Dynamic strain and chip damage during ultrasonic flip chip bonding

The distribution of strain under a bump generated by ultrasonic flip chip b onding was dynamically measured using two-directional strain gauges. The st rain gauges were designed to be sensitive in both the horizontal and vertic al directions. Dynamic strains generated at the surfaces of the substrate a nd the chip were measured. The distribution of strain during Au bump format ion was also measured and compared with that during flip chip bonding. Stra in variations with time and position have been successfully measured during the bonding process composed of pre-press, ultrasonic and post-press steps . The strain field during ultrasonic application of flip chip bonding is fo und to be divided into two regions, while the strain field during Au bump f ormation is divided into four regions. Generation of chip damage such as cr ack and pad delamination, which was sometimes observed in ultrasonic flip c hip bonding, is explained in term of the strain field in the bump area. It is shown that a high pressing load is effective to avoid damage of the chip surface.