Observing In Situ Degradation of Metallized Aluminum Nitride Substrate by Acoustic Emission and Digital Image Correlation

Metallized aluminum nitride produced by active metal brazing (AMB-AlN) substrates is commonly used in power modules for heat dissipation but is susceptible to damage under large temperature variations. While previous studies have used thermal cycling tests ranging from -40 to 250 degrees C, in situ observations of degradation in AMB-AlN have not been reported. In this work, internal cracking and 3-D deformation of AMB-AlN substrates were monitored by acoustic emission (AE) and digital image correlation (DIC) methods, respectively, throughout successive thermal cycles. The AMB-AlN substrates were significantly delaminated after eight thermal cycles. In the first five cycles, negligible deformation and delamination were observed by 3-D DIC and scanning acoustic microscopy. The cracks detected by AE produced low-amplitude signals only around -40 degrees C. From the sixth to eighth cycles, the AE signal increased rapidly with the clear deformation of the substrate and depended on the temperature. A good correlation was found between the accumulated number of cracks detected by AE and the height of the Cu delamination from the substrate determined by DIC. In light of these findings, the delamination of the AMB-AlN substrate was attributed to the propagation of cracks in the substrate and their interconnected growth.