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Old 25th December 2002, 01:12 AM   #11
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I got the samples in finally (only like three WEEKS later) in the form of two 8.5x11 sheets of 1 mil Kapton 100MT. I'll do a write-up and some basic #s on it in the next few days when I get the chance.

oO
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Old 27th December 2002, 03:50 AM   #12
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Nelson Pass mentioned in a previous thread that.....

"I like Thermalloy's white thermal grease, but it's kinda messy"

Messy isnt the appropriate word to describe that stuff and I'm not sure there is a word that can! I once had a big tube of it squish out all over the inside of my tool box cause I forgot to place it back in its "safety" container . Man, one daub of that stuff and you can paint your whole house!!

Mark
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Old 27th December 2002, 04:55 AM   #13
Hartono is offline Hartono  Indonesia
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Default Re: DuPont Kapton MT as IC/transistor insulator

I did use the arctic silver compound + copper heatsink(for smallest possible footprints), the one that form like a glue, for cooling RF amp IC on the CD transport

cool stuff, arctic silver
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Old 27th December 2002, 06:48 AM   #14
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Default Bio Degradable Insulation.....

Philips in the past used a Mylar/Kapton like insulator under the line output transistor in televisions.
In time these fail by darkening and becoming brittle under the middle of the TO-3 device used, and breaking down to the heatsink (peak voltages are over 1000V).
Standard practice is to replace with a mica insulator.

Eric.
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Old 27th December 2002, 08:19 AM   #15
ALW is offline ALW  United Kingdom
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Default Messy Grease

I too hate the white thermal compound, it's ability to spread over the widest possiblwe area, to include my clothes etc. is irritating to put it mildly. It works very well though, with a mica insulator.

A word of warning about some of the alternatives, more than one commercial early adopter of the silicone-based pads experienced significant failure rates from such products in their power amps.

I only use the Kapton-based pads (I use Bergquist ones) and these have proven to be utterly reliable, and have good thermal performance for the higher grades.

I have also experienced failure, after time, of the earlier silicone based pads, the material creeps with time, causing eventual breakdown.

Andy.
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Old 27th December 2002, 10:14 AM   #16
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Exclamation Kapton

Hi All,
I have seen some very alarming reports on Discovery Channel about Kapton used as electrical wire insulation in commercial airplanes of Boeing and Airbus.
According to the report when the isolation gets hot as a result of a shortcircuit it spontaneously gets into fire and EXPLODES causing the fire to spread.
For this reason this compound is no longer used in military planes.
For commercial aviation the situation is simply denied by the manufacturers.
In the view of above I would never think about using Kapton as a transistor insulator in my home equipment.
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Old 27th December 2002, 11:11 AM   #17
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From memory, the cause is brittleness of the kapton insulation, which cracks away when running over hard corners and burrs, and then the further process of burning when overheated.
In heatsink application this failure mode is not a concern.

Eric.
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Old 27th December 2002, 03:16 PM   #18
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1. Kapton in power amps should not be a problem. Aircraft failures are typically due to wear and water causing sparcing.
2. The best material for electrical isolation and thermal resistance is Beryllium Oxide which is illegal in many places due to the toxicity of dust if ground. Availability is limited -- but I have seen TO-3 form factor.
3. The second best material is probably the relatively new fired Aluminum Oxide washers. Various form factors are available.
4. If you don't want a mess, consider using SilPad 2000 or equivalent. I bought some of these from Bergqvist. You will not get the performance benefit of reduced capacitance offered by the fired ceramics (2 and 3 above), but you will be much more unlikely to mount the devices wrong and loose performance that way.
5. Thick thermal grease is not recommended -- it is too hard to work with
6. Arctic silver etc. are not recommended as they contain conductive material.

There are further posts on this in the archive if you are interested.

Petter
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Old 27th December 2002, 04:19 PM   #19
sam9 is offline sam9  United States
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Default Bergquist

The Bergquist web site is:

www.bergquistcompany.com

not as much fun as relating personal experiences/opinions but it does include specs and application notes on all manner heatsink pads including a number of products not even listed in digikey.
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