Lucy,
     The Qualified Products List (QPL) of MIL-C-46058 will list all 
     coatings which have passed the tests described in that document.
     It addresses some of your concerns, mostly physical and electrical, 
     not application.
     
     Your requirements will be difficult to satisfy. 
     
     If one assumes that the 130 degree C operating environment is firm, 
     then a silicone would seem to be in order. 
     
     Although silicones are resistant to moisture in that they will retain 
     physical properties when exposed, they have very high moisture vapor 
     transmission rates, when compared to other coatings. This may or may 
     not be an issue with this product. Moisture would not seem to be an 
     issue after being placed into service at 130 degrees C. It would seem 
     prudent to bake the unpowered boards immediately prior to placing into 
     service.
     
     They are mostly applied by thinning with solvent and spraying onto the 
     board.
     They also have relatively high outgas rates, in vacuum, and one would 
     assume that they would retain this relatively quality in atmosphere.
     
     Parylene C would come closer to meeting the physical requirements, 
     but, it's costly, difficult to apply and the rework cycle is no 
     shorter than the initial application. It's vacuum deposited.
     
     The views stated above are not necessarily those of my employer.
     
     


______________________________ Reply Separator _________________________________
Subject: Conformal Coatings
Author:  [log in to unmask] at internet
Date:    8/6/96 3:53 PM


On Conformal Coatings:
     
  I was wondering if anyone can recommend manufacturers of a conformal coating
that will be placed on an PCB with a complex topography.  Some of my require- 
ments are as follows:
    -high dielectric strength
    -good adhesion to flux residues
    -UL and/or Mil-Spec approval
    -able to withstand high temperature applications (~130 C) for extended
     periods
    -fast cure
    -easy to apply
    -easy to rework
    -moisture resistant
    -solvent-free
    -no outgassing
    -volatile organic compound-free (VOC-free)
    -relatively same thermal expansion coefficient as PCB panel
     
Lucy Rojao
[log in to unmask]
phone: (416) 448-5866
fax:   (416) 448-4736
     
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