On the Evalutation of Contact Temperature from Potential-Drop Measurements

The temperature of an electrical contact is usually evaluated from a measurement of the potential drop across the contact through the well-established relation f Tm V2 =8 ~ ~odT. · ´ TO and p are, respectively, the thermal conductivity and the electrical resistivity of the junction material; To and Tm are, respectively, the temperature of the junction body and of the contact spot; and V is the potential drop. Experimental evidence is presented which indicates that this relation, and more generally classical Contact theory, is inapplicable to junctions where the contact spots are small (typically <0.05 µm in aluminum). The origin of this breakdown of the theory is explored.