Properties and interfacial microstructure of Sn–Zn–Ga solder joint with rare earth Pr addition

The effects of rare earth (RE) Pr on the wettability, bond strength and interfacial microstructure of Sn–Zn–Ga (SZG)/Cu joints were investigated. The wetting balance results showed that adding a proper amount of Pr greatly improved solder wettability by increasing the wetting force and decreasing the wetting time. Micro-joint strength test results showed that the Pr addition enhanced the shear bond strength of solder joints after both soldering and thermal aging at 100 °C. The interfacial microstructure evaluation indicated that the addition of Pr can inhibit the formation of Cu5Zn8 intermetallic (IMC) layer during soldering and the growth of Cu6Sn5 IMC during thermal aging. However, it was discovered that the presence of Pr causes the risk of Sn whisker growth at the joint interfaces due to the oxidation of RE-rich PrSn3 IMCs during aging. Since RE-containing solders have been recommended for future applications because of their superior properties, the findings indicated that further reliability assessments on RE-containing solder joints should be conducted.