A method of using thermal test chips with diodes for thermal characterization of electronic packages without calibration

For characterizing the thermal performance of electronic packages, specially designed thermal test chips are used. These test chips have heaters for powering and diodes for sensing the chip temperature during the test. Prior to tests, the diodes are calibrated and the calibration data consisting of voltage output (at a fixed constant current) versus temperature is usually fitted to a straight line. During the tests, the voltage output of the diode is measured (at the same fixed constant current) and the chip temperature is determined using the calibration curve. This paper reviews another method of using the diode for measuring the chip temperature without calibrating the diode first. In this method, the diode is operated at two different known current levels, I₁, and I₂, and the corresponding forward voltage drops, V₁, and V₂, are measured at a known temperature. At the unknown temperature the forward voltages are again measured at the same two current levels. Using a simplified form of Shockley´s ideal diode equation, the difference in the forward voltages is used to determine the unknown temperature. Compared to the constant-current method, the current-switching method is more susceptible to measurement errors. However, it is relatively simple to use since it does not require calibration of the diode over the temperature range prior to use