APEX 2011 - Pb-Free Solder Joint Reliability

Two different temperature cycling profiles were used to compare the thermal fatigue reliability of Pb free and SnPb solder joints in 16 different, high strain surface mount (SMT) packages. In some applications, high strain Pb free (SnAgCu) components are expected to fail earlier than the equivalent SnPb version. In this program, test results were compared for a 0100°C thermal cycle used often for evaluating high reliability applications to those of a comparatively mild accelerated thermal cycle condition of 20-80°C. A total of 6957 cycles was completed in the 0-100°C testing and a total of 9792 cycles was completed in the 20-80°C thermal cycling. The program was completed after over more than two years of elapsed test time. Weibull analysis, acceleration factors between the tests and failure analysis are included. The results indicate that the SnAgCu (SAC) components that create a high strain in thermal cycling tend to perform worse in 0-100°C testing than identical SnPb soldered components. However, when the strain is reduced by testing with the reduced T in the 20-80°C cycle, the SAC thermal fatigue performance is equal to or better than that of identical SnPb soldered components. The encouraging SAC performance in the 20-80°C cycle tends to mitigate Pb free reliability concerns because the lower strain test conditions are closer to actual service conditions. Background Thermal fatigue combined with solder creep is considered the major source of wear out failure of surface mount (SMT) components.