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July 2008

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Subject:
From:
Grunde Gjertsen <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Thu, 10 Jul 2008 07:52:05 +0200
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Hi

You can also use transparants for overhead projectors, the thickness is 
very consistant. Alternatively you can mask off just next to where you 
measure the coating thickness.

Grunde 




Graham Naisbitt <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
09.07.2008 18:23
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Graham Naisbitt <[log in to unmask]>


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Subject
Re: [TN] Conformal Coating






Craig

Take a bare piece of copper or aluminium and measure its thickness 
using a micrometer.

Now apply the coating as per your normal method and leave it to dry 
for around 1 hour.

Now re-measure the sample and subtract one from t'other et voila: you 
know the thickness you have applied.

If you now apply a second coat you will not get the same thickness 
added to the first because the solvents in the coating will partially 
dissolve the existing coating.

Of course you will experience some RF loss with a ticker v a thinner 
coating, but they should not affect the end performance once the data 
has been "dialled in".

When you qualify a conformal coating for an RF application, it is 
assumed that you would actually determine the maximum thickness 
allowable on that circuit design.

When you make your measurement first make sure the coating is FULLY 
CURED. In the case of an acrylic I would recommend baking at 80C 
overnight or leaving it for 1 week at room temperature before measuring.

Hope this helps

Graham Naisbitt


On 8 Jul 2008, at 16:53, Craig Sullivan wrote:

> Hi Everyone,
>
> I have a few questions about conformal coating. Specifically 
> acrylics. For
> reference, we apply the coating manually.
>
> What are the average coating thicknesses that you see after 1 coat? 
> After 2
> coats? Are you getting more than 0.001" of coverage in 1 or 2 coats?
>
> Given that soldermask is very lossy when it comes to SI, I would 
> assume the
> coating has similar properties (still waiting for vendor data). Have 
> you had
> any odd failures (from an RF stand point) with a 0.001" coating 
> thickness
> versus say 0.002" or 0.003"?
>
> The data sheet specs a Dk and Df @ 1 MHz, but I am extremely 
> interested in
> these at RF frequencies.
>
> Has anyone done any studies about this that can share the findings?
>
> Thanks,
> Craig
>
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