mosFET - Controlling heat

[Falcon69]

So, I've been trying to find info on this, and can't seem to find much.  I am probably looking in the wrong spot or simply don't know what it's called to look for it.

Anyway, When designing a PCB.....What part of the mosFET (surface Mount) is best to make the pad bigger to help spread the heat?  For example, I have a mosFET that is a SOT-23 package. The drain is the single pin, while the source and gate are the two pins on the other side.  Is it the Drain pin that you want to try and make the biggest you can for PCB copper pour?  And if so, is it still a good idea to use thermal reliefs so the solder can reflow?  Does the heat still get distributed with the thermal reliefs?

Does it make a difference if P-Channel or N-Channel (like, do it for Source on one, and Drain on the other?)

So something like the picture?

[Mr.B]

In a lot of the higher power SMD FETs I have used, the Drain is the large tab under the device.
An example is this NTTFS4930N.
I am not sure about SOT23 though...

[Falcon69]

Ya, I saw that as well, but this SOT-23 package doesn't show any extra copper for the land pattern in the Data Sheet.  I've seen, on same data sheets, as you have shown, where more copper is listed, but have not seen it yet for a SOT-23 package or a SOT-363, SOT-23-6, etc. Since the smaller package are such low Amps (<5A), is it even needed?

[Mr.B]

I would have my doubts it is even needed.
If you are pushing the FET to the limits of its power rating, I would be inclined to select another more appropriate FET.

[Falcon69]

nah, not even close. it's rated at 3.5A, It will have at most 250mA through it.  I just want to improve on my PCB designing skills.

[Falcon69]

awesome! thank you