Because of the increasing need for high-performance electronics, advanced devices with fast microprocessors and high transistor densities are being manufactured. This technical modification in such electronic components has resulted in increased heat load during operation. The proper heat sink ensures the best possible performance of electronics.
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In this article, we will answer the question: What is a heat sink? what does a heat sink do? We would also explore the importance of a heat sink, the basics of a heat sink design, and how to choose the right heat sink for optimal electronics performance. Let&#;s get started.
We may ask what is heatsink. A heatsink is a device used to dissipate heat from electronic components, such as processors or graphics cards. It typically consists of a metal or aluminum structure with fins that increase the surface area for better heat dissipation. The heatsink absorbs the heat generated by the component and transfers it to the surrounding air, helping to keep the component cool and prevent overheating.
The proper heat sink ensures the best possible performance of electronics. There are six different types of heat sinks that can be used in an active or passive system. They are usually constructed of aluminum or copper. Some of the main types include:
Bonded Heat Sinks
These heat sinks are made by bonding fins to a base plate using thermal adhesive or epoxy. They can be made of either copper or aluminum or a combination of the two. They are cost-effective and suitable for low to medium-power applications.
Skived Heat Sinks
Skived heat sinks are made by cutting thin fins from a solid block of aluminum or copper. Skived heat sinks have a series of tightly packed fins on a base made of a single piece of metal, resulting in minimum thermal resistance. This manufacturing process allows for high fin density and efficient heat dissipation. Skived heat sinks are commonly used in high-power applications.
Stamped Heat Sinks
Stamped heat sinks are made by stamping or pressing fins into a base plate. The stamped metal fins are held together by one or more zipper fins that run perpendicular to the regular fins and interlock to maintain the distance. They are cost-effective and suitable for low to medium-power applications. However, they have lower fin density compared to skived heat sinks.
CNC Machined Heat Sinks
CNC-machined heat sinks are made by removing material from a solid block of aluminum or copper using computer-controlled milling machines. This allows for precise customization and complex designs. CNC-machined heat sinks are commonly used in high-performance applications where specific thermal requirements need to be met.
What does heat sink do? Actually, a heat sink is a device used to dissipate and disperse excess heat generated by electronic devices, such as computer processors or power transistors. When electronic devices are in operation, the electrical energy flowing through them is converted into heat energy due to resistive losses and other factors. If the heat produced is not efficiently dissipated, it can result in a temperature rise that exceeds the device&#;s operating limits, leading to reduced performance, instability, or even permanent damage.
Analyzing the thermal performance of each electronic item is a difficult process. It is designed to absorb the heat and transfer it to the surrounding environment, thereby preventing the device from overheating and potentially malfunctioning or getting damaged.
1. Budget
Determine how much you are willing to spend on a heat sink. There are various options available at different price points, so it&#;s important to find a balance between cost and performance.
2. Space Restrictions
We may consider a bigger high-heat sink. A larger heat sink means high thermal management. However, this is only true if the appropriate heat sink is chosen for the application. Heat sinks are frequently confined by the other components surrounding them, therefore a larger heat sink is not always possible. Furthermore, a more efficient heat sink design may have better thermal management than one that is simply larger.
3. Use of Thermal Paste
Thermal paste is required for heat sinks to effectively transfer heat from the component to the heat sink. The thermal resistance between the heat sink and the component increases if it is not used. This will have a negative impact on the heat sink&#;s performance.
4. Features of Heat Sinks
Different heat sinks have various features like fins, heat pipes, or liquid cooling systems. Fins increase the surface area for better heat dissipation, heat pipes help transfer heat more efficiently, and liquid cooling systems can offer even better cooling performance. Consider the specific requirements of your device and choose a heat sink with the appropriate features.
5. Airflow Interaction
Proper airflow is crucial for effective heat dissipation. Consider how the heat sink&#;s design interacts with the available airflow in the system. Ensure that there is sufficient space around and above the heat sink for adequate airflow and that the heat sink&#;s fins or other design elements align with the direction of the airflow.
6. Heat from Surrounding Components
Some electronic components, such as memory modules or power transistors, may also generate heat that can affect the performance of the heat sink. Consider how the heat from surrounding components may impact the heat sink&#;s effectiveness and choose a suitable heat sink that can handle the combined thermal load.
7. Material Composition
Heat sinks are commonly made of aluminum or copper due to their high thermal conductivity. Copper has better thermal conductivity but is more expensive, while aluminum is lightweight and cost-effective. Consider the requirements of your application and choose a material that best suits your needs.
