I'm at the last stages of re-spinning a board (4 channel RGBW WiFi controller). Mostly some general cleanup of repositioning some parts but I do have one issue.

I use a SOT-223 as a voltage regulator. It drops the 12V in to 5V at not quite 0.1 amps, so there is at most .7 watts being dissipated. The current spin, when measuring the temperature of this device via un-calibrated finger tip indicated the thing is quite warm (though you can leave your finger on it). I would prefer to bring this temperature down.

Currently the board sits in free air, but possible one day will be mounted inside a box.

Is there a guide I can use for connecting the thermal tab to a large copper area? Should this area be unmasked or is a mask not such an issue?

 

This may help: https://www.ti.com/design-resources...models-simulators/pcb-thermal-calculator.html

 

If you can keep your finger on it then it is less than 60C which is a comfortable for semiconductors.

 

Thanks gentlemen. The interactive graph from TI says I should have a junction temperature under 100 °C, which makes me comfortable.

@AlbertHall: I once worked with an engineer (who incidentally had no degree, worked his way up from repairing guitar amplifiers, and last I saw him was the engineering manager at one place) had a well calibrated fingertip. By touch he could tell you the case temperature within about 3°C. I forget his scaling factors but my board is now at the top of his range.

 

As a chemist, we also had to estimate temperatures. My definition for 60°C is that it feels a little uncomfortable (first sign of pain), but you can tolerate it. It is also the pasteurization temperature (low-temp version = 60° for 30 minutes) and a good temp for sous vide.