We published a video on with some tips on soldering header pins on to your Teensy board.
A couple of tips to remember when soldering header pins to your board:
1 – You MUST solder the pins. Setting the Teensy on the header pins without completing the soldering will not work.
2 – Use a breadboard to keep the pins straight and stable when soldering
3 – Leave the soldering iron on the pad for a moment after you solder. This will bring all the components – the pad, the header pin, and the solder up to the same temperature so they will cool together to form a proper molecular bond.