Heat conduction properties of thermally conductive interface
materials with exfoliated graphite platelets
The thermal interface material technologies used for electronic packages encompass several classes of materials. However, there is still a need for thermal interface materials and methods for making thermal interface materials having improved thermal conductivity property by maximizing the anisotropic benefit of exfoliated graphite platelets to the fullest extent. The effect of filler volume fraction on the thermal resistivity of the thermal contact and the thermal conductivity of the thermal interface material is investigated for graphite platelets and carbon black. The effect of pressure on the bond line thickness of the thermal interface material is evaluated for smooth and rough surfaces. The present study aims to provide a thermal interface material with aligned graphite nanofibers in the thermal interface material to enhance the material performance. Particular emphasis is placed upon the heat conduction properties of thermally conductive interface materials with exfoliated graphite platelets. The results indicate that polymeric elastomer materials offer both high thermal performance and reasonable gap filling capability to enable good contact between a semiconductor component and a heat sink. Under mechanical pressure, the soft thermal interface material conforms to the microscopic surface contours of the adjacent solid surfaces and increases the microscopic area of contact between the thermal solution surface and the silicon die surface and therefore reduces the temperature drop across this contact. The heat dissipating component should advantageously be relatively anisotropic, as compared to a metal and exhibit a relatively high ratio of thermal conductivity to weight. Thermal interface materials provide a limited heat-conduction path and may include flexible heat-spreading materials and one or more layers of soft thermal interface material. Reducing the strain on the thermal interface material may reduce the potential for pump-out and the associated increase in thermal resistance due to loss of material from the interface. Thermal conductivity is driven primarily by the nature of the filler, which is randomly and homogeneously distributed throughout the matrix. Pump-out of the thermal interface material results in increased thermal resistance due to loss of material from the interface. The thermal interface material can migrate out of the interface volume between the thermal conducting members and onto the power input pads, resulting in excessive heating and part failure at the power interconnect.
Keywords: Interface materials; Thermoplastic materials; Smooth surfaces; Rough surfaces; Graphite platelets; Carbon black