The dissolution of Cu into molten Sn-3.8at.%Ag (Sn-3.5wt.%Ag) solder and its effect on microstructure were studied by light microscopy, scanning microscopy, and x-ray microanalysis. X-ray microanalysis of the average Cu content of samples soldered under various conditions showed that the amount of Cu dissolved during soldering increased with increasing soldering temperature and time and that the rate of dissolution could be described by a Nernst-Brunner equation. Microstructurally it was found that the volume fractions of primary β(Sn) dendrites and η-phase dendrites increase with increasing soldering temperature and time. The microstructural changes can be explained using SnAg-Cu phase equilibrium data. A numerical method was developed for calculating the amount of Cu dissolved under non-isothermal conditions, which describes dissolution reasonably well.

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Alloys that undergo solidifi cation over a wide range of temperatures generally exhibit a difference in the contraction behavior of the ensuing solid and liquid phases. Furthermore, dissolution of substrate metals during process refl ow can lead to shifts in phase composition, additional primary phases, and volumetric contraction artifacts. The extent and frequency of surface roughness, shrinkage voids, fi llet lifting, and hot tearing seen in lead-free solders are different than for eutectic tin lead solder. Shrinkage effects have been reported in Sn/Pb, Sn/Pb/Ag, Sn/Ag/Cu, and Sn/Cu/Ni solders for various components, but few studies have examined their impact on solder joint reliability. Nevertheless, they warrant proper identifi cation due to the shift toward lead-free solders. This article is a review of the effects of shrinkage in Sn-Pb and lead-free solders as well as a discussion of some of the factors that contribute to their formation. Visit the site regularly and click on "What's New" to fi nd out the most up-to-date information on meetings, publications, membership activities, and more. www.tms.org ■ CMS-Plus is available to accept abstracts for the 2006 TMS Annual Meeting. http://cmsplus.tms.org ■ The Members Only site has been updated and reorganized. http://members.tms.org/members/mempage.asp ■ The Metal-Matrix Composites database is now available as a member benefi t. http://members.tms.org/MMCDatabase/MMC.asp

issue of JOM, and 31 papers were accepted for publication in the current issue of JEM. Out of these 31 papers, the two most popular subjects of research reported are: interfacial reactions between Pb-free solders, and surface finishes or under bump metallizations, and mechanical properties of solders and their impact on the reliability of the solder joints. Among the several Pb-free solder candidates, Sn-Ag eutectic and Sn-Ag-Cu ternary eutectic alloys have received the most attention from the investigators. This special issue is certain to help enhance our understanding of Pb-free solders and soldering technologies and pave the way for a smooth transition to environmentally friendly electronic packaging.