To solder the boards there were few SMT (surface mount)  components (mainly diodes and resistors) and some THT (through hole). For SMT usually you will have a stencil, pick and place machine, reflow oven to do all of that automatically but in my case for prototype all was done by hand. 

I've put some solder paste onto the board with solder paste dispenser and reflow it using the hot air. Doing so requires some patient as you cannot add to much of the blow or temperature as you might move the components out of the pads. Exact positioning is not required as solder will move it and position nicely when it is hot.

For the first time it can take longer but already on the second board it is just around one minute. 

On this board passive components and diodes are only 0603 imperial so it is 1.6mm x 0.8mm. Going as small as that does not introduce any major difficulty. 

Soldering is a rewarding process and after maybe an hour boards are fully assembled:

And one of my favourite view on the bench after the work:

Next is testing