Hi Tom -
     
     The words gold embrittlement really mean job security for 
     metallurgists! You would think that as well researched and 
     investigated the gold embrittlement mechanics of failure has been over 
     the last 20 years we would stop making the same mistakes. Two rules of 
     thumb to follow:
     
     a) Is there enough solder volume to allow the gold to uniformly go 
     into solution?
     
     b) Is the soldering operation of sufficient temperature and time to 
     allow (a) to occur?
     
     The thickness of the gold finish isn't the only deciding factor of 
     having a solder joint embrittled by gold/tin intermetallics - the 
     process is equally important. Also, you can avoid the whole gold 
     embrittlement issue by keeping the gold below 10 microinches but you 
     then have to deal with poor solderability on the components if this 
     thin gold plating is of poor quality (and plating a quality gold 
     finish below 20 microinches requires good control and knowledge of 
     one's plating system). 
     
     
     Dave Hillman
     Rockwell Collins
     [log in to unmask]


______________________________ Reply Separator _________________________________
Subject: Gold Embrittlement
Author:  [log in to unmask] at ccmgw1
Date:    3/19/97 3:17 PM


To those who have heard enough of this subject I send my deepest apologies, 
but to those who still have some energy left to help a double 'E', who has 
found himself doing a lot of PCB design lately, I need to try to obtain 
some information on Gold Embrittlement.
     
My question is: 
     
Can SMT components be attached to PCB's, which are fabricated using 50 
micro inch 'Hard Cobalt Gold' over 200 micro inch low stress nickle, 
without having to worry about Gold Embrittlement, and if so, are there any 
special process steps which need to performed or monitored. We are using a 
mixed bag of SMT packages with 1mm pitch being the finest.
     
I have encountered conflicting data on this subject so far.
     
Thank you
Tom Guerriere
Staff Engineer
Controlotron Corporation
(516) 231-3600 x81
[log in to unmask]
     
     
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