What Is a Heat Sink?
Heat sinks are mechanical devices that prevent extreme heating in a device using natural and forced convection. A heat sink within an integrated circuit helps to dissipate generated heat due to its high thermal conductivity material.
The heat sink cools down an electrical heating component, especially a power transistor, by expanding the heat across the surface area and allowing the device to cool down to a perfect operational temperature. Generally, most manufacturers often fit heat sinks in processors and transistors with a built-in fan to efficiently prevent temperature rise.
Different Types of Heat Sink
There are two standard heat sink types based on their airflow type, fin efficiency, orientation, and material:
Active Heat Sinks
These types are the powerful and efficient type that runs on the device’s power source. They use a forced convection mechanism in which fluid or air is moved across the hot area to achieve heat transfer in components. They use one or more fans to force the air across the elements, ensuring the gradual cooling of the component.
Active heat exchangers have fans installed beside or above the heat sink, while some use liquid cooling mechanisms. Typical electrical components with active heat exchangers include GPU coolers, CPU coolers, etc.
Passive Heat Sinks
A passive heat sink is a common alternative that uses natural convection/airflow to dissipate heat. However, it is not as effective as an active heat sink. Nonetheless, they are usually inexpensive and need no additional electrical power to operate a blower or fan. Common examples of components with a passive heat exchanger include microcontrollers, microprocessors, chipsets, etc.
Using either of these heat sink results in significant variation in design. For example, active heat sinks use a light-material fan and need a smaller surface area to transfer the same degree of heat as a passive conductor.
Why Is Heat Sink Important?
A heat sink is essential in any electronic device because it helps avoid overheating in electrical components. Here are other reasons why a heat sink is critical in electrical products:
- Increases Electronic Reliability. A heat sink increases the reliability of electronic products because of its ability to protect a component from overheating or breaking down.
- Maintenance of Thermal Energy. Heat sinks control the electrical device’s thermal energy by transferring the created heat from the circuit components to the ambient air.
- Heat Generation. Heat sinks are a good source of heat generation or provision within electrical circuits whenever there is a drop in temperature.
Aside from these benefits, they are usually an integral part of many electronic devices. For instance, they constitute the central processing unit of computer systems.
Common Heat Sink Applications
There is an extensive range of heat sink applications, primarily in electronic devices. The reason is that electronic devices generate high heat while functioning and cannot mitigate their temperature. The heat generated by these devices can affect the semiconductor’s performance within the device. Thus, the need to constantly regulate the temperature of such devices to maintain favorable working conditions.
Here are some applications of heat sinks:
Power Amplifiers
The heat generated in power transistors can result in current leakage. This increase in collector current can lead to high dissipated power, which causes an increase in temperature—ultimately leading to a loop of thermal runaway damaging the transistor. However, a heat sink can prevent damage by quickly transferring heat via its surface.
CPUs
Computers produce significant heat during operation when the CPU chips and graphic cards are overclocked. A heat sink thermally paired to the CPU quickly extracts the heat from the chip, moves it across its surface, and dissipates it into the surrounding air.
Optoelectronics
Heat sinks are often used with Light-emitting diodes (LEDs) and lasers, as these devices cannot minimize operational temperature levels. A cooling medium is crucial in these devices to ensure longevity because their operating temperatures influence their lifespans.
Common Manufacturing Techniques for Heat Sinks
This section discusses the three most compatible techniques for making aluminum heat sinks:
CNC Machining
CNC machining is a versatile technology comprising milling, drilling, grinding, and turning processes. This machining process allows flexibility in fabricating parts according to their structure to fit their intended use. CNC machining is well-suited for designing heat sinks with the most complex specifications. CNC-machined heat sinks are ideal for devices requiring high thermal conductivity or complex design options. However, this process can be pretty costly.
Extrusion
Extrusion is a typical process that involves forcing materials such as aluminum alloys into desired shapes. It is the most common heat sink production process across industries. Heat sink extrusion is cheaper and enables easy manufacturing of custom heat sinks—aluminum alloys such as the aluminum 6063 offer excellent thermal conductivity suitable for hit sink applications. However, the maximum width of extrusion hinders the dimensions of extruded heat sinks.
Die Casting
The die-casting process dissolves aluminum alloy into liquid at high pressure, after which the liquid aluminum is poured into a mold. This process offers impressive design flexibility, good thermal performance, and a low unit cost for large-scale production. Die-cast heat sinks are well-suited for thicker heat sinks and natural convection applications. In addition, this process is ideal for making heat sinks with thin, strong, and complex designs.
Thermal Resistance Calculation for Heat Sink Design
You must understand specific thermal resistance calculations to design a heat sink that fits the intended purpose perfectly. It gives you a foresight of the performance of how well the heat sink will dissipate heat. So, you can calculate the Thermal Heat Resistance of electronic components using the equation below:
Rhs = (Tj-Tmb/P) – (Rth-jc) – Rinterface
- Tjunction – highest junction operating temperature of an electronic device in 0c
- P: Heat transferred from the heat source
- Rth-jc: Junction to casing thermal resistance
- kinterface: Interface material’s thermal conductivityRinterface = (tint/Ls x Ws x kinterface)
- Rinterface: Thermal interface material resistance
- Tinterface: Thermal interface material thickness
- Tambient: Ambient air temperature at 0c
- Ws: Heat source’s width
- Ls: Heat source’s length
Total thermal resistance refers to the resistance to heat transfer from the junction to the case, interface material thermal resistance, and resistance between the ambient air and the heat sink.
