Figure 4. Effect of filler volume fraction on the thermal conductivity of the thermal interface material for graphite platelets and carbon black.
The high-resolution scanning electron micrographs of the exfoliated graphite platelets are illustrated in Figure 5 for the production of the thermal interface material. Conventional polymeric thermal interface materials may be used as the thermal interface material. However, currently used polymeric thermal interface materials are typically cure in place silicone gel materials that are required to be shipped and stored frozen. They also have short pot lives upon opening, short shelf lives, and require special dispensing equipment to apply. Therefore, it is necessary to eliminate, avoid, or at least reduce these aforementioned drawbacks associated with conventional polymeric thermal interface materials. A thermal interface material in the form of a pad of self-healing, thermoplastic material may or may not be naturally tacky. The thermal interface material may have a softening or melting temperature higher than a normal operating temperature of a central processing unit, for example, normal operating temperature from about 60 °C to about 100 °C or from about 30 °C to about 40 °C. Consequently, the pad of thermoplastic material will soften or melt once, for example, during an adhesive curing stage or during an initial operation of the central processing unit, and then solidify. Thereafter, the pad of thermoplastic material may be used below its softening or melting temperature and remain solidified. The thermal interface material comprises a thermoplastic phase change material having a softening or melting point temperature that falls within a range from about 80 °C to about 200 °C or about 100 °C to about 180 °C. Or, for example, the thermal interface material may have a softening or melting temperature of about 40 °C, 60 °C, or 80 °C. The thermal interface material may have a thermal conductivity of about 0.8 Watts per meter per Kelvin or more, or 2.0 Watts per meter per Kelvin or more, which thermal conductivity may be enhanced by incorporating thermally-conductive filler into the thermoplastic material. The thermal interface material may comprise a low melting alloy having a melting temperature of about 200 °C or less. The surface features protrude from the mating surface of the particular heat transfer component into selected areas of the interface. The protruding features may limit the relative movement of the mating surfaces in the selected areas of the interface during thermal cycling due to coefficient of thermal expansion mismatch. Limiting the relative movement may reduce strain on the thermal interface material in areas of the interface proximate to the protruding features. Reducing the strain on the thermal interface material may reduce the potential for thermal interface material pump-out and the associated increase in thermal resistance due to loss of material from the interface. The protruding features are incorporated onto the heat sink and protrude out from the heat sink mating surface into selected areas of the interface between the heat sink mating surface and the module lid mating surface. The protruding features may be incorporated onto the heat sink through a forming process during manufacturing of the heat sink. Channels may be machined or otherwise incorporated into the heat sink, and the channels may be filled with a material that is appropriate for the heat sink in order to form the protruding features. In some cases, the heat sink may be formed from a heat sink material, such as an aluminum-based material or a copper-based material, among other alternative materials. When the heat sink is formed from an aluminum-based material, the channels may be filled with an aluminum-based material that is the same as the aluminum-based material of the heat sink or that is substantially similar to the aluminum-based material of the heat sink. Alternatively, with respect to the example in which the heat sink is formed from an aluminum-based material, the channels may be filled with other materials compatible with the aluminum-based material for efficient transfer of heat to the heat sink.