Influences of material and structural factors on the stress conditions in Cu/low-k chips during Cu wire bonding

An incrementally coupled mechanical-ultrasonic finite element model is developed to model the thermosonic Cu wire bonding process on Cu/low-k chips, in order to study the influences of key process and design parameters on the stress conditions in the chips. The model takes into account of both mechanical oscillation effects and the softening effects of ultrasounds, and stresses developments during the whole wire bonding process can be obtained through an incrementally coupling scheme. With the model developed, the stress conditions have been numerically analysed for various material and geometrical designs, including elastic modulus of low-k material, number of Cu/low-k layer, and the application of passivation. The results obtained can be useful in guiding the designs of Cu/low-k chips and developments of their copper wire bonding process.