Mounting LM3875 on anodised surface

alleycat · 22nd January 2006, 08:04 AM

I am considering using a piece of anodised aluminium plate as a heatsink for an LM3875TF. I was wondering if the anodising will have any significant effect on thermal transfer from the chip to the heatsink.

Upupa Epops · 22nd January 2006, 08:13 AM

Anodising make thermal transfer little bit worse, but in practical case it is free... be calm ...

peranders · 22nd January 2006, 04:12 PM

Anodised aluminium is the normal surface for a heatsink you know.

alleycat · 23rd January 2006, 06:26 AM

Thank you for the reassuring replies. I asked this question because I have only seen heatsinks with anodising on the finned side and a machined surface for mounting components on the other.

Nordic · 23rd January 2006, 06:39 AM

Well if it bothers you... stick some sanding paper to a flat piece of glass with woodglue (so you can pull it off later) then use this as a sanding block to wear though the anodised part....

Way too much effort.

maxro · 23rd January 2006, 06:40 AM

If you really wanted to, you could lap the contact surface of the heatsink with progressively finer grades of wet-dry paper. This will remove the anodising and, if done properly, provide a flatter, smoother surface (read better thermal transfer) for the chip. All you need is a very flat surface like a pane of glass or, better yet, a toolmaker's granite surface plate. Start with 400 grit, then 600, 800 and finally 1000. Keep the paper wet with water and hold the heatsink firmly, flat on the paper on the surface plate. Move the heatsink in a circular fashion and change your grip on the heatsink by 90 degrees every so often.

Max

maxro · 23rd January 2006, 06:41 AM

Dang simultaneous posters!

Max

peranders · 23rd January 2006, 07:00 AM

Quote:

Originally posted by alleycat
Thank you for the reassuring replies. I asked this question because I have only seen heatsinks with anodising on the finned side and a machined surface for mounting components on the other.

Perfect

What more could you ask for?

Nordic · 23rd January 2006, 08:43 AM

Great minds think alike and all that...

speaker · 24th January 2006, 01:11 AM

Quote:

Originally posted by alleycat
I am considering using a piece of anodised aluminium plate as a heatsink for an LM3875TF. I was wondering if the anodising will have any significant effect on thermal transfer from the chip to the heatsink.

My company makes amplifiers and use an anodized strip of aluminum as the electrical insulator between the heatsink and the output devices. Anodizing is not conductive electrically and thermally far more conductive than a silpad or mica insulator.

22nd January 2006, 08:04 AM	#1
alleycat diyAudio Member Join Date: May 2005 Location: Melbourne	Mounting LM3875 on anodised surface I am considering using a piece of anodised aluminium plate as a heatsink for an LM3875TF. I was wondering if the anodising will have any significant effect on thermal transfer from the chip to the heatsink.

22nd January 2006, 04:12 PM	#3
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	Anodised aluminium is the normal surface for a heatsink you know. __________________ /Per-Anders (my first name) or P-A as my friends call me

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22nd January 2006, 08:13 AM	#2
Upupa Epops diyAudio Member Join Date: Aug 2003 Location: Prague,Czech Republic	Anodising make thermal transfer little bit worse, but in practical case it is free... be calm ...

23rd January 2006, 06:26 AM	#4
alleycat diyAudio Member Join Date: May 2005 Location: Melbourne	Thank you for the reassuring replies. I asked this question because I have only seen heatsinks with anodising on the finned side and a machined surface for mounting components on the other.

23rd January 2006, 06:39 AM	#5
Nordic diyAudio Member Join Date: Sep 2005	Well if it bothers you... stick some sanding paper to a flat piece of glass with woodglue (so you can pull it off later) then use this as a sanding block to wear though the anodised part.... Way too much effort.

23rd January 2006, 06:40 AM	#6
maxro diyAudio Member Join Date: Dec 2004 Location: Survey says: Least happiest city in Canada	If you really wanted to, you could lap the contact surface of the heatsink with progressively finer grades of wet-dry paper. This will remove the anodising and, if done properly, provide a flatter, smoother surface (read better thermal transfer) for the chip. All you need is a very flat surface like a pane of glass or, better yet, a toolmaker's granite surface plate. Start with 400 grit, then 600, 800 and finally 1000. Keep the paper wet with water and hold the heatsink firmly, flat on the paper on the surface plate. Move the heatsink in a circular fashion and change your grip on the heatsink by 90 degrees every so often. Max

23rd January 2006, 06:41 AM	#7
maxro diyAudio Member Join Date: Dec 2004 Location: Survey says: Least happiest city in Canada	Dang simultaneous posters! Max

23rd January 2006, 08:43 AM	#9
Nordic diyAudio Member Join Date: Sep 2005	Great minds think alike and all that...

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