Why?
Required for a University project, I had 10 ESP8266 - ESP12 modules that individually needed to be:
-Flashed with up to date NodeMCU firmware.
-Flashed with a specific written Lua script for each module.
-Reprogrammed if non-functional or if better scripts were made available.

Solves?
Solutions sought out on the web recommended soldering leads to every pin required for flashing. Issues with that solution:
-Every time a module would need to be re-flashed, several wires would have to be re-soldered onto the modules.
-Overly time consuming with so many modules.

How?
I followed many online tutorials to find out what pins needed to be connected to enable the flashing mode.
Included a FLASH and RESET button for firmware flashing.
Currently, I am using the NodeMCU Development board to supply 3.3V, which will be replaced with a LM3940 voltage regulator.
I am using a USB -TTL cable to communicate with the modules (VCC of USB not connected)