Comparison of two technologies for the automated optical inspection (AOI) of PCBs

Every electronic device has a printed circuit board (PCB) at its core. The assembly process of a PCB is divided in two separate technologies: surface mount technology (SMT) and through-hole technology (THT). Both of them utilize solder for fixing components, therefore it is important to inspect for soldering defects the entire production of PCBs. Any soldering defect that passes undetected from the SMT or THT assembly line can cause the final electronic product to be not functional. In order to prevent such events (i.e., defects that pass the assembly lines), the final work station of such lines is the Automated Optical Inspection (AOI). The aim of this work is to compare two different technologies for PCB optical inspection, with two AOI machines that are both utilized today for industrial purposes: (i) the PARMI Xceed 3D AOI equipped with a high-speed CMOS camera with dual laser technology; (ii) the Omron VT-S730 equipped with a CCD camera and an illumination projector unit. To assess the capability of these two AOI machines, the same product with five different types of soldering defects was inspected using both of them. Several parameters of each AOI were considered in the comparison: the ability to detect every soldering defect, the ability to detect the same defects for ten times, the time consumed for each inspection and the contrast of the images obtained using each AOI. Results are compared to those provided by Optical Coherence Tomography (OCT), to asses the eventual complementarity of these methods for optimizing such industrial investigations.