I have a TO-220 voltage regulator on my board, and it will be mounted flat, and screwed down onto the board. I would like to use the board itself as a heat sink. How should I go about this?
My plan was for the screw to attach it to the ground layer on the other side of the board. But the part outline I used has a keepout region which the ratsnest routed around. So I added a rectangle of copper to my bottom layer around the hole which filled it in. I then placed another rectangle on the bStop layer which I think stops the solder mask from being poured there. So now I should have a bare copper square around the hole for the screw.
Would you say this is the correct way to go about it? Or do I need a grounded copper layer on the top as well?
Also, is simply bolting the TO-220 down sufficient, or will I get next to nothing out of doing that alone?
Btw, when I say sufficient, I mean ideal. I don't think my regulator even gets hot because it's not used to anywhere near it's full potential 99% of the time. I'm asking this mostly because I'm interested in knowing the right way to go about it. I couldn't find much on google about it.
ground wise your idea sounds ok(ish) thermal wise you pretty much add an insulator tween your device and the heat dispersal design with only a screw acting as a via
usually heatsinks are about expanding the surface area to the air, not pinpointing it to a specific location (plus heat rises)
You want the bare copper touching the part conducting the heat to the air, not separated from it by a steel screw with crappy thermal conductivity.
One way you can make this work is by putting a bare copper pad under the tab on the same side as the part and then dropped a bunch of thermal vias through to a matching bare copper pad/pour on the opposite side. This works even better if you solder the tab down with a bit of paste and hot air.
The thing about using a PCB as a heat sink is that to be effective you need a large area of copper, larger than the device itself. Thermal vias are a good idea ans so is a clip on or bolt over heat sink. They come in all sorts of shapes and sizes. Heat sink compound also helps.
Does the copper need to be bare? The idea was to use the ground plane... but I wasn't planning to make the whole thing bare, just the bit around the screw.
I guess if the screw doesn't conduct well though, I could put the ground plane on top so it makes contact with the TO-220 without adding a ton of vias...
I guess I'll just leave it as is for now though. I had problems with the work I'd done to make the bare copper area being undone as I rerouted the board over and over trying different trace widths and other parameters.
Most TO-220 regulators in free-air have around a 70degC/W thermal resistance.
How much power are you dissipating?
If you want to use a large copper pad on the PCB as a heatsink I would use
an SMD part like a D2PAK. You can look at the thermal resistance graphs
in the datasheet to determine the amount of copper area you need on the PCB.
It can consume a lot of board area.
I am not sure about your layout requirements but I like to
place TO-220's near the edge of the board. For low power dissipation
I can use a clip heatsink and for high power dissipation I can mount the TO-220s
flat on a large heatsink or cold-plate. See the bottom picture at
No but if it is coated with a solder mask it is less effective as the mask acts as an insulator. That said commercially we never bother making it bare.