A calibration and part
inspection method for the inspection of
ball grid array, BGA, devices. Two cameras image a precision pattern
mask with dot patterns deposited on a transparent
reticle. The precision pattern
mask is used for calibration of the
system. A
light source and overhead light reflective diffuser provide illumination. A first camera images the
reticle precision pattern
mask from directly below. An additional mirror or
prism located below the bottom plane of the
reticle reflects the reticle pattern mask from a side view, through prisms or
reflective surfaces, into a second camera and a second additional mirror or
prism located below the bottom plane of the reticle reflects the opposite side view of the reticle pattern mask through prisms or mirrors into a second camera. By imaging more than one dot pattern the missing state values of the
system can be resolved using a trigonometric solution. The reticle with the pattern mask is removed after calibration and the BGA to be inspected is placed with the balls facing downward, in such a manner as to be imaged by the two cameras. The scene of the part can thus be triangulated and the dimensions of the BGA are determined.