I think the concern is intermetallic compound formation with attendant
brittle failure.  You better do some home work.  It might be possible to
qualify the joints, but I doubt anyone would want to risk it.

Pat Hogue
Materials and Processes

 ----------
From:  Kevin Minney[SMTP:[log in to unmask]]
Reply To:  TechNet E-Mail Forum.;Kevin Minney
Sent:  Friday, May 29, 1998 10:38 AM
To:  [log in to unmask]
Subject:  [TN] ADVICE ON GOLD/JOINT EMBRITTLEMENT

Dear Sir/Madam,
I wonder if you can help, please forgive me for emailing you directly I
was unsure as to whether
the Technet forum was open to the 'general public' for posting ..
I stumbled across an article that a Mr Bill Fabry had posted to the
Technet forum
regarding gold and embrittlement. I am working on the design of a single
board computer and have designed in a surface mount connector which I am
now told by the manufacturer (Samtec) that they can only supply with a
gold finish. Our main customer for this board is a defense contractor
and our own in-house rules (derived I assume from military standards) is
that all connectors with a gold lead finish must be solder dipped prior
to assembly onto the board. Our board is FR4 with tin/lead finish on the
pads. So far two sub contractors have failed to solder dip these
connectors, and even if they did succeed there would likely be a
co-planarity problem.

here is an extract of Bill's original posting to the Technet Forum ..

>>SNIP
From: "Bill Fabry" <[log in to unmask]>

Subject: Re: Re[2]- Electroless Ni/Im

To: [log in to unmask], "Thad McMillan" <[log in to unmask]>


Reply to: RE>Re[2]: Electroless Ni/Immersion A
Thad:

Based on a reliability report generated by HP: If the gold content is
less
than 2% of the resultant solder joint volume, no appreciable solder
embrittlement will occur. Therefore, the VOLUME of gold on ANY pad must
be
less than 2% of the resultant solder joint VOLUME, or ~1% of the VOLUME
of
solder paste applied to that pad. (e.g. if 0.005" solder paste is
applied, gold
thickness should be < 50 micro-inches.)
>>SNIP



Could you please advise, or refer me to someone who is able to advise on
the following ..

Q/. could I apply your guidelines to my connector or is it specifically
only applicable to a gold finish on the board ?

Q/. Could you give me a contact where I could acquire this HP
reliability report ?


many thanks, in anticipation,

Kevin Minney



 ----------------------------------------CUSTOMER FIRST, QUALITY ALWAYS
        KEVIN MINNEY     DY 4 Systems Inc         ****             ***
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  Tel: 613-599-9199 x208 Canada                   * ***  * ***  *** **
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