Thanks for this tidbit, Greg. ~10 years ago I tracked contamination of copper and gold in a wave solder pot, after fresh solder was put in, for about 1.5 years, at intervals of 1 month. I remember copper rose in the first 6 months or so to about 0.22%, then increased only a few hundredths over the next year. Right now I'm looking at our solderability test pot and the HASL machine itself. In view of what you saw, I can believe the top layer does protect the solder.  Louis

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Gregory Munie
Sent: Friday, February 08, 2013 9:17 AM
To: [log in to unmask]
Subject: Re: [TN] solder skimming and contaminants

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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