Using Electrical Capacitance and Mechanically Representative Hardware to Evaluate the Thermal Mechanical Stability of Thermal Interface Materials

The experimental study of electronic materials is a necessary complement to virtual qualification efforts that rely on modeling and simulation to streamline development of new electronic assemblies. The durability of thermal interface materials in large complex printed circuit board (PCB) assemblies is difficult to model and therefore, experimental study and verification is needed. In this study, the thermal mechanical stability of dielectric thermal interface materials is monitored using electrical capacitance, the inverse of which has the same geometric dependence on bond line and area as thermal resistance. Electrical capacitance is a straightforward, fast and accurate measurement method which can be used with mechanically representative hardware very early in the development cycle. This study includes four thermal interface materials (TIMs) classified as pre-cured thermal putties which are evaluated on hardware that is easily prototyped and mechanically representative of large complex PCBs. Electrical capacitance of the TIMs was measured in situ during thermal cycle testing and was able to distinguish both stability and degradation. Analysis of the TIMs after the test confirmed structural degradation in the form of cracks, fissures and material movement. In summary, electrical capacitance has broad application in evaluating the stability of dielectric TIMs in application specific designs very early in development by using easily procured mechanically representative hardware.