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 This message (including any attachments) may contain material, non-public information or proprietary information and is for the intended recipients only. If you are not the intended recipient, you should notify the sender and delete this message. Any disclosure, copying, or use of this information is strictly prohibited and may subject you to legal liability. 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 ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. 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