A Simple Method for Characterizing the Bondability of Metallization Surfaces

A probing technique is described which measures breakdown voltages of contaminating films on metal surfaces. These breakdown voltages are correlated with the bondability and wettability of the surfaces. The probe setup consists of a fine gold wire with a ball terminal and a tungsten whisker. Three examples are described. The breakdown voltage on Al metallization on a Si chip and on plated Ag film on a leadframe both correspond to the ease of Au wire bonding. In contrast, the Au-Si eutectic layer demonstrating a large breakdown voltage features poor solderability and low bonding reliability. The An ball probe is confirmed to be a convenient tool for quality control in thin-film manufacturing and device assembly processes.