I dunno Dean, T-50 has yet to put the term De-Douged, as in, be careful, 
this document draft has not been De-Douged yet.  So I have little faith 
that anything involving Mr. Welk would make it through.    Hmmmm

A welkish mass of bubbles
Bubbles must be dispositioned if more than 3.5 Welk Units
Coating masses with more than 2.7 Welk Areas must be De-Welked

Curse you Dean, now my mind is going to be on this track all morning......

Doug Pauls



From:   "Stadem, Richard D." <[log in to unmask]>
To:     TechNet E-Mail Forum <[log in to unmask]>, 
"[log in to unmask]" <[log in to unmask]>
Date:   03/22/2013 08:40 AM
Subject:        RE: [TN] Conformal Coat and Bubbles



Boy, it sounds like conformal coat welking to me. Perhaps that is 
something we want to add to the Definitions in T-50. 

http://mp3skull.com/mp3/forever_blowing_bubbles.html


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls
Sent: Friday, March 22, 2013 8:01 AM
To: [log in to unmask]
Subject: Re: [TN] Conformal Coat and Bubbles

Inge,
I LIKE the IMHO reference.  May I use it elsewhere?

1.  I don't disagree on microscopic bubbles but zillions is a little hard 
to quantify.  Bubbles are process indicators up to 0.375 zillion, but at
0.376 zillion, it is a defect.  If I have very small bubbles out in the 
middle of nowhere on my assembly, on top of a solder masked surface, not 
exposing any leads or conductors, that bubble is never going to cause a 
problem in service, as least in the aerospace environments I work with. 
But if I have the zillions of small bubbles, it indicates an underlying 
problem, perhaps too much moisture or volatiles in my solder mask that 
could affect coating adhesion in service.  How to draw the line?

2.  When you talk about bubbles higher than 50% of the thickness, would 
that be on the order of a 2 mil bubble in a 4 mil thick coating?  If so, 
how would you measure that, top to bottom or side to side?

3.  I agree that when you start getting clusters of bubbles you have a 
process problem, but how do you quantify a "cluster" of bubbles?  Is 2 a 
cluster (leave it alone Dewey)?

4.  On the extension, do you mean above the surface of the surrounding 
coating, i.e. a 30 mil tall bubble over a 3 mil coating?

Doug Pauls



From:   Inge Hernefjord <[log in to unmask]>
To:     TechNet E-Mail Forum <[log in to unmask]>, 
[log in to unmask]
Date:   03/21/2013 07:05 PM
Subject:        Re: [TN] Conformal Coat and Bubbles



IMHO (In My Hallucinate Opinion) :

- zillions of microscopical bubbles does not matter
- bubbles higher than 50% of the coating thickness do not matter if only 
few -bubbles higher than 50% and building clusters matters -all bubbles 
with an extension 10 times the coating thickness matters -if the above is 
repeated on many boards, the MRB should suspect a process failure -for all 
coatings

Inge

On 21 March 2013 16:18, Douglas Pauls <[log in to unmask]> wrote:
OK, Minions, your next question in the quest to improve J-STD-001 and
A-610 relates to bubbles in the conformal coating.

I think we can all agree that the ideal conformal coating layer contains
no bubbles or voids and is "purdy".    BUT:

1.  Are there bubbles in coatings in areas where they will not impact 
reliability and their presence should be viewed as a "Process Indicator"?
If so, where and what limits would you use?

2.  What would you classify as a bubble requiring disposition, i.e.
Becomes an actionable defect?  If so, where and why?

3.  Would any of your answers change depending on what KIND of coating it 
is, i.e. Acrylic vs. silicone vs. Parylene?

Well, OK, that is three questions.  I'm on a roll.


Doug Pauls
Chairman, IPC Cleaning and Coating Committees Galactic Emporer



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