Fatigue life estimation of a bed-of-nails ultra-fine-pitch wafer level package using the macro-micro modelling approach

This paper presents package warpage and interconnect fatigue life estimates of bed-of-nails (BON) interconnect in a 20 mm by 20 mm package with 100 μm pitch. The modelling was carried out in two stages using the macro-micro modelling approach. The effect of BON orientation, as well as chip thickness and substrate CTE (coefficient of thermal expansion) on fatigue life is discussed. The results suggest that the substrate CTE will continue to be the key factor in determining the thermo-mechanical reliability of a large package with small interconnects.