Changes in microstructure of Al/AlN interface during thermal cycling

Abstract

Changes in the microstructure of the interface between an Al layer and an AlN plate during thermal cycling was studied to clarify the fracture mechanism of the Al/AlN interface. Observation of the interface with an ultra-sonic flaw detector indicated that a crack was generated at an edge of the Al layer after approximately 2000 thermal cycles. Cross-section observation using SEM-AsB (Angle Selective Backscattered electron detector) revealed that the crack propagated into the Al layer and ran along the interface. The grain size of Al around the crack tip is 0.2-1.0 μm. This size is much smaller than that in the initial Al layer, which was approximately 500 μm. It is considered that the refinement of Al grains was due to the accumulation of strains in the Al layer during the thermal cycling. Observations using SEM-AsB of higher magnification and TEM revealed that the crack was formed in the Al layer during thermal cycling, and propagated along the Al grain boundaries. SEM-EsB (Energy Selective Backscattered electron detector) image with a low accelerating voltage revealed that Si particles were precipitated in the Al layer during the thermal cycling. The Si particles were thought to be effective to hinder the progress of the refinement of Al grains. © 2008 The Japan Institute of Metals.