Characterization of epoxy based highly filled die attach materials in microelectronics

In semiconductor technologies thermally and electrically conductive adhesives are widely used to attach the die to the substrate. Focus of this work are Isotropic Conductive Adhesives (ICA) with a high amount of electrically conductive filler particles and the characterization of such materials.One of the challenges of the characterization of die attach materials is to obtain a stable material response, since the material is highly sensitive to the applied curing and temperature loading conditions. This leads to significant changes in the material properties due to post curing and aging caused by decomposition. Viscoelastic material properties from samples with different curing conditions were determined by dynamic mechanical analysis (DMA) in order to evaluate the material model for thermomechanical simulation in a wide temperature range. The stresses in a package are predominantly driven by the mismatch of the coefficients of thermal expansion (CTE) of the involved materials. Thermomechanical analysis (TMA) was used to measure the orthotropic CTE of die attach materials. Additional material parameters for thermomechanical simulation such as Poisson's ratio are mostly assumed. In this paper Poisson's ratio measurements at different temperatures are evaluated by Digital Image Correlation (DIC). The verification of the material model using validation samples like bulk samples are included and the results are discussed.