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Date: | Thu, 14 Nov 96 09:37:15 cst |
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Hi Russell-
Do you have the option of not having a soldermask on the board? We
recently went through an exercise of poor bondability and our simplest
solution was the removal of soldermask from the design. We had put
soldermask on the board to help prevent "thieving" of solder from the
solder pad areas onto the traces. With some extra process control
steps we resolved that concern. The exposure of soldermask to the gold
bath, curing of the solder mask, etc - all those process steps
would/did/could contaminate the bondable gold pads and made wire
bonding problematic. One other thing to consider - are you using
soldermask as a dielectric ? Ask the question if the soldermask was no
longer on the board would you have shorting, arcing, possible dendrite
problems between traces because of their exposure either due to the
testing (thermal cycling) or use environment? Good Luck.
Dave Hillman
Rockwell Collins
[log in to unmask]
______________________________ Reply Separator _________________________________
Subject: FAB: Wire-bondable gold
Author: [log in to unmask] at ccmgw1
Date: 11/13/96 9:17 PM
greetings all
I am having difficulty with successful production of heavy deposit gold
[30-35 micro-inches] of wire-bondable soft gold, since Aurelon shut down
their Ni-Au operation. My customer is currently bonding aluminum wire, but
desires to go to gold wire.
Problems have been:
1. Peeling nickel from copper [resolved]
2. Peeling gold from nickel [mostly resolved]
3. Spotting and discoloration [solved by better rinsing]
4. Texture on gold surface; following the pattern of the tarnish after
soldermask and nomenclature oven curing [better after micro-etching before
Ni-Au plating]
5. Entrapment of conductive chemistries/metals under the developed edges of
Probimer LPI soldermask
6. Marginal peel strength
7. I don't know what is comming next!
My process is:
Panel plate
Tent and etch [cupric chloride]
LPI application, now Probimer 52 [but not for long]
Nomenclature application, Hy-sol Cat-L-Ink [legend]
Immersion/auto-catalytic gold, 30-35 micro-in. [applied by sub-contractor]
NC rout
Ship
[and currently] Receive trash and rejections
Can anyone advise me of good combinations of LPI soldermask and Ni-Au
chemistries / processes.
I don't plate, so I need a contract supplier of Ni-Au plating services, in
the So-Cal area? . . . or in No-America as my second choice.
Direct responses can be sent to :
Russell Ruff at The Circuit Tree [NOT THE MAGAZINE!]
818-303-4648
email [log in to unmask]
or to all here at the IPC TechNet forum.
Thanks,
Russell
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