Andy,

I'm afraid you may be in for problems.  We designed a 43mm x 43mm ceramic BGA 
w/1089 balls and tested it on FR-4 and if failed fairly early in it thermal 
cycling.  So the vendor said to use solder columns instead of balls.  That also 
failed rather early.  So the vendor said to use longer solder columns.  That 
also failed and was expensive as well as difficult to assemble.

So we tried a controlled CTE material like DuPonts thermount.  That worked but 
the thermal life was not as high as we wanted in order to have some insurance.  
Last solution is a ceramic pad grid array (gold) in a socket.  That works and is
field replaceable.  No literature has been published that I know of.

Happy Holden
HP Printed Circuit Operation-Ft. Collins,CO

______________________________ Reply Separator _________________________________
Subject: BGAs
Author:  Non-HP-Andrew-Buonviri ([log in to unmask]) at 
Date:    11/18/96 11:59 AM

     
  I am working on the design of a PCB with rather large ceramic BGAs (47mm 
  sq., 1284 pins) and one of my main concerns is stress in the balls as a 
  result of the TCE mismatch between package and board. We plan on using 
  FR4 but would consider other materials if the improved reliability is 
  worth the cost. If anyone has experience with this and can give me any 
  advice, or at least recommend some literature, I would greatly appreciate 
  it. We have never done a design like this and are mostly worried about 
  reliability. Thanks,
  Andy Buonviri ([log in to unmask])

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