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August 2015 • SMT Magazine 53 and pitches when the stencil thickness is re- duced. 4. More study is required to understand fine pitch BGAs such as 0.65 mm pitch and below, in applications that use 3–4 mil stencil thick- nesses. It is reasonable to expect an even lower warpage acceptance criteria may be required in applications with finer pitches and using thin- ner stencils. SMT References 1. Chris Oliphant, Bev Christian, Kishore Subba-Rao, Fintan Doyle, Laura Turbini, David Connell and Jack Q. L. Han, "Head-On-Pillow Defect—A Pain in the Neck or Head-On-Pillow BGA Solder Defect," IPC APEX 2010. 2. Richard Coyle, Russell Nowland, Peter Read, George Wenger, "Telecommunications Case Studies Address Head-In-Pillow (Hnp) De- fects and Mitigation through Assembly Process Modifications and Control," IPC APEX 2010. 3. Peng Su and Guhan Subbarayan, "Effects of Component Warpage on Board Assembly De- fects and Effective Mitigation Measures," SMTAI 2010. 4. Dudi Amir, Raiyo Aspandiar, Scott Buttars, Wei Wei Chin, and Paramjeet Gill, "Head-and- Pillow SMT Failure Modes," Proceedings SMTAI 2009. 5. JEITA, JEITA ED-7306, "Measurements Methods of Package Warpage at Elevated Tem- perature and the Maximum Permissible Warp- age," Japan Electronics and Information Tech- nology Industries Association, 2007. 6. JEDEC Publication 95, SPP-024 Issue A, "Reflow Flatness Requirements for Ball Grid Ar- ray Packages," JEDEC Solid State Technology Association, 2009. This paper originally appeared in the SMTA Journal in July 2013. To read Part 1 of this ar- ticle, click here. about the authors: Alex Chan, Paul Brown and Richard Coyle are with alcatel-lucent, ottawa, on, canada. Lars Bruno and Anne-kathrine knoph are with Ericsson, Katrineholm, Sweden. Thilo Sack is with celestica inc., Toronto, on, canada. David Geiger, David Mendez and Ron kulterman are with flextronics international, Milipitas, california. Mulugeta Abtew and Iulia Muntele are with Sanmina Corp, Milpitas, California and Huntsville, alabama. kirk vanDreel is with plexus corp, neenah, Wisconsin. for more information, click here. groundbreaking work at two Department of Energy national laboratories has confirmed pluto- nium's magnetism, which scientists have long the- orized but have never been able to experimentally observe. The advances that enabled the discovery hold great promise for materials, energy and com- puting applications. After seven decades, this scientific mystery on plutonium's "missing" magnetism has been re- solved. using neutron scattering, researchers from the Department of energy's los alamos and oak ridge (ornl) national laboratories have made the first direct measurements of a unique characteris- tic of plutonium's fluctuating magnetism. in a re- cent paper in the journal Science Advances, Marc Janoschek, from los alamos, explains that pluto- nium is not devoid of magnetism, but in fact its magnetism is just in a constant state of flux, mak- ing it nearly impossible to detect. using neutron measurements made on the ArCS instrument at ornl's Spallation neutron Source, a DoE office of Science user Facility, Ja- noschek and his team determined that the fluctua- tions have different numbers of electrons in plu- tonium's outer valence shell—an observation that also explains abnormal changes in plutonium's volume in its different phases. Neutrons Find "Missing" Magnetism of Plutonium WARPAGE ACCEPTANCE PROPOSAL continues FeAture

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