An Automated X-Y Dimensional Stability Measuring System for Printed Circuits Substrates

A system is described for measuring length (width) changes in printed-circuit substrates under environmental (temperature/humidity) changes. A fixture for samples 20 inches in length is also described. Data are given for temperature coefficient and humidity coefficient of epoxy-glass substrates 0.010 in and 0.020 in thick, both bare and partially covered with an etched copper pattern. Two approximate mathematical models are discussed. One is static and linear; the other is time-dependent and nonlinear, but treated as a linear expansion. Additional Key Words for Information Retrieval--Circuit boards, circuit stability, dimensional stability, environmental effects, humidity coefficient of expansion, measurement of X-Y coordinates, substrates, temperature coefficient of expansion.