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Repeatable Surface Temperature Measurements Under High Heat Flux Conditions.
Keywords: Theta JC , Case temperature measurement, calibration standard/simulation correlation
Surface temperature measurements are required to characterize the thermal performance of high power electronic packages. In particular, the junction-to-case thermal resistance, Theta jc, requires the measurement of the case temperature at the surface in contact with the cold plate or heat sink. There are technical challenges due to the high temperature gradients between the case and cold plates making a measurement difficult under high heat flux. The objective is to identify the most accurate and precise way of measuring the steady state case temperature of FCBGA packages under high heat flux through the use of insulated copper columns of varying areas. The insulated copper columns are used as calibration standards and linked through finite element analysis to obtain a steady state case temperature correction across the TIM II. The measurement methods explored consist of a spring loaded thermocouple protruding through the cold plate and making contact with the copper standard surface and the package lid. The second measurement method embeds the thermocouple junction into the cold plate, providing flat contact area for the copper standard and the package lid, measuring the temperature of the case and the temperature drop thorough the TIM II at steady state. The copper standards are insulated copper columns with thermocouples spaced through the height of the column, where the surface temperature is extrapolated using Fourier’s law under the assumption of 1D heat transfer. The extrapolated temperature is compared to the coldplate-thermocouple measured temperature from where the case temperature correction is calculated. The case temperature correction is correlated to the surface area of the copper standards under constant 150W power input. The resulting temperature corrections are applied to the case temperature measurements of lidded FCBGA packages with varying die areas to test the applicability of both methods. Case temperatures were made on an FCBGA package with three different die sizes, 7.77mm2, 13.01mm2, and 18.23mm2. The case temperature measurements and corrections from the copper standard to the FCBGA packages are connected through finite element analysis simulations to show the correlations is valid with different sizes and styles of packages. Preliminary results show the case temperature correction for the embedded thermocouple has a linear relationship to the surface area, where the greater the surface area of the copper standard is inversely related to temperature correction.
Eduardo De Los Heros, Thermal Engineer
Amkor Technology
Chandler , AZ

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