Asymmetric accelerated thermal cycles: An alternative approach to accelerated reliability assessment of microelectronic packages

This work uses MicroBGA assemblies on organic substrate to compare different symmetric and asymmetric Accelerated Thermal Cycles (ATCs) using numerical simulations and experimental measurements. This work has developed several finite-element models: a 2-D Plane Strain Model, a Generalized Plane Deformation (GPD) model, and a 3D Quarter Symmetry model, with different solder constitutive models: bi-linear kinematic hardening, multilinear kinematic hardening with power-law creep, and Anand's viscoplastic model. The symmetric cycles examined in this work are: (a) 125degreesC to -40degreesC with ten-minute dwell each at 125degreesC and -40degreesC, and (b) 150degreesC to 65degreesC with ten-minute dwell each at 150degreesC and -65degreesC. The asymmetric cycles examined are: (c) 150degreesC to -65'C with a ten-minute dwell at 150degreesC and a five-minute dwell at -65degreesC and (d) 150degreesC to -65degreesC with a ten-minute dwell at 150degreesC and a three-minute dwell at -65degreesC. Transient thermal analysis has been done to ensure that the components will reach steady-state temperature, when the dwell time is reduced. The numerical simulations show that there is little difference in the predicted number of cycles to failure, between symmetric and asymmetric cycles, and the experimental data agree with the predictions by the numerical models.