Thermal management of LEDs: package to system

Abstract

Light emitting diodes, LEDs, historically have been used for indicators and produced low amounts of heat. The introduction of high brightness LEDs with white light and monochromatic colors have led to a movement towards general illumination. The increased electrical currents used to drive the LEDs have focused more attention on the thermal paths in the developments of LED power packaging. The luminous efficiency of LEDs is soon expected to reach over 80 lumens/W, this is approximately 6 times the efficiency of a conventional incandescent tungsten bulb. Thermal management for the solid-state lighting applications is a key design parameter for both package and system level. Package and system level thermal management is discussed in separate sections. Effect of chip packages on junction to board thermal resistance was compared for both SiC and Sapphire chips. The higher thermal conductivity of the SiC chip provided about 2 times better thermal performance than the latter, while the under-filled Sapphire chip package can only catch the SiC chip performance. Later, system level thermal management was studied based on established numerical models for a conceptual solid-state lighting system. A conceptual LED illumination system was chosen and CFD models were created to determine the availability and limitations of passive air-cooling.

Thermal Management and Interfacial Properties in High-Power GaN-Based Light-Emitting Diodes Employing Diamond-Added Sn-3 wt.%Ag-0.5 wt.%Cu Solder as a Die-Attach Material

“…Recently, high-power GaN-based LEDs have attracted much attention and are considered candidates for next-generation general illumination applications due to their high luminous efficiency, long operating life, energy savings, and so forth. 1 However, a power saturation phenomenon 2 was often encountered in the operation of GaN-based LEDs packaged with silver paste when the current injection level was raised. This is because the thermal conductivity of silver paste is poor and the heat generated from LEDs was not being efficiently dissipated, resulting in reduced conversion efficiency with increasing junction temperature.…”

Performance of LED street lights in hot environments

“…With the use of large LED arrays, it is possible to generate a large heat loads at the system level which can cause challenges for overall heat dissipation, especially when passive cooling is used. The large array with passive cooling techniques leads to elevated LED die temperatures, which have been linked to lower quantum efficiencies, shorter lifetimes, emission wavelength shifts and, catastrophic device failure [1][2][3][4][5][6]. A heat flux from a 900 high brightness LED chip, has already reached approximately 125 / [3] which is considered relatively high heat flux and comparable to heat generation in integrated circuits.…”

Mathematical simulation of heat transfer processes at the maximum possible electrical loads in typical light-emitting diodes

“…As a rule, their functional loss is a consequence of overloads, short circuits and deformations [1]. The processes regularities analysis allows making a conclusion describing, first of all, a regulation conditions disruption of LED heat exchange with the environment and, as a result of it, the LED fails [2,3].…”

“…The balanced models and software applications based on them (the LED's thermal resistance calculation models [2], taking into account the infrared radiation effects [6], p-n junction temperature change [4], as well as CFD-simulation [7]) are the mostly widely used. However, many experiments [3,5,6,8,9] with different LEDs showed that the balanced models application domain is very limited.…”