Measurements of thermal expansion coefficients of anodized aluminium substrates for hybrid circuits

摘要

High-power substrates for hybrid circuits that combine aluminium with an anodic coating are highly efficient as the heat generated from chips mounted on the coated substrates can be dissipated rapidly. However, due to the difference between the thermal expansion coefficients of the two materials, a large thermal tensile stress can be built up during heating of the substrate, which causes cracking in the coating and subsequently the loss of electrical integrity. In this investigation a simple method of measuring the thermal expansion coefficient for an anodic substrate is described. Measurements were taken from an aluminium/coating composite and the thermal expansion coefficient of the coating was determined using the principles of elementary mechanics.