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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