ESP8266 Community Forum

As the ESP modules sends out RF bursts, they will draw bursts of current pulses from the supply. In order to ensure stable operation, it is recommended to place a 10-100nF decoupling capacitor as close as possible to the module supply terminals, with as short leads as possible. I recommend ceramic type capa, having a good high frequency response. If the environment is very noisy, or the power supply used close to its rating (not recommended) a larger (10-100 µF) electrolytic capa should be included on the PCB near by. Electrolytic capas are slower than the ceramic, but holds larger charge, and serve the purpose as low frequency current buffer.
Below is an example of an ESP-01 with a ceramic capa directly on the ESP module. It is a good idea to plug all the module pins into a socket while soldering, the socket will then serve as thermal shunt - helping to avoid the ESP pins from getting displaced when it gets hot. Finally, it is a good idea to cover this by a glob of e.g. hot-melt glue to fix and insulate.

Are you sure about laying the cap right on top of the MCU? Wouldn't it be an obstacle to thermal dissipation? And couldn't the heat damage the cap, or seriously lower the capacitance?

[quote="MeNoGeek"]Are you sure about laying the cap right on top of the MCU? Wouldn't it be an obstacle to thermal dissipation? And couldn't the heat damage the cap, or seriously lower the capacitance?[/quote]
No, that will not be a problem. If the MCU would dissipate that much power you would be looking at a dead ESP...

In your photo, I believe that there is already a surface-mount 0.1uF capacitor to the left side of the ESP8266 chip. What's the point of adding another one? I just add a 10-100uF ceramic capacitor across the power rails as close as possible to the module.

For example, the NODEMCU development board only has a 100uF tantalum across the rails...

https://raw.githubusercontent.com/nodemcu/nodemcu-devkit/master/Documents/NODEMCU_DEVKIT_SCH.png

-Jeff