Issue link: https://iconnect007.uberflip.com/i/1111672
MAY 2019 I SMT007 MAGAZINE 21 • Component selection criteria, including consolidation of parts lists to reduce redundancy and eliminate obsolete parts • Surface finish and solderability considerations • Paneling considerations • Fiducial requirements • Land-pattern design • Solder-mask considerations • Via-hole location • Design for test (DFT) • Anything unique to your design With the widespread use of high-pin-count BGAs and BTCs that cannot be inspected visually, sufficient test coverage for in-circuit test (ICT) should be seriously considered. Keep in mind that no inspection method is perfect. The only way to prevent defects from escaping to the field is to rely on over - lapping test and inspection methods. Once a DFM document developed by a well-trained team is finalized and released, the possibil- ity of DFM violation generally does not arise. Creating a DFM document is not easy; however, it will correct problems at the source and prevent their recurrence. This is critical in an environment where essen- tially all manufacturing is being outsourced or sent offshore. SMT007 Ray Prasad is the president of Ray Prasad Consultancy Group and author of the textbook Surface Mount Technology: Principles and Practice debuting his first column in SMT007 Magazine. Look forward to more insights from Mr. Prasad in future issues. Mr. Prasad is also an inductee to the IPC Hall of Fame—the highest honor in the electronics industry—and has decades of experience in all areas of SMT, including his lead- ership roles implementing SMT at Boeing and Intel; helping OEM and EMS clients across the globe set up strong, internal, self-sustaining SMT infrastructure; and teaching on-site, in-depth SMT classes. He can be reached at smtsolver@rayprasasd.com and has an upcoming SMT class July 22–24. More details at rayprasad.com. Precision Control of Complex Electrochemical Interfaces for Separations Researchers working within Pacific Northwest National Laboratory's (PNNL) Separations Science program suc- ceeded in coupling a highly controlled way of modifying sur- faces, called ion soft landing, with an electrochemical cell designed and built by PNNL to achieve precise control over the chemical composition of complex interfaces. This allowed them to make atom-by-atom changes to electrodes to study the effect on performance and stabil - ity. They revealed that substitution of only one to three tung- sten atoms by molybdenum atoms in complex metal-atom clusters resulted in a pronounced improvement in their electronic behavior, which controls how efficiently these species accept electrons for separation applications. The experiments, combined with theoretical calculations by col - laborators in Spain, were published in ACS Nano. In electrochemical devices used for separations, a lot is going on at once as electroactive ions, solvent molecules, and supporting electrolytes interact, exchanging electrons and mass during charge transfer processes. To understand these processes, it is necessary to decouple the different charge transfer and ionic interactions occurring on elec - trodes. In this study, the researchers did just that, and fur- ther exerted control over the process by tuning electrodes at the atomic level. The researchers are now studying how to modulate the efficiency of separating different ions in solution using well-defined electrodes with precisely controlled anions and membrane layers. The fundamental insights gained in understanding molecular-level electrochemical interfaces may serve as a foundation for designing superior electrodes for separations, or even energy storage, at the device scale. (Source: Pacific Northwest National Laboratory)