I am facing an issue that I do not understand.
I am using a STM32F030K6T6 microcontroller with a capacitor X7R 0603 100nF 10% 50V connected to the ground, whose the value corresponds to the preconization specified in the datasheet as follows:
Most of the time, I do not have any problem. But on really few boards, the microprocessor stays blocked in reset mode because the voltage of the NRESET pin which stays quite low, around 470mV. There is nothing more connected on NRSET signal: only the microprocessor, the SWD connector (without any plugged-connector) and the capacitor.
Do you have any explanation? Could it be because of ESD? A broken capacitor series ? (I have measured its resistance with the ohmmeter to check if there is a short circuit, but it's greater than 1Meg Ohm) Or an issue of capacitor charge/discharge?