Mechanical Modelling of Electrically Conductive Adhesives for Photovoltaic Applications

Electrical conductive adhesives are a promising alternative to common soldering technologies. Advantages are lower process temperatures (<150°C), meaning lower mechanical stresses, relatively simple process technology with opportunity for automation and environment-friendliness, since there is no lead and flux necessary. This paper focuses on the mechanical characterization for finite element simulation. For this purpose samples are prepared for mechanical tests to identify time and temperature dependent material properties. On the assumption of a thermo-rheological simple material, master curves are constructed and parameters for a linear-viscoelastic model are identified. Additionally the thermal expansion behavior is measured in order to obtain the opportunity to simulate temperature induced strains accurately. The material models are applied to analyze stress situations in thin film photovoltaic modules were back contact and cross bar contacting is done with conductive adhesive material. A comparative study between soldering and conductive gluing is presented to quantify the reduction of mechanical stresses in back contact solar cells.