A diffuser plate made of Aluminum alloy is used between the honeycomb sandwich panels and a high heat dissipating electronic package to diffuse concentrated heat loads in spacecraft. At present, diffuser plates are fixed to face sheet of honeycomb sandwich panel using Hysol EA 9392 adhesive. The surface of diffuser plate must be prepared for this adhesive bonding process. Currently, sulfo-chrome etching is in use. Two other alternate surface treatments, namely, sulphuric acid anodization and chemical cleaning are also developed. In order to consider these new surface treatments for the diffuser plate, experiments are considered for the relative comparison of thermal contact conductance between diffuser plate (with three different surface treatment processes) and honeycomb sandwich panel with Hysol EA 9392 adhesive bonded interface. In order to determine the thermal contact conductance across this adhesive bonded interface, experimental test setup is realized and experiments are carried out under defined boundary conditions. An inverse methodology, which uses the experimental steady state temperature data at known locations together with the corresponding simulated temperature data from a detailed mathematical model using UGNX−TMG software, is developed for the estimation of thermal contact conductance across the bonded interface. The inversely estimated thermal contact conductance ranges from 9.26 to 11.16 W/°C and the corresponding heat transfer coefficient are 926 to 1116 W/m²°C.