Introduction
The commercialization of light emitting diodes (LED) with their application to general lighting has led to an increase in demand for high power LED packages. The basic conditions that need to be met by LED packages include excellent light extraction efficiency [1] and a heat dissipation structure for the package, which releases the heat created from the chip die during operation to outside the package [2] and [3]. As the light extraction efficiency and heat dissipation structure are not independent of each other, photons and heat are produced from the chip active area when power is supplied to the LED package. Except for some photons that are extracted outside the package, most photons are dissipated as heat. Thus, effectively expelled heat produced from the chip enhances the extraction efficiency and reliability of the LED package. Conventional LED lighting modules can be categorized into a structure where the LED package is attached to the printed circuit board (PCB) using the surface mount technology (SMT) process and a chip on board (COB) structure where the LED device is attached directly to the PCB board [4], [5] and [6]. The LED light source module applied to the SMT process has numerous thermal nodes that are structurally complex. Therefore, an increase in the thermal resistance of each thermal node is inevitable in order to release the heat produced by the chip to the surrounding air. Although the COB structure has less thermal nodes in comparison to the LED light source module with the SMT process applied, the thermal resistance of the insulating layer was installed in the PCB structure where the LED die is located. This resistance increase hinders the release of heat caused by the LED die. Previous studies reported up to now the LED junction temperature, which is directly related to the optical characteristics of the LED package [7], [8], [9] and [10]. However, studies on heat dissipation structures, where the insulating layer between the LED device and the base metal of the board is partially removed, as well as an analysis of the thermal characteristics of this kind of structure have yet to be published.
In this paper, after removing the insulator of the PCB area layer where the chip was packaged to minimize the thermal nodes, and directly packaging the chip to the PCB metal layer, a chip on metal (COM) package heat dissipation structure is proposed in order to effectively dissipate the heat produced by the chip during operation. Both COB and COM package types were fabricated to analyze the thermal characteristics of the proposed COM package. The chip junction temperature and thermal resistance for each specimen were measured. Furthermore, the change in spectrum, color coordinates, and speed of light were comparatively analyzed according to the driving time.