Matte tin finish for electronic components

A. During a recent conversation about offshore outsourcing to China, someone used an expression that was new to me, John; he said some buyers "throw the parts over the wall".

I think we're starting to see something like that with lead-free parts. "You said you wanted lead-free parts; so we left the lead out when making up the plating bath". But there is more to electronics-grade lead-free plating than just leaving the lead out; for example it may be necessary to have a small bismuth content. I think you'll need to reference or write a spec that your plater will need to certify to that will insure you don't have a contact resistance issue. Keeping the parts under nitrogen until they are put into use is fine, but if the oxidation issue isn't clearly addressed, it may achieve nothing but forestalling the problem until the bags are opened, guaranteeing costly field failure in lieu of in-house rejects :-(

A. The increased contact resistance is certainly due to oxidation. A thin film of oxide layer (a few nanometers) is formed on the tin plated contacts and devices. Because of this reason, insertion force is considered as an important aspect in tin plated connectors. It is essential that the insertion force should be sufficiently high so that the soft tin coating could extrude through the hard tin oxide layer and establish a good electrical contact between the mated contacts.

The extent of oxidation on the tin plated contacts and devices could vary depending on the exposure conditions. Packing devices in vacuum or nitrogen filled bags could help to prevent further oxidation during storage and transit.

A. The Matte Tin of lead finished got higher contact resistance due to surface oxidation during assembly process, especially for the annealing stage that prevents whisker growth purpose and almost a standard stage in lead free assembly flow currently form a cover layer of Sn oxidation already that means follow up of packing method or storage conditions can't reduce these layer of contact resistance but prevent come to the worst.