Error in LibreServo v1b

With the website finished, I finally had time to continue programming and testing my LibreServo, but the joy was short-lived.

After soldering the three PCBs together, I proceed to power the LibreServo for the first time from a battery instead of the ST-link programmer ... and a white smoke preceded by sparks made an appearance. The STM32F302 microcontroller has been completely blown up, and there is a huge short between ground and the 3.3V line. After looking closely, I see that there are tin chips between the legs of my microcontroller, right between vdd and vss! Is it possible that when welding the three PCBs I was not careful enough and some "chips" has ended up where it should not, or has it been the sparks themselves that have caused it?

I unsolder the microcontroller and re-solder a new one. I check the power lines and there is no short circuit. Let's get to work again! And again white smoke... What's going on?!

Desperate I disassemble the PCBs, power up the PCBs again with the linear regulator... and I see the catastrophe. Where it should generate 3.3V, there is 6V (with a 7V input from the lipo)... I check my eagle documents and I see the mistake, the schematic does not correspond to the PCB! When I made a special footprint for the linear regulator, at the time of linking that footprint with the scheme I changed the order of the pins and from there everything is history and white smoke.

Design error
LibreServo v1b layout bug

Here it is some photos for posterity of LibreServo v1b completely soldered:

LibreServo v1b Gallery


In order to correct this failure it is necessary to change the design of the LibreServo PCB... so since I am going to design new PCBs, I will try to collect everything I learned (from what little I have been able to test) and generate a new design with several fixes on all PCBs, not just this error. LibreServo v1c, here I go!

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