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Voids in solder joints have been considered as a defect in electronics assembly. The factors that affect void formation are complex and involve the interaction of many other factors. There are no established standards for void size and void area in a solder joint for it to be deemed defective. Inspection criteria have been very subjective. The effect of voids on the reliability of a BGA/CSP solder joint may depend not only on the size, but also on other factors such as frequency and location. This study focused on investigating the effect of voids on the reliability of solder joints. The effect of void size, location and frequency on reliability were studied. Testing was done by a mechanical deflection testing (torsion) system and air to air thermal cycling (-40/spl deg//125/spl deg/C). Failures were analyzed and failure modes were identified by cross sectional analysis. Additionally, a finite element model was developed for a package with voids of varying sizes in the corner solder joint of the package. The results from the model were compared with the results from reliability testing and are presented in this paper. Analysis indicates that voids reduce the solder joint life. Voids which are greater than 50% of the solder joint area decrease the mechanical robustness of the solder joints. Small voids also have an effect on reliability. However, this effect is dependent on the frequency and location of voids.