In article ,
Phil Allison wrote:

N_Cook wrote:



Stay with mica slivers, been around for geological time, no plasticer to
leach out. The only time I've come across failure of a mica insulator
was when some swarf got under it at manufacture, that would do for all
other insulators as well.
Trouble with mica is it is dirt cheap and not patentable.

Also somewhat poorer thermal performance ...

Isaac


If you mean mica is poorer, don't go by product data sheets.
I did a realworld expt one time , comparing mica and sillypads on an
amplifier. Running with fixed input and controls and load, and
monitoring the temp of the heasink and IR thermo of devices. The mica'd
version ran with noticably hotter heatsink and cooler devices.
IIRC the datasheets quote an (fraudulent?) impossible degree of
squashing of pads, not obtainable with one screw thru a tab.



** Thin mica (0.05mm) is still the best performing insulator material for
semiconductors you can get at a sensible price AND will easily handle 200V or
more. Just a smear of white, silicone grease on each side and you are there.

The reason makers ever use silicone pads is saving assembly time.

Sometimes, pads are used to increase spacing and minimize
device-to-ground capacitance.

Isaac