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I've received my heatsink and mounts for my voltage regulators. It's the first time for me. I'm not sure about the way to mount the regulator on the heatsink. Mainly a little film, not sure about the composition. Feels like plastic but it's really fragile and composed by multiple layers. after a google search I've found some posts talking about a kind of thermal paste replacement.

Here's what I have :

enter image description here

To mount it I've place the little film between the regulator and the heatsink.

enter image description here

Does it sound ok for you ? Do you have more information about that little film ? Should I mount it on the other side of the heatsink ?

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If the little film appears to be made of several layers, it is likely mica - it should go between the part and the heatsink. –  Peter Bennett Jan 6 at 17:39
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2 Answers

up vote 2 down vote accepted

Here is a site that shows the uninitiated how to mount components on heat-sinks (amongst other things). Towards the end they touch-on mylar insulating washers (like the one you have). For a simple regulator you don't need this insulating plate providing you make sure the heatsink doesn't touch parts of the circuit that are not at 0v (centre pin on most regulators)

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Typically you put either thermal paste or a pad between the device and the sink. Most TO-220 devices, the tab is tied to one of the pins of the device; sometimes it's not, but those devices tend to be rated for much lower power dissipation. On regulators, the tab is typically tied to the COM pin. On transistors, the tab is typically tied to the collector or drain. If you use grease or a metal mounting screw, the device tab will be tied to the sink. This can cause clearance concerns. It's less of an issue with regulators, since having an area of COM around the regulator isn't likely to cause a clearance issue. But if your transistor tab is at 1200V, now you have a big heat sink also at 1200V. And if the device is switching, the heat sink acts as an antenna broadcasting that switching signal, potentially causing further issues.

Thus the film, which is insulative. However, I wouldn't bet too much on that insulation, since there's a metal screw in contact with both the tab and the sink! You might get by with a few volts, but if you actually need repeatable guaranteed voltage insulation, use a nylon screw or a shoulder washer, as shown here. https://electronics.stackexchange.com/questions/45574/how-to-electrically-isolate-a-pcb-from-a-heat-sink/45579#45579

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