Understanding the JTAG connector/adaptor attached to a smartphone
That small green board likely just contains a surface-mounted pin header style shrouded connector on it's bottom side (hidden) that is connected to the mating connector on the cell phone's motherboard. That connector exposes the JTAG signals. 

Here is another example:



The JTAG port is circled in red and enlarged in inset. This motherboard is missing the connector on the motherboard side, so that green adapter PCB wouldn't be necessary. Instead, you would have to solder ("weld" in your terminology) high gauge wires to the exposed pads on the PCB like in your photo between the green adapter PCB and the larger adapter PCB. 

That second PCB is yet another adapter that goes from the bare soldered wires into a connector that is compatible with the JTAG interrogator unit (visible in the background with the blue LED).