  As the integration and the miniaturization of electronics devices, design
space become narrower and interactions between design factors affect their
reliability. This paper presents a methodology of quantifying the interaction
of each design factor in electronics devices. Thermal fatigue reliability of
BGA assembly was assessed with the consideration of the interaction between
design factors. Sensitivity analysis shows the influence of each design factor
to inelastic strain range of a solder joint characterizing the thermal fatigue
life if no interaction occurs. However, there is the interaction in BGA
assembly since inelastic strain range depends on not only a mismatch in CTE but
also a warpage of components. Clustering can help engineers to clarify the
relation between design factors. The variation in the influence was taken to
quantify the interaction of each design factor. Based on the interaction,
simple evaluating approach of inelastic strain range for the BGA assembly was
also developed. BGA package was simplified into a homogeneous component and
equivalent CTE wascalculated from the warpage of BGA and PCB. The estimated
equation was derived by using the response surface method as a function of
design factors. Based upon these analytical results, design engineers can rate
each factor's effect on reliability and assess the reliability of their basic
design plan at the concept design stage.
