Debugging an MCU short circuit
Finding a short on a board can be a challenge. One technique involves injecting a fairly high current into the board and then using a micro voltmeter to profile the voltage drops across the board to zero into the key area. I've tried this several times with mixed success. 

One time some 15 years ago we had done a board spin on a fairly complex board that was full of digital, telcoms, audio and video in a mixed signal design. A half dozen of the new boards were built and in initial testing we noticed injection of digital noise patterns into the audio output from the board. It became clear that someplace on the board a digital GND was shorting into the audio GND. (Note that the audio GND and digital GND had to be tied together at one point under the audio chip). Finding the improper GND connection ended up being a fruitless exercise over more than a day of investigation. In the end I determined that I needed to sacrifice one board and used a Dremel tool to grind the board surface in two places down into the digital GND plane and the audio GND plane. Two 10 AWG solid copper wires were then soldered down to the GND plane copper (that took a lot of heat to achieve). I then shorted the two heavy copper wires across a fully charged 12V car battery allowing many many Amps to flow into the board. It took about 12 seconds for the short to reveal itself. A small plume of smoke rose up out of a via hole. In this case it was an improperly placed digital via that encroached on the audio GND plane pour. PCB DRC failed to flag an error because as far as it was concerned GND = GND.

The lesson learned was that it is a good idea to consider isolating two GND areas like this through some ferrite beads. Sometimes zero ohm resistor components can be used for the same thing. This makes the two GND areas separate nets on the PCB and the DRC checking can flag shorts.