Lead free solder joint reliability characterization for PBGA, PQFP and TSSOP assemblies

Abstract

In this study, thermal cycling test from -40/spl deg/C to 125/spl deg/C with 1 hour per cycle for Sn/sub -3.8/Ag/sub -0.7/Cu solder joint electronic assemblies was conducted for PBGA316, PQFP208, PQFP176, and TSSOP48 components. Two PCB surface finish conditions were investigated for ENIG and OSP. Daisy chain, in-situ resistance monitoring with data logger, was used for failure detection when the resistance value is larger than 300/spl Omega/. A two-parameter Weibull distribution model was used to determine the mean time to failure (MTTF) for different components. The Weibull parameters such as characteristic life and slope are compared for PBGA assembly with Ni/Au and OSP surface finishes. Microscopy was used to determine the crack path and failure mode. It was shown that components with Ni/Au surface finish have higher thermal fatigue life than those with OSP surface finish. PBGA solder joints are more sensitive to thermal fatigue failure than solder joints in PQFP and TSSOP components. More failures occur at the package side than board side for PBGA assembly. Fatigue life prediction was conducted using fatigue life prediction model and FEA analysis results for different component types. Quarter model with submodeling technique was used in FEA simulation due to symmetric geometry and uniform loading for PBGA, PQFP and TSSOP assemblies. Effect of solder joint location on fatigue life was studied based on FEA result for different assemblies. It was shown that test and predicted fatigue life results have a good agreement for different component types.