Hi Michael - there are several opinions on the "exact" number but if you
don't exceed  3 weight % limit in the solderjoint then you should be in
good shape for a large number of use environments. Take a look back in the
archives for some industry publication references for examples of
calculating the limit number. The past threads also document the issues of
having gold embrittlement due to segregation zones. Good Luck.

Dave Hillman
Rockwell Collins
[log in to unmask]




"Alderete, Michael" <[log in to unmask]> on 03/05/99 11:26:16 AM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
      to "Alderete, Michael" <[log in to unmask]>

To:   [log in to unmask]
cc:
Subject:  Re: [TN] Solder Attachment [Au plating in...]




Wes-

5 micoinch Au is a typical, minimum thickness Au plating.

If you can calculate that it will go into solution, and form a solder joint
with less than 5% [less than 2%??] Au in PbSn, than you most likely are ok.

If the Au isn't allowed to disperse throughout most, or all, of the solder
joint, you may have localised high Au concentrated areas, which might pose
a
reliability risk.

Can any of you metallurgists clarify whether this <5% Au rule of thumb (or
blind faith?) is in terms of volume or weight percentage of Au?

This is of great interest to those of us who'd like to convert from HASL
PWB
pad finishes to Au/Ni, for SMT PWBs.

Regards,

Michael Alderete
Aerojet




Wes wrote...
------------------------------

Date:    Thu, 4 Mar 1999 14:23:20 -0500
From:    Malewicz Wesley <[log in to unmask]>
Subject: Solder Attachment

        I have a part that is made out of .005 thick Beryllium Copper with
a
finish per MIL-G-45204 Type 1 with 5 micro-inches Hard Gold.  This part is
a
surface mount part and attached to the PCB via solder paste then re-flowed.
My question is, should I experience any long term reliability or soldering
problems with the attachment of this part?

Thanking you in advance for your comments.

Wes

------------------------------