Why copper so import in liquid cooling solutions

1. Types and Characteristics of Copper for Heat Dissipation

The core advantage of copper as a heat dissipation material comes from its excellent physical properties. From a thermodynamic point of view, the thermal conductivity of copper is as high as 401 W/(m·K), which is second only to silver (429 W/(m·K)) among common metals, but its cost is only 1/50-1/100 of that of silver. Copper has a specific heat capacity of 0.385 J/(g·K), meaning it can efficiently absorb and store heat per unit mass. Furthermore, copper's melting point reaches 1083°C, well above the operating temperature range of electronic devices, ensuring thermal stability.

At a microscopic level, copper's face-centered cubic (FCC) crystal structure provides it with excellent thermal conductivity. In this FCC structure, each copper atom is tightly packed with its 12 nearest neighbors, allowing free electrons to move almost unimpeded within the lattice. This highly free electron cloud enables copper to rapidly transfer heat energy. In comparison, aluminum (thermal conductivity of 237 W/(m·K)) exhibits significantly inferior thermal conductivity, a difference that is particularly pronounced in high-power density applications.

2. Copper Components for thermal conductive, Heat transfer, Heat dissipating, and Thermal Interface Materials

A. Copper thermal conductive components

1). Copper Base Plate

Function: Directly contacts heat sources (such as CPU/GPU chips) to quickly conduct heat.

Parameters: Thickness 3–10mm, surface flatness ≤ 0.05mm, thermal conductivity ≥ 380 W/(m·K).

Applications: Server CPU heat sink bases, LED lighting modules.

2). Copper Foil

Function: Used as a heat spreader for thin devices.

Parameters: Thickness 0.05–0.3mm, capable of being stamped into complex shapes.

Applications: Heat dissipation on the back of smartphone SoCs and flexible printed circuit boards.

3). Copper Block

Function: Heat storage and diffusion in areas of localized high heat flux density.

Parameters: Volume 5–50 cm³, commonly used in passive cooling designs. Applications: Graphics card memory cooling, 5G base station RF modules.

B. Copper Heat transfer components

1). Heat Pipe

Structure: Copper shell + sintered copper powder wick + working fluid (water/acetone).

Performance: Effective thermal conductivity reaches 5,000–10,000 W/(m·K), 10–20 times that of pure copper.

Specifications: Diameter 3–8 mm, Length 50–300 mm (5–6 mm diameter is common for laptops).

Applications: Laptops, server GPU cooling modules.

2). Vapor Chamber

Structure: Flat copper cavity with internal microchannels/sintered core, operating similarly to a heat pipe.

Advantages: Two-dimensional heat dissipation, with a heat diffusion area 3–5 times larger than a heat pipe.

Dimensions: 0.4–1.5mm thick, 20–100cm² (small vapor chambers for mobile phones can be as thin as 0.3mm).

Applications: High-end smartphones, ultra-thin notebooks.

C. Copper Heat dissipating components

1). Copper Fins

Design: Single chip thickness 0.1–0.3mm, with 1–3mm pitch, bonded to the baseboard via soldering or fin-through bonding.

Optimization: Serrated/wavy edge design increases turbulence, improving convection efficiency by 10–15%.

Applications: Air-cooled heat sinks (such as CPU tower coolers) and power modules.

2). Copper Radiator

Construction: Copper tubes (φ6–12mm) + aluminum/copper fins, for liquid cooling systems.

Performance: A single rack-scale radiator typically requires 6–10 m² of surface area (for a 40kW heat dissipation requirement).

Applications: Data center immersion liquid cooling and high-performance computing (HPC) clusters.

D. Copper Thermal Interface Materials

1). Copper Thermal Pad

Features: Copper powder/graphite-filled flexible gasket with a thermal conductivity of 5–20 W/(m·K).

Advantages: Fills gaps on uneven surfaces (compression rate 20–30%).

Applications: SSD controller cooling, automotive electronics.

2). Direct Copper Bonded(DCB)

Structure: Ceramic (Al₂O₃/AlN) sandwich copper plate, copper layer thickness 0.2–0.5mm.

