My experience is that thermal cycling and vibration exacerbate the problem
very greatly. We have been making both commercial and military products for
a long time, and we started seeing the problem in military products much
before we ever saw it in commercial products.
The intermetallic compound is conductive, so unless you have some mechanical
effect that pushes the conductors apart, the contact will not necessarily be
lost.
Look closely at a PWB that is gold plated (not just the plug-in contact
area, but some older PWBs were entirely gold plated). Look at the interface
where the solder joint meets the gold. On anything that is more than a few
years old, you are likely to see a darker grey ring where the two metals
meet. There you have it. You don't see that on a new board. Remove the
solder from one of these joints with solder wick or a desoldering iron,
clean real good with a small brush and redo the solder joint using a good
cleaning flux, and the solder joint will look normal.
Didier KO4BB
-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Tom Van Baak
Sent: Thursday, August 30, 2007 9:17 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] HP 5370B low frequency modulation, gold
This is an interesting discussion about gold. Thanks to all
those who have posted. My question is -- I've noticed that
almost all my old HP instruments, from the 60's and some
decades thereafter, use a large amount of gold on all the PCB
traces and many component leads. It gave them a premium look,
even artistic beauty in some cases. I always assumed it was
for performance, reliability, and longevity.
So when was it discovered that using gold was a bad idea?
Is this only for mil-spec stuff or for regular laboratory
test equipment too?
/tvb
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