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topic 356

Solder plated copper wire turns black in baking oven


(1996)

Q. We are involved in solder plating of copper wires. We have a problem referred from our customers about our plated wire. When the wire passes through an oven stage in a resistor plant for example, it becomes completely black. The plating we do is electroplating involving fluoborates. We can't seem to pinpoint the problem.

Please give references or addresses of research institutes or consultants who can help us.

[last name deleted for privacy by Editor]
outdated


Tin and Solder Plating

A. Hi. Some consultants are listed in our Directory of Consultants, and others may e-mail you as a result of this posting.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

(1996)

A. My guess is that the black color on tin (or solder?) plate after heating is copper that has diffused up through the coating and oxidized. It may also be the organic brightener burning out of the coating, depending upon your system.

Thin coatings of gold undergo a similar process if a barrier plate such as nickel is not applied over copper alloys. The time to surface appearance depends upon thickness of coating and temperature.

bill vins
Bill Vins
microwave & cable assemblies
Mesa (what a place-a), Arizona 


(1996)

A. Another possibility is that there may (for some reason) be sulfur in the oven atmosphere and stannous sulfide is forming.

Paul Stransky
- Putnam, Connecticut


(1996)

A. I agree with the guess of Bill Vins. It happens when the coating is thin, copper will diffuse up to the surface.

Mark [last name deleted for privacy by Editor]
Hong Kong
(1996)

A. We ran into this problem plating small nails that were heated for some reason. We used an acid tin bath with brighteners. We overcame this problem by running the nails thru a hot alkaline immersion cleaner and hot spin drying. I don't know what you could do. Good luck.

David Guleserian
- Rhode Island

(1996)

A. A big step in the right direction would be to analyze the black surface. EDAX will ID significant elements present and costs about $150/hour. One hour will be more than enough time to ID the culprit. Be open minded ... the last time I experienced this problem, my customer was unpacking my contamination-free parts and then leaving them for extended periods of time nearby an idling forklift in a hot-muggy warehouse in Malaysia! OF COURSE it was my dirty process that was to blame until surface analysis fingerprinted exhaust gas components on the surface only after arrival, as I sent analysis results of as processed surfaces prior to shipping from my plant which indicated the absence of contamination on my end. Immediate surface analysis at customer's site indicated no contamination, but analysis of same parts prior to use yielded contamination! OF COURSE, they were unpacked the whole time! Did the warehouse admit to this? Nooo! Good Luck,

Dave Kinghorn
Dave Kinghorn
Chemical Engineer
SUNNYvale, California




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