When to Use Heat Pipes, HiK™ Plates, Vapor Chambers, and Conduction Cooling
When it comes to cooling electronics and maintaining optimal performance, there are many different thermal management options available on the market today. Conduction cooling and two-phase heat transfer methods are the most ideal ways to manage temperatures. But which one is right for your particular application? Keep reading to learn the difference between the two and how to determine which method will work best for your project.
Conduction Cooling vs. Two-Phase Heat Transfer
Conduction cooling is the standard cooling method for many high-end applications where two-phase cooling is not suitable. Conduction cooling methods move heat from the source to a cooler area over a short distance; the heat can then be removed by liquid- or forced-air cooling.
The two-phase cooling process works by using the latent heat of a working fluid to efficiently transfer the heat from the source to a remote heat sink. The heat input vaporizes the working fluid at the wick surface. The vapor and its associated latent heat flows toward the colder section and condenses, giving up its latent heat.
| There are two different types of conduction cooling options: | There are three different types of Two-Phase Cooling options: |
| – Heat Pipes – HiK™ Plates – Vapor Chambers |
The table below summarizes each thermal management technology discussed in the following sections.
| Material | Density | Spreading | Thermal Conductivity W/m K | Max. Heat Flux, W/cm² | Minimum Thickness | Max. Height, cm | Direct Die Attach | Cost |
| Aluminum | 1 | 2-D | 200 | Depends on Geometry | Structural Considerations | N.A. | N | $ |
| Heat Pipes | ~ 1.3 | 1-D | 10,000 – 100,000 | 75 (500) | 3 mm (< 1.8 mm flattened) | ~ 25 cm (10 .in) | N | $ |
| HiK™ Plate | 0.98 – 1.2 | 1.5-D | 600 – 1,200 | 75 | 1.83 (0.072 in.) | ~ 50 cm (20in) | Y | $$ |
| Vapor Chamber | ~ 2.8 | 2-D | 5,000 – 100,000 | 750 (1 cm²) | 3.0 mm (0.120 in.) | 15 cm (6 in.) | Y | $$$ |
| Encapsulated Conduction | 0.9 – 1.0 | 2-D | ~ 550 | Depends on Geometry | 1.5 mm (0.060 in.) | N.A. | N | $$$$ |
In general, two-phase heat transfer devices weigh more than aluminum or encapsulated conduction cards, but they have higher effective thermal conductivity. As a result, two-phase heat transfer devices have higher specific thermal conductivity.
The maximum heat flux for Heat Pipes, HiK™ Plates, and Vapor Chambers is set by the design of the wick.
The maximum heat flux for Aluminum Encapsulated Conduction Plates is set by the maximum allowable temperature of the component to be cooled and, due to its lower thermal conductivity, the heat flux is lower compared to two-phase heat pipe solutions. Encapsulated conduction cooling is also considerably more expensive when compared to HiK™ plates or vapor chambers, so it is typically only chosen when passive two-phase devices can’t be used due to favorable orientation, required thickness, or systems working vertically over 50cm (20in).
Which Cooling Method Should You Choose?
In this section, we’ll explore the different types of conduction cooling methods and how they are applied to the thermal management of electronics.
Baseline Aluminum Plates
What is an aluminum plate?
The lowest performing and cheapest solution for thermal management, the baseline aluminum plate is just that –an aluminum plate.
How do aluminum plates work?
Aluminum plates work as heat spreaders, transferring heat from the source to a heat exchanger or heat sink.
When are aluminum plates used?
Baseline aluminum plates are best suited for systems with low power requirements and low densities (as compared to two-phase systems).
Heat Pipe
What is a heat pipe?
A heat pipe is a sealed vessel that is evacuated and backfilled with a small amount of working fluid and an internal wick structure to help move the working fluid.
How do heat pipes work?
Heat pipes work by using a combination of evaporation and condensation of the working fluid; the working fluid moves from the cool (condenser) side of the heat pipe to the hotter (evaporator) side, where it vaporizes. The vapor then moves to the condenser’s heat sink along the wick, where it condenses, releasing its latent heat; then the cycle begins again.
When are heat pipes used?
Heat pipes are used to move heat from one area to another, often from a heat-producing component to a remote heat sink. They can transform heat from a high heat flux at the evaporator to a lower heat flux at the condenser, making it easier to remove overall heat with conventional methods such as liquid or air. Heat pipes also provide an isothermal surface, maintaining constant temperatures across the entire unit. They are useful for decreasing the temperature to increase maximum power output, for cooling individual components, and routing heat around other components (as heat pipes can be bent and manipulated).
HiK™ Plates
What is a HiK plate?
HiK™, or high conductivity plates are heat spreaders with strategically placed heat pipes for maximum heat transport. They are particularly useful for cooling multiple high-power components and managing the thermal load.
How does a HiK™ plate work?
Embedding heat pipes in an aluminum plate increases the thermal conductivity of the base plate by 2 to 4 times and allows for the direct bonding of electronics. This is particularly useful for cooling multiple high-power components and managing the thermal load. HiK™ plates collect and move heat from discrete heat sources to the liquid-cooled edge or air-cooled heat sinks with minimal temperature gradients.
When are HiK™ plates used?
HiK™ plates are used to enhance thermal conduction to cold rails, to act as more efficient and smaller forced and natural convection heat sinks, and to enhance card guides and metal chassis assemblies.
Vapor Chamber Cooling
What are vapor chambers?
Vapor chamber heat spreaders are planar heat pipes, sealed containers with a wick formed on the inside wall and a small amount of fluid that is in equilibrium with its own vapor.
How do vapor chambers work?
Vapor chambers spread heat from concentrated heat sources to a large-area heat sink with effective thermal conductivities greatly exceeding those of copper. As one side of the vapor chamber heats up, the working fluid evaporates, and the vapor spreads to the entire inner volume of the chamber and spreads the heat uniformly over a large area as it condenses.
When are vapor chambers used?
Vapor chambers are generally used for high heat flux applications or when genuine two-dimensional spreading is required on a single plane. They can be used to cool a single microprocessor or multiple processors on a single plane.
Encapsulated Conduction Cooling
What is encapsulated conduction cooling?
Encapsulated conduction cooling uses a highly conductive, fragile material that is typically encapsulated in aluminum.
How does encapsulated conduction cooling work?
Similar to HiK™ plates, encapsulated conduction cooling moves heat from the source to a cooler heat sink or heat transfer method.
When is encapsulated conduction cooling used?
Encapsulated conduction cooling cards are not affected by acceleration or gravity, so they can be used when there isn’t favorable positioning for heat-pipe-related cooling. They have an operating temperature range of -40°C to 100°C, and they are ideal for long thermal transport distances.
Making the Choice
Ultimately, the choice for your thermal management needs lies in the carefully constructed planning and design process, wherein expert ACT engineers will comb through the details of the project needs to construct the ideal solution. Whether in the beginning stages or retrofitting an existing system, ACT is here to get the job done with you every step of the way.
To get some insight into what ACT has already done, and to demonstrate the difference in heat transfer technologies, several trade studies are available.
Ready to start discussing your project with our team?
