Failure mechanisms of aluminum bondpad peeling during thermosonic bonding

Aluminum bondpad peeling was observed in a newly developed thermosonic wirebonding process for chip-on-board assembly. Through detailed failure analysis and with the help of finite element analysis on stress simulation, the true root cause of the peeling is identified. It is found that the true root cause is the effect of skidding force as a result of the constrained movement of the bonding tool as bonding is done on a chip assembled in a plastic casing. With a change in the bonding tool movement, the peeling phenomenon is completely eliminated.