Application of extension rings in thermography for electronic circuits imaging

Abstract

ABSTRACT Thermographic cameras are often used in areas, where resolutions below 100 µm per pixel are required, as for example in electronics. Such resolutions can be obtained using dedicated lenses. As an alternative, some manufacturers are offering extension rings to be added between the lens and the camera housing, to increase the final image spatial resolution. To test the latter solution and its impact on thermographic temperature measurements, a set of aluminium extension rings was manufactured and mounted in different combinations between an InSb cooled thermographic camera and its lens. Next, the camera, a blackbody IR source, a thick-film resistor on alumina substrate, a microscope reticle calibration glass, and two integrated test circuits were used to investigate the impact of the rings on the temperature measurement accuracy and the achieved spatial resolution. It was demonstrated, that extension rings are a very useful tool in thermography, as long as their impact on the measurement system is taken into account, considering numerical aperture reduction, rings heating by the operating camera, and the cold stop related vignetting. The impact will greatly depend on the specific design of the camera to be used and its lens configuration.