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The dominant technology for manufacturing backlight illumination structures is typically based on use of individually packaged Surface Mount Device (SMD) Light Emitting Diodes (LEDs). The optical power from sources is coupled to the light guide having a special structure to couple light out so that uniform illumination is achieved to the illuminated component, typically LCD display. In practice the structure contains several separate diffuser films, which results to a thick and costly structure. In addition, the light coupling from LED to the light guide is sensitive to alignment errors causing nonuniform and inefficient illumination. The developed alternative packaging structure for backlighting solutions is based on inorganic LED devices and multilayer polymer substrate. Polycarbonate substrate material was used, which is highly transparent at visual band allowing low absorption and has good lamination properties in hot lamination process allowing compact integrated structures. In the manufacturing process the individual polymer sheets with an individual thickness of 100 μm were printed with conductive patterns produced by screen printing using silver-based thick film pastes. The final integrated multilayer structure containing embedded LED devices was produced in a hot lamination process. Two types of LED devices were embedded within the laminated structure, namely blue LED, type C470RT290 and green LED, type C527RT290. The bottom area of the chip was 300 μm × 300 μm and the thickness 115 μm. The devices were manufactured by Cree. Test samples containing 3 × 3, 5 × 5 and 5 × 7 LED devices were designed, implemented and characterized. The final laminated structure thickness was typically 300 μm. The performed designs verified by test structure implementations and characterizations showed that the final thickness of the backlight illumination structure depends of the required uniformity of illu- - mination and allowed LED device pitch and used diffuser efficiency. The main advantages of the implemented system compared to traditional light guiding system are easy optical coupling with high efficiency in an integrated and thin package. The developed technology seems to be suitable to produce backlight illumination structures for applications in which thin, lightweight, efficient and cost-efficient backlight illumination structure is essential, such as, hand-held devices. In addition, the developed technology seems to be possible to apply in several other applications, such as, information tables, signboards and displays.
Date of Conference: 13-16 Sept. 2010