Dynamic fracture process of solder/intermetallic interface in lead-free solder interconnects using cohesive zone model

Abstract

Solder joint reliability (SJR) is an important requirement in electronics packaging. Most of the failures in a package are found in solder joints and interconnections. Brittle solder/intermetallic (IMC) interface fracture is the dominant failure mode in cases of impact loading and fast mechanical fatigue loading. In this study, the response of a single solder specimen subjected to cyclic shear deformation and a typical ball grid array (BGA) package undergoing board-level drop test is investigated. The finite element (FE) analysis of the single reflowed solder specimen and the BGA package is employed to understand the mechanics of the solder joints and the brittle solder/ IMC fracture process. Inelastic behavior of the solder joints is described using unified inelastic strain model (Anand model) with optimized model parameters. The brittle solder/IMC interface fracture is demonstrated using cohesive zone model (CZM). The accuracy of interface fracture description depends on the CZM model prescribed in the analysis. The CZM model is modified further to ensure better predictive capability especially in cyclic loading. FE results for single solder specimen under shear fatigue test simulation shows that the CZM parameters degraded as the number of cycles is increased. Rapid damage progression occurs at the beginning of cycle and propagated slowly for subsequent cycles. For a boardlevel drop test simulation, the critical solder joint is located the farthest away from the center of the board. The highest stress and inelastic strain are confined to a small edge region at solder/IMC interfaces. Damage initiated from the outer peripheral solder and propagated into the inner peripheral solder joint.