Test methodology for durability estimation of surface mount interconnects under drop testing conditions

This paper presents a generic methodology to determine the durability of surface mount interconnects in electronic assemblies, under drop loading conditions. Damage accumulated in the interconnects due to repeated drops is quantified in terms of local Printed Wiring Assembly (PWA) response (flexural strain, strain rate, acceleration, number of flexural cycles), rather than the loading (total impact energy, orientation and number of drops). The advantage is that the results are more generic and can be extrapolated to different assemblies and different loading/orientation conditions. A damage estimation model, based on the observed failure mechanism and mode, is used to determine the durability of the surface mount interconnects under the applied loading history. The same model can be used to extrapolate the results to field conditions. A case study, using a simple specimen, is presented to demonstrate the proposed methodology. Failures are observed in the interfacial intermetallic layer of the component bond pad in the corner solder joint. The generality of the method is demonstrated by calibrating the model constants with in-plane drop tests and then successfully predicting the durability for an out-of-plane drop test. Thus, the approach and model constants are shown to be independent of impact orientation and boundary conditions.