Heat and fluid flow in high-power LED packaging and applications

Abstract

Light-emitting diodes (LEDs) are widely used in our daily lives. Both light and heat are generated from LED chips and then transmitted or conducted through multiple packaging materials and interfaces. Part of the transmitted light converts into heat along the light propagation; in return, the accumulation of heat leads to the degradation of light output. The accumulated heat negatively influences the reliability and longevity of LEDs, and thus thermal management is critical for LED packaging and applications. On the other hand, in LED packaging processes, many fluid flow problems exist, such as phosphor coating, silicone injection, chip bonding, solder reflow, etc. Amongst them, phosphor coating is the most important process which is essential for LED performance. Phosphor gel is a kind of non-Newton fluid and its coating process is a typical fluid-flow problem. Overall, since LED packaging and applications present many heat and fluid flow problems, obtaining a full understanding of these problems enables advancements in the development of LED processes and designs. In this review, the emphasis is placed on heat generation in chips, heat flow in packages and application products, fluid flow in phosphor coating process, etc. This is a domain in which significant progress has been achieved in the last decade, and reporting on these advances will facilitate state-of-the-art LED packaging and application technologies.

Directional heat transport through thermal reflection meta-device

“…But the weakened thermal reflection effect could be improved with thinnerlayer structures or larger layer number N. 20 It is demonstrated that the present thermal reflection meta-device can also be made by nature-existing isotropic materials. With directional heat transfer, the present meta-device could be used to realize local heating/cooling for electronic devices 34 and high-efficient energy harvesting/utilizing.…”

Spot phosphor concept applied to a remote phosphor light-emitting diode light engine

“…29,30 According to literature, 31 YAG:Ce-silicone white phosphor-converted LEDs can withstand phosphor luminance levels of up to 1e6 cd∕m 2 without undergoing thermal quenching in the steady state. In our device, the luminance reaches a maximum value of 2.2e5 cd∕m 2 , hence, no thermal quenching is expected to occur.…”

On a relationship among optical power, current density, and junction temperature for InGaN-based light-emitting diodes

“…[4][5][6][7][8] In general, there are interactions among these photometric, electrical, and thermal aspects. [9][10][11][12] In their works, the photo-electro-thermal theory has been presented by linking the luminous flux, thermal resistance, electrical current, junction temperature, heat dissipation coefficient, etc. Here, by studying theories of spontaneous emission rates and carrier recombination mechanisms, we derive a simple and useful model only linking the optical powers, junction temperatures or heat-sink temperatures, and current densities.…”