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Thermal Paste VS Mica Insulators

Kris_R

Kris_R

Active Member
On all of these rebuild threads, I keep seeing people using thermal paste instead of insulator strips, which is what is stock in the equipment (at least the ones I've dug into.) Is there an advantage of the thermal paste over the insulator strips?
 
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You have to have insulator strips. This can be either mica or the newer silicon rubber type (Silpads). With mica, you must use thermal paste--a very tiny amount, not gobs!-- to aid the heat transfer between the mica and the metal. The paste fills in the gaps in the rough surface of the mica and metal since air doesn't conduct heat.

With Silpads, the silicon rubber is flexible enough to fill in the gaps without paste. The tradeoff is the performance: the Silpad doesn't conduct heat quite as well as the mica.
 
I use both thermal paste and mica insulators on every rebuild I've done.
 
If there is more than 1 transistor fastened to the heatsink and the sink is fastened to chassis ground.. You best damn well use both. Otherwise you will short your rail voltages to ground.That dim bulb will never dim.Then you will be scratching your arse wondering WTF is up with this amplifier. It won't damage the transistor, but will pop fuses left and right.
 
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We only talk about the paste because the computers might use a conductive paste which will do like Avionic says, cause problems. We all know to put the mica (or silpad) in there to prevent the short circuit from the transistor to the chassis. That is why there is no discussion of the micas.
 
And, for those who may not realize it, the transistor screws also need to be insulated to prevent them from grounding out to the heatsink. There's usually some type of nylon washer on the head side as well as a bushing to go through the hole in the transistor body (sometimes the washer and bushing are integrated into one piece). The screw does not get any thermal paste.
 
nashvillebill said:
And, for those who may not realize it, the transistor screws also need to be insulated to prevent them from grounding out to the heatsink. There's usually some type of nylon washer on the head side as well as a bushing to go through the hole in the transistor body (sometimes the washer and bushing are integrated into one piece). The screw does not get any thermal paste.
Click to expand...

Should specify.. When mounting TO-220 transistors to a grounded heatsink or a sink with more than one transistor. Then the nylon screw bushing applies as well as mica and thermal compound.
 
nashvillebill said:
With Silpads, the silicon rubber is flexible enough to fill in the gaps without paste. The tradeoff is the performance: the Silpad doesn't conduct heat quite as well as the mica.
Click to expand...

Where is the proof of this? Let's see some figures.

Lee.
 
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