SMT007 Magazine

SMT007-Oct2018

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82 SMT007 MAGAZINE I OCTOBER 2018 There are many factors that influence void frequency and size. This study showcases serval design, process and chemistry impact on voiding. There are many drivers for LED designs today. Particularity the design of solder pads both influences the thermal, electrical and mechanical characteristics of the LED package. The impact of pad symmetry which is directly related to total solder volume can influence the voiding performance. Adjusting the reflow profile is a very easy way to reduce voids. Using a soak pre-heat profile reduces voiding in BGA devices. Increasing the time above liquidus reduces voiding in BTCs as well. Solder paste chemistry also has a significant effect on voiding. SMT007 Editor's Note: Originally published in the proceedings of SMTA International 2017. References 1. M. Holtzer, T.W. Mok, "Methods of Reducing or Eliminating Voids in BGA and BTC Devices" SMTA Penang – MY March 2016. Matthew Siebenhuhner is an applica- tions engineer for Argomax and die attach solutions at Alpha Assembly Solutions. Gyan Dutt is global portfolio manager for die attach, and technical market- ing manager for LED at Alpha Assembly Solutions. Mitch Holtzer is the director of Americas Reclaim Business of Alpha Assembly Solutions. T.W. Mok is an applications engineering manager for Asia-Pacific at Alpha Assembly Solutions. Ranjit Pandher is the R&D manager for LED and semicon- ductor soldering products at Alpha Assembly Solutions. Amit Patel is no longer with the company. There has been an intense research conducted for developing lithium-sulfur (Li-S) batteries with high energy density because lithium-ion batteries (LIBs) only allow for a very short travel distance of electric vehicles per charge. However, Li-S batteries are still unable to provide a longer lifecycle due to the poor reversibility of the lith- ium metal cathode. To tackle this issue, a research team from the Korea Advanced Institute of Science and Technology (KAIST) led by Professor Hee-Tak Kim from the Department of Chem- ical and Biomolecular Engineering used lithium sulfide (Li 2 S) cathodes and combine them with graphite anodes to enhance energy density and lifecycles for the batteries. Yet, Li 2 S is costly and, so far, there has not been an elec- trode architecture and electrolyte design that enables a longer lifecycle between the graphite anodes and lithium sulfide cathodes. To address this, the team produced a doughnut-shaped Li 2 S cathode active material from low- cost Li 2 S developed from raw materials. They have also developed a Li 2 S ion battery with a graphite anode and Li 2 S cathode using a high concentration salt electrolyte. Through this technology, the team achieved 30% higher energy density than that of conventional LIBs and secured a lifecycle of more than 600 cycles. This dough- nut-shaped lithium sulfide-based electrode can be manu- factured using low-cost raw materials and a single heat treatment process. The electrode can also be applied to existing LIBs. (Source: Korea Advanced Institute of Science and Technology) Using Donut-shaped Lithium Sulfide for Higher Performing Batteries

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