Here is how to solder the pogo board. The name comes from the spring-loaded contact pins in the picture above that look like ant-size pogo sticks. They are needed to connect the foil contacts on the print head to the electronics in the printer. Commercial printers use another foil that has contacts with dents that are pressed against the printhead. But these foils are custom made and extremely expensive as one-offs, though cheap in the thousands.
Our Pogo Board uses a PCB with holes just big enough for the pins, and 36 pins that must all be soldered in straight and with the same length.
We use two PCBs to form a rig for the depth, using four 3mm bolts to create the correct space. Feel the distance from the PCB to the foil by mounting everything in the holder and using a wire as a doth gauge. Mount the top board 2mm higher than the depth gauge to allow for some compression of the pogo pins. Lay flat and solder away!
Oh, you should test each pin before soldering it in to avoid desoldering duds. Also, make sure that the springy end points down before soldering.