3D Multi Scale Modeling of Wire Bonding Induced Peeling in Cu/Low-k Interconnects: Application of an Energy Based Criteria and Correlations with Experiments

Abstract

Amongst solutions to connect the die to the package, thermosonic wire bonding process remains widely used. However, the introduction of low-k dielectric materials, and the feature size decrease of IC chips to follow Moore's law, pose great integration challenge.This paper aims to demonstrate the compliance of the proposed modeling approach with the aids of experimental validations. 3D multi scale simulation of both bonding process and wire pull test is carried out. Using a previously validated homogenization procedure to include pad structure description even at the global scale, stress fields acting in the copper/low-k stack are evaluated. The modeling strategy also includes an in-house developed energy based analysis.For the experimental part, a wide range of wire bond trials have been performed in order to qualify the 65-nm technology node. On behalf of that, several bond pad architectures have been implemented and wire bonded on a test vehicle. It was found a significant effect of the copper/low-k design on peeling failure rates, in particular with severe bonding conditions. In this paper, typical modeling results are presented. Contrary to stress based one, the energy based analysis shows a better ability to forecast the observed failed interface. From simulation results obtained, it is confirmed that the bonding process plays major role in the peeling failure, despite the fact that most of them are observed during the wire pull test. Failure mechanisms are also proposed. Then, the implemented pad structures are evaluated and analyzed. Both general trends and architecture ranking are provided. Simulations are then faced to experimental results and a full agreement is found. The complementary nature of the energy based failure criteria is again highlighted through a clearer discrimination of the tested structures.Finally, the simulation procedure with confirmed experimental results demonstrates its ability in design and process optimizations by providing a better understanding of pad peeling failure mechanisms.

Fine and ultra‐fine pitch wire bonding: challenges and solutions

“…Finite element analysis (FEA) is a useful tool to investigate processes (Sun and Zhong, 2002; Luan et al , 2003; Tee et al , 2003a; Zhong and Yip, 2003; Tee et al , 2004; Tee and Zhong, 2004a, b; MacKerle, 2005). There is increasing research on applying FEA to wire‐bonded packages (Chen, K.M., et al , 2006; Ishiko et al , 2006; Saiki et al , 2006; Fiori et al , 2007a, b; Viswanath et al , 2007; Chen et al , 2008; Gao et al , 2008; He et al , 2008).…”

Numerical Analysis of the Reliability of Cu/low-k Bond Pad Interconnections Under Wire Pull Test: Application of a 3D Energy Based Failure Criterion

“…Finally, the proposed method could help in many application cases [15]. The described simulation method is useful for different problematics such design optimization and process development.…”

“…Same consequences are observed during the bonding process during which the pressure and ultrasonic displacements applied between the pad. Indeed, the wire bonding process itself cause micro-cracks [15] and to weaken the Cu/Low-k stack.…”

Package induced low-k delaminations: Numerical developments and experimental investigations to address FEBE compatibility fracture phenomena.

“…This method is quite attractive since both the nucleation and the propagation are included in the model. The second one has been in-house developed, the named Nodal Release Energy (NRE) method [9] (inspired from Area Release Energy technique [10]) has demonstrated its robustness and efficiency through similar applications [11][12]. However, since a virtual crack must be initially assumed, only propagation phenomenon is addressed by this method.…”