1. An inspection method, comprising: using a X-ray generator for generating X-ray to a printed circuit board (PCB); using a X-ray detector for detecting the X-ray transmitted through the PCB, so as to generate a scanned image of a solder of the PCB; reconstructing the scanned image for a reconstructed volume, wherein the step of reconstructing the scanned image for the reconstructed volume comprising is performed by using shift-and-add or computed tomography; adjusting a slicing direction associated with the solder of the PCB for slicing the reconstructed volume into a sliced image, wherein the slicing direction comprises a non-horizontal slicing direction; inspecting the sliced image for detecting whether the solder of the PCB has one or more defects in real time during a drive mechanism is transferring the PCB; and outputting an inspection result of the solder of the PCB.