Microstructures and properties of SnAgCu solder doped with Eu

The effect of rare earth Eu on the microstructures and properties of SnAgCu solder was investigated. The results indicated that small amount of rare earth Eu could markedly improve the wettability of solders on Cu substrate and the tensile force of solder joints, and the optimum content of rare earth Eu was around 0.04%. When the Eu content was higher than 0.04%, the spreading area of lead-free solders and tensile force of solder joints decreased obviously. Based on the analysis of microstructure of SnAgCu, it was found that the microstructure of solder matrix could be markedly refined with the addition of rare earth Eu, meanwhile, the size of intermetallic compound particles could be reduced, too. During 150 ℃ isothermal aging(1000 h), the coarsening of SnAgCu and SnAgCuEu solder occurred obviously, especially for the Cu6Sn5 phase. Compared with the microstructure of SnAgCu solder, the coarsening of the SnAgCuEu solder microstructure was not that obvious. However, with excessive rare earth Eu added, the wettability of solders and the tensile force of the solder joints were both deteriorated significantly, and the whiskers could be found in the matrix microstructure. However, small amount of Eu did not result in the whiskers. The oxidation mechanism could be used to explain the whisker growth of SnAgCu solders bearing rare earth; the volume of RE-rich phase expanded due to oxidation, which would result in compressive stress which was the driving force of whiskers. ©, 2015, Editorial Office of Chinese Journal of Rare Metals. All right reserved.