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.
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 ghtening. 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:
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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