Features: High voltage resistance (>2kV), low thermal resistance (0.2–0.3 K·cm²/W).

Applications: IGBT modules, electric vehicle inverters.

3). Copper-graphite composite

Ratio: Copper accounts for 60–80%, with graphite providing anisotropic thermal conductivity.

Performance: In-plane thermal conductivity of 400–600 W/(m·K), 40% lighter than pure copper.

Applications: Ultra-thin notebook mid-covers, drone flight control boards.

3. Liquid Cooling System Copper Application

Copper Cold Plate

Design: Internal microchannels (0.5–2mm width), ΔP < 50 kPa at flow rates of 3–10 L/min.

High-performance model: Targeted at AI server GPUs, with a heat flux handling capacity > 100 W/cm².

Applications: NVIDIA HGX systems and supercomputing liquid cooling modules.

Copper Quick Disconnect Fittings

Requirements: Nickel-plated surface for corrosion resistance, pressure resistance ≥ 1 MPa, leakage rate < 1 × 10⁻⁶ mbar·L/s.

Applications: Maintainable liquid cooling circuits in data centers.

4. Copper in 3C

Copper Heat Dissipation in Smartphones:

Modern smartphone cooling has evolved from early graphite sheets to a composite heat dissipation solution. Typical flagship models employ a multi-layer structure: the SoC is in direct contact with copper foil (0.1-0.3mm thick), connected to a copper vapor chamber (0.4-0.6mm thick) via thermally conductive gel. A graphene film is then applied to the vapor chamber to enhance lateral heat conduction. Test data shows that copper vapor chambers can reduce SoC junction temperature by 8-12°C, significantly outperforming pure graphite solutions. The Apple iPhone 14 Pro's A16 chip uses a copper alloy heat sink, reducing thermal resistance by approximately 15%. The Samsung Galaxy S23 Ultra's vacuum chamber vapor chamber boasts a 2724mm² area, combined with a copper grid structure for uniform heat dissipation throughout the device.

Copper Heat Pipes in Laptops:

High-performance laptop cooling systems typically include two to four copper heat pipes with diameters of 5-8mm and wall thicknesses of 0.3-0.5mm. Products like the ROG Zephyrus G14 utilize 3D vapor chamber technology, combining traditional heat pipes with vapor chambers to increase heat flux to 80W/cm². Notably, when the porosity of the copper powder sintered core within the heat pipe is controlled between 50-70%, capillary force and fluid resistance are optimally balanced, achieving an effective heat transfer distance of 30-50cm. Some manufacturers are beginning to experiment with copper-graphite composites, which maintain 85% of copper's thermal conductivity while reducing weight by 40%.

Copper Heat Dissipation in Miniaturized Devices:

Due to space constraints, wearable devices utilize ultra-thin copper films (<100μm thick) combined with phase change materials (PCMs). The Huawei Watch GT3 Pro uses a 0.08mm copper foil and paraffin wax composite material, increasing thermal capacity by 30%. TWS earbuds commonly utilize copper plating technology, depositing a 2-5μm copper layer on the plastic surface to control weight and mitigate localized hot spots. Data shows that copper coating can reduce the standard deviation of temperature distribution inside the headphone charging case from ±4.2°C to ±1.8°C.

5. Copper in AI Servers

Copper's Advanced Application in AI Server Cooling Systems

Copper Cooling Solutions for GPUs and CPUs

The NVIDIA H100 GPU utilizes a fully covered copper cold plate with a contact area of 38 cm². Its microchannel structure has a hydraulic diameter of 0.5 mm and a thermal resistance of only 0.08°C/W at a flow rate of 3-5 L/min. The AMD EPYC 9654 processor's heat sink utilizes copper-solder soldering technology, with a base thickness of 8 mm, achieving 68% higher heat dissipation efficiency than aluminum. In liquid cooling systems, the flow channel design of the copper cold plate is crucial: a staggered fin structure (1.5 mm pitch, 5 mm height) can increase the Nu number by 1.8 times that of conventional designs.

