Effect of surface deformations on thermal contact conductance of coated junctions

Thermal contact conductance is normally a significant contribution to the total thermal conductance of electronic packages. Extensive work has been done to predict thermal contact conductance using coating techniques, however, only limited research has been conducted on the effect of surface deformations of coatings. The nature of the deformations of surface asperities had strong influence on the thermal contact conductance. Based on classical theories of contact mechanics, the surface deformations could be either plastic or elastic. How the different coating materials, coating thickness, and surface roughness influence the surface deformation is still not clear. Hence, the aim of the present work is to present the effect of coatings on surface deformations. Various surface treatment samples are used in this study including one-surface, two-surface, and phase-mixture coatings upon aluminum substrates. Five different coating materials are employed in this investigation under low contact pressures where little experimental data exist. Results showed that coating interfaces deform plastically during the first loading-unloading process under light load. Nomenclature C = constriction parameter correction factor H = Vickers microhardness, Pa h — uncoated thermal contact conductance, W/m2K hc = coated thermal contact conductance, W/m2K k = thermal conductivity, W/mK P — contact pressure, Pa S = asperity slope t = coating thickness, )um cr = surface roughness, /mi Superscript ' = effective