Comparison of interface evolution of ultrasonic aluminum and gold wire wedge bonds during thermal aging

Ultrasonic gold and aluminum wire wedge bonding are widely used for electrical and signal interconnections of the integrated circuit chip packages. In this paper, based on the metallurgical theories and thermal aging test methods, the long-term thermal reliabilities of gold and aluminum wire wedge bonding on aluminum and Au/Ni/Cu pads, were investigated, respectively. At 200 °C, the Au/Al bond interfaces evolved little when the storage time was less than 48 h; with the aging time increasing, the interfacial intermetallic compounds (IMC) grew up from the pad (vertical growth); the primary compounds were Au5Al2 near the bond toe and heel, and Au2Al at the periphery. Then, the thickness of IMC was unchanged, and extended horizontally (lateral growth), Au5Al2 transformed into more stable Au2Al phase, furthermore, cracks ran through the interface of the gold and IMC because of severe Kirkendall voids. However, Al/Au bond was more stable, and the IMC grew slowly. The purple plague AuAl2 resulted in interfacial cracks. Moreover, the bond wire was filled with cavities.