Guenter,
I'd sooner ask you the question than Colin Lea!
Colin has alot of respect over here but you are the only person I would pose
questions of this nature to.
I myself would not have thought that the intermettalic growth would be limited
by anything until it had used up the available tin. Pads with a measured solder
thickness of 1 micron on a PCB, in the past for me, have yielded intermetallic
problems in the from of unsolderable surfaces after multiple thermal cycles. I
would have said, intermetallic growth doesn't depend on the volume it is in, but
can continue until available tin is used up. I'm not a metallurgist!
Guenter, you study this stuff every day!
Are you saying that Colin is wrong in this statement?????
Regards
Edward Brunker


______________________________ Reply Separator _________________________________
Subject: [TN] Intermetallics
Author:  "TechNet E-Mail Forum." <[log in to unmask]>           Guenter Grossmann
<[log in to unmask]> at INTERNET
Date:    08/02/99 11:15


Hi all


I have a question concerning the growth of Intermetallics:


Collin Lea states in his book, that the thickness on a copper specimen
immersed into a large solder volume reaches an equilibrium which is
0.5um at 240deg to 0.9um at 345 deg. The dissolution rate of the
intermetallic layers is equal to the growth of the intermetallics after
this equilibrium is reached. However, this is in a large solder volume.
Is the thickness of the intermetallics in solder joints with a limited
volume also restricted to the equilibrium or does the intermetallic
layers grow bigger since the solder will see an certain enrichment of
copper?


Best regards


Guenter

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