Free drop test performance of portable IC package is a key reliability criteria for handheld products. Various experimental test methods are widely applied to measure the drop test response and to test for visual and electrical failures after the drop test. However, the experimental data we can collect is very limited, especially for the impact of stress wave propagation and distribution to the component and device.For understanding the physical transient dynamic failure problem, modeling is an effective method that provides details of the dynamic stress wave and the response at any time, any cross-section or position.

This paper investigates several issues in finite element modeling of electromigration in solder joints: current density and thermal stress singularities; negative divergences of atomic fluxes due to electron current and thermal stresses; and submodeling accuracy. A copper post wafer level package is used as a test vehicle for simulation. Coupled electrical-, thermal-, and mechanical finite element modeling is performed. Results show that the values of maximum current density in solder balls significantly depend on finite element mesh sizes, indicating a singularity exists. Negative values of the divergences of atomic fluxes due to electron current and thermal stresses are obtained under certain loading conditions. Submodeling presents accurate results if cut boundary is appropriately chosen.

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