Study on failure mode and mechanism of bond pad under Cu ball bonding process using wire pull test and finite element modeling

In this work, wire pull test combined with finite element analysis (FEA) were conducted to investigate failure mode and failure criterion for bond pad reliability assessment under Cu wire bond process. Pull test was conducted for bonded Cu wires with different pull locations changing from the first ball bond to the second wedge bond. Failure forces were recorded and failure site and modes were studied. The effect of pull location on failure mode was observed. Failure modes change from wire neck broken, ball lift, pad peel to wedge broken when pull location is changing from the first bond towards the second bond. Based on wire pull test and FEA simulation results, failure mechanism and failure criterion were developed for different Cu wire bond failure modes. The effects of wire loop height on pull test results and modeling stress were also investigated.