Stm32F103C8T6 Custom board problems

[TMaie.1]

Hi,

i have some rather strange problems with my custom with an STM32F103C8 mcu on it. It is programmed via an Nucleo ST Link v2/1 and it works fine most of the time. I can load some test sketches on it via Platform IO or STM32CubeIde. But after a few minutes of running that code the problem start. The over Current feature of that nucleo starts to cut the connection and when i measure the resistance between VCC and GND on my custom board it shows 0Ω. When i now reheat all the connections on the STM it works fine for a few minutes and the the same problems start again.

I am pretty sure that there are no faulty solder connection as i have tried it many times now always with the same outcome(Different MCU, desolder and solder again...) Has anyone ever had similar problems or has an idea what the problem could be? I have also attached a picture of my schematic.Maybe there is a mistake?

Thanks!

[TMaie.1]

I should add that this schematic is for a DIY St Link V2. That is why the SWO Pins are at the wrong position. This mcu is programmed via Uart and not via St Link. But on my other custom board that is programmed via SWO there is the same problem.