Oct 01, 2010 
Although the tin-zinc system has a eutectic at nine percent zinc that looks promising as the basis for a low melting point lead-free solder, so far only very limited success has been achieved in realizing that potential in commercial mass production. The problems that have limited the success of alloys based on this eutectic include their chemical reactivity, which tends to make it unstable in solder paste formulations, and its susceptibility to corrosion in service.
Options for enhancing the performance of alloys based around the tin-zinc eutectic include modification of the alloy with targeted dopants and formulating solder paste flux mediums that do not react with the alloy until the point of reflow. In this paper, the authors report work that has successfully addressed these issues to produce a solder that appears to have a real prospect of filling a well recognized gap in the application range of lead-free solders.
Keith Sweatman is a graduate in metallurgical engineering and began his involvement with soldering technology with the International Tin Research Institute, an organisation that did much of the work that established a scientific basis for what was previously the art of soldering. He took that experience with him to Multicore Solders where he worked in a variety of technical and management roles that culminated in the position of managing director of Multicore Solders operations in the Asia Pacific Region. Since 2001 he has been assisting Nihon Superior Co, Ltd. in the development of their global business in lead-free solders. Over that period he has given some 30 presentations at conferences and seminars around the world and published articles in various industry journals.
Currently he represents Nihon Superior in projects related to lead-free soldering technology in iNEMI and the HDP User Group and in the NASA/US Department of Defence lead-free solder project. He is a corresponding member of several IPC standards committees relating to soldering technology and is a member of the technical committee of the IPC Solder Products Value Council
Nihon Superior was founded in 1966 when it began marketing unique flux products imported from the US. The company made its mark on society by gathering the most advanced soldering and brazing technologies and products from around the world, and supplying them to companies in the metal-joining industry. A turning point for the company came when it started developing its own soldering materials and with the success of its unique SN100C lead-free solder alloy Nihon Superior has become a major player in the global market. To support the growing demand for its products Nihon Superior has established manufacturing and sales centers in Japan, China and other Asian countries and formed business partnerships with companies in other markets.
