Simulation of shear tests on bond wedges for the assessment of the bonding quality of new thick wires on aluminum basis
Computer-Aided Design of Materials and Simulation of Materials Behaviour from Atomic to Microscopic Scale
Final Report Abstract
Wire bonding is a micropressure welding process in which similar or dissimilar materials are bonded together in the solid state by the application of pressure, temperature and/or ultrasound for a limited period of time. The shear test, which is preferred because of its simplicity of application, is considered to be a qualifier for an adequate bond, especially for thick-wire bonds. The criteria for the shear test are summarized in DVS Merkblatt 2811. However, it is not sufficiently clear to what extent the recommendations presented with regard to the shear code can be transferred to the various newly available wire materials. Therefore, in order to improve the possibility of interpretation, new fundamentals are to be created within the scope of this project. These result, among other things, from interrupted shear tests with subsequent metallographic analysis by means of cross-sections and instrumented indentation testing. It was found that the hardening and softening processes during the shear test are strongly material- and alloy-dependent. The high-purity Al H11 wire, after hardening in the first part of the shear test, showed relative softening as it progressed. In the case of an alloyed and significantly finer-grained AlMg0.5 wire, pure hardening was confirmed in the course of the shear test. It should be noted that this difference in strain hardening behavior has an influence on the damage progression and should be taken into account in the interpretation, especially of shear codes. In the case of the high-purity aluminum wire Al H11, failure in the interface or interfacial area is significantly less likely than for the highly hardening AlMg0.5 wire. Furthermore, it was shown that for an aluminum-encased copper wire (trade name: CucorAl PLUS), complete shearing is not possible due to the high strength difference between the two materials. In parallel to the experimental investigations, simulation models were created using the open-source software package FEniCS. In doing so, it was possible to build on previous work on damage mechanics by the external cooperation partner Abali, in which the damage parameter model according to Lemaitre was used. In addition, an updated Lagrangian formulation for large deformations was implemented for the present case. Further, it was found that the deformations were so large that they led to convergence problems due to element deformation. Numerical robustness has been increased by implementing an approach for remeshing. The calibration of the Lemaitre damage parameters was performed by means of uniaxial tensile test and corresponding simulation of the same. Here, the function of the implementation in the FEniCS environment was validated at the same time. Furthermore, first simulations of the shear test showed that a consideration of the triaxiality beyond the formulation made by Lemaitre is necessary. For this purpose, a limitation of the damage development as a function of the triaxiality according to Bao et al. was introduced. Finally, the different approaches were compared and their strengths influences were shown.
Publications
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Numerical Simulation of a Wire Bond Shear Test Using Nonlinear Adaptive Remeshing. 2022 23rd International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems (EuroSimE), 1-3. IEEE.
Kuttler, Simon; Wittler, Olaf & Schneider-Ramelow, Martin
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Determination of Lemaitre Damage Parameters for Al H11 Wire Material. 2023 24th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems (EuroSimE), 1–3.
Kuttler, Simon; Abali, Bilen Emek & Wittler, Olaf
