The experimental measurement of wire sag of long wire bonds for 3-dimensional and multi-chip module packaging

Concerns about wire sweep and wire sag on the applications of the 3-dimensional packaging technology in the multi-chip module systems have been highly raised recently. Because the interconnection distance of the multi-chip modules is usually longer than that in single-chip system. It had been proved by authors' previous studies that the longer the bond length and the higher the bond height of a wire bond, the smaller the sweep stiffness of the bond system. The lower sweep stiffness of the wire bond will always cause higher risk of wire sweep which may induce device shorting and/or current leakage leading to IC failure. Therefore, most of the studies in the literature focus on how to precisely predict the wire sweep for a specific profile of wire bond. For 3-dimensional and multi-chip packaging, excessive wire sag can lead to wire touch to the lower layer and then cause short circuit and failure of chips. This paper will mainly study the wire sag problem for long wire bonds applied in 3-dimensional and/or multichip module packaging. A definition of the sag stiffness of a wire bond will be proposed to represent the sag resistance of a specific profile of wire bond. Furthermore, the wire sag experiments of wire bonds will be conducted to verify with numerical analysis.