Reliability and microstructure of lead-free solder joints in industrial electronics after accelerated thermal aging

The reliability of lead-free (LF) solder joints in surface-mounted device components (SMD) has been investigated after thermo-cycle testing. Kirkendall voids have been observed at the interface component/solder together with the formation of fractures. The evolution, the morphology and the elemental analysis of the intermetallic layer have been evaluated before and after the thermal treatment. Voids produced by the release of volatile species during the soldering process due to the application of flux were present. If compared with SnPb soldered systems, lead-free joints are characterized by larger and a higher amount of voids. In several electronic joints (ball grid arrays (BGA), surface-mounted device components (SMD), etc.) fractures developed after the thermal stresses generated during the accelerated thermal aging. Warpage of the PCB has also been observed. Backward and forward compatibility of SnPb and lead-free BGA connections has been performed on pads with an ENIG finish. The effect of the reflow peak temperature on the structure of the intermetallic layer has been assessed