[time-nuts] HP 5370B low frequency modulation
didier at cox.net
Thu Aug 30 19:10:56 EDT 2007
> -----Original Message-----
> From: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Richard
> (Rick) Karlquist
> Sent: Thursday, August 30, 2007 10:22 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] HP 5370B low frequency modulation
> I have heard of assembly lines that do not allow any gold
> whatsoever in the building!
That sounds totally unjustified. It's not like gold is going
to jump at the solder joint and contaminate it cold.
The effect of gold contamination is to weaken the joint (the
intermetallic compound of gold and tin is hard and brittle).
Over time, and particularly in high stress environments
(temperature cycling, vibrations), the solder joint
eventually breaks down at the interface and leaves you
with an intermittent connection.
The way we deal with it in the military business (where
temperature cycling and vibration is a way of life) is that
we first remove the gold plating from the solder pin side of
connector pins by tinning the pin a couple of times and each
time sucking the solder with fresh braid or other tool.
That dissolves the gold in solder that is then discarded,
leaving the solder end of the pin free of gold. At that point,
the pin can be soldered normally and the solder joint will show
Alternately, we use a solder pot and dip the end of the part
that is to be cleaned in it. The problem with that is that
the concentration of gold in the pot increases over time until
the content of the pot has to be discarded and replaced, so
if you try to use the pot for too long, you may not get rid
of the gold completely.
Our manufacturing engineering people have developped rules
for how many times you can use the pot before replacement,
and that seems to work as long as it is controlled.
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