Characterisation of cooling curves for power device die attach using a transient cooling curve measurement

In this paper the analysis of cooling curves for power levels of up to 65 W is presented. The paper details a constant temperature fixture to keep a test vehicle at a constant temperature for these power levels. The test vehicle consists of a special designed copper block, a die attachment layer and a bare die for heating and sensing. The diode V/sub f/ is used for sensing junction temperature. The tooling curve method of temperature characterisation is used instead of the widely used heating curve measurement because at this power level heating curves are difficult to obtain when specially designed thermal test chips are not available. The design of the special test vehicle is presented in detail. It is designed to achieve an equal temperature distribution across the test diode. The test vehicle has a three-layer structure to minimise the number of thermal interfaces. This enables a more precise cooling curve analysis later in this work. The experimental results were correlated through the use of CFD models and thermal equivalent electrical networks. From these CFD models, the thermal resistance and thermal capacitance of the die attach layer can be evaluated. A network model is used to implement the thermal performance in network analyser tools such as SPICE. The paper shows a good agreement between the CFD model, the lumped thermal network and the measurements.