Thank you very much Fraser.
I was troubleshooting a home router that auto-reboots under heavy load, I suspected heat issue, so I added a heatsink, but still not solved. So I'm pretty sure it's a software problem. (I have 2 different routers using the same SOC and same version of OpenWRT, both are affected, so there's no way for the hardware to be defected.)
This is the first time I actually use my thermal camera to diagnostic electronic stuff, I start the adventure of thermal camera just because I was amazed by it's picture, from the first time saw it, that looks like a device only in sci-fi movie.