Purpose
Thermal grease is primarily used in the electronics and computer industries to assist a heat sink to draw heat away from a semiconductor component such as an integrated circuit or transistor.
Thermally conductive paste improves the efficiency of a heatsink by filling air gaps that occur when the imperfectly flat and smooth surface of a heat generating component is pressed against the similar surface of a heatsink, air being approximately 8000 times less efficient at conducting heat than, for example, aluminum (a common heatsink material). Surface imperfections and departure from perfect flatness inherently arise from limitations in manufacturing technology and range in size from visible and tactile flaws such as machining marks or casting irregularities to sub-microscopic ones not visible to the naked eye. Thermal conductivity and "conformability" (i.e., the ability of the material to conform to irregular surfaces) are the important characteristics of thermal grease.
Both high-power handling transistors, such as those in an audio amplifier, and high-speed integrated circuits, such as the central processing unit (CPU) of a personal computer, generate sufficient heat to benefit from the use of thermal grease to improve the effectiveness of a heatsink. The need for heatsink compound can be minimised or removed by lapping the surfaces of the hot component and the matching heatsink face so that they are virtually perfectly flat and mirror-smooth. Computer overclockers, who increase computer speed by measures which increase heat production, resort to lapping and other extreme cooling methods such as water-cooling.
Read more about this topic: Thermal Grease
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