[time-nuts] HP 5370B low frequency modulation

Magnus Danielson magnus at rubidium.dyndns.org
Thu Aug 30 19:40:59 EDT 2007


From: "Didier Juges" <didier at cox.net>
Subject: Re: [time-nuts] HP 5370B low frequency modulation
Date: Thu, 30 Aug 2007 18:10:56 -0500
Message-ID: <061301c7eb5b$063275b0$6501a8c0 at didierhp>

> ); SAEximRunCond expanded to false
> Errors-To: time-nuts-bounces+magnus=rubidium.dyndns.org at febo.com RETRY
> 
> > -----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 
> good characteristics.
> 
> 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.

Even these measures can be argued as overdoing it, even if I understand why
they run popular. The key point is that it is only when the gold concentration
in the solder joint is too high that you start to get these problems. For very
low levels of concentration there is no problem. The issues is really about
how much gold concentration do you end up with and do you have sufficient
control over amount of gold, amont of solder and amount of dissolvement time
for gold to distribute in the tin. These are process control variables.

Cheers,
Magnus



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