With the surge in 5G communication, artificial intelligence acceleration, and high-performance computing (HPC) loads, the integration and power density of power devices continue to increase, leading to a significant rise in the heat flux density per unit area of chips. Traditional copper-based cooling, heat pipes, and air cooling systems are gradually approaching their limits when faced with hotspots of hundreds or even thousands of W/cm², creating a demand for “higher thermal conductivity, lower thermal resistance materials + more efficient fluid cooling structures”. The combination of high thermal conductivity diamond materials and efficient microchannel flow cooling is considered a promising engineering path to address extreme heat flux.
How Diamond Microchannel Substrates Precisely Match High-Power Scenarios
High-power chips (such as GaN power amplifiers, AI accelerators, GPU/TPU, etc.) can reach heat flux densities of hundreds of W/cm² at hotspots; in packaging or module-level thermal design, extremely low contact thermal resistance and very high in-plane/volumetric thermal diffusion capabilities are required to prevent local overheating and device thermal failure. Microchannel cooling has become a mainstream research direction due to its high heat transfer coefficient and compact volume.
Why Choose Diamond?
Diamond (especially in high-quality CVD or single crystal form) has the highest thermal conductivity among materials, with common reference values ranging from 1000 to over 2000 W·m⁻¹·K⁻¹, far exceeding that of copper and common metals; this means that rapidly “spreading” local hotspots in the plane and quickly transferring heat to nearby cooling channels becomes possible, thereby reducing the peak temperature of the chip and the interconnect layers.
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Channel Geometry: According to the thermal flow distribution of the device, denser channels or smaller channel spacings can be used in local hotspot areas to enhance local heat transfer; numerical simulations (CFD, flow boiling models) and visualization experiments are typically used to optimize channel cross-sections, longitudinal distributions, and inlet layouts.
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Composite Material Ratio: The DC (diamond–copper) composite system obtained by embedding diamond particles into a copper matrix can achieve a compromise between thermal conductivity, coefficient of thermal expansion (CTE) matching, and mechanical strength by adjusting the diamond volume fraction (e.g., reported DC60, DC75). The reported DC75 uses a graded particle structure with different particle sizes to enhance filling density and thermal conductivity.
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Structural Function Integration: Open or integrated microchannel heat sinks (i.e., forming microchannels, inlet/outlet ports, and heat dissipation structures together during the manufacturing stage) can reduce interface thermal resistance and assembly complexity, and exhibit more stable pressure drop and heat transfer characteristics under flow boiling conditions.
The Role of Diamond in Microchannel Systems
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Microchannel Substrate (Core): Directly in contact with the chip, responsible for rapidly conducting the chip’s heat into the microchannel coolant; for high-performance packaging, the thermal resistance of this layer determines the peak temperature of the chip. Existing numerical/experimental studies have shown that all-diamond or high-proportion diamond composite microchannels can maintain low temperature rises under heat flux levels of hundreds of W/cm².
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Heat Sink Fins / Heat Dissipation Extension Structures: If the system further needs to exchange heat with gas-side or larger-scale coolers, diamond fins can enhance the thermal conductivity within the fins, reducing the temperature gradient within the fins, thereby improving overall heat transfer efficiency (suitable for hybrid cooling scenarios).
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Thermal Interface Material (TIM) Enhancer: Adding nano/micro diamond particles to thermal conductive greases, phase change materials, or metal-based TIM can significantly improve the thermal conductivity of the composite material and reduce contact thermal resistance, with academic papers and patents supporting this strategy.
Challenges (Technical Bottlenecks) When Combined with Metals/Systems and Existing Responses
Interface and Bonding Issues
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CTE Mismatch Leading to Thermal Stress: The linear expansion coefficient of diamond is extremely low, resulting in significant differences in thermal expansion compared to metals like copper, which can generate thermal stress at the interface during repeated thermal cycling, leading to cracks or delamination.
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Connection Process and Material Stability: Traditional high-temperature pressure infiltration, diffusion welding, etc., can form diamond-metal bonds, but there is a risk of graphitization or interfacial chemical changes at high temperatures, and the process equipment requirements are high and costly. To improve interface thermal resistance and bonding, research has employed surface metallization (coating), liquid metal wetting/alloying, and thin buffer/transition layers (e.g., carbide or metal carbide layers) to enhance wettability and thermal conduction pathways.
Microchannel Processing Precision and Cost
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Processing Difficulty: Diamond (especially single crystal or dense CVD) is extremely hard, making conventional machining difficult. Manufacturing micron-level channels typically relies on laser micromachining, deep reactive ion etching (for alternative substrates like silicon/glass molds), or pre-forming molds followed by transfer (mold casting/infiltration), which can be either expensive or complex.
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Material Cost: High thermal conductivity diamond (especially large size/high-quality CVD or single crystal) is significantly more expensive than traditional metals and ceramics, making diamond-based heat sinks more suitable for high-end, weight/volume/performance-sensitive niche markets (such as specialized RF amplifiers, aerospace, and certain data center hotspot management) rather than large-scale consumer-grade alternatives.
System Integration and Compatibility
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Multi-Component Coordination: Higher-level cooling systems (cold plates, pumps, flow channels, packaging) need to be optimized in coordination with diamond microchannel modules, including inlet pressure, pressure drop, coolant type (liquid cooling/two-phase), and reliability testing. How to insert diamond microchannel units without significantly altering the existing chassis/system structure is a common obstacle in engineering applications.
Research and Engineering Breakthrough Directions (Short, Medium, and Long Term)
Interface Engineering (Short-Term High Yield):
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Research and develop low-thickness, high-conductivity diamond surface metallization (e.g., Cr/Cu, silver/indium plating) and buffer layers to optimize wettability and interfacial phonon/electron coupling, reduce interface thermal resistance, and control graphitization. Existing studies have used liquid metals/surface coatings to enhance interface performance.
Graded Composites and Functionally Graded Materials (Medium Term):
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By using a gradient in volume fraction (high thermal conductivity diamond region → metal buffer region → structural metal) to reduce CTE discontinuities, and employing graded particles (large/small particle mixtures) to enhance filling density and improve mechanical/thermal performance, this has already been reflected in the ideas of DC60/DC75.
Manufacturability and Cost Reduction Pathways (Medium to Long Term):
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Develop low-cost large-area thermally conductive diamond films (e.g., commercial-grade thermal CVD films), and combine with mold transfer/low-temperature bonding techniques to reduce processing complexity (refer to Element Six’s thermal-grade product roadmap).
Cooling System Joint Optimization (System Engineering):
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Conduct joint simulations and prototype tests among device packaging, substrates, microchannels, coolants, and pump systems, especially evaluating the stability and potential impacts of two-phase boiling on diamond microchannels (existing flow boiling tests have shown positive results for the DC series but still require more long-term lifespan data).
In Conclusion
The combination of diamond and microchannel cooling demonstrates significant theoretical and experimental advantages in high heat flux density cooling scenarios, as the extremely high thermal conductivity of diamond can significantly reduce planar thermal resistance and quickly transfer local hotspots to cooling channels, with experimental/numerical results supporting its superiority at heat flux levels of hundreds of W/cm², such as in DC60/DC75 composite materials and all-diamond microchannels.
Meanwhile, diamond-metal interface engineering, high-precision manufacturing of microchannels, and overall system integration are currently the most critical engineering bottlenecks; through interface metallization/liquid metal wetting, functionally graded composites, and manufacturing process optimizations (e.g., laser processing, low-temperature bonding/transfer), there is hope to push these solutions towards engineering and scaling in the medium to long term.
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