I am not sure I can talk to hard or soft gold, and suitability for
soldering. 
But, I can say that it is possible to solder to electroplated gold, which is
different from Immersion Gold finish. 
I think some people say hard gold when they mean electroplated gold. 
There is a brief discussion of this in Coomb's Handbook.
Guy

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Glidden, Kevin
Sent: Tuesday, August 14, 2012 12:12 PM
To: [log in to unmask]
Subject: [TN] PCB finish: ENIG vs. hard gold

Hi everyone,

We have a PCB supplier who is offering "Hard Gold" as an alternate to ENIG
finish, due to PCB size and processing capabilities.  The application is
Class 3 (mil/aero).  The circuit is thin FR4 and subject to SMT reflow w/
Sn63Pb37 (non RoHS) solder alloy, and moderate flexing in end application.

Can anyone offer info on the differences between the two finishes, and/or
their suitability?  Is there an IPC spec (or specs) that outline "hard
gold"?

Thanks,

Kevin Glidden


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