Prediction and measurement of thermal conductivity of diamond filled adhesives

Heat cured epoxy tape adhesives were made with high filler loadings of (a) silver, (b) aluminum, (c) alumina, and (d) diamond powder. For a, b, and c the thermal conductivity agreed with values predicted from the percentage of filler and the k value of the pure filler. For diamond powder, however, the conductivity data extrapolated to a diamond powder k value of only about 300 W/m°K. This lower k value is believed to be due to nitrogen impurity atoms in synthetic diamond powder. The k for diamond filled adhesives is therefore higher than for the best previous AlN, BN, Al₂O₃, or ZnO filled dielectric adhesives, but is not as high as for previous silver or other metal filled adhesives. For estimation purposes, adhesive conductivity can be predicted from the volume fraction filler and the filler conductivity (using 300 for diamond) via a specified graphical method