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A high sensitivity, infrared (IR) microscope operating in the wavelength range 800 to 2500 nm has been applied to a variety of packaging related issues. Applications can be divided into three categories. 1) For flip chip devices the advantage of the IR microscope is that most silicon is effectively transparent at wavelengths greater than 1100 nm. This enable defects such as voids, delamination cracks and corrosion to be investigated while the chip is mounted on the substrate. 2) The IR microscope enables thermal images of devices to be obtained with a temperature resolution of approximately 1 K and spatial resolution of 2-3 μm. 3) The transparency of silicon to IR radiation has proved particularly valuable for characterising micro-electro-mechanical systems (MEMS) devices such as microphones, at various stages of packaging, e.g., after die bonding and wire bonding.