Hi Jim - welcome back! A couple of things you should be concern about: (1) 
gold embrittlement - you need to make sure that the gold content of the 
final solder joint is less than 3 weight % or you will form a gold/tin 
intermetallic phase which degrades the solder joint integrity; (2) 
dissolution of the thick film gold plating - you need to make sure that 
the soldering process doesn't completely leach/diffuse the thick film gold 
plating from the package substrate. This may not be an issue depending on 
what type of plating is between the gold and the package substrate (i.e. 
do you have a nickel subplating layer). 

Dave Hillman
Rockwell Collins
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[TN] Solder Ball Attachment to Thick Film Gold






Good Day Technet:
I've been a way from Technet for a number of years, but now I'm glad to be 
back.

Not being all that familiar with the thick-film process, maybe someone can 
help.  We are in the process of designing a BGA multichip module where 
we're working with a supplier who will supply the empty package.  The 
supplier wants to use thick-film gold for the external I/O pads, where we 
will be attaching solder balls after the component is assembled.  I have 
no experience soldering tin-lead solder balls to thick-film gold and was 
wondering if this is a standard practice or if we're breaking new ground.  
Although this is a developmental program, this assembly will eventually be 
flight-worthy for a military avionics project.

Thanks in advance for your help,

Jim Marsico
ITT Corporation
1500 New Horizons Blvd.
North Amityville, NY 11701
631-630-5079
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