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94 SMT Magazine • January 2017 used as a basis for the establishment/develop- ment of your own tin whisker test. For refer- ence, these documents are: • JESD201A—Environmental Acceptance Requirements for Tin Whisker Susceptibility of Tin and Tin Alloy Surface Finishes [1] • JESD22-A121A—Measuring Whisker Growth on Tin and Tin Alloy Surface Finishes [2] Within these standards, the testing proto- cols call out three different environmental ex- posures: high temperature/humidity storage, low temperature/humidity storage, and ther- mal cycling. Given the nature of tin whisker formation, which is slow and incremental, the testing typ- ically performed is long, relatively speaking, to other common environmental exposure tests. For example, a common duration for the storage tests is 4,000 hours, which is almost 24 weeks, and 1,500 cycles for the thermal cycling test. Additionally, the specific test conditions—tem- peratures and humidity levels—can vary depen- dent on the exact test method being followed. Supplementing the environmental expo- sure tests themselves, visual examination is a critical part of the evaluation process. Stereomi- croscopes and scanning electron microscopes (SEM) are common tools of the trade for this type of inspection, as whisker formations can easily range from the micron level up to milli- meters. Of interest, in addition to the JEDEC doc- uments, other groups have provided informa- tion on the whisker phenomenon, most nota- bly iNEMI [3] . Also, others have developed addi- tional test methodologies. The automotive and commercial electronics industries have had in- terest in the topic of tin whiskers for many years now as the RoHS directive's ban on lead forced manufacturers to make the change to Pb-free materials, most notably solder as it pertains to the printed circuit assembly sector of the indus- try. Currently, the more traditional high reli- ability sectors of the industry—aerospace, med- ical, military…to name a few—are beginning to make some transitions for various reasons. Sup- ply chain issues are a key factor in this more recent shift as component level manufacturers scale back their Pb-containing operations. Ultimately, as with any process change for whatever the reason might be, a solid test protocol is crucial to ensuring that your prod- uct can meet your customer's expected level of reliability. SMT References 1. JEDEC, JESD201A 2. JEDEC, JESD22-A121A 3. Keith M. Sellers is operations manager with NTS in Baltimore, Maryland. GOT WHISKERS? While at electronica in Munich recently, I-Connect007 Technical Editor Pete Starkey spent time in Electrolube's booth with Phil Kinner, technical director of the company's Coatings Division. As the resident expert on conformal coatings, Kinner explained the role of conformal coatings in various appli- cations of the automotive industry. They discussed some of the things that the automotive industry is demanding from the solutions people in terms of the right conformal coatings for the right applications, and how Electrolube is help- ing customers to address those applica- tions. Kinner also elaborated on the condensa- tion testing work that Electrolube is doing with the National Physical Lab, which he said he hope could lead to a standardized test that everyone on the supply chain should use. Read the interview here. Meeting Current and Future Requirements of the Automotive Industry

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