Confocal microscopes will also perform the action. Wayne's way is a lot
cheaper than the confocal microscope. I have used an uncalibrated
procedure to determine if particulates are beneath or on top of a
surface.
mark
mark
Mark Woolley |PTRL Laboratory | Avaya | 1300 West 120th Ave |
Westminster, CO 80234 USA |
Voice (Lab): (303) 538-2166 | email: [log in to unmask] |
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls
Sent: Tuesday, June 28, 2011 12:04 PM
To: [log in to unmask]
Subject: Re: [TN] The best method to measure acrylic conformal coating
thickness (dry film) over populated PCB.
Wayne,
Is there any way you can give me a more detailed procedure for this, and
maybe a few photos? I would be interested in trying this method out,
and
it probably has a place in the IPC Coating Handbook as well. I've never
heard of this method before.
Doug Pauls
"Thayer, Wayne - IIW" <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
06/27/2011 06:32 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
"Thayer, Wayne - IIW" <[log in to unmask]>
To
<[log in to unmask]>
cc
Subject
Re: [TN] The best method to measure acrylic conformal coating thickness
(dry film) over populated PCB.
Hi Andy-
If the coating is clear, lightly contaminate the surface with a fine
inert
powder. Then use a high power (200X or more) optical microscope with a
calibrated vertical access to look at both the contamination and the
surface which was coated. Typically, the depth of field on these
microscopes is about +/-3 microns, so you can get a pretty high
resolution
for the measurement.
Wayne Thayer
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of andi1978
Sent: Monday, June 27, 2011 4:24 AM
To: [log in to unmask]
Subject: [TN] The best method to measure acrylic conformal coating
thickness (dry film) over populated PCB.
Dear TechNet gurus ...
Our company is looking for equipment to verify the conformal coating
thickness on fully populated PCB after the product is received from our
subcontractor (measure on fully dry conformal coating).
Our assemblies are heavily populated so that standard tool (calliper or
similar) are useless in this case.
We were considering to use eddie currents technique (measuring tool with
5mm tiny probe with 45 degree angle) but we are unclear on the measuring
method use by this system.
Basically on their website
http://www.conformalcoating.co.uk/Conformal-Coating-Thickness-Measuremen
t-Systems.php
they said: measurement is taken over the ferrous or non-ferrous material
which in my opinion means the measurement is taken through the conformal
coating + solder resist to the closest/first copper layer inside the
PCB.
By using this tool and to correctly calculate the conformal coating
thickness, we have to add the solder resist thickness (with tolerance)
plus we must be sure that the ground plate/layer is located just
underneath the solder mask/measuring point.
In our case (complex assembly) this condition will not be always be
achievable (read: no ground plate in the measuring area), complex build.
Have you guys any idea what would be the best, accurate tool/technique
to
verify the acrylic coating thickness on populating product.
Please bear in mind our boards are FTI equipment and conformal coating
parameter is critical from product functionality/reliability point of
view.
And again, there are not much "real estate" and the sensor to measure
the
thickness must be small in diameter as possible.
Much appreciate your advise,
Andy
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