Research on contact characterization for microelectromechanical system (MEMS) switches has been driven by the necessity to reach a high-reliability level for micro-switch applications. One of the main failures observed during cycling of the devices is the increase of the electrical contact resistance. The key issue is the electromechanical behaviour of the materials used at the contact interface where the current flows through. Metal contact switches have a large and complex set of failure mechanisms according to the current level. This paper demonstrates the validity of a new methodology using a commercial nanoindenter coupled with electrical measurements on test vehicles specially designed to investigate the micro-scale contact physics. Dedicated validation tests and modelling are performed to assess the introduced methodology by analyzing the gold contact interface with 5 μm 2 square bumps at various current levels. Contact temperature rise is measured, which affects the mechanical properties of the contact materials and modifies the contact topology. In addition, the data provide a better understanding of micro-contact behaviour related to the impact of current at low-to medium-power levels.
Abstract. Mechanical properties of freestanding electroplated gold thin films were studied in relationship to their geometrical and microstructural properties. Three different techniques of characterization were used: nanoindentation, bulge tests and microtensile tests. Results were compared to literature and also discussed according to physical phenomena related to the elaboration process of the specimens like seed layer exodiffusion or internal stress state. The observed plasticity and failure mechanisms were found to be in good agreement with the literature and are consistent with the microstructure. The measured Young's modulus is slightly higher than expected, and SIMS analysis is exploited to explain such a high value.
This paper describes a new technique allowing the monitoring of damage in metallic freestanding thin films during micro-tensile test by using electrical characterization. After a presentation of the set-up, results obtained on Aluminium thin coatings by using two calculation methods for damage variable are presented and commented.
This paper deals with an identification methodology of the interfacial fracture parameters to predict the lifetime of a metallic brazed joint. The methodology is based on an experimental-numerical study whereby the optimal parameters are obtained. The experimental data, using the scanning electron microscope analysis, allowed approving that failure of the assembly based AuGe solder seems first to appear near the interfaces. These results were confirmed by micrographs analysis of the solder/insert and solder/substrate interfaces. Then, using shear test results and parametric identification coupled with a finite elements model (FEM) simulation, the damage constitutive law of the interfacial fracture based on a bilinear cohesive zone model are identified. The agreement between the numerical results and the experimental data shows the applicability of the cohesive zone model to fatigue crack growth analysis and life estimation of brazed joints.
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