A Comparative Study of the Failure Mechanisms Encountered in Drop and Large Amplitude Vibration Tests

Abstract

Drop tests are commonly used to study the reliability of components under shock loading conditions. However, to overcome some of the drawbacks inherent to drop testing systems, the applicability of large amplitude vibration test to reliability assessment has been investigated by comparing the vibration behaviors and failure modes of component boards in the two tests. The component boards and the drop test parameters are in accordance with the JESD22-B111 standard and the parameters of the vibration test are adjusted to produce equivalent loading. The drop and vibration tests were compared by evaluating first the loading conditions with the finite-element method as well as experimentally. The results show that by applying the harmonic vibration loadings to component boards at their natural resonance frequencies very similar loading to drop testing can be achieved even though there are some differences in the bending behavior of the boards during testing. The vibration amplitude was found to be the key parameter determining the type of failure mode in the vibration test. The failure modes in the vibration test were found to be the same as those in the drop test: failure of the reaction layers on the component and board side of the solder interconnections and failure of the resin coated copper layers of the printed wiring boards. In addition, failures of copper traces were observed in vibration tested assemblies. The cracking of the bulk solder was observed with small vibration amplitudes (2.3 mm), but the failure mode changed to intermetallic cracking -as in drop testing - once the vibration amplitude was increased to 4.7 mm. According to the results of this study the vibration test can be employed in studying failure modes and mechanisms under shock loading conditions.