The Effect of Ultrasonic Frequency on Gold Wire Bondability and Reliability

This paper presents a systematic study on the effect of 120 KHz ultrasonic frequency on the bondability and reliability of fine pitch gold wire bonding to pads over an organic substrate with gold metallizations. The study was carried out on a thermosonic ball bonder that is allowed to easily switch between ultrasonic frequencies of 60 KHz and 120 KHz by changing the ultrasonic transducer and the ultrasonic generator. Bonding parameters were optimized through the design of experimental methodology for four different cases: 25.4 μm wire at 60 kHz, 25.4 μm wire at 120 kHz, 17.8 μm wire at 60 kHz, and 17.8 μm wire at 120 kHz. The integrity of wire bonds was evaluated by six response variables. The optimized bonding process was selected according to the multiattribute utility theory. With the optimized bonding parameters developed on one metallization for each of the four cases, 8,100 bonds were made on five different metallizations. The samples were then divided into three groups. The first group was subjecte...