Even at an "infinite" distance (say, 1 mil), 0.3% copper is allowed (and
some is to be expected) in 63/37 tin-lead solder.
Tim Reeves
-----Original Message-----
From: Don Vischulis [mailto:[log in to unmask]]
Sent: Sunday, October 07, 2001 6:46 PM
Subject: Re: Copper migration
Mike
I agree with Earl. The answer depends upon your frame of reference. The
basis metal is copper. The solder at an infinite distance from the
solder/copper interface is pure solder of whatever alloy you're using. In
between, you have two intermetallic compounds (IMC) composed of tin and
copper (off hand I forget the two compositions). This implies that there
might be a lead rich layer adjacent to the IMC. The question is where and
how you are going to sample for your analysis. The entire sampling process
should be evaluated to verify that there is no bias in the sample. If you
catch my line of reasoning, the sampling techinique, analysis method, and
reporting method will affect the reproted results. A small sample diameter
will have variable results depanding on where it's aimed, and a large sample
diameter will have entirely different results.
Regards,
Don Vischulis
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Earl Moon
Sent: Sunday, October 07, 2001 1:58 PM
To: [log in to unmask]
Subject: Re: [TN] Copper migration
Mike,
Part of the answer to your question lies in the following:
This ?metal? layer can be a very high tin concentration on the solder side
and a very high copper concentration on the other side - meaning the base
metal side. In the case of PCB's, this mostly means copper.
Whether copper extends, or can do so, above the IMC layer, I cannot answer
but I believe it should not. How much is too much has always been a question
needing an answer. I think solder joint experts as Werner, and other
soldering and solderability experts, should have this answer to your
important question.
Earl
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