Too small components
Recently I tried to make a small humidity and temperature sensor board that was powered by ESP32 C3. The PCB design was made and boards and components are ordered separately. Which means I will assemble them. However, I have not expected how small ESP32 C3 chip really is. It's about 5x5mm, and the chip legs are underneath the component.
However, I thought that would not be a problem because I ordered a stencil for that. The idea was to put soldering paste on PCB with a stencil, and use hotplate to solder the components to it. However, after assembling a board I hooked it up to the USB and the board started heating up really bad around the main chip.
Maybe I wired the chip wrongly in the schematic. I tried assembling another board and for some reason when powered with the USB, PCB started getting really hot around voltage regulator IC. Well now I can eliminate schematic mistake. It must have been a bridge underneath that small microcontroller chip.
It's hard to see but small legs under there are visible if you look at it from the side. They seem jagged, but all connections seem ok. Maybe with use of a hot air soldering iron it can be soldered more precisely, but currently don't have one of those.
Anyway, the lesson for the future is: Don't choose the absolute smallest component packages. It's possible to get fooled when designing the PCB board because there is no sense of scale. 0805 resistors and capacitors are good choice for assembling it myself. 0402 is possible, but too small. It requires too much attention when placing.
Microcontrollers with exposed legs packages are the best. You can see if there is a bridge, and I've heard its possible to solder them with just a soldering iron. And for the end, IC packages with soldering pads underneath are really tricky. Best to leave those to the pick and place machines.
