MEASURING THE ALIGNMENT ACCURACY OF SURFACE MOUNT ASSEMBLY CIRCUIT BOARD MASKS

An automated system for measuring the alignment accuracy of an exposed photosensitive film resist circuit pattern on a metalized ceramic substrate is described, The system is robust and capable of handling low contrast images with high noise levels and varying degrees of degradation of the circuit pattern. The technique that we will present involves estimating, with the aid of a calibrated vision system, the actual coordinates of two predefined salient features of the circuit pattern, component pads, and calculating the horizontal, vertical, and rotational deviation of the expose mask. The vision algorithm that was implemented will be detailed and its development as an optimization problem, to satisfy the speed, accuracy, and hardware constraints of the system will be discussed. Measurements are accurate to the nearest 2.5 microns and the processing time of each ceramic substrate is not more than sixty seconds using an IBM AT microcomputer…