Thermal Conductivity of Thermal Interface Materials
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1053-EE05-08
Thermal Conductivity of Thermal Interface Materials Travis Z. Fullem, and Eric J. Cotts Materials Science Program and Department of Physics, Binghamton University, Binghamton, NY, 13902 ABSTRACT While detailed theories exist for thermal conduction due to electrons and phonons in crystalline solids, phonon scattering and transmission at solid/solid interfaces is not as well understood. Steady increases in the power density of microelectronic devices have resulted in an increasing need in the electronics industry for an understanding of thermal conduction in multilayered structures. The materials of interest in this study consist of a polymer matrix in which small (on the order of microns to tens of microns) highly conductive filler particles (such as Ag or alumina) are suspended. These materials are used to form a thermal interface material bondline (a bonding layer up to several hundred microns thick) between a power device and a heat spreader. Such a bondline contains many polymer/filler interfaces. Using a micro Fourier apparatus, the thermal conductivities of such thermal interface material (TIM) bondlines of various thicknesses, ranging from ninety microns to three hundred microns, have been measured. The microstructure of these bondlines has been investigated using optical microscopy and acoustic microscopy. Measured values of thermal conductivity are compared to values for bulk samples, and considered in terms of microstructural features such as filler particle depleted regions. The influence of polymer/filler particle interfaces in the TIM bondline on phonon transport through the bondline is also considered. INTRODUCTION Providing good thermal contact between two solid objects is a technical challenge which is encountered in many areas of engineering. If two relatively smooth solid surfaces are placed in intimate contact, the actual contact area is significantly less than the area of the two surfaces; the contact area may be as small as 2% of the surface area.[1] This small contact area is due to microscopic surface roughness. Therefore, the interface between the two surfaces consists of a few regions of solid/solid contact and the rest of the surface area is separated by a gap as shown in figure 1a. This poor contact results in a large thermal resistance between the two objects. This issue is particularly important for the electronics industry. Many electronic components dissipate power, which causes their temperature to increase. The performance of an electronic device will degrade if its operating temperature exceeds a certain threshold; therefore it is necessary to provide a path for the heat to escape the device so that its temperature does not increase too much. A common solution to this issue is to attach a heatsink to the device; it is desirable to minimize the thermal resistance between the device and the heatsink. This can be accomplished by placing a thermal interface material (TIM) between the two surfaces as shown in figure 1b. Many types of TIMs are commercially available, includin
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