Thermal management problem solution for high brightness LED applications

However, the amount of heat from the LED source is not the main problem affecting the LED, and the concentration of heat (and thus the formation of hot spots) is the key to the problem. For general standard LED devices, the heat flux of a 1W LED device is about 100W/cm2, and the heat flux of a 3W LED device is as high as 300W/cm2, while the heat flux of a typical CUP is 60~130W/cm2. . The heat is concentrated in a wafer having a small size, the temperature of the wafer is raised, the distribution of thermal stress is uneven, the luminous efficiency of the wafer, and the emission efficiency of the fluorescent powder are lowered. When the temperature exceeds a certain value, the device failure rate increases exponentially. When a plurality of LEDs are densely arranged to form a white light illumination system, the heat dissipation problem is more serious.

The heat dissipation path of LED devices is mainly heat conduction and heat convection. Traditionally, the heat dissipation structure of an LED luminaire includes a substrate, a heat sink, and a heat sink. The substrate conducts thermal energy from the grains and is thermally conductive but not electrically conductive. The heat sink spreads heat away from heat build-up at the LED source and increases the efficiency of the heat sink. The heat sink can be thermally and efficiently dissipated in the air. However, the extremely low thermal conductivity of the substrate material tends to cause an increase in the thermal resistance of the device, resulting in a severe self-heating effect, which has a devastating effect on the performance and reliability of the device.

Microloops' Vapor Chamber enables ultra-high heat flux heat transfer to solve hot spots in high-power LEDs. The soaking plate is a vacuum chamber with a micro-structure on the inner wall. When the heat is transmitted from the heat source to the evaporation zone, the working medium inside the cavity will begin to produce liquid phase gasification in a low-vacuum environment. At this point the medium absorbs thermal energy and the volume expands rapidly, and the medium in the gas phase quickly fills the entire cavity. When the gas phase medium contacts a relatively cold area, condensation occurs. The condensation accumulates the heat accumulated during evaporation. The condensed liquid medium returns to evaporation by the capillary phenomenon of the microstructure. Heat source. This operation will be repeated in the cavity, which is how the soaking plate works. Since the microstructure can generate capillary forces when the working fluid evaporates, the operation of the soaking plate can be prevented from being affected by gravity.

Figure 1: The heat sink structure of the soaking plate LED lamp removes the substrate.

Figure 1 shows the heat dissipation structure of an LED lamp using a soaking plate that removes the substrate and reduces a large portion of the thermal resistance. The LED devices can be closely packed and directly bonded to the soaking plate, and the LED devices and related circuits are directly packaged in a standard wire-bonding machine to form an independent light source.

This method of directly bonding LED devices to a soaking plate has significant benefits. The lower part of the LED device is in contact with the soaking plate, and the point heat source can be diffused through the soaking plate and the heat can be efficiently transmitted to the back end, thereby reducing the hot spot temperature Tj and improving the life of the LED. In addition, this method can also focus on the placement of LED devices, allowing the light source to be concentrated, which is advantageous for secondary optical design. SMIs in SMD packages can also be mass-produced using SMD automation equipment.

Figure 2 shows the temperature comparison of a high-power LED lamp with a soaking plate (bonding multiple LEDs with a total power of 50W directly to the soaking plate) to the same power LED with a copper substrate.

Figure 2: Temperature comparison of a high power LED lamp using a heat spreader (VC) and a copper substrate (Cu).

In addition to high-power LED streetlights , today's soaking board solutions are also used in power semiconductor cooling, blade servers, graphics cards, telecom infrastructure, power amplifiers, radar transmitter modules, satellites and laptops. Maike's soaking plates are customizable in size and shape, with a minimum thermal resistance of 0.05 degrees per watt and a thickness of less than 3 mm. The company has also developed a soaking plate that can handle more than 300W of thermal power to solve the heat dissipation problem of high-end image cards. The ultra-thin design provides a 3.0mm thick soaking plate that provides 150W of heat dissipation for a single-slot image card.