FAILURE MECHANISM OF SAC 305 AND SAC 405 IN HARSH ENVIRONMENTS AND INFLUENCE OF BOARD DEFECTS INCLUDING BLACK PAD

摘要

In this study accelerated thermal cycling has been performed on a test vehicle including BGAs, CSPs, LGAs, LQFPs, and MLF20s. They were assembled on ENIG finished boards using both the most popular Sn-Ag-Cu alloy, 3% Ag - SAC 305, and the alloy with higher Ag content, SAC 405 solder. BGAs and CSPs had SAC 305 and SAC 405 balls, therefore pure SAC 305 and SAC 405 solder joints were formed. Thermal cycling using a -55°C to 125°C profile was conducted on assembled test boards for 3000 cycles. As-assembled and thermal cycled solder joints were examined using optical and scanning electron microscopy. This paper discusses fatigue life of Ball Grid Array and leaded components in comparison with 0°C to 100°C cycling, and similarities and differences in the performance of pure SAC 305 and SAC 405 solder joints in Harsh Environments. Special attention was focused on studying interfacial cracking on the ENIG finish in lead-free solder joints after -55°C to 125°C cycling.