Thank you, Joyce, Steve, and Mary! Great info.
I really appreciate it.
dean

-----Original Message-----
From: Yuan-chia Joyce Koo <[log in to unmask]> 
Sent: Thursday, July 16, 2020 4:47 PM
To: TechNet E-Mail Forum <[log in to unmask]>; Stadem, Richard D <[log in to unmask]>
Subject: Re: [TN] Bubbles in coating of ASIC leads

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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