Heatsinking the Chipamp, problems

[pjpoes]

Hey guys, I am almost finished making the wooden enclosure for my chip amp. Some might remember my thread a while back on tone woods affecting the sound of circuits. I built an enclosure out of maple which isolates everything, chips included on pieces of maple. The heatsink is of course metal, aluminum, and is quite oversized.

I am sorta still doing a mock up for this, as I have not done final assembaly. I put a dab of heatsink compound on the chips and mounted them in some pre-existing holes on the heat sink, which were slightly too low The chip is not completely touching the heatsink, I would say about 1/8" is exposed to air instead of metal. Also, for whatever reason, the chip is not sitting flush against the heatsink. as a result, I believe the chips are not cooling properly, and are getting quite hot. The screws going through them are too hot to touch for long, though probably not hot enough to burn you, and the heatsink is only mildly warm around the chip. I wanted to make sure I wasn't missing something here, like some other aspect of mounthing that I missed, which could cause this. Otherwise, I will assume it simply is the chips not making good contact, and try and fix the holes. Is the paste real important, should I put more on.

[ofb]

just drill new holes. regular aluminum is quite soft. and self-tapping screws should make their own threads in the new holes easy enough. (if it feels tough, just screw in a bit, back off, screw in a bit, etc. you work your way in.)

the paste is there to get good contact between the less than perfect surfaces. you just want a little bit. more will start acting as insulation.

Also, for whatever reason, the chip is not sitting flush against the heatsink.

figure out the reason. it should sit flush. if you don't have good contact, the heatsink can't work.

another option: instead of drilling new holes, can you just turn the works upside down? depends on how you're mounting the pcb etc of course, but just remember that the chip doesn't care which way is "up", so consider a re-arrangement.

[maxro]

Originally posted by ofb
just drill new holes. regular aluminum is quite soft. and self-tapping screws should make their own threads in the new holes easy enough. (if it feels tough, just screw in a bit, back off, screw in a bit, etc. you work your way in.)

Not the route I would choose. If you're going to use aself tapping screw, then countersink the hole first, or the edge of the hole will flare out. The flared edge won't allow a flush fit of the chip. Also, with all the friction of a self-tapper, you wont be able to tell when you have the screw tight enough and may crack the chip. Better to tap and countersink the hole and use a bolt.

see:
http://sound.westhost.com/heatsinks.htm

Max