I have a circuit board with several MOSFETs in TO252 and TO263 packages as well as other IC with exposed pad on the bottom.

I need to cool these parts and have 2 options:
1. Glue a heat sink directly to the case of the parts.
2. Create an exposed copper area on the other side of the PCB, bellow each part and glue the Heat sink to there (or solder it if I can find one with that option).

What is better from thermal perspective?

Thanks.

 

Thermal resistance through the plastic case is very high. You DO REQUIRE to use the exposed metal tab to remove heat.

Use a 1” square pad on the PWBA to solder the Mosfet’s drain. Use thermal vias sparingly and duplicate the square pad on the bottom layer.

There are solderable heat sink extrusions that can be soldered to the pad for additional dissipation.
But you first require to know, how many watts the devices are going to dissipate to ensure a correct solution. Do you know??

 

You could also have an opening thru the PCB and a heat sink extending thru to contact the devices.
Find and dismantle a larger flat screen TV and see the different heat sink schemes they use for all of those power devices. Some are very creative.

 

I use this around a TO-220. It solders to the transistor.

datasheet digikey
There is a smaller version. The picture is upside down.

 

Thermal resistance through the plastic case is very high. You DO REQUIRE to use the exposed metal tab to remove heat.

Use a 1” square pad on the PWBA to solder the Mosfet’s drain. Use thermal vias sparingly and duplicate the square pad on the bottom layer.

There are solderable heat sink extrusions that can be soldered to the pad for additional dissipation.
But you first require to know, how many watts the devices are going to dissipate to ensure a correct solution. Do you know??

Thank you.
I do know how many Watts each device is going to dissipate, is varies of course between the devices.
In any event, for devices that have an exposed pad, I will solder it to the PCB and create a duplicate pad on the other side (and in the inner layer as well) + vias.
The question is, what is more effective, connecting a heat sink to that copper square or to the plastic case.
Is there a big difference?

 

I use this around a TO-220. It solders to the transistor.
View attachment 336068
datasheet digikey
There is a smaller version. The picture is upside down.
View attachment 336069

Thank,
I am familiar with those.
Di you have an example (and a link or MPN if possible) to TO252 and TO263 packages?

 

In normal practices the PCB, which should have a ground plane and/or a power plane, but not always ground or power. When the PCB is designed it's taken into account that these devices are going to need thermal bonding. The (for instance) ground plane acts as a heat sink. As for the notion of putting an additional sink on top of the chip - unless you're using military grade chips heat sinking the tops is going to be highly ineffective. Military grade chips are not plastic, they're something like ceramic, with good thermal properties. In that case heat sinking the tops of the packages would prove more useful.

 

Di you have an example (and a link or MPN if possible) to TO252 and TO263 packages?

to-263
It looks like the two transistors are 6mm and 10mm wide. I can find one and not the other.
I have put heat sinks on the back side of the PCB. I put copper in all the layers under the pad and vias.