The dominant technology for manufacturing backlight illumination structure (BLIS) is typically based on the use of individually packaged Surface Mount Device (SMD) Light Emitting Diodes (LEDs) and special light guide plate (LGP) and diffuser films. The BLIS implementation, however, contains several separate diffuser films, which results in a thick and costly structure. In addition, the light coupling from LED to the LGP is sensitive to alignment errors causing non-uniform and inefficient illumination. The developed packaging structure for backlighting solutions introduced in this paper is based on inorganic LED chips and multilayer polymer structure. The performed designs of 3 x 3, 5 x 5 and 5 x 7 LED chip matrices, verified by test structure implementations and characterizations, showed that the final thickness of the backlight illumination structure depends on the required uniformity of illumination, allowed LED device pitch and efficiency of the diffuser. In the manufacturing process the polycarbonate sheets with an individual thickness of 100 µm were screen printed with conductive patterns using silver-based thick film pastes. The final integrated multilayer structure containing embedded LED chips was produced in a hot lamination process. Two types of LED chips, manufactured by Cree, were embedded within the laminated structure, namely blue LED, type C470RT290 and green LED, type C527RT290. The final BLIS demonstrator size was 50 x 75 mm2 consisting of six 25 x 25 mm2 modules. Each module consisting 5 x 5 LED devices resulting total number of 150 LED devices with 5 mm pitch. The measured key characteristics of the demonstrator were as follows: average brightness 11.600 cd/m2 (ILED=2 mA), luminous efficiency 22 lm/W, color temperature 5550 K, CIE values (x=0.331, y=0.411), CRI = 70 and total power conversion efficiency of 6.3%. A performance simulation of BLIS structure based on the characterization results of the test structure and was implemented in MatlabTM software. This simulation system together with a complementary Cost-of-Ownership (COO) modeling module enabled BLIS structure performance optimization against manufacturing cost.
Key words: backlight illumination structure, inorganic LED chips, hot lamination, embedding, multilayer polymer substrate