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Re: [Amps] SSPA & Heatsink Compounds

Subject: Re: [Amps] SSPA & Heatsink Compounds
From: Manfred Mornhinweg <>
Date: Mon, 16 Dec 2013 20:24:14 +0000
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Steve, and all,

One word of caution with Manfred's technique - be very careful if applying clamping pressure onto a transistor with a ceramic cap.

Yes, that's right! I had plastic parts in mind, like TO-220 and such.

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.

True. With ceramic encapsulated transistors, it's a good idea to be reasonably gentle when pressing down in the middle. Like finger pressure only.

With those, I usually tighten the screws very slowly, and help pressing down with my thumb. The flange on these deforms easily, so one has to be really gentle with the screws too. Heating helps, to soften the compound.

Also be aware that some compounds are MUCH softer than others! I wouldn't use any of the stiff ones with this sort of transistor! Instead the stiff ones work fine with plastic cases.

The bad thing is that compounds with better heat conductivity tend to be stiffer too, because they have more densely packed granules, and less fluid between them!


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