The use of implicit mode functions to drop impact dynamics of stacked chip scale packaging

The dynamic response of Sn3.5Ag solder balls interconnecting bilayered chip scale packages under board-level drop impact is studied in this paper. The structural response of the solder balls was obtained by finite element simulations of an elastic model of board-mounted assembly under the JEDEC-defined half-sine acceleration profile. The distribution of the von Mises stress and peeling stress were examined in the critical solders. The Hilbert-Huang Transform (HHT) technique was then used to calculate the implicit mode functions (IMFs) of the dynamic response at the critical solder balls. As each IMF carries important amplitude and frequency information intrinsically retained to the processed signals, the IMFs enable a preliminary analysis about questions such as how much of the solder stress buildup is contributed from board vibrations.