The danger with "thin"gold is that it may be porous and if it is,  the
Nickel underneath will oxidise and give rise to solderability issues. The
flash gold process, though, is self-limiting in the thickness it achieves,
so you may be OK. Just in case, don't store the boards too long before
using them. I usually specify 4-5 microinches gold on my boards.

Peter



Dave Chapman <[log in to unmask]>  04/01/2003 01:51 AM
Sent by: TechNet <[log in to unmask]>

Please respond to "TechNet E-Mail Forum."; Please respond to Dave Chapman

              To:  [log in to unmask]
              cc:  (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
              Subject: Re: [TN] 'Thin' Immersion Gold Finish?








If the gold is going to be used under a contact switch where there is going
to be movement or wiping, the gold should be thicker. If the gold will just
be for component attachment we have used the thinner "Flash" gold.

Dave Chapman
Mfg. Engineer
Circuit Service Inc.
-----Original Message-----
From: Rick Thompson [mailto:[log in to unmask]]
Sent: Friday, January 03, 2003 11:29 AM
To: [log in to unmask]
Subject: [TN] 'Thin' Immersion Gold Finish?


We have an overseas board supplier that is supplying an immersion gold
finished board that is only 1-1.5 microinches of gold over 100 microinches
of nickel.  I believe this may be too thin a gold layer for adequate
protection of the nickel but don't have any objective evidence for this.
Can anybody give me any feedback or other information sources that might
support this?  IPC-2221 specifies approximately 3-9 microinches of gold
which is what we generally require, but I'm looking for additional
objective
evidence for requiring thicker gold deposits.

Thanks in advance.

Rick Thompson

Sr. SMT Process Engineer
SMTEK International, Inc.
+1 (805) 532-2800
[log in to unmask]

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