Drop impact test - mechanics & physics of failure

This paper deals with the mechanics and physics of board-level drop test with the intention of providing the fundamental understanding required to design and analyse the results of a drop test. Three finite element analyses were performed to understand the physics of failure in board-level drop impact: (i) velocity impact of a PCB - modeled as a beam; (ii) velocity impact of a PCB with centrally mounted package - modeled as a beam; (iii) velocity impact of a drop assembly - solid elements with submodeling. Parametric studies have been performed on the solid model for a number design variables: drop height, fall plate thickness, PCB length, PCB thickness, solder bump height, solder bump size, solder bump number, and impact cone diameter. Differential flexing as well as inertia has been identified as the key failure drivers. In both cases, the transverse stress, S33, is the most critical stress component. Geometrical stress concentration and intermetallics of the interconnection are critical in the impact strength of interconnection.