Development of capillaries for wire bonding of low-k ultra-fine-pitch devices

Although wire bonding has been a well-established technology for many years, the bonding tool design becomes more complex and the process is very sensitive for wire bonding of low-k ultra-fine-pitch microelectronics devices. In this study, two different types of external transition profile were considered in order to use lower ultrasonic-generator power for preventing pad damage. The ultrasonic vibration displacements of the capillaries were measured using a laser interferometer. The measurement results revealed that the amplification factor (the ratio of the vibration displacement at the capillary tip to that at the transducer point) of a capillary with a small radius transition between the bottleneck angle and the main taper angle was 37% higher than that of a capillary with a sharp transition, and this led to satisfactory results in terms of ball size, ball height, ball shear and stitch pull. To solve the ball lift problem for wire bonding of low-k ultra-fine-pitch devices, optimization of the capillary internal profile was attempted to improve bondability. Actual bonding responses were tested. Compared to a standard design, a capillary with a smaller chamfer angle, a larger inner chamfer and a larger chamfer diameter could increase the percentage of the intermetallic compound in the bond interface. Metal pad peeling and ball lift failures were not observed after an aging test.