Dow Corning provides reflective silicones for CSP and COB LEDs14-03-2017
Dow Corning has brought three new silicone coatings that the company says are highly reflective and each is optimized to specific uses in packaged LEDs. The products includes materials that can be distributed traditionally and one that can be applied by increasingly popular screen-printing processes. The new silicones will be especially used to chip-scale package (CSP) and chip-on-board (COB) LEDs as component manufacturers hope to maximize light extraction.
All of the new silicones share some operating parameters. They provide maximum reflectivity from a very thin applied layer and keep the photometric properties at lasting temperatures of 150°C. Dow Corning said many organic coatings turned bad at such temperatures. With manufacturers enabling higher drive currents and greater power density in new LEDs, it is much important for materials used near the semiconductor junction to endure and indeed perform excellently in a high-temperature environment.
The environmental challenges come at a time when LED factories are also hoping to either reduce component size as is the case with CSP LEDs, or pack emitters more densely as is the case with arrays in COB LEDs. The WR-3001 Die Edge Coat material specifically targets high-power CSP LEDs. Some manufacturers produce products that emit light from five sides or surfaces — the top and the four sides. Such a product may be suitable in an application where it is placed under a total internal reflection (TIR) lens or used in a linear lighting fixture with a broad beam pattern. But many applications require tighter beam control.
The related WR-3100 Die Edge Coat material has similar properties to the WR-3001 and is produced primarily for low- and mid-power LEDs. As we know, mid-power devices are increasingly popular in general LED lighting applications. The WR-3100 material also offers a hardness value of Shore D 65 after curing. That durability means that the material can be applied at the wafer level before die singulation, and many manufacturers are adopting wafer-level processing as one way to greatly reduce production costs.
The final new material is the WR-3120 Reflective Coating that can be applied via screen printing and that Dow Corning says offers the highest reflectivity. Those characteristics make the silicone a good match for COB LED manufacturing. A component manufacturer would screen print the material onto the COB substrates before assembling the LED die. The material has a high hardness value and can endure the assembly process while maintaining its photometric properties.