Issue link: https://iconnect007.uberflip.com/i/373246
September 2014 • SMT Magazine 15 13. Choose a proper conformal coating If needed, conformal coating can help. However, the material and thickness of the con- formal coating need to withstand the environ- mental exposure without degradation and to resist the protruding force of whisker growth. 14. Consider dipping process For low-volume production, an additional dipping process to convert pure tin coating into a less whisker-prone coating composition can work. Exercise prudence by not creating undue damage to the parts. 15. Change to a composition that is less prone to whisker When using the alloying tactics in a lead- free environment, among the likely working elements including Bi, In, Ni, Pb, Sb and Zn, bismuth offers the most effectiveness. In terms of working alloys, I anticipate that the com- positions of SnBi and SnZn alloys are most ef- fective in mitigating tin whiskers and SnCu and SAC are most vulnerable to producing tin whiskers. Among these 15 tactics, 1–4 are directly controlled by the plating process; 5 and 6 are directly related to the substrate base; and 7–9 are associated with the subsequent han- dling and the end-use environment. Ten and 11 are the result of system design including the material selection, and 12–14 are alter- nate steps that can be adopted. The alloy se- lection shown in 15 is the most fundamental approach. It should be noted that the industry testing methods described in the published documents do not guarantee that whiskers will or will not grow under field life conditions. The uncertain- ties associated with tin whisker growth make it difficult to predict if or when tin whiskers may appear, nonetheless, this list of tactics provides options and approaches for reducing the risk of tin whisker-induced failures. So, which tactic(s) should we adopt to best formulate an effective strategy? By considering both practicality and the in- trinsic effectiveness of the tactics, selecting the tactics to craft an effective strategy depends on three things: • The specific system • The service environment • The criticality of end-use applications The bottom-line objective is to suppress the driving forces to a level that falls below what I call the "whisker threshold"; in other words, the objective is to reduce tin whisker propensity to an acceptable level for a given system. The Sun Tzu philosophy is right: "The supreme art of war is to subdue the enemy without fighting." Appearances Dr. Hwang will present a lecture on "Tin Whiskers – What is Important to Know" at the SMT International Conference and Exhibition on September 28 in Chicago. Smt Dr. hwang, a pioneer and long- standing contributor to SMT manufacturing since its incep- tion, as well as to the lead-free development and implementa- tion efforts, has helped improve production yield and solved challenging reliability issues. Among her many awards and honors, she is a member of the WIT International hall of fame, elected to the national Academy of engineering, and named an r&D-Stars-to-Watch. having held senior executive positions with lockheed Martin Corp., Sherwin Williams Co., SCM Corp, and IeM Corp., she is currently Ceo of h-Technologies Group, providing business, technology and manufacturing solutions. She has served on u.S. Commerce Department's export Council, various national panels/com- mittees, and the boards of fortune 500 nYSe companies and university, as well as civic boards. She is the author of 400+ publica- tions and several textbooks, and an interna- tional speaker and author on trade, business, education, and social issues. her formal edu- cation includes four academic degrees (Ph.D., M.S., M.A., B.S.) as well as harvard Business School executive Program and Columbia uni- versity Corporate Governance Program. To read past columns, click here. SMT ProSPeCTS & PerSPeCTIveS tin Whiskers, part 6: preventive and mitigating measures—Strategy and tactics continues