Understanding the above calculations helps to know the ideal thermal resistance compatible with the operating temperature of the heat. So, incorporating these parameters in your heat sink design becomes easy. More importantly, it allows for a thermal resistance more significant than the maximum operating temperature of a semiconductor. In addition, you can calculate the heat sink’s highest dimension to determine the lowest heat source temperature.
Size Calculation for Heat Sink Design
Determining the dimensions of your heat sink is one of the initial steps in calculating its size. After setting these dimensions, there are a few calculations simplified using the heat sink calculator
- Finding Heat of Convection:
Qc = 2hA(Tcompent – Tambient ) Where
h = 1.42[( Tcompent – Tambient )/H ] ＾0.25
A = HL + t(2H + L)
Qc : 2hA( Tcompent – Tambient )
- You will discover there is a separate surface where heat can transfer, determining the heat of convection at A2:
Qc = 2h2A2(Tcompent – Tambient ) Where
s = 2.71 [ gβ(Tcompent – Tambient )/Lαv ]
A2 = L[2( H – b) + sb] + tL
- The calculation for finding the heat generated through radiation:
Qr2 = 2ϵσA2( T4compent – T4ambient )
Qr = 2ϵσA1( T4compent – T4ambient
Where
A2 = L(t + s) + 2(tH + sb
- The total number of fins is calculated by:
Fn = 1 + [(Q – Qr2 – Qc2) / (Qr1 + Qc1)]
- The width of a fin is calculated by:
W = (N – 1) + Nt
Tips to Consider During Heat Sink Design
The right heat sink design offers a reliable thermal management solution in an electronic device. The passive heat forcing mechanism in a passive heat sink should facilitate the seamless heat transfer to the surrounding air.
This transfer of heat is often by radiation, conduction, or convection. It sometimes features the combination of the three heat transfer means. It is essential to consider the following factors during heat sink design for custom machining:
Suitable Material for Heat Sink
The material used for the heat sink significantly impacts the design. There are different kinds of materials to consider in this case:
- Interface Materials
Thermal interface materials comprise the material that fills the space between the heat sink. Most manufacturers often use materials like mica other than regular air. The thermal interface materials offer electrical components lower thermal resistance, allowing their quick thermal energy dissipation. The thermal energy created by the electronic device is a combination of its component-generated heat.
However, it is difficult to guarantee a productive heat transfer because each component has different heat resistance. So, you have to incorporate a thermal interface material to ensure a successful heat transfer from the electronic device, minimizing thermal resistance.
- Heat Sink Material
Due to their high conductivity, copper and aluminum are typical materials for making most heat sinks. Aluminum is cost-effective and flexible, making it perfect for application and easy to fabricate into heat sinks. On the other hand, copper heat sinks have high corrosion resistance and thermal conductivity. Although copper is a standard alloy used in heat sink design, aluminum is the most used material. However, the careful combination of these alloys provides excellent heat sink construction results.
Heat Sink Fins Shape and Arrangement
Fins are essential components in heat sinks that facilitate fast and efficient heat transfer to the surrounding air. Their shape and arrangement can impact the flow of heat energy, while their sheer number and sizes significantly influence efficiency.
Thus, the location or placement of these fins should facilitate easy and efficient air passage. You must ensure that the fins for your heat sink have the best shapes, sizes, and arrangements to allow effective heat flow from the electrical component.
Thermal Resistance
This means the heat sink’s resistance to heat moving between the semiconductors and the environment. The environment may be a coolant fluid or ambient air. When choosing a heat sink for your device, it is crucial to determine its thermal resistance.
The path for heat transfer must have a significant degree of resistance to heat. This determines how fast the dissipation of heat occurs. Thermal resistance reveals whether temperature reduces. It guarantees the efficiency of a heat sink.
Heat Sink Attachment Methods
Heat sinks are used in different devices, primarily mechanical components, and the attachment technique often significantly impacts their efficiency at dissipating heat. Before choosing the ideal attachment technique, consider your device’s mechanical and thermal requirements. Several methods are used in attaching a heat sink to an electronic device. The typical ones include:
- Wire Clips
- Push Pins
- Thermal Tapes
- epoxy
- Plastic Clips
- Spring Loaded Screws
However, some factors hinder the compatibility of these attachment techniques with your components. For example, although epoxy is an ideal option in thermal management, it has high costs and requires higher skills. Likewise, thermal tapes are not suitable for large and heavy heat sinks.
Conclusion
Heat sink design is fundamental to the adequate performance of heat sinks. Heat sinks are essential in electronic devices; hence, you must be meticulous in designing them. Therefore, you must understand the differences between the types of heat sinks and consider the factors that help in the design.
AT-Machining is your reliable on-demand manufacturing company that can help with your heat sink design optimization for better performance. We have a team of highly-trained and skilled engineers with good years of experience in heat sink design and manufacture. Upload your design and get an instant quote today. Feel free to contact us for your next project!
