This paper focuses on the mechanical properties of polydimethylsiloxane (PDMS) relevant for microelectromechanical system (MEMS) applications. In view of the limited amount of published data, we analyzed the two products most commonly used in MEMS, namely RTV 615 from Bayer Silicones and Sylgard 184 from Dow Corning. With regard to mechanical properties, we focused on the dependence of the elastic modulus on the thinner concentration, temperature and strain rate. In addition, creep and thermal aging were analyzed. We conclude that the isotropic and constant elastic modulus has strong dependence on the hardening conditions. At high hardening temperatures and long hardening time, RTV 615 displays an elastic modulus of 1.91 MPa and Sylgard 184 of 2.60 MPa in a range up to 40% strain.
A unified viscoplastic constitutive law, the Anand model, was applied to represent the inelastic deformation behavior for solders used in electronic packaging. The material parameters of the constitutive relations for 62Sn36Pb2Ag, 60Sn40Pb, 96.5Sn3.5Ag, and 97.5Pb2.5Sn solders were determined from separated constitutive relations and experimental results. The achieved unified Anand model for solders were tested for constant strain rate testing, steady-state plastic flow and stress/strain responses under cyclic loading. It is concluded that the Anand model can be applied for representing the inelastic deformation behavior of solders at high homologous temperature and can be recommended for finite element simulation of the stress/strain responses of solder joints in service.
A viscoplastic constitutive model, the Anand model, in which plasticity and creep are unified and described by the same set of flow and evolutionary relations, was applied to represent the inelastic deformation behavior for solder alloys. After conducting creep tests and constant strain rate tests, the material parameters for the Anand model of the Pb‐rich content solder 92.5Pb5Sn2.5Ag were determined from the experimental data using a nonlinear fitting method. The material parameters for 60Sn40Pb, 62Sn36Pb2Ag and 96.5Sn3.5Ag solders were fitted from the conventional model in the literature where plasticity and creep are artificially separated. Model simulations and verifications reveal that there is good agreement between the model predictions and experimental data. Some discussion on this unified model is also presented. This viscoplastic constitutive model for solder alloys possesses some advantages over the separated model. The achieved Anand model has been applied in finite element simulation of stress/strain responses in solder joints for chip component, thin quad flat pack and flip‐chip assembly. The simulation results are in good agreement with the results in the literature. It is concluded that the Anand model could be recommended as a useful material model for solder alloys and can be used in the finite element simulation of solder joint reliability in electronic packaging and surface mount technology.
The Low Temperature Joining Technology (L T JT) creates silver joints by a sintering process. It is an alternative die-attach technology to soldering. To initiate the sintering process the temperature has to be raised above � 215°C. The quality of a sintered joint is strongly enhanced by applying pressure to the specimen during the process, thus reducing the porosity in the sintered material. After the interconnect process, residual stresses occur in the sintered material, as well as in the joined parts.The examined specimen was a silicon MOSFET attached to a copper substrate at a sintering pressure of 50 MPa. The scope of this paper is to provide information about residual stress after production and thermo-mechanical stresses during thermal cycling. The focus is put on the investigation of the reliability of sintered silver by simulation.
The present work investigates the UV stability of the dye-sensitized solar cell (DSC) by parametrical investigation of the material influence on UV stability. UV illumination has been observed to cause degradation by slow photocatalysis in the DSC. Photooxidized impurities represent an unwanted side reaction with the redox pair of the electrolyte as the released electron will deplete the triiodide concentration. A study on the DSC cell was carried out with intermediate electrical characterization by cyclic voltammetry (CV) and electrical impedance spectroscopy (EIS) to map the influence of UV illumination as a function of the H2O concentration in the electrolyte, the plate distance and the triiodide concentration. The results show that the H2O content has a detrimental influence on the DSC stability during UV illumination. A higher concentration of triiodide can buffer the reaction with impurities, so that a longer-term stability is achieved. A recovery of triiodide in UV aged cells with either no remaining triiodide or with such a low concentration that the cell current has been diffusionlimited, was seen during CV to -0.75 V under illumination. The reappearance of triiodide was accompanied with a production of hydrogen bubbles, which was related to the H2O content in the electrolyte and the exposure to UV. Our approach can be used to test the purity and the UV stability of various electrolytes.
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