| Measurement of Stress in Tin and Tin Alloys |
The growth of tin whiskers poses an enormous threat to the reliability of modern lead-free microelectronics. The U.S. microelectronics industry has clearly articulated a need for measurement methods to predict and prevent tin whiskers. In order to prevent or mitigate whisker growth, a consensus list of concerns has emerged: understand the influence of electroplating conditions, grain structure/ shape/ orientation, compressive stress in the electrodeposits, intermetallic compound (IMC) formation at the Sn-Cu interface, diffusion of tin, and thermal cycling effects on electroplated components. A series of industry and academia sponsored workshops has been held over the past six years to address these issues. The Metallurgy Division has participated in all 5 iNEMI Tin-Whisker workshops, and co-chaired and co-organized the 2005 (Orlando), 2006 (San Diego) and 2007 (Reno) iNEMI Sn Whisker workshops. In response to these workshops, NIST has focused its current efforts on stress measurements in an effort to determine the root causes of whisker growth and thereby enable whisker mitigating strategies.
The Metallurgy Division has been hosting Diffusion workshops since 2003, starting with two workshops that year. Since then the workshop has been held as an annual event. The 15 to 20 workshop participants from outside NIST are experimentalists and modelers from government laboratories (NASA, ORNL), academia (Ohio State, Penn State, RPI, George Mason, KTH, and many others) and industry (GE, QuesTek, Thermo-Calc, etc.). Specific focus areas are selected for each workshop. Presentations are given by participants and are discussed by all the workshop attendees. Most of the presentations are published on the workshop website: http://www.ctcms.nist.gov/~cecamp/workshop.html.
The discussions at the workshop have resulted in significant progress in areas such as the analysis and modeling of multiphase multicomponent diffusion, extraction of diffusion parameters from experiments, experimental methods (EPMA), the Kirkendall effect in multiphase systems, first principles calculations of diffusion coefficients and diffusion in multicomponent ordered phases. The 2008 workshop will focus on diffusion challenges associated with sustainable energy applications. The workshop participants have also been active in organizing symposia on multi-component multiphase diffusion at a number of TMS conferences.