Effect of die attach adhesive defects on the junction temperature uniformity of LED chips

Abstract

In the literature, the junction temperature of a light emitting diode (LED) has been considered having a uniform distribution over the whole chip. Such a perception is based on the assumption that the die attach adhesive (DAA) covers the whole bottom of the LED chip with a uniform thickness. However, in reality, there may be insufficient DAA during the chip mounting process. As a result, non-uniform junction temperature may be induced and hot spots could occur. Therefore, it is essential to investigate the effect of DAA on the creation of hot spots at the LED junction. In the present study, LED chips were mounted with various amounts of DAA on a leadframe designed for high power LED. A high resolution infra-red (IR) camera was used to measure the temperature on the surface of the LED chip. The obtained IR images were calibrated carefully in order to eliminate the influence from IR emissivity. Hot spots were observed at the junction areas where DAA was missing. Detailed analysis for illustrating the effect of DAA distribution on hot spots is presented and reasons for such a phenomenon are discussed.

A Critical Review on the Junction Temperature Measurement of Light Emitting Diodes

“…The application of IR thermography can be seen for the thermal inspection of various types of LEDs, including chip on board (COB) [ 104 ], surface mounted devices (SMD) [ 105 ], and flip-chips [ 106 ]. This method is widely preferred for various thermal management-related problems in LEDs [ 107 , 108 , 109 , 110 , 111 , 112 ]. The basic principle of IR thermography is to capture electromagnetic radiation emitted from the surface of objects in the IR spectrum and monitor the corresponding 2D temperature maps.…”

Charging method of micro heat pipe for high‐power light‐emitting diode

“…If the junction temperature of the LED is too high, the effective compound of the carrier is likely to decrease. It results in the luminous efficiency becoming small and even the LED chip being damaged [5][6][7]. Therefore, effective heat dissipation is important for high-power LEDs.…”