Copper Applications in Rack-Scale Liquid Cooling

Immersion liquid cooling utilizes copper tubing with a purity exceeding 99.9% and a wall thickness of 1.5-2 mm to resist corrosion from fluorinated liquids. For a single rack cooling system with a 40kW cooling requirement, the copper radiator surface area requires 6-8 m², and a wind speed of 0.3 m/s can maintain a ΔT < 15°C. Google's TPU v4 cabinet uses a copper-aluminum composite heat sink, achieving optimal cost-performance when the copper content is 60%, with a thermal resistance of 0.0045 m²·K/W. It's worth noting that the electrochemical corrosion rate of copper in dielectric fluids must be controlled to <5μm/year, which requires rigorous surface passivation.

Copper Heatsinks in Power Modules

In 80 Plus Titanium-certified power supplies, copper heat sinks account for 15-20% of the weight. GaN devices utilize a direct copper bonding (DCB) substrate with a 0.3mm thick copper layer, resulting in a low thermal resistance of 0.24K·cm²/W. In three-phase rectifier modules, the cross-sectional area of the copper busbars is related to current: 25mm² is required for every 100A, and the temperature rise can be controlled within 40K. The copper heat sinks in server power supplies are typically treated with micro-arc oxidation to form a 10-20μm ceramic layer, which maintains thermal conductivity and increases the withstand voltage to over 3kV.

6. Challenges and innovations facing copper heat dissipation

Challenges and Innovations in Copper Heat Sinks

Weight and Cost Optimization

Copper's density (8.96 g/cm³) is 3.3 times that of aluminum, presenting a significant disadvantage in mobile devices. New copper alloys, such as C7025 (2.5% Ni-0.65% Si), have increased strength to 450 MPa while maintaining 85% thermal conductivity. Porous copper materials (50-70% porosity) can achieve densities of 1.8-2.5 g/cm³ while still maintaining thermal conductivity of 150-200 W/(m·K). Regarding cost, copper recycling technologies can increase waste reuse rates to 95%, resulting in 85% energy savings compared to virgin copper.

Advanced Manufacturing Processes

3D-printed copper heat sinks have achieved wall thicknesses as low as 0.2 mm, and their complex internal structures increase surface area by 3-5 times. Copper heat sinks formed by selective laser melting (SLM) exhibit 20% lower thermal resistance than conventional processes at a heat flux of 50 W/cm². Nano-copper sintering technology can achieve a joint thermal resistance of less than 5 mm²·K/W at low temperatures of 250°C, making it particularly suitable for chiplet packaging. Microinjection molding technology can produce copper microneedle arrays at the 100μm level, with a boiling heat transfer coefficient as high as 100kW/(m²·K).

Heterogeneous Material Integration

Copper-diamond composites (containing 50 vol% diamond) have a thermal conductivity of 600 W/(m·K), but cost limits their commercial application. Graphene-reinforced copper-based composites increase thermal conductivity by 25% at a 1wt% addition, and the CTE can be tuned to match the chip. Recently developed copper-carbon nanotube vertical array structures have achieved an axial thermal conductivity exceeding 800 W/(m·K), promising applications for 3D IC heat dissipation. Notably, the thermal resistance of the heterogeneous material interface remains a major challenge. Molecular-level bonding technologies can reduce this interface resistance to less than 10 mm²·K/W.

7. Summary

Copper's fundamental advantages as a heat dissipation material are difficult to completely replace, but its applications will continue to evolve. Driven by the trend toward thinner and lighter 3C devices and the increasing power density of AI servers, copper's use in heat dissipation is moving toward heterogeneous integration, intelligent control, and nanostructures. Over the next decade, we may witness a leap from quantitative to qualitative change in copper's thermal management capabilities.

Characteristics	Copper	Aluminum
Thermal Conductivity	401 W/(m·K)	237 W/(m·K)
Melting Point	1083°C	660°C
Processing Method	CNC, Die Casting, Electroplating	Extrusion, Die Casting
Cost (Relative)	1.5–2 times that of Aluminum	Base
Applications	High Power Density Areas	Low ~ Medium Power Devices