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February 2015 • SMT Magazine 49 As mentioned in my previous columns, testing the tin whisker propensity, due to its underlying mechanisms, is a more challeng- ing endeavor than testing solder joint reliabil- ity, particularly in defining the optimal testing temperature for a system. To understand grain boundaries, it requires substantial micro-scale and atomic-scale analyses. In addition to per- forming electron backscatter diffraction (EBSD) and energy dispersive X-ray spectroscopy (EDS) for identification of phases and uncovering tex- ture, transmission electron microscope (TEM) and ideally atom probe scanning electron mi- croscope-focused ion beam (SEM-FIB) system are needed to examine the grain boundary structure and its interaction with impurities, which is often characterized by the inhomoge- neous distribution of impurity atoms between the grain boundary and the grains. As selecting testing parameters that are in sync with the intrinsic properties of the system is a critical step, it is plausible to choose the test parameters based on the anticipated underlying process and/or a postulated "theory" so that the tests can capture the "action." Just as impor- tant, the tests for the intended purpose are to gauge the relative susceptibility to whiskering. When proper test parameters are identified, es- pecially the testing temperature, testing the ab- sence of whiskers is as meaningful as the pres- ence of whiskers. For determining the testing temperature, identifying the endgame is a real thing—is the testing temperature intended to demonstrate the occurrence of tin whiskers, or is it to dem- onstrate the absence of tin whisker, or is it that under the most plausible condition for the spe- cific system to see tin whisker will or will not occur? Determining plausible testing tempera- ture is a challenge, but it should be considered before carrying out the test. A different testing temperature can change the outcome, qualitatively or quantitatively. SMT references 1. Professional Tutorial book: "Tin Whis- ker—What is Important to Know," SMTA Inter- national Conference/Exhibition, 2014. 2. Webinar Book: "Tin Whisker—All You Need to Know," SMTA Webinar Series 2014. 3. JEDEC Standard No. 201: "Environmen- tal Acceptance requirements for Tin Whisker Susceptibility of Tin and Tin Alloy Surface Fin- ishes," JESD201. 4. JEDEC Standard No. 22A12: "Measuring Whisker Growth on Tin and Tin Alloy Surface Finishes," JESD22A121. 5. JEDEC Standard No. 22-A104D, "Temper- ature cycling," JESD22-A104D. upcoming appearances Dr. Hwang will present a lecture on "Pre- venting Manufacturing Defects and Product Failures" at IPC APEX EXPO on February 22, 2015, San Diego, CA. Dr. Hwang, an international busi- nesswoman and speaker, and business and technology advisor, is a pioneer and long-standing contributor to SMT manufactur- ing since its inception, as well as to the global lead-free electronics implementation. among her many awards and honors, she is inducted to the international Hall of Fame—Women in Technology, elected to the national academy of engineering, and named an r&D-Stars-to-Watch. Having held senior executive positions with lockheed Mar - tin Corp., Sherwin Williams Co., SCM Corp, and ceo of international electronic Materials corp., she is currently ceo of H-Technologies Group, providing business, technology and manufacturing solutions. She has served on the u.S. Commerce Department's export Council, chairman of assessment panel on DoD army research laboratory, various national panels/ committees, and the board of Fortune 500 ny Se companies and civic and university boards. She is the author of 400+ publications and several textbooks, and an international speaker and author on trade, business, education, and social issues. Her formal education includes four academic degrees as well as the Harvard business School executive program and Colum - bia university corporate Governance program. For further info, visit To read past columns, click here. Feature TIN WHISKerS: WHy TeSTING TeMPeraTure CaN CHaNGe THe OuTCOMe continues

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