Jim,
     
     For true conductor protection, all exposed surfaces must be
     coated. If conductive liquids bridge the gap between balls
     of different potentials you've got trouble.
     
     So, this would seem to dictate vertical dipping as the only reliable 
     means of coating. But, the coating must not be allowed to remain 
     in the space between the board and the device, after dipping,
     due to high relative thermal expansion mismatch of solder
     and cured acrylic. 
     
     The opinions expressed herein are not necessarily those of my 
     employer.
     
     Lyn R. Lynch
     Coates ASI


______________________________ Reply Separator _________________________________
Subject: ASSY: CONFORMAL COATING BGAs
Author:  [log in to unmask] at internet
Date:    6/26/97 9:18 AM


Does anyone have any experience applying conformal coating on an assembly which 
contains BGA components?  Is it necessary to ensure that all solder joints are 
coated?  If so, how it it done and how is it verified?
     
My specifics are:   Military contract
   625 ceramic BGA
   .030" stand-off
   Acrylic coating
     
Any opinions will be welcome.
     
Thanks,
     
Jim Marsico
(516) 595-5879
[log in to unmask]
     
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