FreeLists / si-list / [SI-LIST] Re: Potting/encapsulation/conformal coating and SI

[Ray Anderson <reanderson@xxxxxxxxxxxxx>]

George Tang wrote:

>In military electronics application, this PCB sealing process is called
>conformal coating.  I did a quick search on the web, and here is one of the
>companies I found which provides this service.
>
>Regards,
>
>George
>  
>
Potting and conformal coating are two different things.

Conformal coating is a thin layer of material applied to the PCB that 
"conforms" to the boards contour and whos prime use is to seal out moisture.

Potting usually involve encasing a circuit in a "block" of material and 
ususally in used to provide either mechanical protection or to inhibit 
reverse engineering. Long ago at Calif. Microwave we had a small module 
encased in x-ray proof epoxy to inhibit others from seeing what was inside.

Removal of the hard potting material usually results in destruction of 
the encased circuitry. One application that I'm aware of actually used a 
soft potting material (the consistancy of cured RTV rubber). This was in 
a military avionics radar beacon (APM-154). The modules were actually 
repairable. One had to pick out the potting cmpound with a dental pick,  
troubleshoot and repair the circuit and repot the circuit using the 
special molds the vendor provided. This particular application  of 
potting was mostly for the mechancial protection afforded in hi-G 
environments.

-Ray Anderson
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