Determination on the Coefficient of Thermal Expansion in High-Power InGaN-based Light-emitting Diodes by Optical Coherence Tomography

Abstract

The coefficient of thermal expansion (CTE) is a physical quantity that indicates the thermal expansion value of a material upon heating. For advanced thermal management, the accurate and immediate determination of the CTE of packaging materials is gaining importance because the demand for high-power lighting-emitting diodes (LEDs) is currently increasing. In this study, we used optical coherence tomography (OCT) to measure the CTE of an InGaN-based (λ = 450 nm) high-power LED encapsulated in polystyrene resin. The distances between individual interfaces of the OCT images were observed and recorded to derive the instantaneous CTE of the packaged LED under different injected currents. The LED junction temperature at different injected currents was established with the forward voltage method. Accordingly, the measured instantaneous CTE of polystyrene resin varied from 5.86 × 10−5 °C−1 to 14.10 × 10−5 °C−1 in the junction temperature range 25–225 °C and exhibited a uniform distribution in an OCT scanning area of 200 × 200 μm. Most importantly, this work validates the hypothesis that OCT can provide an alternative way to directly and nondestructively determine the spatially resolved CTE of the packaged LED device, which offers significant advantages over traditional CTE measurement techniques.

Characterization of Electrical–Thermal–Mechanical Deformation of Bonding Wires Under Silicone Gel Using LF-OCT

“…Scanning-point OCT systems have been applied to inspect the shape of antennas and detect voids in encapsulant [26,27]. Swept-source OCT was applied to measure the coefficient of thermal expansion (CTE) of polystyrene resin in light-emitting diode packaging [28]. Yaqoob et al [29] proposed a spectral-domain line-field phase microscope to measure the motion of biological cell membranes.…”