As commercial and military electronics applications continue to “push the envelope” with higher powers and smaller packaging requirements, it is becoming more critical to minimize the thermal resistance from the heat load to the heat sink. Ideal packaging materials must have high thermal conductivity and coefficient of thermal expansion (CTE) values that are compatible with the integrated circuit device while remaining lightweight and affordable. Given these constraints, removing high heat loads and/or high heat flux from these electronics presents some interesting challenges for design engineers.One approach is to spread the heat to a larger area for dissipation through high thermal conductivity bulk materials or custom designed heat spreaders. Bulk metallic components such as copper or aluminum have high CTE values compared to most electronic components. Because of this CTE mismatch, heat spreading materials require the use of stress reducing components such as intermediate substrates, thermal pads, or grease for attachment to the semiconductor device. These materials compensate for the expansion differences between the semiconductor electronics and the heat spreader. However, they often provide significant thermal resistance due to their poor thermal conductivity. Thermal gap pads have thermal conductivities ranging from 0.5 to 3 W/m-K. This is significantly less than the metallic spreaders which range from 180 W/m-K in aluminum to over 400 W/m- K in copper spreaders.
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