Micross

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Thermoplastic Optical Polymers with Lead-Free Solder Reflow Resistance for HB-LED Packaging and Assembly
Keywords: Optical Polymer, LED Packaging, Solder reflow resistant
An injection moldable optical polymer that can withstand a lead-free solder reflow process is of great interest for LED manufacturing. It would allow a more economical packaging and assembly of LED devices for general lighting and illumination. A new class of optical polymers made by substantially fully hydrogenating block copolymers of styrene and butadiene, known as cyclic block copolymers (CBCs), were recently discovered to exhibit solder reflow resistance up to temperature as high as 260 degree C. This kind of behavior is uncommon to traditional thermoplastic polymers. The block copolymer design and the resulting nanostructured morphology lead to strong elastic and soft solid type of characteristics for CBC, which may explain why CBCs can maintain good dimensional stability when exposed to high temperature (>Tg) during the reflow process. This hypothesis was examined by a numerical calculation of a molded CBC lens for use in a surface mounting device (SMD) LED. The simulation results confirmed the change in physical dimension of the molded CBC lens is negligible after solder reflow. In combination with its excellent optical transparency, low moisture absorption and long time photo stability, injection moldable CBCs become a promising class of materials for LED packaging and assembly use.
Weijun Zhou, Research Scientist
The Dow Chemical Company
Freeport, TX
USA


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