Wedge bonding technologies: microstructure, mechanical properties and electrical properties of fine Al–Zn–Si alloy wire

Aluminum is widely used as a heavy current with thick wire and is also used for aerospace and automotive in recent years. In addition, Al wires usually apply to semiconductor with bonding wire process. In this study, the wire material contained Al-7 wt% Zn-0.3 wt% Si, called ZS703, with drawing and heat treatment to obtain 12 mil (300 μm) and 4 mil (100 μm) Al alloy fine wires. These wires form an isometric crystal structure, which resulted in hardness decrease with annealing heat treatment. After heat treatment, the grain size and elongation increased obviously. Regardless of the diameter of Al wires, the electrical measurements (I–V curve) indicated abnormal increase in resistance (platform zone of I–V curve) at a certain current. This result caused incandescence (the void effect and joule heat). After platform zone of I–V curve, the resistance of all Al wires increased and the fuse current decreased because of decreasing of electrical effective cross-sectional area. After chlorination, the mechanical properties of the wires did not change obviously for both of the 4 mil Al wires (ZS703 and ZS703H), but elongation decreased significantly. Especially for ZS703H wire, the wires were brittle due to poor resistance to chlorine. In electrical analysis, the thin film formation of Al(OH)₃ was found that increased the cross-sectional area of effective conduction. As a result, the resistance of the Al wires decreased before incandescence phenomenon, and the fusing current decreases because of melt-void effect of current.