Sadly, i have to quit.
the serial pin headers on the pcb are too small.
i've tried to print some kind of clamp to hold the pins on the pads, but my printer is not able to print this tiny holes and so on.
the second difficulty is that the second pcb is blocking this pads on the main pcb. i need the second pcb, otherwise i have no rj45 jack for tftp 
if somebody has some better Autodesk Fusion skills or some better ideas, feel free to contact me - i can send the f3d file
...