Effects of PCB Substrate Surface Finish and Flux on Solderability of Lead-Free SAC305 Alloy

The solderability of the SAC305 alloy in contact with printed circuit boards (PCB) having different surface finishes was examined using the wetting balance method. The study was performed at a temperature of 260 °C on three types of PCBs covered with (1) hot air solder leveling (HASL LF), (2) electroless nickel immersion gold (ENIG), and (3) organic surface protectant (OSP), organic finish, all on Cu substrates and two types of fluxes (EF2202 and RF800). The results showed that the PCB substrate surface finish has a strong effect on the value of both the wetting time t0 and the contact angle θ. The shortest wetting time was noted for the OSP finish (t0 = 0.6 s with EF2202 flux and t0 = 0.98 s with RF800 flux), while the ENIG finish showed the longest wetting time (t0 = 1.36 s with EF2202 flux and t0 = 1.55 s with RF800 flux). The θ values calculated from the wetting balance tests were as follows: the lowest θ of 45° was formed on HASL LF (EF2202 flux), the highest θ of 63° was noted on the OSP finish, while on the ENIG finish, it was 58° (EF2202 flux). After the solderability tests, the interface characterization of cross-sectional samples was performed by means of scanning electron microscopy coupled with energy dispersive spectroscopy.

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