Effect of high temperature cycling on both crack formation in ceramics and delamination of copper layers in silicon nitride active metal brazing substrates

Abstract

Crack formation in Si3N4 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 Si3N4 substrates with 0.30mm thick Cu layers revealed crack formation beneath the corner of the copper plate after 100 cycles, whereas no cracks were detected on the Si3N4 substrate with a 0.15mm thick Cu layer, even after 1000 cycles. The residual bending strength of the Si3N4 substrates with 0.30mm 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 Si3N4 substrates with 0.15mm thick Cu layers exhibited a gentler degradation of residual strength than those with 0.30mm thick Cu layers. In contrast, the residual bending strength of AlN-AMB substrates with 0.15mm or 0.30mm 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 Si3N4-AMB and AlN-AMB substrates. The crack-growth rate in the Si3N4-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.