The Application of Vapor Chambers

In thin, lightweight, and miniaturized portable devices, the problem of dissipating non-uniformly distributed hotspots generated by increasingly high-power chips has severely impacted the efficiency, stability, and reliable service life of these devices. The increasingly prominent "thermal barrier" poses a significant challenge to Moore's Law, making the application of high-performance, high-efficiency heat dissipation technologies in mobile devices an urgent necessity. This paper discusses the advantages of vapor chamber technology over traditional cooling techniques, explores the upgraded application of ultra-thin vapor chambers in portable mobile devices with ever-increasing heat flux densities, and addresses the issues and development directions in their evolution.

In 2017, IBM announced a breakthrough in 5 nm chip manufacturing technology, enabling a single fingernail-sized chip to contain up to 30 billion transistors, resulting in a substantial improvement in computing performance. The pursuit of smaller process nodes stems from the trend of high integration and lightweight design of chips, which has led to increasingly severe heat generation issues. The ultra-high heat generated inside miniaturized mobile terminals requires better thermal conductors to meet the heat transfer demands of high heat flux densities, making heat dissipation one of the core factors restricting the development of such products.

1. Introduction to Vapor Chambers

Vapor chamber (VC) rapidly diffuses heat throughout its cavity by utilizing the phase-change evaporation of a cooling working fluid in a sealed space. At the condensation end, the working fluid condenses back into a liquid and flows back to the heat source end via capillary force and gravity. The vapor chamber is a typical phase-change heat conduction device.

The thermal conductivity of phase-change heat transfer components far exceeds that of traditional heat dissipation devices, with a thermal conductivity (greater than 5000 W/(m²·°C)) that can be dozens of times higher than traditional heat transfer methods (the thermal conductivity of air convection and liquid convection is 10–100 and 100–1000 W/(m²·°C), respectively). Additionally, as vapor chambers conduct heat in a two-dimensional surface-to-surface manner, they offer higher heat transfer efficiency compared to the one-dimensional linear heat conduction of heat pipes. Due to their excellent thermal conductivity, they are widely used for heat dissipation in high heat flux density electronic chips, such as smartphone chips, laptops, and servers, and represent the optimal solution to current high heat flux density problems.

2. Global Status

Mobile and portable devices (especially smartphones) are becoming increasingly compact. To enhance heat dissipation performance, phase-change heat conduction devices are universally adopted. When the total thickness of a smartphone body drops below 8 mm, there is an urgent demand for ultra-thin vapor chambers, particularly those with a total thickness of less than 0.8 mm. The internal cavity thickness of such ultra-thin vapor chambers has reached its physical limit, leading to a sharp increase in the thermal resistance of the vapor cavity. Generally, vapor chambers with a total thickness of less than 2 mm are classified as ultra-thin. As the thickness of a vapor chamber decreases to a certain extent, the thermal resistance of its evaporation cavity increases significantly, and heat transfer efficiency decreases accordingly.

In recent years, the technological evolution of vapor chambers has focused on the following areas:

1. Diversification of materials: Benefiting from the middle frame-VC integrated heat dissipation solution, stainless steel VCs have emerged.
2. Innovation in packaging processes: Laser packaging is expected to replace copper-plated brazing processes.
3. Diversification of capillary structures: The dominance of copper mesh sintering capillary processes for ultra-thin VCs is expected to be broken, with printed capillary and semiconductor photomask etching capillary structures gaining traction.
4. Further reduction in thickness: VC vapor chambers are expected to reach thicknesses of less than 0.3 mm.

3. Existing Problems

1. Low yield rate of ultra-thin vapor chambers: When the total thickness of a vapor chamber drops to 0.8 mm, its overall structural strength is poor, making it prone to deformation. The welding and packaging of the upper and lower cover plates become difficult, resulting in low production yields. There is an urgent need for low-cost, mature, and effective forming processes to improve the packaging and welding technology.
2. Insufficient research on manufacturing processes for vapor chambers using aluminum-magnesium materials: Aluminum-magnesium alloys are highly susceptible to surface oxidation, making welding challenging. Currently, atmosphere diffusion welding is the primary method, but there is very limited research on diffusion welding for ultra-thin lightweight materials, especially for 0.2 mm thick aluminum alloys, with almost no available literature.
3. Need for further optimization of the wick structure in ultra-thin vapor chambers: It is necessary to optimize the wick structure, determine the optimal ratio of vapor and liquid cavities, and develop methods to stably control this ratio during manufacturing to improve yield rates.
4. Large errors in traditional numerical simulation models: There is insufficient research on the changes in heat and mass transfer characteristics caused by the ultra-thinning of VC plates, with limited literature available. As the thickness of the vapor chamber decreases, the thickness of the outer shell, vapor cavity, and wick all decrease. The structural deformation resistance of the vapor chamber weakens with reduced shell thickness, while the reduced vapor cavity thickness increases the pressure loss of saturated vapor flow from evaporation to condensation. Additionally, the thinner wick increases the flow pressure loss of the working fluid returning from the condensation end to the evaporation end. Thinner is not always better for vapor chambers, and there is a lack of theoretical research on the heat and mass transfer characteristics of ultra-thin vapor chambers.

4. Conclusion

In the future, the demand for ultra-thin vapor chambers, especially those with a total thickness of less than 0.8 mm, will continue to grow. Furthermore, the trend toward lightweight design will drive the gradual adoption of lightweight materials such as aluminum-magnesium alloys in ultra-thin vapor chambers. With the maturation of advanced manufacturing and lightweight manufacturing processes, lightweight and ultra-thin vapor chambers have broad application prospects, and mobile electronic product heat sinks are poised for an upgrade.

• Written by

  CoolingThermal Engineering Team

  CoolingThermal is an automation equipment manufacturer based in Kunshan, China, specializing in heat pipe and vapor chamber production equipment since 2017. Our engineering team designs, builds, and commissions complete production lines covering forming, degassing, welding, testing, and assembly processes. The technical content on this blog is written by the same team that develops the equipment — based on real production experience, not secondary research.