Securing component to heatsink

[signalman72]

I want to use a heat sink on a voltage regulator (TO-220). I have thermal paste, but the heatsinks I purchased also come with a film wafer. What would be the proper way to ensure maximum heat transfer? Thanks in advance!

 

[KrisBlueNZ]

If you need to insulate the package's metal tab (which is normally connected to the centre pin) from the heatsink, then use the insulating washer with a small amount of thermal paste on each side of it. If you don't need insulation, use a very small amount of thermal paste between the package and the heatsink. Don't tighten the screw excessively.

 

[signalman72]

Just disregard the wafer?

ETA, I think the wafer is an insulator, but it was not specified. I don't think it is a heat exchanging media, but I know little about the subject. BTW, it came with insulating washers also. I don't think I'm going to need them.

 

[KMoffett]

More than you probably want to know about heat sinking: http://sound.westhost.com/heatsinks.htm
Also Google Images: mounting TO-220 to heat sink

Ken

 

[OLIVE2222]

Another good information:

http://www.irf.com/technical-info/appnotes/an-1012.pdf

 

[shrtrnd]

There are mica electrical-insulating wafers, and blue thermal-heat transfer wafers.
If you need the mica, electrical-insulation wafer to isolate the heat sink from the TO-220 component, be sure to use nylon fastening hardware, not a metal screw (which would defeat the mica wafer insulator).
Some techs I've known over the years forget that fact, and zap the device unintentionally.
Depending on the component, some need to be directly bonded to the heat-sink with thermal grease.
The websites offered by KMoffett and OLIVE2222, probably tell you this, as well as a lot of other useful information.

 

[(*steve*)]

And after all of that, it's still good insurance to use your multimeter to check that the heatsink is actually insulated from the device.

I recall cases where I thought I had done everything right, but hadn't.

The important thing to realise is that the metal bolt is almost always electrically connected to the heatsink, or not reliably insulated from it, so you need to insulate the device from the bolt, and the device from the heatsink.

There are three ways to do this:

1. Use a "plastic" device. If it's not metal, a short isn't going to happen.
2. Use a device with an isolated tab. The junction is insulated from the case internally.
3. Use the appropriate insulators.
4. Attache the heatsink to the "plastic" part. I've seen glue on heatsinks, and more solid structures bolted over the top of devices.

It's also interesting that none of the top 3 above apply to the vast bulk of surface mount devices that will be effectively soldered to their heatsink. I guess (2) could apply, but I've not seen one.