Tolerance Study of Printed-Circuit Process Steps for a Microwave Application

This study provides tolerance-distribution data for a microwave printed-circuit development utilizing "strip-line" type filters, 50-ohm transmission lines, and tuning stubs. Irradiated polyethylene is the dielectric. Data is given on tolerance distribution in the following process areas: Artwork cutting; Photographic (reduction, exposure and development, contact printing with glass and film, step-repeat camera work); Etching (including resist exposure and development). Dimensional instabilities in the irradiated polyethylene was found to be a key problem. Some of the total tolerance must be left for dimensional changes in the substrate, so the three process areas must give better than plus or minus one mil over-all tolerances. Generally speaking, on dimensionally stable material the required one-mil tolerance. (can be held throughout the three processes; where this tolerance was not held, the problem is, as noted, material instability.