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Re: [Amps] SSPA & Heatsink Compounds

Subject: Re: [Amps] SSPA & Heatsink Compounds
From: Steve Thompson <>
Date: Fri, 13 Dec 2013 21:42:11 +0000
List-post: <">>
One word of caution with Manfred's technique - be very careful if applying clamping pressure onto a transistor with a ceramic cap. The cap is strong round the outside edge, but weak in the centre. If your clamp happens to push too hard in the wrong place you can end up breaking the cap and the broken pieces fall in and mash up the bond wires. The magic smoke is still inside but your transistor is dead.


Manfred wrote:
For that reason I use a radically different technique: I apply
a single thick round blob of thermal compound to the middle of
the mounting surface, or if the device is long, I apply a
single nice smooth string of compound to it. Then I mount it,
pressing it down strongly but evenly, to make the compound flow
out and fill the whole space. In this way the formation of air
pockets is avoided. When thermal compound appears squeezed out
all around the device, I can be sure that no air remains
anywhere under the part. From this point on, additional
pressure can be used to thin out the layer of thermal compound.
This pressure should be well distributed over the device, to
avoid deforming it. Just tightening the mounting screws is not
a good idea. A clamp in the middle of the device is ideal.

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