Numerical Study on the Effects of Bond Parameters on Thermosonic Bond Strength

Thermosonic ball bonding is a popular joining technique in microelectronic interconnect. In this paper, the effects of bonding parameters on the bond strength are investigated mainly using the finite element method. The complete ball bonding process including both the impact and ultrasonic vibration stages is modeled, and the strain rate sensitivity of the gold ball and pad is considered. Five variables were defined to establish the relationship between bonding interfacial deformation and bond strength: the segment extension epsiv_i, the ratio of segment extension k_i, the contact ratio S, the sum of segment extensions in bond interface Sigmaepsiv_i , and the ratio of the sum of segment extensions k . It was found that the bond strength at the bond interface increases from the center to edge; the bond strength increases with the growth of the initial impact velocity; the bond strength increases firstly with the increasing of the bonding time, then decreases; and there exists an appropriate temperature to let the bond strength to be maximum. Finally, the simulation is compared with the experimental results.