Screen Printed Thick Film Resistors — Better Yields with Shorter Set‐up Times

A set of rules is presented for printing thick film resistors, whose implementation minimises losses due to resistors firing too high or too low, and also results in the shortest possible set‐up times. To the best of the authors' knowledge, some of the concepts and relations reported here are nowhere to be found spelled out in the published literature, let alone presented in quantitative form. One example is the relationship between sheet resistance vs resistor length curves and the mesh/emulsion of the screen used to obtain such curves. Another example is the relationship between the choice (or lack of it) of resistors used to set up thickness at the beginning of a print, and the spread in resistance values. Then there are better known relationships, like the dependence of thickness on resistor width or print direction—still no quantitative data are available and the potential relevance of these effects is generally not appreciated. Long set‐up times and yield losses need not exist, as they arise from non‐rigorous printing rules which call for a standard dry thickness (usually 25±3 µm) regardless of resistor dimensions, print direction and ink jar value, and which only call for a range of screen mesh/emulsion values, rather than for specific ones. In fact, for any given sheet resistance vs resistor length curve, only one choice of screen mesh/emulsion and resistor thickness is logically possible. Also reported are experimental data relating resistor thickness to resistor length as a function of screen mesh/emulsion, resistor width and print direction as well as data on sheet resistance as a function of resistor dry thickness. Finally, results from thirty‐eight production runs are reported and discussed.