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Thermalyze Thermal Image Analysis Software


Emissivity Tables



Many electronic devices, including semiconductor die, are made up of a variety of materials such as semiconductor substrates, metal traces, gold coatings, and ceramics. These materials have different emissivity properties and therefore emit infrared energy at different levels. For example, when a bare semiconductor die is unpowered, its temperature will be very uniform due to the high thermal conductivity of semiconductor materials. A thermal image captured of the unpowered die will generally show differences between the semiconductor materials and any metallization. These differences in the thermal image are not a result of temperature differences, but are due to the lower emissivity of the metallization.

In order to accurately measure the true temperature of semiconductor devices, it is necessary to compensate for surface emissivity differences on a pixel-by-pixel basis. A single emissivity value applied to a group of pixels is not an effective way to compensate for emissivity differences as emissivity often varies continuously at the junction between materials.

An emissivity table is a two-dimensional data array that contains a separate emissivity value for each individual image pixel. Emissivity tables are used to correct thermal images for variations in surface emissivity. After an unpowered device has been stabilized at a temperature that is higher than ambient temperature, an emissivity table can then be created of the device. Applying the emissivity table to thermal images of the device applies a correction to each individual pixel temperature, allowing you to measure the true temperature anywhere on the device.



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