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Old 21st March 2005, 12:34 AM   #1
Adam M. is offline Adam M.  United States
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Default 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
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Old 21st March 2005, 12:37 AM   #2
HDTVman is offline HDTVman  United States
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Let's see, Radio Shack, Newark, Digi Key, Mouser for starters. It is part of the insolator kit.
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Old 21st March 2005, 12:50 AM   #3
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Jameco have mounting kits. Each kit(TO-3) has 20 washer,20 screws,20 nuts and 10 mica insulators.
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Old 21st March 2005, 01:07 AM   #4
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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.
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Old 21st March 2005, 01:54 AM   #5
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Default Re: Attaching chip to heatsink

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.
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Old 21st March 2005, 05:15 PM   #6
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Try this link smallparts.com
these guys have most things needed for chassis building.
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Old 21st March 2005, 11:29 PM   #7
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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.
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Old 22nd March 2005, 03:15 AM   #8
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A bit of tape should hold it...











-Matt
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