Attaching chip to heatsink

Adam M. · 21st March 2005, 12:34 AM

How does everyone attach a non-isolated chip to a heatsink to achieve isolation? I have some mica insulating plates to keep the chip off the heatsink, but I do not have a nylon washer that will fit inside the hole in the chip as well as have a lip to prevent the flat portion of the screw contact the chip?

I have a metal lathe and about 10 feet of nylon rod, but I'd really rather not have to make screws. Does anyone know a source for an appropriate washer/screw?

Thanks,
Adam

HDTVman · 21st March 2005, 12:37 AM

Let's see, Radio Shack, Newark, Digi Key, Mouser for starters. It is part of the insolator kit.

jaudio · 21st March 2005, 12:50 AM

Jameco have mounting kits. Each kit(TO-3) has 20 washer,20 screws,20 nuts and 10 mica insulators.

leadbelly · 21st March 2005, 01:07 AM

If you have a junked PC power supply around you can steal the screws/washers from that. Another option is to just buy a nylon screw at the hardware store. I just use a nylon 6-32 x 1/2" to attach my LM3875T and oxide insulator to my heatsink.

jackinnj · 21st March 2005, 01:54 AM

Quote:

Originally posted by Adam M.
How does everyone attach a non-isolated chip to a heatsink to achieve isolation? I have some mica insulating plates to keep the chip off the heatsink, but I do not have a nylon washer that will fit inside the hole in the chip as well as have a lip to prevent the flat portion of the screw contact the chip?

I have a metal lathe and about 10 feet of nylon rod, but I'd really rather not have to make screws. Does anyone know a source for an appropriate washer/screw?

Thanks,
Adam

Home Depot has nylon screws -- the other companies cited above have the "hip washers" in fiber or plastic which will work.

moreismore · 21st March 2005, 05:15 PM

Try this link smallparts.com
these guys have most things needed for chassis building.

TwoSpoons · 21st March 2005, 11:29 PM

Don't use the mounting hole in the chip's leadframe. Use a bar across the body of the chip, with a bolt at each end. A thin piece of rubber sheet under the bar helps with pressure distribution. Using the bar will give much better pressure distribution across the copper heatsink tab of the chip, meaning it sits flatter to the heatsink giving better thermal performance. There's also less risk of distorting the leadframe of the chip by accidental over-torqueing of the mounting screws.

zagisrule! · 22nd March 2005, 03:15 AM

A bit of tape should hold it...

-Matt

21st March 2005, 12:34 AM	#1
Adam M. diyAudio Member Join Date: Feb 2004 Location: Pittsburgh	Attaching chip to heatsink How does everyone attach a non-isolated chip to a heatsink to achieve isolation? I have some mica insulating plates to keep the chip off the heatsink, but I do not have a nylon washer that will fit inside the hole in the chip as well as have a lip to prevent the flat portion of the screw contact the chip? I have a metal lathe and about 10 feet of nylon rod, but I'd really rather not have to make screws. Does anyone know a source for an appropriate washer/screw? Thanks, Adam

21st March 2005, 12:37 AM	#2
HDTVman diyAudio Member Join Date: Aug 2001 Location: Chicago area	Let's see, Radio Shack, Newark, Digi Key, Mouser for starters. It is part of the insolator kit. __________________ What ever makes the tunes flow

21st March 2005, 01:07 AM	#4
leadbelly diyAudio Member Join Date: Dec 2002 Location: Calgary, Alberta	If you have a junked PC power supply around you can steal the screws/washers from that. Another option is to just buy a nylon screw at the hardware store. I just use a nylon 6-32 x 1/2" to attach my LM3875T and oxide insulator to my heatsink. __________________ Aerodynamics are for people who can't build engines. Enzo Ferrari

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21st March 2005, 12:50 AM	#3
jaudio diyAudio Member Join Date: Oct 2004	Jameco have mounting kits. Each kit(TO-3) has 20 washer,20 screws,20 nuts and 10 mica insulators.

21st March 2005, 05:15 PM	#6
moreismore diyAudio Member Join Date: Jun 2004 Location: Toronto	Try this link smallparts.com these guys have most things needed for chassis building.

21st March 2005, 11:29 PM	#7
TwoSpoons diyAudio Member Join Date: Oct 2004	Don't use the mounting hole in the chip's leadframe. Use a bar across the body of the chip, with a bolt at each end. A thin piece of rubber sheet under the bar helps with pressure distribution. Using the bar will give much better pressure distribution across the copper heatsink tab of the chip, meaning it sits flatter to the heatsink giving better thermal performance. There's also less risk of distorting the leadframe of the chip by accidental over-torqueing of the mounting screws.

22nd March 2005, 03:15 AM	#8
zagisrule! diyAudio Member Join Date: Apr 2004 Location: Edgewood, NM	A bit of tape should hold it... -Matt

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