Heat spreaders are objects with a high thermal conductivity that either connect a heat source to another heat exchanger or that release heat to ambient air to prevent the overheating of critical components. These heat-dissipating devices are typically made of copper, aluminum, graphite, or diamond. Different types of heat spreaders, including metallic heat spreaders; phase-change devices like heat pumps and vapor changers; and thermal transfer compounds to fill air gaps, have been designed to maximize heat transfer efficiency for different applications. Heat spreaders are commonly used in computer processors, mobile devices, and automotive electronics, among other things. This article will review what heat spreaders are, and explain the different types and applications to ensure you have the information you need to complete your project.
What Is a Heat Spreader?
A heat spreader is an object that facilitates the dissipation of heat from a higher-temperature source to an additional heat exchanger or to a cooler medium, such as ambient air. Heat spreaders are often used in electronics and electrical systems. They are also commonly used in HVAC systems, water heaters, power plants, and other industrial applications.
What Is the Importance of a Heat Spreader?
Heat spreaders are important devices for preventing the overheating of critical components in electronics and industrial systems. Overheating harms the performance of electronics in two ways: it degrades the performance of semiconductors, whose resistivity drops with increasing temperature, as well as the performance of the metallic connections of the electronic components to the rest of the electronic system. This causes the hard drive and processor to slow down. If too much heat is developed without being dissipated, the excessive heat can cause computer systems to crash and damage components.
How Does Heat Spreader Work?
A heat spreader works by conducting thermal energy from a heat source to either a secondary heat exchanger or to a cooler medium. This can be accomplished using either solid pieces of materials with high thermal conductivity or by taking advantage of the absorption of heat required to change a material from one phase to another (usually liquid to vapor).
In solid heat spreaders, the heat is conducted through the metal block and away from the source. Phase change heat spreaders work by changing the state of matter of a volatile liquid or gas. The cool liquid changes into a vapor after contacting the hot, outer surface. This vapor then travels through a heat pipe or vapor chamber to a secondary heat exchanger to carry heat away from the source. The vapor then recondenses into a liquid and repeats the cycle.
What Are the Components of a Heat Spreader?
Heat spreaders contain one or more of the components listed below:
1. Base Material
The base material forms the primary sheet, block, or gap-filling structure of a heat spreader that transfers heat from the higher-temperature source to the secondary heat exchanger. Base materials must have high thermal conductivity. This makes copper, aluminum, graphite, and diamond good choices.
2. Thermal Interface Material
The thermal interface material (TIM) is a substance placed between the heat spreader and the heat-generating device to help improve heat transfer. TIM is typically a silicone-based thermal grease or thermal paste with metal oxide, silver, or graphite fillers.
3. Fins
Fins are protrusions from the primary body of the heat spreader that enhance the amount of surface area available for conduction away from the heat source. Ambient air flows between the fins and further removes heat from the fins, and thus from the system, by convection. Fins are made from the same base material as the rest of the heat spreader.
4. Heat Pipes
Heat pipes are closed pipes consisting of a thermally conductive outer structure, a wick, and a working fluid. One end of the heat pipe lies in the zone that is to be cooled and absorbs heat from it. This heat evaporates the liquid in the wick, on the inside wall of the heat pipe. The resulting gas moves down the center of the pipe to the condenser section, where the cooler walls recondense the vapor in the wick. Capillary action then pulls that liquid back to the hot (evaporator) zone, providing a continuous circulation of cooling fluid within the sealed pipe.
5. Fans
Fans are typically placed at the end of the heat spreader. The fans help dissipate heat further due to forced convection.
6. Enclosure
Some electronics don’t have space for heat spreader components. Therefore, large flat enclosures made from copper or aluminum are used to dissipate heat. Enclosures are typically used for electronics that operate in applications with excess vibration or in applications where electronics must be protected from the environment.
What Are the Types of Heat Spreaders?
The types of heat spreaders are described in the list below:
1. Metallic Heat Spreaders
Metallic heat spreaders are usually fabricated from copper or aluminum. They are often used in electronics and in industrial applications. Their primary advantage over other types of heat spreaders is that they are easy to manufacture and are efficient at dissipating heat. Some disadvantages of metallic heat spreaders are that they can be heavy, and costly when using copper.
