If I have a three terminal TO-220 voltage regulator where the center terminal and heat sink are connected ground terminals, is there any reason not to mount the heat sink directly to an aluminum chassis (with a bit of thermal grease)? I have a device that has an L78S12CV 12 volt regulator mounted to a finned heatsink, which itself is mounted to the chassis. Between the device and the heatsink there is a mica insulator, but the bolt holding the regulator to the heatsink/chassis is not insulated with a nylon washer. Is there any benefit to using the insulator in this situation?
Electronic – Mica Insulator for TO-220 Grounded Heat Sink
heatsinktransistors
Related Solutions
Typical solutions I've used are either Kapton tape:
Or Sil-Pad:
Sil-Pad 400 is a composite of silicone rubber and fiberglass. The material is flame retardant and is specially formulated for use as a thermally conductive insulator. The primary use for Sil-Pad 400 is to electrically isolate power sources from heat sinks.
If you use a sil-pad the screw will still electrically connect the componet tab with the heat sink. A solution to this is to use a shoulder washer to isolate the screw and the tab:
It is a little bit confusing but the pad to place a heat sink to, is on the under side of the PCB. The pad at the text "md20b".
Maybe you could use small heat sinks for computer graphics card memories? They can be attached with thermal conductive double sided tape.
Doing a Google image search for drv8825 heatsink gave a couple of hints on how to do this. Apparently you put the driver board on a couple of pin header risers, and/or place the PCB upside down.
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Best Answer
If the bolt isn't insulated then it will (electrically) connect the TO220 pad to the heatsink, so the mica insulator serves no purpose. You'll get better heat transfer to the heatsink if you remove the insulator.