HEAT SINK

Heat sinks are used to carry away heat from central processors (CPUs) or in any electrical/electronic circuit for that matter. CPUs generate a lot of heat and this needs to be quickly removed since excessive heat has a detrimental effect on the CPU performance and its life and in extreme cases may even cause a meltdown. A temperature rise up to 180 deg centigrade can occur in high-end processors (P4) and microcontrollers.

How it works:

A heat sink works by carrying away the heat either by convection or radiation. It consists of a good heat conductor like aluminum or copper placed very near or touching the heat source. The sink has metal fins of thin cross section to increase the area for heat dissipation. A motor driven fan is also placed on the top so that it draws the hot air away faster than natural convection. To avoid metal-to-metal contact, thermal grease is used as a thin layer between the heat source and the heat sink.

Selection:

Heat sinks are made of either copper or aluminum alloys. They are classified based on:

Cooling: Heat sinks can be either air-cooled or liquid-cooled. Air-cooled heat sinks can be of bonded fin type, extruded or copper and liquid-cooled heat sinks can be of liquid-cooled plates or cold plates.

Mounting: Heat sinks can be of board level type or fan assemblies.

The basic criteria are:

• Heat dissipation: total heat that is dissipated by the processor.
• Junction temperature: the maximum temperature at the point of contact between the heat sink and the heat source.
• Ambient temperature: air temperature of the cabinet where the heat sink is placed.
• Sink temperature: maximum temperature of the heat sink.
• Thermal resistance: temperature rise per unit rate of heat dissipated.
• Dimensions: the height, width and length of the device.
• Fan: Where space is a restraint and the amount of heat generated is large, fan assemblies are used. The number of fans used and their power/speed rating.

Applications:

Heat sinks are used in computers, laptops, semiconductor devices, microcontrollers, etc.

© 2005. PartMiner, Inc. All Rights Reserved.