Interfacial microstructure evolution and shear strength of Sn0.7Cu–xNi/Cu solder joints

Abstract

The microstructure and growth behaviors of interfacial intermetallic compounds (IMCs) between the Sn–0.7Cu–xNi (x = 0, 0.1, 0.25, 0.5, and 1.0 mass%) solder alloys and copper pad were explored to reveal the influence of the Ni addition into the Sn–0.7Cu based solder on the formation of interfacial IMCs and shear strength of the solder joints in the present study. The impacts of adding different Ni on the growth behavior and total thickness of Cu6Sn5/(Cu, Ni)6Sn5 and Cu3Sn IMCs layers were compared and discussed after reflowing at 533 K for 600 s and aging at 423 K for various aging durations. The thickness of interfacial IMC layers increased drastically with addition of small amount of Ni into the Sn0.7Cu solder alloy, however, the particle sizes of the IMC grains obviously decreased with the addition of Ni into the solder, compared to the Sn0.7Cu/Cu system. The results indicated that, Cu6Sn5 turned into (Cu, Ni)6Sn5 due to the addition of Ni element and would enhance the growth rate of interfacial IMC resulted from more Ni added. It is quite obvious that 1 wt% Ni addition to the Sn–0.7Cu solder alloy extremely enhance growth and formation of the IMC in Sn–0.7Cu–xNi/Cu joints. In addition, the single-lap shear tests were also carried out to evaluate the mechanical properties of the as-reflowed Sn0.7Cu–xNi/Cu solder joints. The results of shear tests indicated that the shear stress of Sn–0.7Cu–xNi/Cu solder joints gradually increased with the increase of Ni concentration, and the maximum shear strength was reached with 1 wt% Ni addition. Besides, doping Ni element into the Sn–0.7Cu solder changed the shear fractures morphology of Sn–0.7Cu/Cu joints, which were revealed to be ductile essentially with the moderate strain rate (3.33 × 10−3 s−1) and mainly occurred in the solder matrix rather than through the IMCs layer.