Heat pipes and Vapor chambers: High heat flux Density chip heat dissipation and VC development——2.The development of VC vapor chamber technology

2.The development of VC vapor chamber technology

The technology of vapor chambers (VCs) is now relatively mature (second only to heat pipes), making them the most widely used phase change heat transfer products in the communication and electronics industries. A typical VC features a flat, enclosed structure composed of a housing, capillary structure, support structure, and working fluid. It achieves efficient heat conduction through the evaporation-condensation cycle of the working fluid and capillary transport, diffusing heat from concentrated areas to the entire planar structure.

Thanks to the advantages of large-area capillary properties and two-dimensional or even three-dimensional heat diffusion, VCs (vapor chambers) have higher heat flux carrying capacity. Especially for cooling electronic devices with heat flux exceeding 50W/cm², their temperature uniformity effect significantly outperforms pure metal or heat pipe-embedded cooling substrates, capable of greatly improving the efficiency of heat sinks.

With the development trend of chip heat flux exceeding 100W/cm², VCs undoubtedly serve as a key technology to support the performance upgrade of communication equipment.

Similar to the shells of ordinary heat pipes, VC housings are typically made of metallic materials. Currently, the vast majority of VCs for terrestrial applications are formed by stamping thin copper sheets, as copper boasts excellent thermal conductivity, good machinability and weldability, with relatively simple forming processes and high precision. In consumer electronics, military, or aerospace fields, materials such as stainless steel (high strength, corrosion resistance, low cost) and titanium (high strength, low density, corrosion resistance) have been developed for VC housings to meet the demands of higher strength, ultra-thinness, or lightweighting. Furthermore, to address the market needs of cost reduction and weight reduction, the industry has gradually initiated explorations on aluminum-based phase change heat transfer devices.

Material\Property	Strength-to-Weight Ratio (kN·m/kg)	Yield Stress (MPa)	Density (kg/m³)	Coefficient of Thermal Expansion (ppm/℃)	Thermal Conductivity (W/m·℃)	Resistivity (Ω·m)
Titanium (99%)	288	830	4510	9.5	19	4.78E-07
Copper (OFHC – Oxygen-Free High – Conductivity Copper)	247	730	8930	16.7	395	1.67E-08
Aluminum (606-T6)	214	400	2700	22.2	154	2.65E-08

Comparison of the properties of titanium, copper and aluminium

The selection of the working fluid (a medium that circulates in the system and realizes heat transfer through phase change (evaporation and condensation) or sensible heat transfer) is based on factors such as the operating temperature range, material compatibility (referring to the property that no chemical corrosion, electrochemical corrosion, dissolution or physical damage occurs between the working fluid and the materials in contact with the system, such as pipes, containers, capillary structures, etc.), and thermophysical properties (referring to the physical properties of the working fluid related to heat transfer, which directly determine the heat transfer efficiency and capacity of the system and are the core indicators of the working fluid’s performance).

The working fluid that has the best compatibility with copper is water, which has excellent thermophysical properties, is safe and non-toxic, and is easy to obtain and handle. The working fluids that match aluminum are mainly refrigerants, and such working fluids have a relatively mature civil application foundation as cooling media. Working fluids such as methanol, ethanol, and acetone are also commonly used in various VC performance studies, but they are rarely used in actual applications due to factors such as toxicity, flammability, and explosiveness.

The capillary wick (also called the liquid-absorbing wick: a porous medium structure closely attached to the inner wall of the heat pipe) is an important component of capillary-driven heat transfer or heat diffusion devices such as heat pipes and VCs, and its structural type directly affects the heat transfer performance and heat flux carrying capacity. Due to the characteristic of the flat shape, VCs mainly use four types of capillary wicks: screen type, groove type, sintered type, and composite type.

In fact, the structures mentioned above can be regarded as fundamental wick configurations for vapor chambers (VCs). To further enhance the thermal spreading performance and heat flux handling capability of VCs, many research efforts have been devoted to optimizing the large-scale geometric design of wick structures.

The earliest VCs employed the most classic design: pure metal support pillars. These pillars served solely as structural reinforcements. Later designs evolved to include either:
a) Powder-sintered capillary rings sleeved over the support pillars, or
b) Complete replacement of metal pillars with porous wick pillars, arranged either purely or in hybrid configurations with metal pillars.
This allows condensed working fluid at the cold side to return to the evaporation zone at the hot side through the capillary rings or wick pillars. The return path is significantly shortened, increasing the liquid replenishment rate and thereby enhancing the VC’s heat transfer capacity.

Higher-performance VCs commonly feature locally intensified wick structures in the evaporation zone corresponding to heat source locations. Beyond strengthening capillary forces and liquid return, these wick structures simultaneously expand the evaporation surface area, boosting evaporation rates. From this perspective, another design approach involves intensifying pure metal structures externally coated with wicking material. Since pure metals—especially copper—exhibit higher thermal conductivity than wick structures, internal metal cores transfer heat more efficiently to the surface wick layer. Additionally, pure metals offer superior mechanical strength. These diverse designs enable VCs to achieve heat flux handling capabilities of 30–100 W/cm².

Currently, more advanced specialized wick structures are under research and development, such as:

Etched radial microchannel structures, where liquid replenishes the heat source area through an evaporation layer and a series of laterally converging channels, substantially increasing the ultimate heat flux tolerance.
Biomimetic designs inspired by plant leaf venation mechanisms, which effectively balance the trade-off between permeability and capillary forces, achieving lower thermal resistance and superior temperature uniformity.