Measurement and significance of the effective thermal conductivity of the dielectric in an IMS™

Insulated metal substrates (IMS™) usually consist of a copper circuit layer, an aluminum base layer and an adhesive dielectric layer in the between. Though the dielectric dominates the thermal resistance of the IMS™, the aluminum/dielectric and copper/dielectric interfaces may play a significant role in the overall thermal resistance of the IMS™. In this paper, we present a technique of determining the overall thermal resistance of the IMS™, which could transform to the effective thermal conductivity of the dielectric. The technique is based on ASTM D5470. By plying up different number of layers of IMS™ samples, the formed stacks of 1, 2, 3, 4 and 5 layers are evaluated for the thermal impedance versus the number of layers. The slope of the linear relation is the thermal resistance of a single IMS™ plus the copper-aluminum contact resistance present between the adjacent IMS™ samples in the stack. Since the later could be found using stacks of copper-aluminum pairs of different number of layers, the thermal resistance of a single IMS™ could result. The technique gave an imprecision about 4% in the experimental testing.