ALLPCB
Summary
Using latent heat of a working fluid, phase-change heat transfer technologies represented by heat pipes and vapor chambers provide heat transfer coefficients and cooling capacity far greater than conduction or convection. These technologies are key to addressing increasing thermal demands. With chip power and heat flux density continuing to rise, the development and application of vapor chambers will determine the thermal reliability and performance headroom of communication products.
1. Evolution of Heat Sink Technologies
Thermal management is essential for ensuring long-term reliable operation of electronic equipment. As chips and other heat-generating components are increasingly densely integrated, communications and information technology development has made thermal design a system-level discipline. Research and development in power, security, consumer electronics, automotive, and LED sectors place increasing emphasis on thermal performance.
Current 5G communications and information products trend toward higher capacity, higher performance, and reduced noise and energy use. Device integration increases, single-chip functionality grows, and power consumption rises significantly while layouts become more compact. Heat flux density can increase by orders of magnitude, creating severe challenges for thermal technology.
Traditional cooling systems mainly rely on single-phase conduction to move heat from devices to external fins, then dissipate it to the environment via natural or forced convection. Conduction efficiency is limited by the intrinsic thermal conductivity of the materials used.
Phase-change heat transfer technologies, exemplified by heat pipes and vapor chambers, use evaporation in heated regions and condensation in cooled regions, absorbing and releasing latent heat in cyclic fashion to rapidly spread or transport heat. Latent heat absorption and release is a fast and efficient process, and two-phase systems typically use working fluids with large latent heat. As a result, effective thermal conductivities can exceed 2000 W/m·K, far above those of pure metals such as gold, silver, copper, and aluminum (200–400 W/m·K). These devices support heat and heat flux densities beyond the capability of traditional heatsinks and can be paired with various cooling methods (natural convection, forced air, liquid cooling, radiation), providing flexible application options.
From the earliest and widely applied heat pipes, a range of phase-change devices has evolved including vapor chamber plates, thermosyphons, loop thermosyphons (LTS), and loop heat pipes (LHP). These forms are used across product types to address high device power, high heat flux density, and poor temperature uniformity where traditional heatsinks fall short.
2. Development of Vapor Chamber Plates
Vapor chamber plates are the most mature phase-change heat transfer product after heat pipes and are widely used in communications and electronics. A typical vapor chamber is a flat, sealed structure composed of an enclosure, capillary structure, support structure, and a working fluid. Heat transfer is achieved by evaporation, condensation, and capillary transport of the working fluid, spreading heat from localized sources across the plane.
Thanks to large-area capillary action and two-dimensional or three-dimensional thermal spreading, vapor chambers support higher heat flux densities. For electronics with heat flux densities above 50 W/cm2, vapor chambers provide superior temperature uniformity compared with pure metal or embedded heat-pipe substrates, significantly improving heatsink efficiency. As chip heat flux densities approach and exceed 100 W/cm2, vapor chambers are a key enabling technology for communications equipment performance upgrades.
Like heat pipe casings, vapor chamber enclosures are typically made from metal. Most ground-based vapor chambers use thin stamped copper plates because of copper's high thermal conductivity, good machinability, and weldability, with relatively simple forming processes and high precision. In consumer electronics and aerospace, stainless steel and titanium are also used to meet high-strength, ultra-thin, or lightweight requirements. To reduce cost and weight, aluminum-based phase-change devices are also being explored.
Working fluid selection is based on operating temperature range, material compatibility, and thermophysical properties. Water matches best with copper because of its excellent thermophysical properties, safety, and ease of handling. For aluminum, refrigerants are commonly matched and have mature civilian usage. Methanol, ethanol, and acetone are also used in performance studies but are seldom used in practical applications due to toxicity and flammability concerns.
The wick or capillary core is a critical component of heat pipes and vapor chambers. Its structure directly affects heat transfer performance and heat flux capacity. Due to the flat profile of vapor chambers, common wick types include mesh, grooved, sintered, and composite wicks.
These basic wick types can be further optimized at larger geometric scales to enhance vapor chamber thermal spreading and heat flux capacity. Early vapor chambers used simple metal support posts for structural strength. Designs then evolved to wrap a sintered capillary ring around support posts or replace metal posts with sintered capillary posts, using pure capillary columns or mixed arrays. This shortens the liquid return path from the condenser to the evaporator, increasing replenishment rate and boosting heat transfer capability.
Higher-performance vapor chambers often include localized densified capillary structures in the evaporator region facing the heat source. These increase capillary pressure and liquid return while expanding evaporation surface area, thereby raising evaporation rates. Other designs add a capillary layer over a pure metal structure: because pure metals, especially copper, have higher thermal conductivity than wick materials, an internal metal core conducts heat efficiently to the capillary surface while providing mechanical strength. Such designs yield heat flux capacities in the range of 30–100 W/cm2.
More advanced capillary structures are under research, such as etched radial channel networks where liquid is replenished through an evaporation layer and a series of transverse converging channels, greatly increasing heat flux limits. Biomimetic designs inspired by leaf venation aim to balance permeability and capillary pressure to reduce thermal resistance and improve temperature uniformity.
Unlike the mature processes for heat pipes, vapor chamber manufacturing is still evolving. Although many companies have achieved mass production, challenges remain including high manufacturing cost of wick cores, low welding process efficiency and yield instability, deformation, and reliability issues.
Most vapor chamber manufacturers use mesh-based wicks. Copper mesh is easy to weave, yields consistent product quality, and supports high production efficiency, but its capillary force is relatively low. This limits performance under high heat flux and adverse gravity conditions.
3. Conclusions and Outlook
Over the past two decades, vapor chamber application has developed significantly. Key technological milestones include:
- Composite wicks. Combining materials with different pore sizes helps balance capillary pressure and flow resistance.
- Use of sintered capillary columns/rings. Replacing or augmenting support posts with sintered capillary structures shortens liquid return paths and improves heat transfer while maintaining structural strength.
- Demand from consumer electronics for thinner, lighter designs has driven extensive research into materials, processes, and manufacturing techniques.
- Advances in diffusion bonding have improved vapor chamber performance, appearance, and yield.
The trend toward higher power and higher heat flux density chips places stricter requirements on vapor chamber temperature uniformity. Optimization must improve capillary performance and enhance heat conduction and gas-liquid transport through materials and structure to significantly reduce thermal resistance. This is necessary for maintaining similar temperature differentials from heat source to vapor chamber cold surface even when operating heat flux increases by factors of two or more.
On the theoretical side, while many studies focus on reducing thermal resistance, increasing dry-out limits and critical heat flux, and achieving higher heat flux capacity, accurately predicting and evaluating internal thermal transport and limitations requires appropriate methods to model the gas-liquid interface within different capillary structures. More fundamental theoretical work is needed to analyze the physical mechanisms inside vapor chambers.
On the application side, characterization of vapor chamber heat transfer capability and thermal resistance needs greater precision, and a more comprehensive experimental database is required to summarize how working conditions affect performance. This will enable more accurate integration of vapor chambers into systems and improve design reliability. Material and process improvements across phase-change structures also require industry-wide exploration to strengthen thermal management capabilities for 5G communications and related applications.
