heatsink question

blabley · 2nd May 2002, 04:55 PM

I am new to using heatsinks and I have a trivial question. The heatsink I am going to use (lm3886 amp) is about 3 by 4 inches (fins out type). The casing for my amp is an aluminium box closed in the back. On this back side, if I cut most of the aluminium away and just left a small border (say 1cm), can I bolt on the heat sink to the this border on the back (the back of the casing will be the same size as the heatsink). The lm3886 will still be directly on the heatsink (attached through the cut out window in the aluminium back). Will I run into any problems doing this?

Thanks!

Holger Barske · 2nd May 2002, 06:17 PM

No, this is the best thing you can do. You have most direct contact between the chip and the heatsink, wich is usually far better then putting a layer of sheet metal (your box' wall) in betwwen.

Take care of the volrage on the mounting surface of the LM, I don't know if there is any at the moment. Maybe grounded, check out the datasheet.

And: don't use any thermal grease between chip an heatsink if you ar not going to isolate it proberly.

Jocko Homo · 2nd May 2002, 06:38 PM

Quote:

And: don't use any thermal grease between chip an heatsink if you ar not going to isolate it proberly.

What do the two have to do with each other?

Jocko

Holger Barske · 2nd May 2002, 08:58 PM

If you do isolate the chip (electrically), you have to use that grease for better thermal coupling between the isolator and the heatsink.
If you don't isolate, direct contact between chip and heatsink is far better from a thermal point of view.

Holger

GRollins · 2nd May 2002, 10:02 PM

The heat sink grease should be used either way. It's more thermally conductive than air, and fills microscopic (and some not-so-microscopic) voids between the device and the heatsink.

Grey

HarryHaller · 2nd May 2002, 10:08 PM

Grey is absolutely correct. The metal surfaces are not completly flat or smooth and have gaps that increase thermal resistance. Use the grease. Holger's heatsinks are not the only thing supplying hot air.

H.H. (hot heatsinks)

2nd May 2002, 04:55 PM	#1
blabley diyAudio Member Join Date: Apr 2002	heatsink question I am new to using heatsinks and I have a trivial question. The heatsink I am going to use (lm3886 amp) is about 3 by 4 inches (fins out type). The casing for my amp is an aluminium box closed in the back. On this back side, if I cut most of the aluminium away and just left a small border (say 1cm), can I bolt on the heat sink to the this border on the back (the back of the casing will be the same size as the heatsink). The lm3886 will still be directly on the heatsink (attached through the cut out window in the aluminium back). Will I run into any problems doing this? Thanks!

2nd May 2002, 10:08 PM	#6
HarryHaller Banned Join Date: Feb 2002 Location: Dallas,Texas	heat sink grease should be used either way Grey is absolutely correct. The metal surfaces are not completly flat or smooth and have gaps that increase thermal resistance. Use the grease. Holger's heatsinks are not the only thing supplying hot air. H.H. (hot heatsinks)

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2nd May 2002, 06:17 PM	#2
Holger Barske diyAudio Member Join Date: Jan 2001 Location: Ruhrgebiet	No, this is the best thing you can do. You have most direct contact between the chip and the heatsink, wich is usually far better then putting a layer of sheet metal (your box' wall) in betwwen. Take care of the volrage on the mounting surface of the LM, I don't know if there is any at the moment. Maybe grounded, check out the datasheet. And: don't use any thermal grease between chip an heatsink if you ar not going to isolate it proberly.

2nd May 2002, 08:58 PM	#4
Holger Barske diyAudio Member Join Date: Jan 2001 Location: Ruhrgebiet	If you do isolate the chip (electrically), you have to use that grease for better thermal coupling between the isolator and the heatsink. If you don't isolate, direct contact between chip and heatsink is far better from a thermal point of view. Holger

2nd May 2002, 10:02 PM	#5
GRollins diyAudio Member Join Date: Feb 2001 Location: Columbia, SC	The heat sink grease should be used either way. It's more thermally conductive than air, and fills microscopic (and some not-so-microscopic) voids between the device and the heatsink. Grey