Tin your soldering iron and touch the tip on BOTH the metal of the module pad AND the PCB pad, introducing a little more solder as required...
Fitting the ESP-12 Module
Here are some tips to help you build Kanga's kit for the m0xpd / Kanga ESP8266 - AD9834 board.
Before starting to un-pack the kit to check the components against this list and to begin construction, it is advised that you take Electrostatic Discharge (ESD) precautions.
The board is supplied with the three important surface mount devices (the AD9834, its oscillator and the FTDI USB UART) already fitted. This leaves the underside of the board perfectly flat - so now is a great time to tackle the first task...
The ESP8266 is supplied in a surface mount ESP-12 module, which must be carefully aligned to the corresponding pads on the PCB for soldering. This can be easily achieved by placing two temporary pieces of single core wire through two of the module's holes and through the corresponding holes on the PCB...
This will align all the other pads, allowing you to solder a couple ON THE OPPOSITE SIDE from the temporary alignment wires, just to tack the module in place.
Once you have a couple of pads soldered...
REMOVE THE TEMPORARY WIRES and solder all the remaining pads, inspecting to ensure there is good connection between module and board on each pad [the solder must flow onto both the metal of the module pad and the tinned surface of the PCB] and that there is no short circuit between adjacent pads:
Fitting the Voltage Regulator
Although not required at this stage for initial 'sign-of-life' testing, some builders may prefer to fit the voltage regulator, IC3, at this point. It is a surface mount component and the board is now free of clutter, leaving good access to this part.
Place the component over its footprint and tack it in place, by holding the tip of your tinned iron on any of the pins AND the PCB pad associated with that pin. Then solder the remaining pins and the tab to their pads.
Assembly for the Sign-of-Life Test
Once you've fitted the ESP-12 module, you should fit all the components required to enable communication with this module - thus allowing a test. These components are:
Component location is identified on the PCB silkscreen and with reference to the schematic - the image below may be of further help in identifying where components are located.
It might be helpful to form the base (central) lead of the transistors (which are supplied with straight leads) to get a better fit to the holes in the PCB...
When you've completed assembly to this point, your board should look like the photo below (the board shown doesn't have the Voltage Regulator fitted)...
You're ready at this stage to try communicating with the ESP-12 module and uploading some simple programs.
Completing the Board
After you've tested the basic ESP8266 functionality, continue populating the PCB, adding all remaining passive components (observing correct polarity when inserting electrolytic capacitor, C5), the Voltage Regulator, IC3 (if not already fitted), the diode, D1 (observing correct polarity - the cathode is identified by the 'white' band) and the header strip associated with JP2 :
Once this stage is reached, you can confirm operation of the board's DDS sub-system by running a simple test script.