Cheol-Hee Moon

Comparison of the Thermal Performance of the Multichip LED Packages

Single chip, 4-chip, and 16-chip light emitting diode (LED) packages were prepared to compare the thermal performance of the LED packages. Vertical type, GaN blue LED chips with alumina submount were used, and thermal transient analysis was conducted to investigate the thermal characteristics of the LED packages. Temperature sensitive parameter value was measured and the junction temperature was predicted. Thermal resistance between the p-n junction and the ambient was obtained from the structure function with the junction temperature evolution during the cooling period of LED. Junction temperature and thermal resistance were investigated with the change of input current level and compared for 1-chip, 4-chip, and 16-chip LED packages. The results showed that the junction temperature and the thermal resistance are strongly related to the number of the chips and the chip arrangement.

Discharge characteristics of a plasma display using vertical auxiliary electrodes

Abstract In a conventional plasma display, the bus electrode was located on the ITO electrode at the outer part of each cell. We propose a new electrode configuration using vertical auxiliary electrodes which play a role of electrically connecting ITO and bus electrodes with the aim of enhancing discharge and luminous characteristics of the PDP (Plasma Display Panel). In this paper, luminance and luminous efficiency of the 3 in.‐diagonal test panel are measured with various number of vertical auxiliary electrodes such as 2, 50 and 150. The change in the luminous characteristics is explained in connection with the discharge characteristics of the PDP cells such as current peak, IR emission peak and ICCD picture image.

The Effect of the ITO Electrode Structure on the Luminous Characteristics of a Plasma Display Panel

The distance between the x and y bus electrodes was varied with the change of the length of the segmented ITO. Ne-5% Xe and Ne-20% Xe gases were used for the comparison, and the measuring frequency was varied to investigate their effects on the luminous characteristics. The ICCD and PR-900 observations of the discharge cell were carried out to analyze the discharge phenomena in the discharge cell. From the experimental results, it was shown that the luminance increased with the segmented ITO length, but the luminous efficiency remained almost the same. However, the frequency dependency of the luminous efficiency was different for the different ITO lengths.

Effects of some factors on the thermal-dissipation characteristics of high-power LED packages

Decreasing the thermal resistance is the critical issue for high-brightness light-emitting diodes. In this paper, the effects of some design factors, such as chip size (24 and 35 mil), substrate material (AlN and high-temperature co-fired ceramic), and die-attach material (Ag epoxy and PbSn solder), on the thermal-dissipation characteristics were investigated. Using the thermal transient method, the temperature sensitivity parameter, R th (thermal resistance), and junction temperature were estimated. The 35-mil chip showed better thermal dissipation, leading to lower thermal resistance and lower junction temperature, owing to its smaller heat source density compared with that of the 24-mil chip. By adopting an AlN substrate and a PbSn solder, which have higher thermal conductivity, the thermal resistance of the 24-mil chip can be decreased and can be made the same as that of the 35-mil chip.

Improvement of Light Extraction Efficiency of LED Packages Using an Enhanced Encapsulant Design

We optimized the design of the flat encapsulant of a light-emitting diode (LED) package to obtain higher light output power (LOP), both by experiment and simulation using three-dimensional ray-tracing software. In the experiment, the refractive index of the encapsulant was varied (1.41 and 1.53). In addition, double-layer structures with these refractive indices (1.41/1.53) were investigated by varying the shape of the interface between the two among flat, concave, and convex. The experiments showed that the LOP of the double-layer encapsulant with convex interface increased by 13.4% compared to the single-layer encapsulant with a refractive index 1.41, which was explained by the increase of the light extraction efficiency (LEE) in connection with the increase of the critical angle (

Enhancement of upward thermal dissipation in a 16-Chip LED package using ceramic barrier ribs

{\theta}_c

The enhancement of the BRCR (Bright Room Contrast Ratio) in a plasma display panel

) and the decrease of the Fresnel reflection.

Effect of radius of curvature of a convex interface on the light output power of light-emitting diode package with double-layered encapsulant

To enhance the upward thermal dissipation characteristics in a 16-chip light emitting diode (LED) package, ceramic barrier ribs were introduced between the LED chips. A FLIR T-250 IR microscopy camera was used to measure the top surface temperature of the package, which decreased from 116°C to 112°C at 2.5W operation because of the ceramic barrier ribs. A finite volume method simulation was conducted to estimate the temperature distribution inside the package, including the junction temperature. This simulation showed that the junction temperature decreased from 119°C to 114°C because of the barrier ribs. This result occurred because the ceramic barrier ribs provided a more effective upward heat dissipation path for the mid-chips, which contributed to the decrease in the junction temperature.

Variation of Junction Temperature According to Chip Configuration for a High-Power LED Package

Luminous efficiency and Bright Room Contrast Ratio (BRCR) are critical issues in a plasma display panel. In the conventional PDP panel structure, an optical filter is used to reduce the reflected luminance and to increase the BRCR. However, this optical filter reduces the peak luminance also, resulting in a decrease in the luminous efficiency. In this study, a new electrode structure with the enlarged black stripe and the auxiliary electrode between the bus and ITO electrode was proposed to investigate the possibility of getting higher BRCR without an optical filter. The experimental results using 3 in. test panels in this study showed that the BRCR of the new structure was enhanced to more than twice of that of the conventional one without any loss of the luminous efficiency.

The effect of the cell size on the discharge characteristics of a plasma display panel

We investigate the effect of the radius of curvature, R, of a convex interface on the light output power of an light-emitting diode package. The encapsulation layers consist of two layers, with refractive indices of 1.41 and 1.53. By using a geometrical calculation and 3-D ray-tracing simulation, we quantify the effect of R on the light extraction efficiency (LEEec) by examining the escape cone and the Fresnel reflection loss. The increase in the LEEec is explained with respect to the change of the incident angle and the re-extraction of the reflected rays at the curved interface.