Orthotropic viscoelastic characterization of thin woven composites by a combination of experimental and numerical methods

Electric mobility is the driving force for the development of power electronic devices embedded in printed circuit boards (PCBs). Fast charge of batteries generates large increase of temperature in PCBs. Therefore, the characterization of the thermo-viscoelastic behavior of laminates is a necessity. Tests have been conducted at elevated temperature, with a specific attention to minimize the oxidation of the material. To model precisely the viscoelastic response of the laminate, since pure resin samples are usually not available, an inverse method based on the comparison of experimental results and finite elements simulations is proposed. Periodic boundary conditions allowing to apply uniaxial tension with an arbitrary orientation are developed. In order to validate this method, resin samples are extracted from pre-impregnated material and tested under the same temperature conditions. In a last step, the cyclic response of a buried hole in a PCB is simulated by finite element calculations, using the identified material data. For large maximum temperature, substantial differences are highlighted between thermo-elastic and thermo-viscoelastic approaches in terms of accumulated plastic strain in the copper barrel. The present work opens new possibilities to model the lifetime of electronic devices facing temperature excursions ranging over the glass transition temperature.