Re: [Amps] SSPA & Heatsink Compounds

[Steve Thompson <g8gsq72@gmail.com>]

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.
Steve

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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