RELIABILITY OF SOLDER JOINTS IN IC PACKAGES

Abstract

Solder joints are key components in widespread levels of electronic packaging; such as the solder-ball connection in Ball Grid Array (BGA) packages and the flip chip connections (C4). They serve both as electrical as well as mechanical connections. Malfunctions of the solder joints could result in the failure of the whole device system. During servicing, the solder joints are subjected to fluctuating thermal stresses resulting from a combination of thermal excursions experienced by the package and differential thermal expansions (CTEs) between the materials due to power transients or environmental temperature changes. The integrity of solder joints is thus a major reliability concern in modern microelectronics systems, especially Surface Mount Technology (SMT) packages. The standard industrial procedure in evaluating interconnect reliability involves the determination of cycle failures under accelerated temperature cycling conditions. Depending on the tests conditions, these tests can be long and intensive. Also, these cycling tests are largely statistical and they do not provide useful insights to the physics of the failure mechanism as well the long-term reliability of solder interconnects in IC packages. It is thus especially advantageous to conduct upfront analysis before undertaking such time-consuming and costly tests. In this thesis, we present an upfront methodology for the analysis and prediction of solder joint reliability in electronic packages using advanced computational simulations. The methodology allows easy interface with standard thermal cycling experiments. Damage mechanisms representative of actual field conditions are duly represented in the computational model. The methodology is capable of supporting both lead-based and lead-free solder materials, with a free choice of constitutive formulation (and corresponding fatigue life prediction model) for the solder joints. Two constitutive formulations were presented in our study, namely the Darveaux-Anand (DA for short) relation and the Elastic-Plastic-Creep (EPC) relation. Experimental results had shown that fatigue life cycles predicted by both DA and EPC formulations agreed reasonably well with actual fatigue-crack occurrences and the accuracy was comparable to other state-of-the-art solder fatigue analysis tools. There were however some inherent differences pertaining to the damage accumulation during thermal cycling for the DA and EPC formulations. This thesis forms the necessary framework for more advanced computational modeling on solder joint fatigue reliability, especially when the solder interconnects become increasingly small and critical.