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Date: | Tue, 01 Oct 96 08:18:18 cst |
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Hi Greg -
Oh boy, did you ask a question that will have the TechNet hopping for
awhile!!! When you have gold finished components & gold plated PCBs
and solder them using 63/37 you run the risk of having gold
embrittlement. Gold embrittlement is one of those topics that
metallurgists and material engineers love to discuss because: (a) it
is a very well documented phenomena, (b) gold-tin intermetallics are
interesting to look at. A couple general rules of thumb to use:
a) Is there enough solder volume for the gold to diffusive into?
The answer to this question is almost always yes. The published
literature consensus is that gold embrittlement occurs at/around 4
wt.%.
b) Is the soldering operation long enough and hot enough to allow #1
to occur?
This is the question that is the problem. Many times the soldering
process is too short to allow the gold to totally diffuse into the
solder thus leaving a thin, heavy concentration of gold-tin
intermetallic where cracks will originate.
I don't have any experience with using a different alloy selection to
avoid the problems but hopefully some of the other TechNetters will
have some good suggestions. The grainy appearance of your solder
joints may be the gold-tin intermetallic particles. A good paper to
read on the subject is:
"The Effect of Gold on the Reliability of Solder Joints", Dr. Judy
Glazer, 1991 Surface Mount International Conference proceedings.
Good Luck.
Dave Hillman
Rockwell Collins
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______________________________ Reply Separator _________________________________
Subject: ASSY: Gold-to-Gold Soldering
Author: [log in to unmask] at ccmgw1
Date: 9/30/96 9:12 PM
Does anyone have experience soldering gold-plated SMT components to
gold-plated PCB's using a eutectic (Sn63/Pb37) solder? The solder
joints exhibit a dull, grainy appearance. Although I know that longer
liquidus dwell times and a maximum reflow temperature of 220 C are
typically recommended when soldering to gold, will other solder
alloys perform better (i.e,, Indium alloys)?
Thanks in advance,
Greg Kilinski
Acuson Corp.
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