Richard,
you got good feedback already.  One trick worked in the past is to  
put coating mixture in vacuum slightly (you need to keep your eyes on  
it and run few experiment).  After mixing, the chemical reaction  
between the 2 parts will create some bubbles upon curing.  if you put  
the fresh mixture into vacuum oven (with glass door you can  watch  
for it), you vacuum until it foams up and immediately release the  
pressure (increase to room  atm- stop vacuum), the mixture will  
settle down with bubble free - if repeat process 2 or 3 times.  you  
need to use the processed mixture immediately (you lost floor life of  
the spray... provide your coating formulation allow sufficient time  
for the floor life).  caution.  if you vacuum too much, you removed  
curing agent - small molecule stuff, and the coating will not cure  
using normal curing schedule(you need to run DSC to validate it).
jk
On Jul 16, 2020, at 12:56 PM, Stadem, Richard D wrote:

> One of the client companies I work for builds extremely high- 
> reliability propulsion control systems. For them, bubbles in the  
> coating between fine-pitch ASIC leads are a defect condition. We  
> are exploring options for elimination of the bubbles.
> The bubbles are not present in the sprayed on coating, and we have  
> tried lightly brushing the leads to further "thin out" the coating  
> before the CCAs go into the curing oven. No webbing or bubbles are  
> seen at that point but manifest themselves after curing.
> I am not an expert at coating but I do know a bit about it. I was  
> wondering just what might be the cause of the bubbles, and how to  
> prevent them from happening? Any information is greatly appreciated!
> dean