A footprint study of bond initiation in gold wire crescent bonding

The morphological features of the crescent bond footprints on the substrate after peeling the wire off were studied to gain an understanding of the effect of process parameters on the crescent bond formation. In the absence of any ultrasonic energy, metallurgical bonding initiated at the peripheral regions of the crescent bond. The bond strength improved at higher substrate temperatures and higher bonding force which promoted higher shear deformation of the substrate. The application of ultrasonic energy drastically improved the growth of micro welds along the bond interface and produced micro weld patterns on the footprint that are characteristic of the level of ultrasonic energy applied. The effect of these process parameters on the mechanisms of crescent bonding are discussed.