2. Graphite Heat Spreaders
Graphite heat spreaders are commonly used in consumer and automotive electronics and in batteries. The primary advantage of graphite heat spreaders is that they are lightweight compared to metallic heat spreaders. They are also just as efficient, if not more efficient, than metallic heat spreaders, and can be used in tight spaces. A major disadvantage is that they are brittle. They are also extraordinarily expensive compared to metallic heat spreaders.
3. Vapor Chambers
Vapor chambers are heat exchange devices that are, like heat pipes, made from a thermally conductive metal, a wick, and a working fluid. They can be thought of as planar heat pipes. Vapor chambers have an evaporator section in which a liquid absorbs heat from a source. This causes the liquid to transform into gas and move to the condenser area. It then cools and re-forms as a liquid which circulates back to the high-heat end of the device by capillary action. Vapor chambers are often used in tight, confined spaces such as mobile devices or laptops. A major advantage of vapor chambers is that they can be used in tight spaces and are efficient at dissipating large amounts of heat. Its biggest disadvantage is that it is the most expensive option compared to other heat spreaders.
4. Heat Pipes
Heat pipes are heat spreader devices that are made from a tubular or flat thermally conductive metal, a wick, and a working fluid. The movement and phase changes of the fluid facilitate the transfer of heat from the heat source to a secondary heat exchanger or ambient air. They are commonly used in electronics and industrial applications. Their primary advantage is that they are best for low-power applications and offer great flexibility when designing a system with many components. Notable disadvantages of heat pipes are that they can be costly, are not effective in high-power situations, and have poor performance if working against gravity.
5. Composite Heat Spreaders
Composite heat spreaders are made up of multiple materials that work together to remove heat from a primary source. These are usually a thermally conductive metal and a highly thermally conductive material such as boron arsenide or graphite. These heat spreaders are commonly used in electronics with high power demand where weight is a concern. Composite heat spreaders can effectively and efficiently remove heat without adding too much weight to the device. However, they are expensive due to the complexity of fabricating these heat spreaders.
What Are the Applications of Heat Spreaders?
Some of the applications of heat spreaders are listed below:
1. Computer Processors
Heat spreaders are often used in computer processors to prevent them from overheating during operation. The heat spreader is typically mounted directly on the surface of the processor to quickly absorb and distribute heat away from the source. Overheating a processor can lead to permanent damage to the component, reduced lifespan, and decreased performance.
2. Memory Modules
Heat spreaders are used in memory modules (random access memory or RAM stick) to prevent overheating and improve processing functions. Heat spreaders made of copper or aluminum typically enclose the entire RAM stick due to the confined area that memory modules are placed in.
3. LED Lighting
Large LED floodlights and overhead lights are energy-efficient but still generate lots of heat. Overheating can lead to reduced lifespan and efficacy. LED lights are typically fixed onto a printed circuit board (PCB). Heat originating from the PCB is removed by a heat spreader that is also attached to the PCB. The heat spreader carries heat to the surrounding air to prevent overheating of the LED components.
4. Power Electronics
Power electronics is the use of electronics to control and convert electrical power. High-power electrical circuits, switches, and components are designed to carry higher currents and generate a lot more heat in the process. Heat spreaders are used in power electronics to prevent overheating, which in turn allows the design of electronics with higher power density, performance, reliability, and service life.
5. Automotive Electronics
As cars become packed with more electronics, the power demand, and thus heat generation, increases. HVAC, infotainment systems, and dashboard instruments are all electronics commonly included in automobiles. Heat spreaders are used to remove heat from the heat-generating components to prevent overheating and reduced performance.
6. Mobile Devices
Due to the power of today’s mobile devices, heat spreaders are essential to prevent overheating and ensure optimal performance and life. Heat spreaders act as backing plates to the Printed Circuit Board that powers the device’s functions due to the confined space within a mobile device. Heat is transferred through the heat spreader to the device’s outer shell, and then released into the ambient air through natural convection.
What Are the Factors That Affect a Heat Spreader’s Performance?
The factors that affect heat spreader performance are described below:
1. Thermal Conductivity
Thermal conductivity refers to the ability of a material to conduct heat. Heat spreaders are made of highly conductive materials, such as copper or aluminum. They can quickly absorb and distribute heat away from the heat source. This leads to more efficient cooling. A higher thermal conductivity generally means a more effective heat spreader.
