An ultrafast mechanical test system for bending fatigue studies of multilayered electronic components

Power electronic devices are subjected to high temperature fluctuations during the service life. One of the reliability concerns of the devices is failure of the multilayered substrates due to thermo-mechanical fatigue with a predominant cyclic bending loading mode. In this investigation an ultrafast mechanical test system for assessment of fatigue lifetime of multilayered structures in bending mode is presented. An ultrasonic testing system operating at 37 kHz in combination with a three point bending device was used to excite specimens consisting of direct bonded copper substrates (DBC) to transversal vibrational loading. Lifetime curves of DBC specimens could be obtained in the high cycle fatigue range. The dominant failure modes of DBC substrates were cracking of the ceramic and delamination of the copper. FEM simulations were conducted to analyze the loading conditions and the distribution of the stress and strain in the Cu and Al2O3 substrate layers. The proposed method provides an extremely time saving reliability assessment system for multilayered structures in comparison with conventional thermal cycling tests. However the failure mechanisms involved in mechanical and thermo-mechanical fatigue should be taken into consideration.