Ted,
Where do you see the dewetting and what processes come before coating? 

In my experience, dewetting comes three general sources:

1.  A problem with the surface energy of the component or solder mask. 
This may be due to mold release agents or the slick nature of the plastic 
itself.  You want surface energies in excess of 40 dynes/cm.  Surface 
energies of 30-35 dynes/cm are a problem.  I use Dyne Pens as a quick 
check.  Has there been a change in process or part supplier?

2.  A problem with a barrier material.  Again, it may be a mold release 
agent, many of which are Teflon or sulfur based, or it may be a process 
residue.  Could be silicone residues, could be fingerprints, could be any 
number of things from second or third shift. 

3.  Dewey Whittaker.

Doug Pauls
Rockwell Collins



Ted Tontis <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
02/05/2009 03:56 PM
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Subject
Re: [TN] Coating material






We are experiencing de-wetting upon application. We are using a PVA coater
and using the same ratio, 1 to 1. The problem is that it is interment 
within
the same lot making it difficult to pin down. 
Samples of bare boards as well as boards that coated fine and ones that
coated poorly have been sent out to a lab for eval. 

Ted

-----Original Message-----
From: Tom P. Hummel [mailto:[log in to unmask]] 
Sent: Thursday, February 05, 2009 2:45 PM
To: TechNet E-Mail Forum; Ted Tontis
Subject: RE: [TN] Coating material

We currently use HumiSeal 1B73AP thinned 1 to 1 with 521 in our PVA
machine and have not had any issues.  Are you experiencing problems?
What type of automated machine are you using?


Thomas P. Hummel
Carlton Industries Corp
[log in to unmask]

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