We investigated the luminance, thermal, and thermo-mechanical properties of vertical (V)-LED and flip-chip (FC)-LED packages with different white silicones for a vehicle head lamp application. The FC-LED package showed higher equivalent maximum stress than the V-LED package. For example, the equivalent maximum stresses for the FC-LED package with white silicone (WR-3020) were 6.05 and 2.45 MPa at −45 and 125 °C, respectively, whereas those for the V-LED one with WR-3001 were 1.09 and 1.56 MPa. Irrespective of currents, the V-LED packages exhibited lower thermal resistance (Rth) than the FC-LED package. The V-LED package showed 25.3% lower Rth value (junction to PCB) at 1000 mA than the FC-LED package. The FC-LED packages illustrated higher luminous flux drop-rate at 85 °C than the V-LED package. The V-LED packages revealed lower surface temperature than the FC-LED package. The contrast ratio depended on the package structures and white silicone coating widths. The packages with the wider edge-coating width had higher luminance and the V-LED packages exhibited higher luminance. The luminous flux maintenance rate was degraded by 0.9%–2.9% after 1000 h. The V-LED package with WR-3001 showed the best performance, while the FC-LED package with WR-3020 displayed the lowest performance.
We investigated the effect of selective coating of white silicone on the output and thermal performance of white LED packages for middle power lighting application. The LED package, where a Zener diode part was coated by TiO 2 particles-mixed white silicone, exhibited lower surface temperature and heat flux than those with the uncoated Zener diode. The white silicone-coated packages resulted in lower thermal resistance (R th ) than the uncoated ones. For example, the R th at 85 °C of the uncoated and coated white LED packages in the junction-PCB was 26.30 K W −1 and 21.98 K W −1 , respectively. The coated blue and white LED packages yielded 6.5% and 4.5% higher luminous fluxes than the uncoated packages, respectively. Far-field emission patterns showed that the coated white LED packages had view angle of 118.06°and 118.10°along the two orthogonal directions, respectively, whilst the uncoated package gave 117.37°and 117.55°. After operation under 60 °C/80% relative humidity condition for 1000 h, the uncoated white LED package yielded maintenance rate of 96.85% whereas the coated packages gave 98.17%. At 85 °C under 200 mA, the thermal resistance of the white silicone-coated white LED packages was lowered by 17.7% than the uncoated packages.
We investigated the effect of different types of die attach adhesives on the performance and reliability of InGaN-based LED packages. At 260 °C, the average shear strength was 10.00 and 22.30 MPa for Ag epoxy and Ag sinter paste samples, respectively. LED packages with the Ag sinter paste produced lower thermal resistance than the Ag epoxy paste sample. The Ag epoxy and sinter paste samples gave the thermal resistance (from junction to PCB) of 9.82 and 9.27 K W−1, respectively. The chip temperature of the Ag epoxy and sinter paste samples was 122.1 °C and 121.5 °C, respectively. The Ag sinter paste contained smaller Ag flake and less resin than the Ag epoxy paste sample. The luminance flux at 700 mA of LED packages with the Ag sinter and epoxy pastes was 177.5 lm and 176.8 lm at 85 °C. Unlike the Ag sinter paste samples, 60% of the Ag epoxy paste samples were cracked at 300 °C. The luminous flux maintenance of the Ag epoxy and sinter paste samples was 97.36% and 99.54%, respectively. Unlike the Ag epoxy paste samples, the Ag sinter paste samples exhibited higher stability against delamination (cracking) and higher lumen maintenance than the Ag epoxy paste samples.
We investigated the electrical and optical properties of chip LED and phosphor-converted red LED (pcR-LED) packages for a vehicle rear fog lamp application. The chip LED package had a lower forward voltage, narrower electroluminescence spectrum, and a larger view angle than the pcR-LED package. At 85 °C under 700 mA, the pcR-LED package emitted 26.8% more luminous flux than the chip LED package. After 1000 temperature cycles (−40 to +125 °C), the chip LED packages exhibited a 7.83% maintenance rate variance, whereas the pcR-LED packages showed a 2.78% change. Furthermore, after 1000 h under relative humidity conditions of 85 °C/85% both the samples demonstrated an average maintenance rate >98.66%. At 85 °C under 700 mA, it was demonstrated that the pcR-LED package exhibited a 48.9% lower thermal resistance (junction to package) than the chip LED package. Also for the chip LED package, the temperatures were 58.6 °C at the central region and 61.9 °C at its periphery, whereas the pcR-LED package had temperatures of 70.5 °C at the center and 55.8 °C at the periphery. Unlike the chip LED package, neither current nor temperature significantly affected the CIE coordinates of the pcR-LED packages.
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