Schottky diode : typical thermal resistance and copper pads area

Thread Starter


Joined Jun 9, 2021
I have the following question about this schottky SS34 datasheet :

The datasheet indicate that the typical thermal resistance RθJA is 50°C/W but the Note at the bottom indicate "P.C.B. mounted with 0.2x0.2”(5.0x5.0mm) copper pad areas"

How to calculate the typical thermal resistance if we just use the "normal" SS34 footprint (1,68*1,52mm pad) ?
Or does it mean we should make a 5*5mm copper area around the pad in order to get this thermal resistance ?



Joined Jan 30, 2016
The thermal info in a datasheet is usually (but not always) based on official JEDEC test fixtures that state how something should be tested to provide the information in the datasheet and allow comparison between different vendors' devices. So the value in the datasheet is given when tested on a PCB where each pad is 5 x 5mm and normally the PCB is horizontal in static air.

The attached paper from TI gives some insight into calculating PCB thermal resistance and has some useful 'rules of thumb'.