2. Thermal Resistance
Thermal resistance is the resistance to heat transfer across a material or temperature gradient and is considered the inverse of thermal conductivity. Higher thermal resistance equates to lower heat transfer rates and is therefore undesirable in heat spreaders.
3. Surface Area
Heat transfer depends on the movement of energy from a higher-temperature area to a lower-temperature area. As a heat spreader absorbs heat from the main source, it needs to transfer that heat to the secondary heat exchanger or to the atmosphere. The larger the surface area of the heat spreader, the more opportunity it has to transfer heat to the environment so that it can continue to absorb more heat from the point source.
4. Heat Sink Design
Heat sink design relates to fin count, fin geometry, and fin placement. A larger number of fins can improve the effectiveness of a heat spreader. More fins increase the overall surface area of the heat spreader. Additionally, fins must be placed strategically to maximize heat transfer.
5. Thermal Interface Materials (TIM)
Heat spreaders are attached to components by a TIM. The thermal resistance of a TIM can reduce heat spreader efficiency due to irregularities in the surface of the interface. Voids and trapped air increase thermal resistance and negatively impact heat spreader effectiveness.
6. Airflow
Airflow from fans can improve the effectiveness of heat spreaders. This is because fans can help remove warm air from an electronic enclosure through forced convection. This keeps the ambient air in the enclosure cooler which makes the heat transfer from the heat spreader to the ambient air occur faster.
7. Operating Environment
The fluid flow rate and fluid temperature impact a heat spreader’s thermal resistance and its effectiveness at dissipating heat. The smaller the difference between the heat source temperature and the ambient temperature, the more difficult it is for the heat spreader to dissipate heat.
What Are the Benefits of Heat Spreaders?
The benefits of heat spreaders are listed below:
- Preventing Component Damage: Heat spreaders are used to dissipate heat away from electronic components, preventing them from overheating and sustaining permanent damage. This can increase the lifespan of the components and improve the overall reliability of the electronic device.
- Improved Performance: Heat spreaders help improve electronic device performance by preventing overheating. This allows devices to run at optimal temperatures and prevents decreased resistivity from adversely affecting system performance.
- Reduced Energy Consumption: Overheating can lead to increased power demand in devices to ensure proper function. Heat spreaders effectively reduce the energy consumed by electronic devices by keeping the circuitry cooler.
- Safety: Heat spreaders contribute to safer products by preventing overheating. This minimizes the potential for burns caused by touching hot surfaces, or even fires.
- Flexible Design: There’s no standard way to design a heat spreader. Therefore, engineers have the freedom to design heat spreaders tailored for specific devices to achieve optimal heat dissipation.
What Are the Limitations of Heat Spreaders?
Some of the limitations of heat spreaders are listed below:
- Cost: Heat spreaders can be expensive, particularly those made from high-conductivity materials like copper or aluminum. This can increase the overall cost of electronic devices.
- Size and Weight: Heat spreaders can increase the weight of electronic devices. Additionally, since many devices are becoming more compact, heat spreaders cannot always remove enough heat from the device.
- Limited Heat Dissipation: The ability of a heat spreader to adequately dissipate heat is limited by the size of the enclosure it serves, the materials and design of the heat spreader, and the ambient conditions to which it must transfer its heat.
- Foreign Debris Can Affect Performance: Dust and other foreign particles can reduce the effectiveness of a heat spreader. These items can limit the amount of surface area exposed to the ambient air or fluid and reduce heat dissipation rates.
- Structural Limitations: Heat spreader design is largely dependent on the available space within an electronic device’s enclosure. Therefore, it can sometimes be difficult to design effective heat spreaders if there is limited space within a device.
Are Heat Spreaders on RAM Necessary?
No, heat spreaders on RAM are not necessary. RAM seldom gets hot enough for its performance to be affected by the temperature.
What Is the Difference Between Heat Spreaders and Heat Sinks?
A heat spreader is a device that transfers heat generated from a heat source to a secondary heat exchanger or to the ambient environment. A heat sink accomplishes the same thing but is considered a “passive heat exchanger” since there are no moving parts. Therefore, a heat sink can be thought of as a type of heat spreader.
Summary
This article presented heat spreaders, explained what they are, and discussed their components and applications. To learn more about heat spreaders, contact a Xometry representative.
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