Effects of Ni and TiO2 additions in as-reflowed and annealed Sn0.7Cu solders on Cu substrates

The growth of Cu6Sn5 and Cu3Sn5 interfacial layers after isothermal annealing and the resultant effect on the solder joint strength are studied in TiO2 and Ni containing Sn0.7Cu solders. These composite solders were fabricated using a powder metallurgy method and reflow soldered on a Cu substrate printed circuit board (PCB) with an organic soldering preservative (OSP) surface finish. With TiO2 additions, a more planar scalloped Cu6Sn5 morphology was observed with reduced interfacial boundary grooves while a fine scallop-shaped interfacial (Cu,Ni)6Sn5 layer was observed in Ni containing solder joints. The interfacial layer was further suppressed with a combination of Ni and TiO2 even after annealing which resulted in superior shear strength and fracture energy.