Thermal Vias?

[dknguyen]

Is a thermal via just a regular via? Or is it physically different somehow? I got a bunch of D2Pak's...do I just fill the tab areas on the PCB full of vias to the opposite side and just stick a heatsink there?

 

[Mikebits]

I think thermal vias are used when no heatsink is present. They are usually bigger than a regular via. I suppose you can use both.

 

[Oblong]

Mounting instruction for SMD heatsink.

"The device and heat sink are soldered directly to the modified drain pad
creating a thermal transfer path from the package tab
to the surface mount heat sink."

Full PDF here

**broken link removed**

 

[OutToLunch]

Thermal vias are dual purpose - they tie power planes together while at the same time they stitch those two planes together thermally. I would suggest smaller vias but your not going to need to fill the entire pad up. If you use larger vias, problems with solder being wicked into the via can happen and that can affect the pad-to-tab solder connection.

There are lots of examples of layouts that include thermal vias. Take a look at the layout for the DPAK fets near the end of the document. They used about 9 vias on the drain tabs.
https://www.electro-tech-online.com/custompdfs/2009/03/an1442.pdf

 

[RadioRon]

If you are not working with microvias, then probably your thermal vias will be identical to any other via on the board. Since they have to go right through to the other side, you can't go too small or the pcb fab house will have difficulty.

 

[Boncuk]

Thermal Via

Hi dknguyen,

thermal vias are used to conduct heat from (mostly top) to bottom of a PCB. Data sheets normally don't contain information about the drill size of the thermal via.

Addionally to conducting heat from one side to the other there is some extra cooling effect resulting from the air passing through the holes.

Here is the example for the MC33486A (dual high side switch for H-bridge applications) capable of 10A nominal continuous current.

Notice the different size areas of the cooling pads: The top side has an area of 2.0 square cm while the bottom size has 8.0 square cm.

I use thermal vias to cool a PCB carrying 256 UV-LEDs with a via between each LED in X- and Y-axis with a radial fan (for higher air pressure) blowing air from the bottom to top.

Hans

 

[dknguyen]

Mounting instruction for SMD heatsink.

"The device and heat sink are soldered directly to the modified drain pad
creating a thermal transfer path from the package tab
to the surface mount heat sink."

Full PDF here

**broken link removed**

THat's the alternative, but I was wanting to stick more durable heatsinks on the opposite of the board that the FETs are on (seems you can get much better heatsinks if you do that and. Just looking at different methods to heatisnk the FETs.