This paper focuses on the numerical analysis of pull test reliability of gold wires bonded on the Cu/low-K wafer. Prior to wire pull, transient analysis of the complete wirebonding process, which involves both impact and ultrasonic vibration stages, is performed to allocate residual stresses within the wire and the Cu/low-K structure. After wirebonding, fracturing of the wire subjected to a pull load is modeled using the eroding technique so that failure patterns and bonding strength of the wire can be investigated. The analysis applies the explicit time integration scheme, which is feasible in dealing with nonlinear transient structural behavior. Parametric studies show that as the yield stress of the low-K material decreases, the pull force reduces significantly. Furthermore, the pull force increases as the bond force increases but not very significantly

Transient simulation of wire pull test on Cu/low-K wafers

Modeling of copper wire bonding process on high power LEDs

Cu wire is increasingly used in microelectronics packaging manufacturing. In the present paper, the deforming procedure of 100 μm diameter Cu free air balls (FABs) is studied using experimental and finite element (FE) methods. Experimental results show that the superimposed ultrasound can make the Cu FAB softer. Then a non-linear FE model is built to study the deforming process of the Cu FAB. Numerical experiments have been carried out to quantify the effects of superimposed ultrasound on the constitutional model of Cu FABs. An improved power law material model is then established to take into the dynamic acoustic softening effects. A good consistency is achieved in numerically predicted and experimentally obtained deformations of the Cu FAB under various ultrasonic intensities.

Effect of superimposed ultrasound on mechanical properties of copper

As the trend for semiconductor packaging is heading towards BGA and flip chip interconnection methods, the conventional wire bonding process still dominates the industry primarily due the flexibility of wire bonds. The reliability of the bonded wires is assessed through wire bond shear test. In this study, the effects of shear ram speed on the stress response of bonded wires during wire bond shear test were investigated. The stress response of two wire materials, gold(Au) and copper(Cu) at varied shear ram speed were evaluated.A 3D non-linear finite element model was developed for the simulation. The shear ram speed of 100 µm/sand 1mm/s were used in this study. The results showed that the shear ram speed has significant effects on the stress response of the bonded wire. The simulation was done using Ansys version 11.

Shearing Speed Induced Stress Comparison on Gold and Copper Ball Interconnection

Thermosonic wire bonding is a common fabrication process for connecting devices in electronic packaging. However, when the free air ball (FAB) is compressed onto the I/O pad of the chip during bonding procedure, chip cracking may occur if the contact pressure is too large. This study proposes an effective simulation technique that can predict the wire ball geometry after bonding in an accurate range. The contact force obtained in the simulation can be used for possible die cracking behavior evaluation. The simulation in this study used the explicit time integration scheme to deal with the time marching problem, and the second-order precision arbitrary Lagrangian-Eulerian (ALE) algorithm was used to deal with the large deformation of the wire ball during the bonding process. In addition, the equilibrium smoothing algorithm in LS-DYNA can make the contact behavior and geometry of the bonding wire almost the same as the experiment, which can also significantly reduce the distortion of the mesh geometry after remeshing.

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Simulation of Wire Bonding Process Using Explicit Fem with Ale Remeshing Technology

Comprehensive dynamic analysis is performed in this paper to simulate wirebonding on Cu/low-K wafers, which involves both the impact and the ultrasonic vibration stages. After the impact stage, the contact region between the pad and the gold ball is welded to allow subsequent ultrasonic vibrations to take place. Parametric studies are carried out to investigate structural responses of the Cu/low-K layer due to variation of the moduli of Cu/low-K components.

Chang-Lin Yeh

Papers

Comprehensive dynamic analysis of wirebonding on Cu/low-K wafers