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June 2011

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Subject:
From:
"Woolley, Mark D. (Mark)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Woolley, Mark D. (Mark)
Date:
Tue, 28 Jun 2011 13:14:37 -0600
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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]>


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<[log in to unmask]>
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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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