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August 2012

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Subject:
From:
Guy Ramsey <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Guy Ramsey <[log in to unmask]>
Date:
Wed, 15 Aug 2012 08:56:05 -0400
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text/plain (139 lines)
We solder through a gold flash to Ni by necessity. I believe the flash is
high purity gold, not "hard".  We confirm, with process control data, that
gold flash is problematic. Too thin and the underlying Ni is not well
protected. Dave's comment is accurate. In practice a thickness 10 micro
inches is about the reasonable lower limit. Joyce's number is practical. 

However, our process DPMO data suggests that small packages, those that
require thin paste deposits suffer from lower yield (tombstone, head in
pillow) and, perhaps, weakened solder connections when the gold is that
thick. My experience confirms Richard's number. 0201 passives, flip-chip,
and microBGA, butt joint RF headers, and RF relays (with sweated ground
tabs) require less than 8 micro inches of gold, unless one is able to
compensate for the problem in some way. 

Confirming, Mike's comment. Gold flash does not protect copper. A barrier
metal is required, namely nickel. IMO gold flash finish can serve to protect
surfaces to be soldered, but it should used for some compelling reason and
it may require special process steps. 

One final bit of advice, if you go down this road. It is probably easier to
deal with excess gold than non-solderable nickel.


Guy

 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Tuesday, August 14, 2012 4:46 PM
To: [log in to unmask]
Subject: Re: [TN] PCB finish: ENIG vs. hard gold

I would suggest 4-8 uinches.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
Sent: Tuesday, August 14, 2012 3:40 PM
To: [log in to unmask]
Subject: Re: [TN] PCB finish: ENIG vs. hard gold

If you go for what ever the gold, keep it thin (8-10 micro inches).  Save
your money and headache. 

Joyce Koo
Materials Researcher - Materials Interconnect Lab Research In Motion Limited
Office: (519) 888-7465 79945
Mobile: (226) 220-4760

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Chuck Brummer
Sent: Tuesday, August 14, 2012 4:30 PM
To: [log in to unmask]
Subject: Re: [TN] PCB finish: ENIG vs. hard gold

Kevin,

Make sure you require a Ni barrier layer between the copper and gold (hard
of soft)!

Chuck


Charles W. Brummer | 3M Manufacturing Engineer 3M Electronic Solutions
Division 3M Canoga Park, 8357 Canoga Ave. | Canoga Park, CA 91304
Office: 818 734 4930
[log in to unmask] | www.3M.com


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From:   "Glidden, Kevin" <[log in to unmask]>
To:     <[log in to unmask]>
Date:   08/14/2012 09:15 AM
Subject:        [TN] PCB finish: ENIG vs. hard gold
Sent by:        TechNet <[log in to unmask]>



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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