The effect of isothermal aging on the harmonic vibration durability of

Sn3.0Ag0.5Cu solder interconnects is examined. Printed wiring assemblies with

daisy-chained leadless chip resistors (LCRs) are aged at 125°C for 0, 100, and 500

hours. These assemblies are instrumented with accelerometers and strain gages to

maintain the same harmonic vibration profile in-test, and to characterize PWB

behavior. The tested assemblies are excited at their first natural frequencies until

LCRs show a resistance increase of 20%. Dynamic finite element models are

employed to generate strain transfer functions, which relate board strain levels

observed in-test to respective solder strain levels. The transfer functions are based on

locally averaged values of strains in critical regions of the solder and in appropriate

regions of the PWB. The vibration test data and the solder strains from FEA are used

to estimate lower-bound material fatigue curves for SAC305 solder materials, as a

function of isothermal pre-aging.