Reliability performance and failure mode of high I/O thermally enhanced ball grid array packages

Thermally enhanced BGA packages can be susceptible to early failures during accelerated thermal cycling. These failures are attributed to a brittle fracture mechanism in which cracks propagate rapidly through package metallization or solder interfaces. Usually these early or "infant mortality" failures are indicative of assembly quality or package quality defects. An hypothesis based on previous reliability testing suggests that these thermally enhanced packages can meet long term reliability requirements once the package quality issue is corrected (Ejim et al., 1997). This paper presents the results of assembly and reliability testing of a set of thermally enhanced packages that are found to be immune to early brittle interfacial failures during reliability testing. Failure mode analysis (FMA) of tested components shows that crack propagation in the improved package is exclusively by a solder fatigue mechanism. The measured higher characteristic life of these packages validates the hypothesis that long term reliability is acceptable when package defects are eliminated. As there is no early failure susceptibility in this set of packages, inspection and FMA are expanded in order to understand the improvement in package quality. The proposed mechanisms or phenomena contributing to brittle fracture are reviewed and discussed with respect to known characteristics of these thermally enhanced packages. A phenomenological approach is used to analyze the inspection and FMA data, to focus on factors critical to initiating brittle fracture, and to suggest a possible root cause in the event of brittle failure.