High-power Light-emitting Diode Chips Research Articles

Highly efficient photonic PCR system based on plasmonic heating of gold nanofilms

The polymerase chain reaction (PCR) is a standard molecular method that has the potential to solve the need for accurate, viable, and immediate infectious pathogen detection at point-of-care (POC) centers in different fields such as pathogen identification, and forensics. In this work, we present a photonic PCR thermocycler that achieves strong optical absorption, more efficient gene amplification, and further improves the effect of temperature distribution through the PCR sample using two gold nanofilms (AuNFs) and a high-power light-emitting diode chip (LED). The photonic device achieved higher heating and cooling rates of 13.20 null°C/s and 7.92 null°C/s, respectively on average, with uniform and reliable temperature distribution throughout the sample with negligible deviations. During amplification cycles, maximum temperatures attained had variations less than 1 °C at 90 °C, less than 0.8 °C at 55 °C, and less than 0.5 °C at 72 °C, showing uniform heating which yielded more accurate and reliable results. Using the fabricated device, PCR amplification for a bacteria genomic DNA was performed in 7.5 minutes for 30 thermal cycles with a sample volume of 20 μL. Due to the device's simple configuration and increased heat transfer rates, this photonic platform will be a highly efficient choice for rapid POC applications in developing countries.

Heat dissipation of high-power light emitting diode chip on board by a novel flat plate heat pipe

A new flat plate heat pipe (FPHP) which has many parallel-arranged micro-fins casted on the condensation surface was designed and fabricated. An experimental system for studying the thermal performance of this FPHP when applied for cooling high-power LED (light emitting diode) COBs (chip on board) was also set up. From experiments, the new FPHP is found to be more effective for heat dissipation of high-power LED COBs than the traditional FPHP. The thermal resistance of the new FPHP is 10–15% lowered and the temperature uniformity at the condensation surface of FPHP is approximately at the same level in comparison with the traditional FPHP. Numerical simulation with respect to LED COB cooling by the new FPHP was performed additionally. The obtained simulation results accord well with the experimental results, inter-proving the reliability of the obtained results and further corroborating the effectiveness of the new FPHP as applied for heat dissipation of high-power LED COBs.

Improved Heat Dissipation and Optical Performance of High-Power LED Packaging with Sintered Nanosilver Die-Attach Material

Heat removal in packaged high-power light-emitting diode (LED) chips is critical to device performance and reliability. Thermal performance of LEDs is important in that lowered junction temperatures extend the LED's lifetime at a given pho-tometric flux (brightness). Optionally, lower thermal resistance can enable increased brightness operation without exceeding the maximum allowable Tj for a given lifetime. A significant portion of the junction-to-case thermal resistance comes from the joint between chip and substrate, or the die-attach layer. In this study, we evaluated three different types of leading die-attach materials; silver epoxy, lead-free solder, and an emerging nanosilver paste. Each of the three was processed via their respective physical and chemical mechanisms: epoxy curing by cross-linking of polymer molecules; intermetalic soldering by reflow and solidification; and nanosilver sintering by solid-state atomic diffusion. High-power LED chips with a range of chip areas from 3.9 mm2 to 9.0 mm2 were attached by the three types of materials onto metalized aluminum nitride substrates, wire-bonded, and then tested in an electro-optical setup. The junction-to-heatsink thermal resistance of each LED assembly was determined by the wavelength shift methodology. We found that the average thermal resistance in the chips attached by the nanosilver paste was the lowest, and it was highest from the chips attached by the silver epoxy. For the 3.9 mm2 die, the difference was about 0.6°C/W, while the difference between the sintered and soldered was about 0.3°C/W. The lower thermal resistance in the sintered joints is expected to significantly improve the photometric flux from the device. Simple calculations, excluding high current efficiency droop, predict that the brightness improvement could be as high as 50% for the 3.9 mm2 chip. The samples will be functionally tested at high current, in both steady-state and pulsed operation, to determine brightness improvements, including the impact of droop. Nanosilver die-attach on a range of chip sizes up to 12 mm2 are also considered and discussed.

Improved Heat Dissipation and Optical Performance of High-power LED Packaging with Sintered Nanosilver Die-attach Material

Heat removal in packaged high-power light-emitting diode (LED) chips is critical to device performance and reliability. Thermal performance of LEDs is important in that lowered junction temperatures extend the LED's lifetime at a given photometric flux (brightness). Optionally, lower thermal resistance can enable increased brightness operation without exceeding the maximum allowable Tj for a given lifetime. A significant portion of the junction-to-case thermal resistance comes from the joint between chip and substrate, or the die-attach layer. In this study, we evaluated three different types of leading die-attach materials; silver epoxy, lead-free solder, and an emerging nanosilver paste. Each of the three was processed via their respective physical and chemical mechanisms: epoxy curing by cross-linking of polymer molecules; intermetalic soldering by reflow and solidification; and nanosilver sintering by solid-state atomic diffusion. High-power LED chips with a chip area of 3.9 mm2 were attached by the three types of materials onto metalized aluminum nitride substrates, wire-bonded, and then tested in an electro-optical setup. The junction-to-heatsink thermal resistance of each LED assembly was determined by the wavelength shift methodology, described in detail in this paper. We found that the average thermal resistance in the chips attached by the nanosilver paste was the lowest, and it is the highest from the chips attached by the silver epoxy: the difference between the two was about 0.7°C/W, while the difference between the sintered and soldered was about 0.3°C/W. The lower thermal resistance in the sintered joints is expected to significantly improve the photometric flux from the device. Simple calculations, excluding high current efficiency droop, predict that the brightness improvement could be as high as 50% for the 3.9 mm2 chip. The samples will be functionally tested at high current, in both steady-state and pulsed operation, to determine brightness improvements, including the impact of droop. Nanosilver die-attach on a range of chip sizes up to 12 mm2 are also considered and discussed.