Low CTE and High Heat Flux Vapor Chamber Heat Spreaders
Vapor Chamber Operating Principles
Vapor chamber heat spreaders are planar heat pipes that spread heat from concentrated heat source(s) to a large area heat sink with effective thermal conductivities greatly exceeding copper. In the most basic configuration, the vapor chamber consists of a sealed container, a wick formed on the inside wall of the container, and a small amount of fluid that is in equilibrium with its own vapor. As the heat is applied to one side of the vapor chamber (evaporator), the working fluid vaporizes and the vapor spreads to the entire inner volume and condenses over a much larger surface (condenser). The condensate is returned to the evaporator via capillary forces developed in the wick.
Vapor Chamber w/ Heat Source
Directly Bonded to the Wall
Advanced Cooling Technologies, Inc. (ACT) recently developed a 3mm thick vapor chamber made of a copper plated ceramic casing that has a coefficient of thermal expansion (CTE) close to silicon. This allows direct bonding of semiconductor chips to the vapor chamber. Direct soldering of the chips to the vapor chamber reduces the thermal interface resistance and eliminates the need for mechanical clamping. The chips can be placed anywhere on the vapor chamber surface. The heat sink locations can also be flexible. For example, the condenser can be at the sides as is typical for liquid cooling or over the entire vapor chamber surface opposite the chip locations as is typical for air cooling.
Vapor Chamber Performance
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Another focus of ACT’s advanced vapor chamber development effort is in the wick design to achieve very high heat flux capability and low thermal resistance. The advanced wick designs enable effective separation of liquid and vapor phases, resulting in vapor chamber performances exceeding 500W/cm2 in heat flux, lower than 0.05°C-cm2/W in evaporator thermal resistance, and lower than 0.12°C-cm2/W in overall vapor chamber thermal resistance. The evaporator thermal resistance has been shown to be independent of the heat sink location and geometry. Additionally, ACT’s advanced wick designs are scalable to accommodate varying heat source sizes, from less than 0.6cm2 to greater than 10cm2, without any adverse effects on the evaporator resistance. ACT’s vapor chambers are recommended as heat spreaders for high heat flux chips (IGBTs, MOSFETs), high power Laser Diode Array’s, Phased Array Radars or similar applications.