Reducing Warpage of Printed Circuit Boards by Using Wavy Traces

Abstract

Printed circuit boards (PCB’s) often warp when subjected to temperature changes, associated with either the manufacturing process or the usage. In order to reduce the warpage, waviness was introduced in the electric traces. Model PCB’s were manufactured and tested. The elastic stiffnesses of the PCB’s were determined using a coupled experimental-analytical vibration method, whereas coefficient of thermal expansions (CTE’s) and warpage were measured by placing strain-gage instrumented specimens in an environmental chamber and varying the temperature. Unit cell finite element (FE) analyses of PCB’s with both straight and wavy traces were performed to predict thermoelastic behavior. Both experimental tests and numerical analyses conclude that the PCB’s with wavy traces warped approximately 40% to 60% less than the PCB’s with straight traces.