Transactions of Nonferrous Metals Society of China
JOURNAL OF RAILWAY SCIENCE AND ENGINEERING
|Vol. 15 No. 4 August 2005|
（School of Mechanical-Electronical Engineering, Central South University,
Changsha 410083, China）
Abstract: Nickel plated on a copper plate was selected as a bond surface for ultrasonic aluminum wedge bonds, and a series of experiments were carried out to study the microstructure characterization of the wedge bond interface. Bond lift-off characteristics were studied by using scanning electron microscopy(SEM) with EDS-test. Characteristics of input power of PZT transducer were analyzed by the driving electric signal measured with GDS-820 Digital Oscilloscope. The results show that the pattern of partially bonded material at the Ni-Al interface of ultrasonic wedge bonds exposed by peeling underdeveloped bonds simulates a ridged torus with an unbonded central and external region rubbed along pulse direction. Bond strength is located between the severely ridged torus and the non-adhering central and external area of the bond. For the same machine variables, ridge-peak and transforming ultrasonic energy of the first wedge bond are greater than that of the second wedge bond. For constant other machine variables, with the increasing load, the total area of bond pattern increases in size, and minor axis of torus extends major axis; with the increasing time, the ridged periphery spreads a whole torus, and the ridged location of the bonded region moves closer to the bond center; the sliding trace and the ridge-like of the bond pattern strengthen when more power is applied. Moreover, the machine variables have an optimal range for microstructure characteristics.
Key words: Ni/Al; electronics packaging; wedge bonding; microstructure; ultrasonic