STM32 MCU gets shorted
Short: Try rotating the controller 180° before soldering :)

Long: The ST controllers have two marks on the top side, only one is for Pin 1. And most times you choose the wrong one.

The rotation will connect some GND and VCC pins so you get a short circuit. 

To identify the right "Pin 1" you could have a look at the chip datasheet in the section Package Information / Device Marking.
( If you could read the text on the chip, pin 1 is in the lower left corner)