Fracture toughness assessment of ACF flip-chip packages under high moisture condition with moire interferometry

A primary factor of ACF package failure is delamination between the chip and the adhesive at the edge of the chip. This delamination is mainly affected by the normal strain at the edge of the chip. This normal strain was measured on various electronic ACF package specimens by micro Moireacute interferometry with a phase shifting method. In order to find the effect of moisture, the reliability performance of an adhesive flip chip in the moisture environment was investigated. The failure modes were found to be interfacial delamination and bump/pad opening which may eventually lead to total loss of electrical contact. Different geometric size specimens in terms of interconnections were discussed in the context of the significance of mismatch in CME between the adhesive and other components in the package, which induces hygroscopic swelling stress. Interfacial fracture toughness between ACF and die chip were evaluated by peel test. The effect of moisture diffusion in the package and the CME mismatch were also evaluated by using the Moireacute interferometry. From Moireacute measurement results, we could also obtain the stress intensity factor K. Through an analysis of deformations induced by thermal and moisture environments, a damage model for an adhesive flip chip package is proposed.