SMTA International Conference Proceedings

Effect of Isothermal Preconditioning on Thermal Fatigue Life and Microstructure of a SAC305 BGA

Authors: Jim Wilcox, Richard Coyle, Lawrence Lehman, Joe Smetana
Company: HDP User Group International, Alcatel-Lucent, Binghamton University
Date Published: 9/28/2014   Conference: SMTA International

Abstract: Solder joints age and degrade during service and eventually fail by the known wear out mechanisms of solder fatigue. For Sn-Ag-Cu (SAC) solders, there are reports that solder joint fatigue life can be reduced if the joints are subjected to elevated temperature preconditioning prior to the thermal fatigue cycle. This phenomenon, sometimes referred to as aging, poses a potential solder joint reliability risk because it accelerates the microstructural degradation that accompanies solder fatigue and creep damage, and precedes service failures. Thermal fatigue performance of solder is critically important for high reliability electronic applications because it is a major source of failure of surface mount (SMT) assemblies.

This paper presents the effect of isothermal precondition aging on the thermal cycle fatigue life of a fine pitch (0.5 mm) BGA component measured in accelerated temperature cycling (ATC). The experiment includes a comparison of the fatigue performance of SAC305 joints with 0, 10, and 20 day preconditioning at 125°C. Temperature cycling was done with a 0 to 100°C temperature range and dwell times of 10 or 60 minutes. Failure data are reported as characteristic life η (N63.2) cycles and slope ß from two-parameter Weibull distribution fits. The ATC data and failure analysis are discussed in terms of the effect of isothermal aging on microstructural evolution prior to cycling as well as during subsequent temperature cycling.

Key Words: 

SnAgCu solder, Accelerated Thermal Cycling, Aging, Thermal preconditioning, Dwell time

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