Thermal Characteristics Analysis of Die Attach Layer Based on Time-Constant Spectrum for High-Power LED

The performance and reliability of the high-power light-emitting diodes (HP LEDs) are closely related to the quality of the die attach adhesive (DAA) layer, because voids or delaminations in the layer may cause higher junction temperature, and even result in the break of the chip. In this paper, a dynamic compact thermal model is constructed for an independent HP LED without being attached on a cold plate. The time-constant spectrum method based on the thermal model is applied to characterize the transient thermal behavior of the DAA layer and other layers along the heat flow path. Thermal transient experiments are carried on HP LED samples with different DAA dosages. The theoretical and experimental results demonstrate that the time-constant spectrum for LEDs tested without cold plate can reflect the thermal characteristics of the DAA layer as well as that with cold plate. Differences in the HP LED samples with different DAA layers can be obviously distinguished in the time-constant spectrums as well. Compared with the traditional testing method with cold plate, direct test in air for HP LEDs has the advantages of easy operation, time saving, and no pollution to samples.