How to use RthJA from datasheet ?

urbanelwiz

Considering TO-247 package for below question.

When heatsink is used, we use RthJC and Rth for TIM and Heatsink and the total would be the RthJA in this case. We can use this to estimate Tj with calculation and also measure temperature at Tc, T_TIM, or T_heatsink and estimate Tj using appropriate Rth.

When heatsink is not used, datasheet RthJA needs to be considered and the heat is spread through the pins and resin package. In this case RthJA can be used to estimate Tj with calculation.

1. However while testing, where do we measure temperature and any of these locations allow us to use datasheet RthJA? (metal case or plastic case ?)
2. For the datasheet RthJA, is this provided for a specific PCB specification ? (board thickness, Cu Oz, etc…)

Thank you!