Fastening of PCB circuit board screws is a key process in infrared thermal imager installation and adjustment. Its assembly quality directly affects the performance of the circuit board and image quality in an infrared thermal imager. First, a quantitative method for tightening the torque of the circuit board screws in an infrared thermal imager was proposed. The theoretical tightening torque of the circuit board screws was then calculated using the proposed method. Finally, combined with the tightening torque value obtained using the proposed quantitative method, ANSYS Workbench was used for the finite element simulation analysis. The results verify the safety of the circuit board under a load of the theoretical screw torque value. This study investigates a quantitative method of an infrared thermal imager circuit board, enabling the quantification of the screw tightening torque value during the assembly process of an infrared thermal imager PCB circuit board. This improved the assembly quality of each circuit component of the infrared thermal imager and the stability of the entire machine.