Hi Jean-Samuel.
As known, hardware developing impossible without soldering iron. With UmTRXv2 I found that was used very infusible solder paste. As I understand it is due to compliance to Pb-free. Nevertheless, could you please to ask fab to use more fusible solder paste . I ask, because lab users can easy damage PCB due to the local overheat. For example, I was forced to use simultaneously soldering iron (300 deg C) and air heater (350 deg C) to solder linear regulators.
Best regards, Andrey Sviyazov.