Contraction stresses development of anisotropic conductive films (ACFs) flip chip interconnection: Prediction and measurement

In this study, the buildup of contraction stresses and the effect of anisotropic conductive film (ACF) properties on contraction stresses were investigated. Both ACF thickness shrinkage and modulus change of four kinds of ACFs with different thermomechanical properties were experimentally investigated using thermomechanical and dynamic mechanical analysis. Based on an incremental approach to linear elasticity, the contraction stresses of ACFs developed along the thickness direction were numerically predicted. In addition, the contraction stresses of ACFs were developed during the cooling process from the glass transition temperature of ACFs to room temperature. The buildup of contraction stresses below T-g was strongly dependent on both the coefficient of thermal expansion (CTE) and elastic modulus (E) of ACFs. A nanoscale deformation field of thin ACF layers was obtained to measure the contraction stresses experimentally using a phase shifting moire technique. Good agreement between the contraction stresses predicted from the incremental approach and the actual vertical stresses measured from a phase shifting moire analysis was obtained. Therefore, the full temperature-evolution of contraction stresses based on the incremental approach to linear elasticity is reliable and thereby can be used to predict the contraction stress behavior of polymeric ACF materials.