Reliability investigations for encapsulated isotropic conductive adhesives flip chip interconnection

Isotropic conductive adhesives (ICA) are gaining more and more application interests in electronic manufacturing, however, their failure mechanism have not been fully understood. This paper presents reliability investigations on encapsulated ICA flip chip interconnection. Experimental work included product lifetime measurement, cross section observation, and whole module warpage scanning. Results revealed the chip-size effect on ICA lifetime was obvious, and the warpage measurement implied that normal stress in ICA rather than shear stress play an important role for ICA reliability. A theoretical analysis was conducted with finite element method (FEM) simulation. Visco-elastic models for adhesives and underfill materials were employed, and the comparison with elastic model was made. Calculated stresses trend fitted well with the experimental lifetime measurement, thus a lifetime relationship similar as Coffin-Manson formula was established to predict the thermal fatigue life of encapsulated ICA flip chip. Furthermore, the influences of underfill properties on the ICA reliability were discussed.