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Old 25th November 2002, 03:25 PM   #1
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Default DuPont Kapton MT as IC/transistor insulator

This relates partially to the "about free samples" thread, but is different enough to warrant its own discussion...

I requested a sample of DuPont's Kapton MT polyimide film, and got word back that they can send me a paper-size (8.5x11) sheet as an engineering sample. (Data on this stuff can be found here.)

When I get the sample I'll cook up a little report on how well it works, how easy it is to use (incl. cutting to fit oddball packages like multiwatt15s) and how well it works.


In the meantime, if anyone has decent sources for tabbed-IC and very large transistor packages, or raw material sheets that can be trimmed to fit applications where pre-cut insulators are impossible to find, please post 'em here so the next visitor will have an idea where to find the stuff.

oO, who's strange enough to use Artic Silver thermal compound (which is the best small-contact-area compound you can get for use on processors, etc.) on transistors...
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Old 25th November 2002, 03:57 PM   #2
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Because it doesn't look like it molds itself to the surface
like silicone, I assume that you would use thermal grease
with Kapton (tm).

I like Thermalloy's white thermal grease, but it's kinda messy.
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Old 25th November 2002, 04:00 PM   #3
sam9 is offline sam9  United States
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Default sam9

When faced with the need for an od sized pad, I've tried a strip of kapton tape. The warehouse in the plant where I work uses it for packaging. I just drop by and ask for a few feet or a stub roll.

It looked like pretty insubstantial stuff. I've tried deliberatly to pass a current trough, but at voltage/current combinations one would find in a SS amp I've been unsuccessful. I also tried melting it with a solder iron - no luck.

This seems too easy, but based on what I've seen so far, it works very well.

PS: I still put a thin film of thermal grease on top of it.
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Old 25th November 2002, 04:02 PM   #4
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Default Re: sam9

Quote:
Originally posted by sam9
I still put a thin film of thermal grease on top of it.
Both sides.
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Old 25th November 2002, 04:48 PM   #5
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Quote:
Originally posted by Nelson Pass
...but it's kinda messy.
I had been wondering....

Don't they say to apply that sauce "sparingly?"
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Old 25th November 2002, 04:55 PM   #6
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Actually, the manufacturer is quite happy with liberal
quantities....
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Old 25th November 2002, 05:04 PM   #7
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Why Kapton? It's not a particularly good thermal conductor and tears easily. Its only advantage is its tolerance for very high temperatures, which is not the issue here (the epoxy in the transistor package will go long before the Kapton). It seems that a loaded silicone should perform better at temperatures more typical of audio amps (<100-150 degrees C).

Now, if you're just going for the coolness factor, you can't beat PEEK.
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Old 25th November 2002, 05:55 PM   #8
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In an effort to avoid that messy grease, I found an Aavid Thermalloy product (Wakefield makes one too) that is much neater; its a waxy stick that comes in a push out applicator (kinda like a small rectangular stick deoderant!) that goes on real easy. It is supposed to be 20% more efficient than grease, no runout or "bleeding", expands once it hits 160 degree F (undergoes phase change), and cleans up easily. You can use it on any two surfaces that you would use the grease on, I think.

DigiKey carries it on the same page as other Thermalloy stuff. Look for the picture in upper left catalog page. Not sure if it has a number. Only drawback: costs about $17 per stick, good for 1000 sq. inches. I used it to interface some heat sink modules to a big thick aluminum plate, after getting rid of the grease that used to provide the thermal interface.

Larry Wright
Seattle area
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Old 25th November 2002, 07:45 PM   #9
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normally the Kapton isolators have a small amount of thermal grease on the wich will "melt" at the first usage. Ive used them for the IRFP240s on my Aleph 5 and am quite satisfied.

They claim a Rth of 0,07K/W for them wich is quite low even when the figure is a bit optimistic.

william
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Old 25th November 2002, 07:55 PM   #10
sam9 is offline sam9  United States
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Quote:
Why Kapton? It's not a particularly good thermal conductor and tears easily.
I find it only tears when one has first cut a nick cut in it. Trying to tear an undamaged strip could give one a coronary. As far as thermal conductivity goes, I Rod Elliot's article on heat sinking. Not too different from mica, better than some other stuff. And of course not of them are in the same league as beryllium oxide toxic though it may be.
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