Abstract
Purpose - To assess the long term reliability of lead-free Sn96.5Ag3.0Cu0.5 (SAC305) under accelerated temperature cycling (ATC) conditions. Test vehicles consisted of commercial 2512 ceramic chip resistors soldered to printed wiring boards (PWBs) using three different Pb-free surface finishes: Organic Solderability Preservative (OSP), Immersion Silver (IAg) and Electroless Nickel Immersion Gold (ENIG). Design/methodology/approach - Two populations of solder joints were monitored continuously during a thermal cycle of 0 ?C to 100 ?C with a ramp rate of 9oC/min and a 30 minute dwell at the temperature extremes. One population was cycled to 2,500 cycles the other population was cycled to 8,500 cycles. Failures were defined in accordance with the IPC-9701A industry test guidelines and failure data are reported as characteristic life ?. Microstructural evolution was characterised using metallographic techniques and back-scattered scanning electron microscopy (SEM). Fractography was performed on post cycled resistors to determine failure mechanisms.Findings - Findings show that the lifetime of the chip resistors can be ranked as follows ENIGOSP >ENIGOSP>IAg after 28,250 thermal cycles, when >73% of the population had failed. It was found that the relative performance of OSP finishes improved with longer periods of cycling and this was proposed to be attributed to diffusion of copper into the bulk solder and this subsequently overtime acted as a dispersion strengthening mechanism. The relatively poor performance of IAg finshes was attributed to void formation.Originality/value - This paper provides new and valuable information to end users on the long term reliability of lead free solder on three commonly used lead free surface finishes. The performance of each surface finish is explained in terms of microstructural evolution and void formation.
Purpose - To assess the long term reliability of lead-free Sn96.5Ag3.0Cu0.5 (SAC305) under accelerated temperature cycling (ATC) conditions. Test vehicles consisted of commercial 2512 ceramic chip resistors soldered to printed wiring boards (PWBs) using three different Pb-free surface finishes: Organic Solderability Preservative (OSP), Immersion Silver (IAg) and Electroless Nickel Immersion Gold (ENIG). Design/methodology/approach - Two populations of solder joints were monitored continuously during a thermal cycle of 0 ?C to 100 ?C with a ramp rate of 9oC/min and a 30 minute dwell at the temperature extremes. One population was cycled to 2,500 cycles the other population was cycled to 8,500 cycles. Failures were defined in accordance with the IPC-9701A industry test guidelines and failure data are reported as characteristic life ?. Microstructural evolution was characterised using metallographic techniques and back-scattered scanning electron microscopy (SEM). Fractography was performed on post cycled resistors to determine failure mechanisms.Findings - Findings show that the lifetime of the chip resistors can be ranked as follows ENIGOSP >ENIGOSP>IAg after 28,250 thermal cycles, when >73% of the population had failed. It was found that the relative performance of OSP finishes improved with longer periods of cycling and this was proposed to be attributed to diffusion of copper into the bulk solder and this subsequently overtime acted as a dispersion strengthening mechanism. The relatively poor performance of IAg finshes was attributed to void formation.Originality/value - This paper provides new and valuable information to end users on the long term reliability of lead free solder on three commonly used lead free surface finishes. The performance of each surface finish is explained in terms of microstructural evolution and void formation.