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June 2011

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From:
"Woolley, Mark D. (Mark)" <[log in to unmask]>
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TechNet E-Mail Forum <[log in to unmask]>, Woolley, Mark D. (Mark)
Date:
Mon, 27 Jun 2011 09:21:17 -0600
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Perhaps working with the acryllic coating supplier to introduce a known amount of fluorescent material into the coating.  
Using a relatively cheap UV Lamp, fixed surface area, and photosensor with filter, the amount of light emitted by the fluorescent dye can be calibrated to the thickness by the amount of light generated.
Just a thought.  Quick, not too difficult and not too expensive.
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 andi1978
Sent: Monday, June 27, 2011 2:24 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-Measurement-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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