A Comparative Thermal and Lumen Performance Study of Thin-film Amorphous Silicon Dielectric Coating on Aluminum as an LED Packaging Substrate

Abstract

Lumen output and efficacy of high-power LEDs have crossed 200 lm/W, and the application of LEDs is growing beyond illumination into other areas like horticulture, UV-C LEDs for disinfection, and health-centric lighting where controlling parameters like the shift in wavelength, Color Rendering Index (CRI), etc. are important. Whether delivering high light output or controlled spectral designs for specific applications, thermal management of LEDs to lower the junction temperature is vital as it directly impacts the intended performance. The packaging substrate on which the LED is mounted plays a critical role in controlling the junction temperature. In this study, a thin film amorphous silicon (a-Si) dielectric coating on an aluminum (a-Si/Al) substrate followed by a 300 nm thick copper trace pattern for LED attachment using magnetron sputtering Physical Vapor Deposition (PVD) process has been carried out. Three other Packaging material substrates of FR4, Metal Core PCB (MCPCB), and Silicon using undoped Silicon wafer were fabricated, and a Nano-ceramic on Aluminum substrate was also procured for comparative Transient Thermal analysis study using Luxeon-Rebel Cool White LED. The Thermal resistance from the LED junction to the bottom of the a-Si/Al packaging substrate attached to the liquid temperature-controlled heat sink measured at 700 mA driving current, as per industry standard JEDEC 51–14 method, was 8.77 °C/W. Compared to this Thermal resistance value of a-Si/Al substrate, the thermal resistance of Silicon substrate, Nanoceramic on Aluminum, MCPCB, and FR4-based packaging substrates were 3.19%, 55.53%, 180.73%, and 405% higher with the corresponding Thermal resistance values of 9.05 °C/W, 13.64 °C/W, 24.62 °C/W and 44.34 °C/W respectively. Light Lumen output measurements for the substrates with the lowest and the highest thermal resistance, namely the (a-Si/Al) and FR4 substrates were also measured and the light output efficacy of the (a-Si/Al) substrate was 9.46% higher than the FR4 substrate. Also, the light output drop of the (a-Si/Al) substrate was only 1.66% compared against 10.66% for the FR4 substrate after 30 min of testing under no heatsink attachment conditions. Thus, the a-Si thin film-coated Aluminum as the LED packaging substrate can help lower the junction temperature with low thermal resistance and improve the color quality, efficacy, lumen depreciation, and reliability.