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Improved z-axis thermal conductivity of TIM-materials by active particle alignment
Keywords: Thermal interface materials, Particle orientation by dielectrophoresis, Enhanced thermal conductivity
CondAlign AS is a technology development company located in Oslo, Norway. CondAlign develops a unique technology where an electric field is applied to polymer resins to manipulate, orient and align particles dispersed in the resin. The particles move in the resin due to dielectrophoresis and dipole-dipole interactions induced by an external electric field. These mechanisms allow a wide range of particles and polymer matrices to be used. The particles need not be metallic, magnetic, or even electrically conductive. The only major limitations are polymer viscosity, particle size, and strength of the external electric field. After alignment, the viscous polymer- particle structures are fixated by curing the matrix. Examples of applications of the technology include electrically and thermally conductive films. The particle alignment permits either a dramatic reduction of particle content while retaining conductive properties, or improved performance and added functionality with unchanged particle content. Without alignment, these materials are typically particle rich systems with concentrations above the percolation threshold. Furthermore, the alignment typically introduces anisotropy to the finished materials. As an example, a polymer film with metallic particles aligned along the film normal, can have resistivity in the film plane 10 orders of magnitude higher than through the film. The anisotropic thermal and electrical properties of the films can be optimized by both the polymer formulation and the processing condition. The process is demonstrated and ready for scale up. CondAlign has developed pilot production capabilities in continuous roll-to-roll (R2R) processes. The first commercial product will be biomedical electrodes, with expected market entry in 2019. At the IMAPS thermal management workshop, CondAlign will present the basic principles of the technology and its recent efforts to produce thermal interface materials using the techniques described above. In silicone matrices using several types of ceramic fillers, we have demonstrated improvements in through- plane thermal conductivity of more than 100%. That is when comparing films of equal composition, prepared with and without particle alignment. Optimizing the process for particles that are themselves anisotropic, such as hexagonal Boron Nitride, we expect even better results. The magnitude of thermal conductivity we can achieve is still limited, because the particles' ability to freely rotate and align is restricted at higher loadings. We are exploring options to overcome this and believe there is room for significant improvements. Looking into practical use of thermal interface materials, we know that overall thermal performance (a system property) is depending on the interfacial resistance as well as the bulk conductivity (the material property). One way to reduce the interfacial resistance is to improve the material’s ability to wet a hard, rough surface. Since the CondAlign technology permits a dramatic reduction in particle contents for the same conductive properties, it allows for better material properties such as softness and wetting, reducing thermal resistance in the overall system.
Henrik Hemmen, CTO
Oslo, Oslo

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