Our wire bonders are K&S 8020 with ultrasonic frequency 120 KHz. In our wire bonding process, ball bond short to the next ball bond (pad opening 75 x 75 um, pad pitch 90 um) was observed. However, this kind of bond short happened on random bond pad and the defect level is around 2000 - 3000 ppm, it is unlikely for us to simulate the ball bond short. The ball bond(squashed ball) with bond short looks like a golf bond and the short is probably caused by spitting the free air ball out of the cap and not sitting the ball into the cap. When the ball touch down to the bond pad, the squashed ball (golf ball) did not sit in the pad center. Thus this squashed ball shorts to the next ball bond.