SMT007 Magazine

SMT-Jan2017

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50 SMT Magazine • January 2017 lar sieve—that is to say, the size and shape of its structural openings are that of H 2 O molecules. And those water molecules are literally sifted from the air inside the cabinet. The desiccant is never touched by operators, and it never needs replacing, because the systems have automatic regeneration cycles. This 0.5% RH enables not just safe storage, but an effective drying of components, even at room temperature. This is impossible to achieve with nitrogen alone. (Disagree? Put an apple in one of each type of cabinet and see what they look like after a day.) Components stored in ultra-low RH cabi- nets utilizing such technology are thus dehu- midified, even at ambient temperature. Increas- ing the temperature to 40°C (the point as not- ed previously, at which most alloys will not ox- idize) while maintaining 1% RH can further accelerate the drying time of components with- out oxidation or intermetallic growth, and at 10% of the operating cost of high-temperature baking. By virtue of the oxidation protection ex- plained previously, longer periods of storage without the use of moisture barrier bags are also practical. Safeguarding the quality and reliabil- ity of electronic assemblies starts with the con- trolled storage of components and PCBs. SMT Richard Heimsch is a director at Protean Inbound and for Super Dry in the Americas. CONTROLLING OXIDATION AND INTERMETALLICS IN MOISTURE-SENSITIVE DEVICES Faster production of advanced, flexible elec- tronics is among the potential benefits of a discovery by research- ers at Oregon State University's College of Engineering. Taking a deeper look at photonic sintering of silver nanoparticle films—the use of intense pulsed light (IPL) to rapidly fuse functional conductive nanoparticles—scientists uncovered a relation- ship between film temperature and densification, which increases the density of a nanoparticle thin- film or pattern, leading to functional improve- ments such as greater electrical conductivity. The engineers found a temperature turn- ing point in IPL despite no change in pulsing en- ergy, and discovered that this turning point ap- pears because densification during IPL reduces the nanoparticles' ability to absorb further energy from the light. This previously unknown interaction between optical absorption and densification creates a new understanding of why densification levels off after the temperature turning point in IPL, and further enables large-ar- ea, high-speed IPL to re- alize its full potential as a scalable and efficient manufacturing process. Rajiv Malhotra, assistant professor of mechan- ical engineering at OSU, and graduate student Shalu Bansal conducted the research. The results were recently published in Nanotechnology. Intense pulsed light sintering allows for faster densification over larger areas compared to con- ventional sintering processes such as oven-based and laser-based. IPL can potentially be used to sin- ter nanoparticles for applications in printed elec- tronics, solar cells, gas sensing and photocatalysis. Products that could evolve from the research, Malhotra said, are radiofrequency identification tags, a wide range of flexible electronics, wearable biomedical sensors, and sensing devices for envi- ronmental applications. Advance in Intense Pulsed Light Sintering Opens Door to Improved Electronics Manufacturing

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