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12 SMT Magazine • September 2014 by Dr. Jennie S. hwang Ceo, h-TeChnoloGIeS GrouP Smt prOSpeCtS & perSpeCtIveS ColuMn tin Whiskers, part 6: preventive and mitigating measures— Strategy and tactics "Strategy without tactics is the slowest route to victory. Tactics without strategy is the noise before defeat… If you know the enemy and know yourself, you need not fear the result of a hundred battles. If you know yourself but not the enemy, for every victory gained you will also suffer a defeat. If you know neither the enemy nor yourself, you will succumb in every battle." —Sun Tzu, celebrated strategist and author of The Art of War (ca. 500 BC) In this installment of the tin whisker series, we'll take a look at the preventive and mitigat- ing measures— strategy and tactics. An effective strategy for prevention and mitigation starts with a good understanding of the causations of tin whiskers (the enemy). Part 4 of this series summarized the causes and contributing factors (March 2014). The tin whisker phenomenon is a thermo- dynamically and kinetically controlled process. The process requires the formation of whiskers as well as their continued growth, which poses challenges to "taking the bull by the horns." Nonetheless, the confluence of test data, field experience, and the fundamental mate- rial crystal growth theory can lead to a work- ing path. Fifteen tactics are listed here. This smorgasbord of material and technique options serves as a guide to prevent or retard tin whis- kers. 1. minimize organic impurity content The level of organic impurities introduced to the coating closely is dependent upon the plat- ing chemistry and the plating process, includ- ing the type of electrolyte, additive/brighteners, current density, process temperature, and the process control. Thus, the source of the coating (i.e., the plating house) makes a difference. The rule of thumb is to keep the organic content in the metallic coating to a minimum—nominally below 0.05% by weight (as represented by the carbon content).

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