The longitudinal ultrasonic vibration is used to bond the Au bumps for electronic packaging. Strip-type Au bumps on the chip and substrate are aligned in a crossed shape, and the ultrasonic is imposed on the chip to form the solid-state bond between the Au bumps.
To expect deformed shape of bump in micro-scale gold bump, F.E.M analysis and compression test of macro-scale aluminum bump is conducted. From analysis and experiment the shape of deformed stripe type Al bump is saddle configuration. This result is confirmed by measurement of deformed shape of gold bump using nano-scale 3D-profiler. As the configuration of the bump becomes similar to that of the saddle by plastic deformation, it provides larger contact surface. Deformed configuration also promotes solid-state bonding because the friction force is imposed on the contact surface similar to the wire bonding. Compared with the previous bonding method between the Au bump and planar pad, higher bond strength is obtained due to larger contact surface and friction force.
