Doug,
Thanks for the description. I will have to try those out. Do you perform
this testing on-the-line on all WIP, or is this used as a development or
process check tool?
Kevin Glidden
Manufacturing Engineer
Luminescent Systems Inc.
4 Lucent Drive
Lebanon, NH 03766
(603) 643-7766 x3152
_____
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Friday, February 06, 2009 11:29 AM
To: TechNet E-Mail Forum; Kevin Glidden
Subject: Re: [TN] Coating material
Kevin,
Dyne pens are generally bought as a set and they look much like magic
markers or highlighter pens. Each contains a different solution with
different surface tensions. You start with a 30 pen and draw a strip of the
fluid on the surface. If the solution has not beaded up, then you go to the
32 pen, and continue until you find the solution where beading occurs. The
sets that I use go from 30 dynes/cm to 44 dynes/cm. If pen 38 did not bead
and pen 40 does, the surface tension was 39 dynes/cm. It is a quick way to
check a surface and the inks are easily cleaned off. I have found that for
many surfaces, you get pretty good adhesion (depending on the coating) for
surface tensions of 40 or better. Tensions of 35-40 are marginal. Tensions
of 30-35 are more problematic. Tensions below 30 are "good luck Charlie".
A decent set of pens runs about $150.
The water break test you describe is a quick and inexpensive qualitative
check on a surface, but not quantitative. When I do more quantitative
evaluations of surface cleanliness, I would prefer to use a device called a
goniometer, which measures the contact angle of a drop of DI water on a
surface. A clean surface has a very low contact angle, a dirty or difficult
surface has a high contact angle.
This is different from a goony-ometer, which largely checks to see if Dewey
is anywhere around. Though, admittedly we have a hell of a time calibrating
it if either Hillman or I are within a mile of the darn thing.
Doug Pauls
Rockwell Collins
Kevin Glidden <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
02/06/2009 08:01 AM
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Re: [TN] Coating material
Doug - I am not familiar with dyne pens...can you explain?
I have also heard of a simpler test called the water break test. Literally
all you do is get a sample of DI water and pipette a few drops onto the PCB
surface. You are looking for the water to spread and wet to the PCB
surface, indicating it is free of contaminants. If it beads up (like on a
well waxed car), then it is indication of a film or contaminant that would
result in poor coating. I am not certain how different solder mask
materials effect the results of this test, but you can't argue the cost and
simplicity.
Kevin Glidden
Manufacturing Engineer
Luminescent Systems Inc.
-----Original Message-----
From: Douglas Pauls [mailto:[log in to unmask]]
Sent: Thursday, February 05, 2009 5:33 PM
To: [log in to unmask]
Subject: Re: [TN] Coating material
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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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
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