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December 2004

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Subject:
From:
Lee Parker <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Lee Parker <[log in to unmask]>
Date:
Tue, 7 Dec 2004 09:38:48 -0500
Content-Type:
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text/plain (178 lines)
Ingemar

I would not minimize either of the issues you mentioned below, gold
embitterment and silicon migration under bias. Both mechanisms were
originally identified by Bell Laboratories many years ago as the result
of server field events. So far as I am aware the laws of Physics have
not been repealed and the threats are still with us. We need to be on
guard.

The real risk is that we as a community are no longer as knowledgeable
as we once were about these issues. Engineers, however, are paid for
their knowledge and judgment even when the technology is dated.

If a dog bits you once, shame on the dog; if he bits you a second time
shame on you; even if it's an old dog.

Best regards

Lee

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ingemar Hernefjord
(KC/EMW)
Sent: Tuesday, December 07, 2004 2:44 AM
To: [log in to unmask]
Subject: Re: [TN] Gold Plated Board

Dear Mr Indium & TN,
don't you think the Au IMC brittlement risk is little exaggerated? The
bright AuSnx are said to be strong, and the darkish ones rotten and
risky. Our company have soldered billions of components last decades, a
lot with gold flash,  and rather few incidents are reported. IMHO there
are other factors that are more important, like temperature profile,
oxide and debris removal, underplate wetting, solder amount etc. The
gold embrittlement hysteria reminds of the 'silicon hysteria' that
appeared some years ago. It was reported, that silicon which happened to
contaminate relay contacts, could cause severe function problems. This
was correct, but the ghost spread to other areas, so now, lots of
persons here have 'siliconitus' , which means that silicon is banned to
100%. Insane kind of extrapolation, I'd say. Same with the AuSn
formations. Instead, investigate the solder joints and make a
professional judgement, TN specialists are certainly eager to assist
you.

many micrometers of gold, that's another situation of course...

Ingemar Hernefjord
Ericsson Microwave Systems


-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Mike Fenner
Sent: den 6 december 2004 18:00
To: [log in to unmask]
Subject: Re: [TN] Gold Plated Board


Down load the Applications Note "Soldering to gold" from our website, it
says same as below but with the numbers, plus a bit more.

Regards

Mike

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Jack C. Olson
Sent: Monday, December 06, 2004 4:31 PM
To: [log in to unmask]
Subject: Re: [TN] Gold Plated Board


The amount of gold on an "Immersion" plated board
is only a few microinches think, usually less than 10.
When you solder a component to that surface, some
or all of the gold (depending on how long the solder
stays heated/melted) mixes in with the solder joint.
If the percentage of gold in the solder joint is high
enough the joint will be brittle, but it won't be that
high with such a thin immersion finish.

Trying to solder to a thick electroplated gold surface
is a different story, however, but you can calculate it
yourself by comparing the thickness of gold plating
with the amount of solder paste you are applying to
the lands in question. I can't remember the exact
percentage that means you are getting into the "danger
zone", but someone here will know it, or you can search
the TechNet archives at:
http://listserv.ipc.org/archives/technet.html

good luck,
Jack

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