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Re: Thermal pad disintegrating
On Mon, 6 Mar 2017 21:56:45 -0000, "Gareth Magennis"

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Back in the 70s they used Mica insulators, and coated them with silicone
grease to transfer heat. Unless the installer cracked them during
installation, they probably last forever.  

I suppose they now came up with some cheap crap substance to save a
buck. If I ran across this, I'd change all of them with the old mica
types before more stuff burns up.  

Re: Thermal pad disintegrating

I have been using as a matter of preference materials from Bergquist for ro
ughly 40 years, albeit in small quantities. Typical output-per-device is at
/around 30+ watts. None have failed over dozens of amps at 4 - 20 pads each
. Some caveats:

a) There are a LOT of counterfeits out there. Make sure what you use is fro
m a reliable source.  
b) DO NOT reuse such pads. They will last 40+ years if left alone. But if r
e-used, they could have micro-tears or punctures from the removal and re-ti
c) DO NOT use them if the heat-sink or substrate is not smooth and flat.The
y are not grease that can be used in excess to fill such gaps.  
d) DO NOT use them with grease/heat-sink compound or any similar material.  
They can be incompatible.  

They are pretty simple, pretty basic, inexpensive items with a single signi
ficant virtue - they are not sloppy. So, compound on leads that interferes  
with soldering becomes a thing of the past (although that is easily control
led with care at application). And there is no measuring issue.  

I have also used these: - only because they w
ere OEM. They can be reused. Expensive. For a number of years, AR used them
 on their US-origin amps and receivers.  

With all that in mind, I keep a small stash of Bergquist materials, mica &  
compound materials and some mica sheeting (also cheap and easy to find at a
 Jewelry Findings, stove or lamp supply) for unusual situations and/or appl
ications. Such as adjustable mica caps on vintage radios. NOTE: Mica does n
ot like to be drilled - better to punch it. And to make a small diameter mi
ca punch, get a piece of brass tubing with the correct ID, and file it shar
p. Punch onto something fairly hard but with some give - I have a piece of  
maple flooring that I use. You will get perhaps 4 holes and need to resharp
en, but you will not flake the mica as you would with a drill. Very sharp t
in-snips or professional fabric shears do a nice job of cutting the stuff.

Horses for Courses.  

Peter Wieck
Melrose Park, PA

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