High-brightness RGB LED modules based on alumina substrate

Light emitting diodes (LED) have penetrated into various lighting applications, such as backlighting of keypads and displays in mobile phones, signs, video screens, traffic signals, and exterior and interior lighting for automobiles. A new trend is to use color-tunable light to set or dynamically vary the ambience of the illuminated space. We developed high-brightness RGB LED modules that use bare chips on an alumina (Al2O3) substrate. The substrate has dimensions of 14.7 × 25.4 mm2 and an electrical power consumption of 4.4 W. Thermal simulations were carried out to find the optimum solution among various substrate thicknesses, interface layer materials and geometry of thermal vias in the substrate. Two commercially available plug pastes were experimentally evaluated for making thermal vias. We realized three module series that use a 0.63 mm, 1 mm or 1.27 mm thick substrate. LED chips were die-bonded using electrically-conductive adhesive and wire-bonded with 25-µm Au wire. All chips and bonding wires were protected with UV-curable adhesive. The simulated thermal resistance for the 0.63-mm thick substrate was 6.3 K/W. The optimum solution using one large thermal via and heat distribution layer on top surface of the substrate decreases the resistance down to 2.8 K/W.