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From: email@example.com (Bob Wilson)
Subject: Re: Thermal effects of potting compound?
Date: Thu, 17 Oct 2002 03:45:55 -0000
Organization: Your Organization
X-Newsreader: WinVN 0.99.9 (Released Version) (x86 32bit)
In article ,
>I have a circuit with surface mount power electronics on it (DPAK MOSFET,
>A.) turning the circuit upside down affect its thermal performance? Heat
>will rise into FR-4 instead of air.
>B.) Encapsulating the whole thing in a 5mm layer (eah side) of potting
>compound affect its thermal performance?
>Is there a certain de-rating I need to do in each instance?
>Are there various grades of potting compound that will actually help
>heat rather than be an insulator?
>Thanks a lot
Your questions are far to general to give any kind of exact answer to,
except to say that heat will not "rise into the FR4". It is just far more
complicated than that. A proper answer requires details about the PCB, the
components generating the heat, the thermal conductivity of the potting
compound, and several other details.
One point: highly thermally conductive potting compund is still a lousy
thermal conductor. It will also offer no real benefit for what it appears
you are doing. The solid-to-air interface is by far the largest thermal
resistance, and is many times worse than even the poorest potting compund.
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