Reliability of CSP Interconnections Under Mechanical Shock Loading Conditions

Failure modes and mechanisms under mechanical shock loading were studied by employing the statistical and fractographic research methods, and the finite element (FE) analysis. The SnAgCu-bumped components were reflow-soldered with the SnAgCu solder paste on Ni(P)|Au-coated and organic solderability preservative-coated multilayer printed wiring boards with and without micro-via structure in the soldering pads. The component boards were designed, fabricated, assembled, and drop tested according to the JESD22-B111 standard for portable electronic products. The test data were analyzed by utilizing the Weibull statistics, and the characteristic lifetimes (eta) and shape parameters (beta) were calculated. Statistically significant differences in the reliability were found between the different coating materials and pad structures. The results on the failed assemblies showed good correlation between the failure modes and the FE calculations. Under high deformation rates the solder material undergoes strong strain-rate hardening, which increases the stresses in the interconnections as compared to those in the thermal cycling tests. Therefore, the failure mechanisms under high deformation rates differed essentially from those observed in thermal cycling tests