How do you size a heat sink for a IC chipSolutionWhen select

How do you size a heat sink for a IC chip?

Solution

When selecting a heat sink, it is necessary to classify the air flow as natural, low flow mixed, or high flow forced convection. Natural convection occurs when there is no externally induced flow and heat transfer relies solely on the free buoyant flow of air surrounding the heat sink. Forced convection occurs when the flow of air is induced by mechanical means, usually a fan or blower. There is no clear distinction on the flow velocity that separates the mixed and forced flow regimes. It is generally accepted in applications that the effect of buoyant force on the overall heat transfer diminishes to negligible level (under 5%) when the induced air flow velocity excess 1 2 m/s(200 to 400 lfm)

The volume of a heat sink is determined by the following table Table 2shows approximate ranges of volumetric thermal resistance of a typical heat sink under different flow conditions.

Flow condition
m/s (lfm)

Volumetric Resistance
cm3 °C/W (in3 °C/W)

natural convection

500-800

(30-50)

1.0 (200)

150-250

(10-15)

2.5 (500)

80-150

(5-10)

5.0 (1000)

50-80

(3-5)

Range of volumetric thermal resistance