One of the fundamentals of electronics cooling is the efficient transfer of heat from a component to the ambient often using a heat sink.
The effectiveness depends on the thermal resistance of the system. This is the addition of all the discreet resistances on the path from component to ambient. One of these discreet resistances is ?spreading resistance?.
When a small heat source is in contact with a large heat sink the heat does not distribute uniformly through the heat sink base and so does not transfer evenly to all of the fins.
The spreading resistance causes a temperature gradient to exist between the point of contact and the edges of the heat sink. This effect can contribute 60-70% of the total thermal resistance.
The spreading resistance can be reduced in a number of ways:
The simplest way to reduce spreading resistance is to increase the base thickness of the heat sink or by changing the Heat sink material to one with a higher thermal conductivity i.e. changing from Aluminium to Copper.
In some applications thickening of the base or changing the material may not be adequate, in these applications ?forced spreading? devices can be used such as Heat pipes or vapour chambers.
Heat pipes or vapour chambers can be embedded into the base of the Heat sink to efficiently spread the heat across the base. Columbia Staver use several methods to embed these devices.