Surface treatment has a significant impact on heat sink performance. The surface of the heat sink must be smooth and free of defects or roughness as these can limit heat transfer. A rough surface can create air pockets and limit the contact area between the heat sink and components, resulting in poor heat transfer and increased temperatures.
Richconn has extensive expertise in surface finishing and the most professional team, delivering the best performance at the most competitive pricing. During the heat sink design process, the following common surface finishing of heat sink that Richiconn can offer:
Heat sinks are of high importance and choosing the proper heat sinks is carefully structured to guarantee effective performance. Therefore, many things must be taken into consideration. This article talks about factors that can help you choose the right one. Do you want the best services of surface finishing on a heat sink at a low price? Contact our support team for surface finishing services on heat sink.
Posted on Jul 21, by webadmin
TweetElectronic devices and circuits will generate heat in operation &#; this is an unavoidable fact. When components overheat, however, it can result in significant loss of performance and even major damage to the device.
The concern, therefore, is how much heat is too much and how to dissipate the excess effectively.
Heat sinks are one answer to this problem. A heat sink allows a component to dissipate heat over a larger surface area and transfer this heat to a cooling media surrounding it &#; usually air or a liquid coolant. This keeps the device running at an appropriately lower temperature.
Heat sinks may assist in both passive cooling and active cooling applications. Passive cooling relies on natural convection and radiation to cool a component. In active cooling, a fan or blower is required to move air through the heat sink to cool the component.
Several factors affect the performance of a heat sink, including:
This blog will look at the thermal performance of heat sinks and explain their features and benefits.
First, let&#;s quickly review a few basic concepts.
The maximum case temperature (Tc-max), ambient air temperature (Ta), and power dissipation (Q) of the component are used to find the required thermal resistance of the heat sink.
The heat flow between the semiconductor die and ambient air can be expressed as a series of thermal resistances to heat flow (Figure 1).
Figure 1. Thermal Resistance Diagram for A Typical Electronic Component Mounting
Resistance is present from the die to the device case, from the case to the heat sink, and from the heat sink to the ambient air.
The sum of these resistances is the total thermal resistance (Rθtotal) and is expressed in units of degrees Celsius per watt (°C/W).
IC die -> IC case -> TIM -> Heat sink -> Ambient Air
Rθtotal = Rθjc + Rθcs + Rθsa = (Tj &#; Ta) / Q
Tj: Device junction temperature (°C)
Tc: Device case temperature (°C)
Ta: Ambient temperature (°C)
Q: Device heat dissipated (watts)
Rθjc: Device junction to case thermal resistance. (Rθjc can be found on the manufacturer&#;s datasheet)
Rθcs: Case to heat sink thermal resistance.
Rθsa: Heat sink to ambient thermal resistance
Because the device junction to case thermal resistance (Rθjc) comes from the device manufacturer&#;s published data, and because the values are different for different devices, we usually do not include this value in the datasheet we provide.
Instead, we provide the case-to-ambient thermal resistance Rθ value, which is expressed as:
Rθ = Rθcs + Rθsa
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For surface mounting devices (SMD), no TIM is needed. The heat transfer pathway is a little different (Figure 2) because the case to heat sink thermal resistance Rθcs is now the conductive thermal resistance from case to heat sink solder feet via drain-pad on PCB.
Therefore, the drain-pad thickness sets a big rule for Rθcs: the thicker the drain-pad, the smaller the Rθcs.
Figure 2. Thermal resistance diagram for a typical Surface Mount Device (SMD)
To sum up:
Rθtotal = Rθjc + Rθcs + Rθsa = (Tj &#; Ta) / Q
If not including the Rθjc, then:
Rθ = Rθcs + Rθsa
Once Rθ is determined, you can consult a chart typically provided by the manufacturer to find the approximate heat sink volume needed for either a natural convection heat or a forced convection heat sink at a given air velocity or a liquid cooled cold plate.
The chart provided by the manufacturer will assist in choosing a proper heat sink size based on the temperature limits for popular devices, such as D2-PAK, TO-126, TO-220, TO-247, TO-264, SOT-227 and other packages.
This chart should also provide graphs showing known values of case temperature rise ΔTc above ambient temperature Ta, and Q (watts). See Figure 3 below for an example of the graph you would find with Ohmite&#;s R2 Series heat sink.
Figure 3. Example graph showing heat sink&#;s case temperature rise above ambient temperature and thermal resistance.
Designers can simply check the graph for natural convection and determine whether the heat sink will meet the thermal design requirement.
If the device has higher power dissipation, an extrusion may be needed. In this case, a quick sizing guide may be used to find the approximate size (volume) of the heat sink to satisfy the thermal requirements.
