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Old 1st April 2008, 08:57 PM   #1
Speeed3 is offline Speeed3  Finland
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Default Kapton tape

Is digi-key's kapton tape good for replacing sli-pads in car amplifiers? Or what insulator from digi-key should I order?

I have a basic car audio repair tutorial but it only gives McMaster-Carr's part number and I don't think it would be wise to order only 1 roll of tape to be shipped to Finland.

And what would be a good Heatsink Compound to order from digikey?
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Old 1st April 2008, 11:11 PM   #2
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It appears to be the same tape as sold by McMaster. It's 1mil thick with a 2mil silicone adhesive.

$42 for a 36yd. roll is far too expensive. Search for the equivalent, 'POLYIMIDE '. Kapton is a trade name for 3M.

I've used a lot of this tape to replace insulators. There are better insulators but I've never had reliability issues using this tape. The Kapton sheet that you can buy from J&R electronics (eBay) or from MCMaster is a probably better thermal conductor but is more difficult to deal with because you have to cut it. It's easy enough to cut but it's not easy to get a long straight cut for long amps.

Before applying the tape, clean the heatsink and make sure there are no burrs on the surface.
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Old 2nd April 2008, 08:17 AM   #3
Clipped is offline Clipped  Thailand
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... if you have to put holes in the tape, use an OLD soldering tip and punch through with it hot.

dont use a good tip, it will ruin it.
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Old 1st May 2008, 04:19 PM   #4
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clipped,

Thank you for that tip!

I have always punched holes, but polyimide is tough stuff!

Regards,
David
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Old 3rd May 2008, 09:17 AM   #5
Clipped is offline Clipped  Thailand
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no problemo, i found out it ruined good tips the hard way.
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Old 8th May 2008, 11:08 AM   #6
KyferEz is offline KyferEz  United States
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I'm looking for something less expensive than the thermal pads I've been using. Polyimide I've never used and would try it, except I'd like to know it's thermal impedance first. Problem is I can't find thermal impedance data (in degC-in^2/W) from any source I'd trust. Does anyone know?

Also, I've looked everywhere I can think of to get thermal silicon/fiberglass pads but no-one has them at decent prices.

Thanks
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Old 8th May 2008, 11:21 AM   #7
AndrewT is offline AndrewT  Scotland
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Hi,
the manufacturers quote the thermal resistance of the film.
But, I see the bigger problem is the lack of information on the adhesive which is often even thicker than the film.
If the film is over 0.002" (=2 thou=2mil) then there is too much thermal resistance for high dissipation use.
Try to find 0.001" to 0.0015" thick film with adhesive that is no thicker giving total thickness <0.003".
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Old 8th May 2008, 11:37 AM   #8
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There are different types of Polyimide. The 200MT (J&R Electronics on ebay or Mcmaster.com - J&R has much better prices) conducts heat better but I've never found it in 1" strips and it's a pain to cut. The 1 mil thickness tape with 2 mils of adhesive is much easier to work with. I've been using it for years.

When you look at specs, you should realize that many insulators must be clamped to a specified pressure/force to meet their specs.
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Old 8th May 2008, 07:12 PM   #9
KyferEz is offline KyferEz  United States
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I found JRElectronics but they aren't selling anything. I can't find J&R Electronics... I did find it on mcmaster, but not in manageable rolls. It's either in sheets 12x12 or 24" wide rolls and it's expensive: 8.27 for a 12"x12" sheet. At that price, the roll from Digikey is a much better buy. There is someone from ebay that has polyimide, but he doesn't list the thickness of it.

I have downloaded the spec sheets from Dupont, those provided on digikey, and other places, and none of them list thermal impedance as a spec. They list the Coefficient for Thermal Conductivity, but that's not what I want. If it's possible to figure thermal impedance from the coefficient for thermal conductivity spec then I'd like to know how. I am aware that to meet a thermal pad's specs one also has to meet pressure, surface roughness, and surface flatness specs.

Thanks!
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Old 8th May 2008, 07:23 PM   #10
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Ebay auction number:
170167316492

You won't find it cheaper.

Some of the thermal pads have a layer of Kapton inbetween two layers of silicon rubber. Others use fibers to reinforce the fragile silicone. The Kapton alone (with heatsink compound) works very well.
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