Over ten years ago as Lucent was phasing out its on-shore manufacturing I
worked with some wave solder engineers monitoring solder pots.

They had recently added N2 inert to several of them and were concerned about
some "changes" in the solder joints.

Over the space of several months we sampled the pots and found that
generally ALL trace elements steadily increased.

We never had a chance to finish the study and the data is long gone but it
was the general belief that the dross was actually helping keep the solder
"clean".

I don't remember any numbers but I believe copper was one element slowly
increasing.

Greg Munie PhD
IPC Technical Conference Director
630-209-1683
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http://www.ipcapexexpo.org/
http://www.ipc.org


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Louis Hart
Sent: Thursday, February 07, 2013 7:05 PM
To: [log in to unmask]
Subject: [TN] solder skimming and contaminants

Technetters, my apologies for asking this question again. It has been 2
years since I asked, and I remember getting some good responses, but digging
through the archives I can't find them. My memory of their content has
gotten quite vague. I can only presume that the responses came directly to
me, and I lost them.

What chemical species are removed from a 63/37 tin-lead molten bath when the
film or coating on the top surface is skimmed off? I had the theory that,
along with some oxide(s) of tin, oxide(s) of copper would be removed. I'm
thinking of wave solder baths. The long-term result would be elemental
copper would reach some stable concentration in the bath, which
concentration based on my limited data appeared to be about  0.23% by
weight.

And does gold, as an element, simply sink to the bottom of the bath?

Louis Hart
Compunetics
Monroeville, PA
USA
[log in to unmask]<mailto:[log in to unmask]>
412-858-1232


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