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Help making a copper base for 80 MM Alpha Heatsink

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spyke

Registered
Joined
Mar 14, 2001
HTML:
 I got this big 80mm Heatsink from Alpha. FH8040.

[img="http://www.micforg.co.jp/images/c_fh.jpg"]

[url="http://www.micforg.co.jp/c_fhe.html"]Specs on HS FH8040[/url]

I also have some 1/8" copper plating that I want to fix to the bottom of the HS. Reckon I will use AS epoxy to join the aluminum and copper. Problem is that I live in a 3rd World Country (Hawaii) and am having a heck of a time finding someone to cut the base of the heatsink from 7mm (1/4" approx) thick to 3.5 mm (1/8" approx) thick. The only place I can find that is willing to do it wants to charge me $125! YIKES.

Anyways, if I just epoxy the copper plate to the HS as it sits, the base will be approx 10 mm (3/8" approx) thick. Is this too thick for the base? Also where i join the copper and aluminum, should I lap these surfaces really good or leave them unlapped? I figure if I leave them kinda rough, the epoxy will grip  better. On the other hand, if the surfaces are smooth then the heat should theoretically transfer better.

Or does anyone know of a place online that I can send the HS to get it cut? Any other input would be most appreciated.

P.S. Gonna use a 68cfm 80mm Delta fan. Probably will have the air blowing upward since this HS came with a skirt.

Mahalo nui`i.
 

Hoot

Inactive Moderator
Joined
Feb 13, 2001
Location
Twin Cities
Perhaps I was not paying attention, but why on earth would you want a thinner copper plate? Thinner equates to poorer performance than thicker. That Alpha sure looks like it has potential. When you epoxy them, do clamp the two pieces as tightly as possible until they cure. The less interface zone thickness, the better. That Delta fan is a sweetie. Please let us know how you make out.

Hoot
 

ken257

Senior Member
Joined
Dec 20, 2000
Don't cut anything down thinner, the extra meat will help spread the heat out. Lap the surfaces good before you join them together. I also don't recomend AS epoxy for this purpose as AS2 grease has a much better heat transfer. I would drill and tap 4 holes 1 in each corner of the base of the sink. Use AS2 grease and bolt the copper plate onto the sink, this will give better heat transfer plus you will get a tighter bond between the base plate and sink.
 

Hoot

Inactive Moderator
Joined
Feb 13, 2001
Location
Twin Cities
Ken, I've never told anyone this, but according to Nevin, at AS, the epoxy out-performs the grease for conductivity, by a small amount.

Hoot
 

ken257

Senior Member
Joined
Dec 20, 2000
Wow that is interesting Hoot! From what I have read I was under the impression that AS2 had a better heat transfer then the epoxy. Might have to do some testing on that here. In that case stick with the epoxy only a very thin layer, but I would still bolt the copper plate to the base to get more preasure between the 2 surfaces.
 

Karsta

Member
Joined
Apr 15, 2001
Location
Turku, Finland
I recently modded P3 HS with 5 mm copper plate. I noticed that applying ASII in between Al and Cu degraded the performance if applied as a thin visible layer. Sanding to flat mirror finish both surfaces and applying ASII and wiping it off was better. I attached the copper plate with screws in corners. That way I could guarantee good overall contact. So if possible I'd avoid attaching with thermal epoxy.

(did also some other mods to it but didn't get the results I was after)
 
OP
S

spyke

Registered
Joined
Mar 14, 2001
Wow so many different suggestions. Thank you all for your input. Will have to try it w/ AS paste first to see the temp results, then as Karsta says to put on the AS2 then wipe it off and screw it together. If results arent satisfatory will try AS epoxy next.

I emailed Artic Silver Inc. about the diff between AS paste and epoxy. This is what Nevin House replied..

"For practical purposes, they are close enough where the application technique will make more difference than the difference in conductivity."

Not a real conclusive answer. Well, lapping both sides seems to be the general concesis here. 2000 grit should be good but damn this is gonna take all day to lap 3X 80mm sides - the aluminum HS side and both sides of the copper plate.

As for thickness, I reckon making the base thicker will be good. The base on my Swifty is like 3/8" thick so this must be a good thing.

Aloha
 

Karsta

Member
Joined
Apr 15, 2001
Location
Turku, Finland
Yeah - Good Luck!
That lapping surely takes some time. With that HS of yours I think you may get good results.

One note - make the screw holes ready before final lapping. Especially the possible threads for screws. Otherwise screw will cause a small bulge on the metal and destroy the contact.