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Thermal imaging of encapsulated LEDs

Thermoreflectance imaging is used to obtain 2D temperature maps of encapsulated LED arrays and elements with sub-micron spatial resolution. Typical LED encapsulation is opaque for infrared light, which prevents direct measurement of the semiconductor die with infrared cameras and thermocouples. A lock-in transient imaging technique with a megapixel silicon CCD is used to obtain the thermoreflectance and electroluminescence signals simultaneously. Transient thermal response in different locations of the die is characterized. Different thermal time constants are observed which correspond to various heat transfer mechanisms.