Numerical and experimental analysis of thermosonic bond strength considering interfacial contact phenomena

Abstract

The theoretical equation of thermosonic bond strength involving interfacial deformation and microcontact phenomena is presented in this study. The constitutive equation of gold considering the ultrasonic softening mechanism was developed based on the thermosonic bonding experiments and coded into the FE software. The numerical model of bonding was established to estimate the surface exposure and the effective normal pressure. The real contact area was calculated by a microcontact model. Accordingly, the nominal bond strength can be obtained and verified by the experimental data. It is found that a better conjunction exists at the edge of the contact area because large surface exposure is produced there, which is also proved by the SEM image of a sheared ball bond. Increasing the bonding force or the ultrasonic power will increase the interfacial plastic deformation, the nominal and real contact areas, but decreases the effective normal pressure. The contact ratio increases to a maximum with the increase in the bonding force, and then decreases while it continues to decrease with the increase in the ultrasonic power. In addition, both the stress analysis and experimental result show that cratering and damage to the pad structure are easily produced below the edge region of the contact area under an excessive bonding force or ultrasonic power.

In-Situ Observation of Adhesion Behavior During Ultrasonic Al Ribbon Bonding

“…The peripheral bond area was between Area A and Area C even in the final stage. Areas B1 and B2 must consist of thin layers formed by some material reaction between Area A and the silica substrate [14,22,[39][40][41][42]. Figure 13 illustrates the mechanisms of increasing adhesion area.…”

“…Because the bonding interface is typically invisible, it is not simple to directly observe the bonding interface during the bonding process. Therefore, in general, off-line observations of the bonded interface have been implemented [1,2,11,12,14,15,17,19,22,28]; in lieu of this, numerical analyses of bonding processes have been performed [4,13,18,[34][35][36][37][38][39]. A few studies Annealed pure aluminum ribbon made by Tanaka Denshi Kogyo, Japan was used in the present study.…”

Modeling of microstructure evolution during cold wire drawing process and properties determination

“…Hence, understanding the bond pad cratering deformation is important to increase reliability. The failure mode of interfacial delamination/stress induced cratering on the Al pad was investigated by He et al [145]. To understand the reasons for the Al squeeze a nonlinear finite element method was adopted and the complete stressstrain behavior of the free air ball was modelled using a power law [146].…”