Mar 01, 2011 
The trend to copper UBM for lead-free area-array packages subjected to drop impact means that the properties of the intermetallic that forms at the solder/copper interface are major determinants of joint reliability. The transformation of the Cu6Sn5 from the close packed hexagonal η to the monoclinic η' at 186°C can reduce the impact resistance and long-term reliability of the solder joint.
In this presentation, the authors report new studies on the effect of Ni over the range 0-9 percent on the stabilization of the η phase. The distribution of Ni in the Cu6Sn5 and its crystal structure, lattice dimensions and thermal stability have been studied using SEM/EDS, TEM/EDS, synchrotron micro-XRF mapping techniques, synchrotron XRD, DSC and dilatometry. The mechanical properties of the intermetallic as a function of nickel content have been measured by nanoindentation. The data collected provides a basis for lead-free alloy formulation for area-array attachment.
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.
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