Fatigue life analysis of solder joints in flip chip bonding

This paper describes the life assessment of filp, chip joints. Flip chip joints of 63Sn-37Pb and 5Sn-95Pb solders on a printed circuit board were stressed thermally for fatigue. Fatigue lives of the joints were determined by an electrical potential drop method and the effect of encapsulation on fatigue life was discussed. The Encapsulation had a significant effect of prolonging the fatigue life of the joints. Thermo-mechanical finite element analysis proved that the encapsulation lowered the strain amplitude of the joints by distributing the strain over a whole package and bending effect. Cracking location uas also discussed in relation with the strain concentration in the joints. Fatigue lives of the flip chip joints were compared with those of bulk round bar specimens and the difference in fatigue life between two types of specimens was discussed from the specimen dimensions and ratchet effect.