Reliability and Failure Mechanisms of Direct Bonded Power Semiconductor Devices in Power Cycling Test

Direct bonding has recently been proposed as a cost-effective, yet reliable alternative to sintering for the die attach of power semiconductor devices. Here, the interconnection is formed by the backside metallization of the die and the metallization of the substrate by applying heat and pressure - without using any additional joint material. In this work, an analysis of the reliability and the occurring failure mechanisms of direct bonded samples in power cycling test (PCT) is presented. In PCT a maximum number of cycles to failure of up to 647,810 was achieved at a temperature swing of 104 K for samples employing standard direct bonded copper substrates (DBC) and insulated gate bipolar transistors (IGBT). To go one step further, the resulting failure mechanisms are separated on the basis of the PCT data, scanning acoustic microscopy (SAM), and cross-section analysis. As a result, three failure mechanisms can be determined: wire bond lift-off, degradation of the IGBT's backside metallization, and delamination of the DBC's top-side copper. For the failure modes related to the new die attach technology, a first quantification of the maximum number of cycles as a function of the temperature swing is presented.