Techies

Eddy-current testing uses electromagnetic induction to detect flaws in  
conductive materials. There are several limitations, among them: only  
conductive materials can be tested, the surface of the material must  
be accessible, the finish of the material may cause bad readings, the  
depth of penetration into the material is limited, and flaws that lie  
parallel to the probe may be undetectable.

However, eddy-current testing can detect very small cracks in or near  
the surface of the material, the surfaces need minimal preparation,  
and physically complex geometries can be investigated. It is also  
useful for making electrical conductivity and coating thickness  
measurements.

Useable for conformal coatings? It doesn't seem suitable. I have been  
experimenting with lasers, but frankly this seems an overkill and  
reminds me of the Pen v Pencil argument. Russia figured the simplest  
way to write in space was to use a pencil... Measuring thickness using  
a readily available micrometer. Granted, measuring thickness on sharp  
lead ends and component legs os real tough - but coatings have been  
used to protect electronics since 1940 and they have done a good job.

Hope this helps

Graham Naisbitt


On 4 Dec 2008, at 19:18, Douglas O. Pauls wrote:

> Good afternoon all,
>
> A question for this most excellent forum.  Does anyone here use eddy
> current methods to measure applied coating thickness on printed  
> circuit
> assemblies?  If so, can you share your opinions on the methods and the
> equipment?
>
> There are testers on the market that do this and one of our design
> engineers is currently suprised at how we are using "stone age"
> technologies (micrometer) to measure coating thickness.
>
> Doug Pauls
> Rockwell Collins
>
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