I have a PCB and trying to measure the maximum junction temperatures of the major components in the PCB which in full working mode. For example like Input Diodes, Buck Regulator ICs, Aluminium Electrolytic capacitors and other Discretes.
I have placed my PCB inside the thermal chamber at 95degC and made the board full operational and measured the temperatures of the components by placing the thermocouples (K-Type) on top of the ICs, diodes and other components as mentioned above.
My questions :
I measured the temperatures of the components on their surface and found to be in the range of 110degC to 120degC. But this is the Surface temperature of those components, right? How can I practically measuring the junction temperature of those components so as to find what margin I have ? Is it something like I add 20% to the measured surface temperature value to arrive at the maximum junction temperature of the components? Or is there another way to measure the junction temperature of the components?
What are the other important things that I need to calculate or note during this thermal stress testing?