[time-nuts] HP 5370B low frequency modulation, gold

Didier Juges didier at cox.net
Fri Aug 31 03:25:14 UTC 2007


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: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] 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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