Simulation of ball bonding on various bond pad structures

Various integrated circuit bond pad structures in aluminum-silicon dioxide (Al-SiO ₂ ) metallization are modeled, with ball bonding stresses applied in static or dynamic simulations. This work follows from our EPTC 2012 paper. Of special interest is the apparent stress reduction in bond pads that mitigates top SiO ₂ film cracking during wirebond of ON Semiconductor's more robust and circuit under pad (CUP) structures having thin top metal. Both gold (Au) and copper (Cu) materials are simulated as bond ball types. Static simulations are helpful to indicate the stress locations, while the dynamic simulations reveal how bonding stress values are affected by bond pad structures. Film thickness decrease directly increases stress coupling into bond pad sub-layers, making SiO ₂ cracks more likely during bonding. Dynamic simulations indicate that Al CUP features surrounded by SiO ₂ result in more stress reduction than removing the Al features of the first sub-layer. Bond pad stress increases more than 2 times when changing from gold (Au) to copper (Cu) ball bond, due to the materials properties change alone, not considering the increased ultrasonic power required for Cu bonding.