Synthesis and characterization of lead-free solders with Sn-3.5Ag-xCu (x=0.2, 0.5, 1.0) alloy nanoparticles by the chemical reduction method

Due to the concerns of human health and the natural environment, the investigation of an alternative Pb-free solder is necessary. Currently, near-eutectic SnAgCu alloys are being developed as a lead-free solder. In this study, lead-free solders with Sn-3.5 Ag-xCu (x = 0.2, 0.5, 1.0) nanoparticles were synthesized by chemical precipitation with NaBH4. The X-ray diffraction (XRD) patterns revealed that the Ag3Sn was formed due to the alloying process. From the XRD patterns, only Cu6Sn5 was formed when Cu concentration was as high as 1.0 wt % in the derived nanopowders. The formation of Ag3Sn and Cu6Sn5 gave strong evidence that the nanoparticles were mixed homogeneously. From transmission electron microscopy observation, the isolated particles were close to spherical shape and the particle sizes of powders were about 5 nm. The field emission scanning electron microscopy morphology of SnAgCu nanoparticles indicates that the major particle size of SnAgCu nanoparticles is in the range of 40 nm. It was evidenced from the differential scanning calorimetry profile that the SnAgCu nanoparticles could be melted successfully. In the wettability test, good metallurgical bonding was revealed between solders and substrates after reflow. Thus, the nanoparticles derived by the chemical reduction method in this study can be used as appropriate solder powders in electronic packaging. (c) 2005 The Electrochemical Society.