I've been trying to make a simple audio player using the STM32F302CBT6, however, the VCC and GND pins of the MCU keeps on getting internally shorted when a 3.3V power supply is provided and a faint burning smell starts to come out of it but it does not get very hot to the touch. The PCB was tested for shorts using a multimeter before powering on.
I'm certain that short is due to the microcontroller because desoldering it removes the short from the board.
Initially, I thought it was a soldering problem but all three PCBs which I soldered have had this issue, including a PCB which was soldered with just the MCU, clocks and a 3.3V low dropout regulator, i.e., these components: The power to the PCB was being supplied by the 3.3V and GND pins of an Arduino Uno connected to my computer via USB.
My PCB is laid out like this (note the ground copper plane was hidden for visibility):
Are there any visible design flaws or issues I have overlooked which could be causing the internal short?