Thermosonic wire bonding process simulation and bond pad over active stress analysis

In this paper, a transient non-linear dynamic finite element framework is developed, which integrates the wire bonding process and the silicon devices under the bond pad. Two major areas are addressed: one is the impact of the assembly 1^st wire bonding process and another one is the impact of device layout below the bond pad. Simulation includes the ultrasonic transient dynamic bonding process and the stress wave transferred to the bond pad device and silicon in the 1^st bond. The Pierce strain rate dependent model is introduced to model the impact strain hardening effect. Ultrasonic amplitude and frequency are studied and discussed for the bonding process. In addition, different layouts of device metallization under the bond pad are analyzed and discussed for the efforts to reduce the dynamic impact response of the bond pad over active (BPOA) design. Modeling discloses the stress and deformation impacts to both wire bonding and pad below the device with strain rate, different ultrasonic amplitudes and frequencies, different friction coefficients, as well as different bond pad thickness and device layout under the pad. The residual stress, after cooling down to a lower temperature, is discussed for the impact of substrate temperature.