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Efficient air flow: Heat sink designs should consider how air currents interface with the surfaces and pathways of the fin structures. High density fin structures will add to the pressure drop of the heat sink because of the increased resistance to the air flow. A balance between high density fin structures and efficient air flow into and across the heat sink fins needs to be considered for a heat sink to meet its design goals.
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Increased heat sink surface: The interface between the heat sink and the surrounding environment occurs on the surfaces of the heat sink fins. To maximize the thermal transfer from the metal to the surrounding air one should maximize the surface area of the heat sink. Options range from increasing the physical size of the heat sink, adding a large array of fins, continuous straight fins and combining fin structures to optimize the heat transfer.
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Efficient thermal transfer within the heat sink: Large heat sink and large fin structures are sometimes ineffective if the heat can not be moved. Good thermal transfer from the heat source to the outer edges of the heat sink and into the fin structures should be considered. Thick fins have better thermal conductivity then thinner fins, the material used for the heat will influence the design (for example aluminum vs. copper vs. graphite vs. other). Combination of materials, embedded materials, embedded heat pipes, and various other ideas can help improve the transfer of heat away from the source.
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Contact with the heat source: The better the surface-surface contact between the heat source and the heat sink the more effective the solution is in meeting a design requirement. A flat surface will allow for less thermal interface material which will help reduce the thermal resistance between the heat source and heat sink.