Those were golden words, Mike. We've found that the empirical 4% rule is
of little use in practice, because you can get LOCAL concentrations even
with a thin gold finish, all depends on the soldering process, as you
mentioned. A good thing is that electrical failures due to gold
embrittlement seem to be rather rare. We have soldered millions and
millions of goldplated leads the last 30 years, and we have had just a
few incidents. (I have seen some really scary cases, but still, very
few on the long time scale)We have few components today with goldplated
leads, and the few that remain will be goldfree too, if there are no
special circumstances.
(Historically, the 4% ghoast was first created by a Dr Becker at
Ericsson, about 40 years ago. The 4% ghoast moved with the speed of
light and the rule was adopted everywhere, as it seems. The same man
presented a paper that warned about the dangerous silicon oil, that
could spread as an invisible film and cause electrical disaster. With
some common sense, you can handle both quite easily.)
Inge
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
Sent: den 1 februari 2007 11:03
To: [log in to unmask]
Subject: Re: [TN] Maximum Au lead plating thickness
Just for late completeness: it will also depend on whether you are hand
soldering, reflowing paste or wave soldering. Wave will wash a lot of
the gold away [and dilute it into the solder pot before redepositing
it], whereas hand or paste will just ad a finite amount of Sn to mix
with the gold.
Regards
Mike
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: Wednesday, January 31, 2007 7:32 PM
To: [log in to unmask]
Subject: Re: [TN] Maximum Au lead plating thickness
Karen,
You won't find it because it does not exist. You want less than 4% by
weight in the final joint for sure. Dr. Cotts of SUNY Binghampton would
argue for much less.
The reason you won't find a lead plating limit is that the results will
depend on:
1) lead size
2) pad size
3) stencil thickness
These will all affect the final joint concentration.
Bev
RIM
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Karen Walters Ebner
Sent: Wednesday, January 31, 2007 2:01 PM
To: [log in to unmask]
Subject: [TN] Maximum Au lead plating thickness
Hi
We are looking for the IPC spec that calls out the maximum Au plating
thickness on leads in order to prevent Au embrittlement.
Can anyone provide this to me.
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