Snyder
plater - Charlotte, North Carolina
2003

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Tom,

Where does the zinc come in?

Jon Quirt
- Minneapolis, Minnesota
2003