Method of making thick film circuits

摘要

An improved method of making a multiple print thick film circuit wherein the alignment between successive conductor print steps is both optically inspectable and electrically testable. The first of two or more successive conductor prints includes a pair of adjacent alignment features (10, 12), and the successive conductor prints include identical alignment features which are printed in registry with the alignment features of the first conductor print. The alignment features are defined by a pair of contiguous mutually perpendicular conductor segments or surfaces resembling a box or an upper case L. With proper print alignment, there is a non-conductive gap between adjacent alignment features, and test probes (44, 46) brought into contact with the features or associated probe pads will reveal a high or open-circuit impedance therebetween. However, if the second conductor print is misaligned relative to the first print, one or more of its alignment feature segments or surfaces will bridge the gap between the first pair of alignment features, and test probes brought into contact with the features or associated probe pads (50) will reveal a low or short-circuit impedance therebetween. The spacing between adjacent alignment features is less than the smallest conductor spacing on the circuit. Because the gap between alignment features is smaller than the circuit spacing, the test equipment can detect alignment errors large enough to short-circuit the adjacent alignment features, but not so large as to cause shorting in the actual circuit. Alignment features may be formed at multiple locations throughout the substrate to detect localized misalignment, and adjacent alignment features may span individual circuits formed on the same substrate (60).