Then, using the data sheet of available extrusions, engineers can select potential shapes and lengths that will meet or exceed this volume.
The material used to produce a heat sink will depend on the manufacturing method, cooling requirements, and cost analysis.
The most common heat sink materials are aluminum alloys. Aluminum is widely available, fairly strong, and tends to extrude well. Different alloys will provide different thermal conductivities and features.
Aluminum alloys and are very common, with thermal conductivity values of 166 and 201 W/m K, respectively. Aluminum alloy has a high thermal conductivity value of 229 W/m K but is mechanically soft.
Copper may also be considered, with thermal conductivity levels apx. 60% higher than that of aluminum. However, pure copper is 3x denser than aluminum &#; and significantly more expensive.
Ceramic (Alumina) material is growing more popular for heat sinks due to the dielectric property for high voltage circuit applications, film-printing and chip-on-heat-sink on the metalized surface, such LED lights.
Fins: Common Types and their Efficiencies
A heat sink&#;s fins serve to maximize the surface area over which the heat can be dissipated. There are several common types of fins:
Fin efficiency is defined as the actual amount of heat transferred by the fin, divided by the heat transfer if the fin had infinite thermal conductivity.
In a real application, fin type is determined by the heat sink manufacturing methods, heat sink material, and cooling mode.
For example, the P series heat sink from Ohmite uses forged pin technology, meaning pins extend from its base (Figure 4).
Figure 4. Ohmite PA/PV series heat sinks use forged pin construction which allow air flow in multiple directions.
These pins make it possible for the heat sink to use either free air convectional cooling mode or forced air convectional cooling mode without the need to re-orient heat sink mounting. This allows versatility as the designer is no longer stuck forcing air in a single direction.
The flow of the coolant media is greatly impacted by the arrangement of fins on a heat sink. For example, in a flared fin heat sink (figure 5), the fins are not parallel to each other. Flaring the fins decreases flow resistance and causes more air to go through the heat sink fin channel.
Slanting the fins can keep the overall dimensions the same, but results in longer fins. Decreasing the aspect ratio of the fins increases the fins&#; overall efficiency.
To maximize heat transfer, there must be close contact between a sink and its selected component. Insufficient contact can increase the thermal resistance at the heat-sink-to-component interface and reduce the amount of heat flow.
At the other end of the spectrum, if a heat sink is attached too tightly, it can damage a component or cause the PCB to warp or camber.
To account for these concerns, most heat sink assemblies are designed to maintain sufficient pressure from component to heat sink and a thermally conductive interface material, such as a layer of thermal grease or a thin pad.
Popular attachment methods include thermally adhesive tape or epoxy, clips (metal spring and wire spring), fasteners, and push pins with ends that expand after installing.
When selecting an attachment, designers must consider the effective heat transfer, supporting of dynamic loads, and ease of device assembly.
For example, Ohmite offers heat sinks fitted with a patented clipping system, eliminating the use of screws-washers-nuts and holes for installation (Figure 6). No tools are required, the device can be locked in for a proper thermal connection with just one finger.
The elimination of mounting hardware also reduces assembly costs and enables uniform pressure and maximum heat transfer. This system ultimately provides an easier, more streamlined assembly process.
Figure 6: Attachment options and Ohmite&#;s patented clipping system
Designed for TO-126, TO-220, TO-247 and TO-264 devices, Ohmite&#;s C series and W series extruded heat sinks use this clipping system. The spring wire clips securely fasten a heat sink with the required contact pressure while remaining fast and easy to apply or remove.
Heat sinks are an essential component in electronic products, creating an efficient path for heat to be transferred away from electronic devices. A heat sink&#;s performance is determined by material, dimensions, surface area, fin type and air flow rate.
Each heat sink's thermal resistance should be characterized by the heat sink supplier to allow users to select the proper heat sink for an application. This selection is based upon several parameters, such as ambient air temperature, power dissipation, and cooling mode.
If the device dissipation in watts is known, the temperature rise of the die over the ambient air can be calculated by referencing thermal resistance graphs or tables. This will optimize heat sink selection so that the choice is not too small, causing burnout, or too big, wasting resources.
To begin the search for the optimal heat sink, start with Ohmite&#;s extensive collection. Ohmite offers an array of low-cost, configurable, scalable, and compact heat sinks to meet the needs of not only power resistors but of all active devices.
Ohmite heat sinks are designed to secure TO-126, TO-218, TO-220, TO-247, and TO- 264 packages, plus provide thermal solutions for TO-252, TO- 263, and TO-268 SMD and BGA devices.
For applications that require significant customization, a broad extrusion profile library is available to develop custom and semi-custom solutions. Get started here.
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