Figure 5. High-resolution scanning electron micrographs of the exfoliated graphite platelets for the production of the thermal interface material.
The transmission electron micrographs of the exfoliated graphite platelets are illustrated in Figure 6 for the production of the thermal interface material. Some of particulate-filled polymers are conductive polymers. Although almost all plastics, whether thermoplastic polymers or thermosetting polymers, are intrinsically good electrical insulators, introduction of graphitic and other carbonaceous materials into the polymers can create electrical conduction paths in the insulating polymer matrix when these particles contact each other above a certain content, or critical volume fraction. Graphite, in general, can be used along with specially-processed electroconductive carbon black as a filler to provide electrical and thermal conductivity to normally non-conducting or poorly conducting polymeric materials. However, the size and morphological characteristics of conventional graphite particles limit the extent that the properties of a polymer composite can be improved. A first thermal interface material or layers may be used between an integrated heat spreader or lid and the heat generating components or device to reduce hot spots and generally reduce the temperature of the heat generating components or device. A second thermal interface material or layers may be used between the integrated heat spreader and the heat sink to increase thermal transfer efficiency from the heat spreader to the heat sink. One or more thermally conductive fillers may be added to create a thermally conductive interface material in which one or more thermally conductive fillers will be suspended in, added to, and mixed into, the thermally reversible gel. For example, at least one thermally conductive filler may be added to a mixture including gellable fluid and gelling agent before the gellable fluid and gelling agent have gelled or form the thermally reversible gel [73, 74]. At least one thermally conductive filler may be added to the gellable fluid and then gelling agent may be added to the mixture containing gellable fluid and thermally conductive filler [75, 76]. At least one thermally conductive filler may be added to the gelling agent and then gellable fluid may be added to the mixture containing gelling agent and thermally conductive filler [77, 78]. At least one thermally conductive filler may be added after the gellable fluid and gelling agent have gelled [79, 80]. For example, at least one thermally conductive filler may be added to the gel when the gel may be cooled and be loosely networked such that filler can be added. The amount of thermally conductive filler in the thermally reversible gel may vary in different cases. A thermal interface material may include not less than 8 percent but not more than 80 percent by weight of at least one thermally conductive filler. Thermal interface materials are typically composed of an organic matrix highly loaded with a thermally conductive filler. Thermal conductivity is driven primarily by the nature of the filler, which is randomly and homogeneously distributed throughout the organic matrix. Commonly used fillers exhibit isotropic thermal conductivity and thermal interface materials utilizing these fillers must be highly loaded to achieve the desired thermal conductivity. Unfortunately, these loading levels degrade the properties of the base matrix material, such as flow, cohesion, and interfacial adhesion. Consequently, the thermal interface material formulator must balance matrix performance with thermal conductivity with the net result being a material with less than optimum thermal conductivity. It is desirable to formulate a thermal interface material with as high a thermal conductivity as possible without sacrificing other physical properties. The protruding features may prevent excessive relative movement of the module lid and the heat sink during power or thermal cycling. The protruding features are positioned in a central area of the interface separating the module lid and the heat sink. During thermal cycling, the module lid may bow upward into the central area of the interface, and the heat sink may bow downward into the central area of the interface. This may result in a significant reduction of interface thickness in the central area. By positioning the protruding features in the central area of the interface, the potential reduction of interface thickness in the central area is limited by a distance that the protruding features extend into the interface from the heat sink mating surface. The protruding features include three protruding features that are distributed substantially uniformly along the heat sink mating surface in the central area of the interface. Each of the protruding features has a substantially similar shape. The number of protruding features, the position or distribution of protruding features on the heat sink mating surface, the size or shape of each of the protruding features, or a combination thereof, may vary. As an example, in some cases, the protruding features may be strategically patterned based on characteristics of the individual components of the electronic component cooling assembly, such as characteristics of the heat sink and characteristics of the module lid, among other possible factors.