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"Tin plate peeling"


Q. Copper strips plated with 100-300 micro inches of pyro-copper then pure tin plated parts pass tape-bend-blast test but when a teflon coat is applied the tin lifts off heated to 350 ° for teflon, the copper is black when tin is removed with teflon but if you strip the tin, copper is nice looking.

Daniel Casey
plating shop - EVERETT, MASS, U.S.A.


A. I waited 24 hours to respond, hoping that some more qualified metallurgist would sound off. I am a little out of my area here but in absence of any other advice here is my 2 cents.

At the temperature you are curing the Teflon the copper and tin and organic plating additives are fusing and cooking together to form some sort of brittle and black intermetallic that is falling apart when you peel.

Try a nickel or palladium diffusion barrier between the copper and the tin, but be careful as tin will also difuse into nickel.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina


A. There is not enough information here to really answer the problem. However, it could be that the tin layer is too thin and porous. You do not say what type of tin you are putting down or whether it is flow melted etc., etc. Unless it is pore free, it will allow gases to seep through onto the copper and react there, especially if the metal is heated to 350 °C. Secondly, tin has a melting point of 232 °C, so heating it this high will cause the diffusion of tin into the copper to go very quickly. This will form an intermetallic compound of Cu-Sn, which could also account for the blackening. This compound will be quite brittle.

I suggest you try this: take your tin plated copper and put it through the PTFE process, but DO NOT put any PTFE down. Then heat it to 350 °C for the same time and see how the adhesion and bend tests stand up. If the same problem occurs, it will be the processing; if it doesn't, the problem lies with the PTFE. Perhaps more information will be beneficial to solving your problem.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK

October 12, 2021

Q. Why do you think that the tin plating is too thin? What is its correlation with plating peel off?

Lea Cabeliza
employee - Sto. Tomas, Batangas

September 12, 2013

Q. Doing repairs on an industrial electronic device. Small ring terminals with 20 AWG tinned wire on a certain set of connections are showing an increased resistance in the crimp, 20 m-Ohms or more, after being in service for 15 years. Wiggling the wire at the crimp causes the resistance to jump around. Terminals appear to be brass with copper and bright tin. I don't recognize the brand. If I remove a terminal and give it a bend between the ring and crimp, the tin flakes off, revealing dark oxidized copper. Terminals carry a short pulse (10 µS) of 25 Amps then sustained 4 A. Typical environment is semi-sheltered and a fair amount of diesel soot. Other terminals on the same device are a common brand, tin over copper. They don't show any increase in resistance after the same years of service. Would experts suspect a process problem when originally made? Or is this a problem with brass/copper/tin? Recently made devices are still using the same type of terminal.

Eric Durfee
Repair company - Fridley, Minnesota, USA

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