Led Design Guide Page 33 LED Design Guide

2015 Littelfuse LED Lighting Design Guide www.littelfuse.com LED Lighting Design Guide Fusible Traces. FR4 and other common circuit board compositions are organic based materials that contain high amounts of carbon. They generally have very low ignition temperatures relative to the melting temperature of copper. Because of this, the combination of copper and epoxy based materials can form a very unpredictable fuse package. Copper circuit traces have a melting temperature of 1083C and are made using a lamination process that embeds dendrites into uncured epoxy. The high melting temperature and low dielectric strength created by the trapped dendrites creates a potential fire hazard ( Figure 20 ) during interruption of overcurrent conditions, especially evident during low overload operation. Figure 20. Progressive destruction of fusible circuit trace intended for overcurrent protection; it ends up igniting the PCB laminate material. Potential Problems with Alternative LED Lamp Overcurrent Protection Technologies (continued) 33

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