Search for the new Pb-free solder materials

Institute of Materials Science, University of Tsukuba
â—‹Son Van Phung Akira Fujitsuka Ken-ichi Ohshima

Environmental and health concerns of lead have increased the pressure towards the development of new Pb-free solders. Japan Electronics and Information Technology Industries Association (JEITA) defines Pb-free solder as the one in which Pb concentration is less than 0.1% of the total weight. We have been searching for the new Pb-free solder materials. The hardness, electrical resistivity and the melting point of Sn-Ag, Sn-Cu and Sn-Ag-Cu solders have been measured and compared with the eutectic Sn-Pb solder as a reference alloy. The results have clearly shown that the Pb-free solder has higher melting temperature, higher hardness and higher electrical resistivity than eutectic Sn-Pb solder. For improving the performance of the Pb-free solder, the carbon black was added into Sn-Ag solder under the high-pressure (5.5GPa) at 1200 oC. The X-ray diffraction data have shown the presence of carbon black in the composite solder. From the differential scanning calorimetry (DSC) data the melting temperature of the composite solder was found to be unchanged with adding the carbon black.