Antor
Member level 2
Thermal paste conducts heat. They do not conduct electricity. In fact, it acts like a dielectric with the IGBT and the heatsink acting like the two parallel plates of a capacitor, the thermal paste sandwiched between them. If the heatsink is connected to earth, then the setup produces common-mode noise when switched rapidly.
Single-ended oscilloscopes like the ones we find everywhere can pick up this noise.
I used metal screws so there is electrical conduction. I tested short circuits with middle pin and yes they are electrically connected. I'm not sure if it is the problem. I think I should get a differential probe to clear the risks.