In-situ thickness method of measuring thermo-physical properties of polymer-like thermal interface materials [microelectronics cooling applications]

A critical property in understanding and accurately predicting the thermal resistance of polymer-like thermal interface joints in micro-electronic cooling applications is the bulk thermal conductivity of thermal interface materials (TIMs). A unique experimental test stand was developed and validated which accurately measures the in-situ thickness of a TIM sample in a vacuum during thermal resistance testing. The system has a resolution capability of ± 1.0 μm and is designed in such a manner as to continuously measure the true relative deflection of a TIM sample taking into account any mechanical and/or thermal deflections of the entire test stand. The data and analysis demonstrate that applying the current American standard test method (ASTM) ASTM D 5470 without accounting for in-situ thickness deviations can result in over estimating the bulk thermal conductivities for these types of materials by as much as 40%. These types of errors in fundamental material properties can cause the over-prediction of thermal heat flux in a system and an under-prediction of the temperatures of the system.