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104 SMT Magazine • June 2016 Las Marias: Aside from miniaturization, what other industry or market trends are affecting the solder paste printing process? Evangelista: The automotive electronics indus- try has grown significantly. Most of the controls and sensors in cars nowadays are dependent on electronics assembly. The medical electronics market is also forecasted to grow. The common challenge for these industries is reliability of solder joints. Las Marias: What can you say about the advan- tages and disadvantages of solder jet paste print- ing and screen printing? Evangelista: Screen printing has the advantage in terms of speed especially for high-volume products, while solder jet paste printing deals with accuracy in solder paste deposit. Another advantage of solder jet paste printing is for pro- totyping that don't require lead time in stencil fabrication. Screen printing best fit high-vol- ume, low-mix (HVLM) and high-volume high mix products (HVHM), while solder jet paste is suitable for low-volume, high-mix (LVHM) and low-volume, low-mix (LVLM) products. Las Marias: Please give a list of best practices for solder paste printing. What factors do users need to consider when it comes to solder paste printing? Evangelista: Design for manufacturability (DFM) is a compilation of best practices that has been developed through design of experiment (DOE) and industry practices. These are the fac- tors to be considered: • Stencil aperture design • Stencil aperture opening (Ratio of paste volume and component solder area) • Stencil thickness • Solder paste selection (Alloy composition/ granule size) • Printer parameter setting (Pressure/ squeegee speed/cleaning capability) • Squeegee material • Reflow oven selection (8 zones/10 zones) • Reflow profiling (speed/temperature/ nitrogen) Las Marias: What do you think is the future for solder paste printing? Evangelista: Scalability is always the challenge to bring down cost. Solder paste printing will still be the future, and nothing can compete when it comes to high volume production. Las Marias: Thank you very much, Knoll. Evangelista: Thank you. SMT THE RELIABILITY FACTOR IN SOLDER PASTE PRINTING Dr. Kyeongjae Cho, professor of materials science and engineering in the Erik Jonsson School of Engineer- ing and Computer Science at UT Dallas, has discov- ered new catalyst materials for lithium-air batteries that jumpstart efforts at expanding battery capacity. The re- search was published in Nature Energy. There's huge promise in lithium-air batteries, but de- spite the aggressive research being done, those prom- ises are not being delivered in real life, according to Cho. His team, including UT Dallas graduate student Yongping Zheng, have demonstrated that this problem can be solved. Cho and Zheng's new research focuses on the elec- trolyte catalysts inside the battery, which, when com- bined with oxygen, create chemical reactions that cre- ate battery capacity. They said soluble-type catalysts possess significant advantages over conventional solid catalysts, generally exhibiting much higher efficiency. Based on that background, Cho and Zheng have collaborated with researchers at Seoul National Univer- sity to create a new catalyst for the lithium-air battery called dimethylphenazine, which possesses higher sta- bility and increased voltage efficiency. The catalyst research should open the door to ad- ditional advances in technology. But Cho said it could take five to 10 years before the research translates into new batteries that can be used in consumer devices and electric vehicles. Co-authors on the study included researchers led by Dr. Kisuk Kang at Seoul National University. Discovery Could Energize Development of Longer-Lasting Batteries

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