LAUSR

Abstract Crack formation in Si 3 N 4 active metal brazing (AMB) ceramic substrates and delamination of copper layers on the AMB substrates subjected to temperature cycling from −40 to 250 °C were investigated to evaluate the reliability of these substrates under harsh environments. Acoustic scanning microscopy (ASM) observation of the Si 3 N 4 substrates with 0.30 mm thick Cu layers revealed crack formation beneath the corner of the copper plate after 100 cycles, whereas no cracks were detected on the Si 3 N 4 substrate with a 0.15 mm thick Cu layer, even after 1000 cycles. The residual bending strength of the Si 3 N 4 substrates with 0.30 mm thick Cu layers was 78% of the as-received substrate after 10 thermal cycles, and gradually decreased with an increase in the number of thermal cycles until ca. 65% of the initial strength after 1000 cycles. The Si 3 N 4 substrates with 0.15 mm thick Cu layers exhibited a gentler degradation of residual strength than those with 0.30 mm thick Cu layers. In contrast, the residual bending strength of AlN-AMB substrates with 0.15 mm or 0.30 mm thick Cu layers were reduced by 50% within only 10 thermal cycles. The depth of cracks developed during the thermal cycles was measured from the fractured surface of the Si 3 N 4 -AMB and AlN-AMB substrates. The crack-growth rate in the Si 3 N 4 -AMB substrates was much slower than that in the AlN-AMB substrates, which could account for the different degradation behavior of the residual bending strength.