The objective of this study is to quantitatively evaluate the impacts of LED components on the overdriving reliability of high power white LED chip scale packages (CSPs). The reliability tests under room temperature are conducted over 1000 h in this study on CSP LEDs with overdriving currents. A novel method is proposed to investigate the impact of various components, including blue die, phosphor layer, and substrate, on the lumen depreciation of CSP LEDs after aging test. The electro-optical measurement results show that the overdriving current can lead to both massive light output degradation and significant color shift of CSP LEDs. The quantitative analysis results show that the phosphor layer is the major contributor to the failure in early period aging test. For the long-term reliability, the degradations of phosphor and reflectivity of substrate contribute significantly on lumen depreciation. The proposed reliability assessment method with overdriving loadings can be usefully implemented for LED manufacturers to make a cost- and effective-decision before mass production.@en

Using the analogue of the electric inductance, we reveal the properties of the thermal inductance in GaN-based light-emitting diode devices by testing their transient thermal behaviors. We find that the devices exhibit a transient thermal response under step-down or step-up currents and observe notable inductive phenomena of the temperature response as time evolves from start up to some hundred microseconds. We define thermal inductance as the rapid change in device temperature that is opposite to the temperature change expected from the power input. These findings can promote new temperature measurements, and novel thermal analyses of high-frequency semiconductor devices that combining the thermal resistances, thermal capacitances, and thermal inductances.@en

The drive to increase electrical currents input, and to achieve high lumen output for High Brightness Light Emitting Diode (HB LED) has led to a series of thermal problems. Hence, thermal management is one of key design parameters as the temperature directly affecting the maximum light output, quality, reliability and life time. For LED arrays, the arrangement of chips will affect the thermal performance and junction temperature is very important in the design. However, because direct junction temperature determination is hard to detect due to the encapsulation, indirect methods are more preferred. Among them, the diode forward-voltage method is the most accurate one. Therefore, we used the diode forward-voltage method to optimize thermal design of LED arrays in this work.@en