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How to mount transistors to heat sink
How to mount transistors to heat sink
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Old 9th July 2017, 11:38 PM   #1
JeffYoung is offline JeffYoung  Ireland
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How to mount transistors to heat sink
Default How to mount transistors to heat sink

I'm planning on using Kapton tape (because I happen to already have some) for insulation.

Do I want thermal grease on both sides of the tape, or if I stick the tape to the heatsink is the adhesive on the tape enough?

Thanks,
Jeff.
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Old 10th July 2017, 06:37 AM   #2
JMFahey is offline JMFahey  Argentina
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Use mica+grease>Silpads>*proper* (ultra thin) Kapton *sheet*+grease (not adhesive tape), in that order.
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Old 10th July 2017, 01:21 PM   #3
JeffYoung is offline JeffYoung  Ireland
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How to mount transistors to heat sink
Thanks JM. If I can't use what I have (the Kapton tape), then I might as well order some mica.

I assume grease on both sides of the mica?
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Old 10th July 2017, 01:39 PM   #4
AndrewT is offline AndrewT  Scotland
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I use the glue as the air excluding medium for pre-glued hard insulators.
The unglued side needs thermal goop, again to exclude any/all air from the interface.

After a few hours of testing you will usually see that some of the glue has migrated to the edge, because it has flowed under the pressure created by the clamping. This helps to reduce the thickness of the heat insulating effect of the glue. It also helps remove any last hint of air trapped with the glue.
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Old 10th July 2017, 04:51 PM   #5
JeffYoung is offline JeffYoung  Ireland
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How to mount transistors to heat sink
OK, this is all a bit more complicated than I thought.

Mica pads for TO-247 are hard to come by in Ireland. I can easily get Silpads and Aluminium Oxide.

The Silpads are a bit more coin, but I presume I don't need grease with them?

Thanks again for all the help.
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Old 10th July 2017, 05:33 PM   #6
Osvaldo de Banfield is offline Osvaldo de Banfield  Argentina
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I prefer the gray silicon gum, pretty good isolation (over 500V) and good thermal transfer. Usually with grease in both sides. Also try the gray boxes that cover all the transistor, available for TO220 and TO247/TO3P.
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Old 10th July 2017, 05:36 PM   #7
scottjoplin is offline scottjoplin  Wales
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Silpads are designed to be used on their own. May not be quite as effective heat transfer as mica and grease. Aluminium Oxide is better still but quite expensive
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Old 10th July 2017, 05:37 PM   #8
rayma is offline rayma  United States
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Quote:
Originally Posted by JeffYoung View Post
The Silpads are a bit more coin, but I presume I don't need grease with them?
Right, just clean the mating surfaces.
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Old 10th July 2017, 09:45 PM   #9
JeffYoung is offline JeffYoung  Ireland
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How to mount transistors to heat sink
Cool. Thanks everyone!
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Old 17th July 2017, 03:18 PM   #10
Eric is offline Eric  United States
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How to mount transistors to heat sink
It may be useful to do some 400 or 600 grit wet sanding on your heat sink to insure that the mounting surface is clean and flat. Many extruded sinks have micro ridges on the back from the manufacturing process.
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