1. Structure and Working Principle
Core Components:
- Internal Flow Channels: Precisely designed channels (e.g., serpentine, parallel, or spiral) guide the flow of coolant to maximize heat exchange area.
- Cooling Tubes: Typically made of copper or aluminum, embedded in a thermally conductive baseplate, directly contacting heat-generating components (e.g., lasers or power chips).
- Thermal Interface Materials: Such as thermal paste or graphite sheets, reduce contact thermal resistance.
- Housing: Provides structural support and sealing, often encapsulated with corrosion-resistant materials (e.g., stainless steel).
Workflow: Coolant (deionized water, glycol solution) is pumped into the flow channels, absorbs heat, and then dissipates it through an external heat exchanger (e.g., cold plate or cooling tower), forming a closed-loop cycle.
2. Application Scenarios
- Lithography Machines: Cooling laser sources and optical components to prevent thermal expansion-induced optical path deviations (e.g., ASML’s EUV lithography machines).
- Etching/Ion Implantation Machines: Controlling reaction chamber temperature to ensure process uniformity (e.g., Applied Materials’ equipment often uses liquid cooling solutions).
- CVD/PVD Equipment: Maintaining substrate temperature stability to avoid uneven film stress.
- Testing and Packaging: Used for high-power chip burn-in testing to prevent overheating damage.
3. Advantages and Challenges
Advantages:
- High-Efficiency Heat Dissipation: Liquid cooling has a high heat capacity, 5-10 times more efficient than air cooling, suitable for heat flux densities above 1000W/cm².
- Precise Temperature Control: Temperature differences can be controlled within ±0.5℃, meeting nanometer-level process requirements.
- Compactness: Thickness can be as low as 10mm, adapting to the trend of equipment miniaturization.
Challenges:
- Sealing: Laser welding or O-ring sealing is used, requiring helium mass spectrometry leak detection (leak rate <1×10⁻⁶ mbar·L/s).
- Corrosion Control: Use of titanium alloys or nickel-plated surfaces, with coolant pH monitoring (6.5-8.5).
- System Complexity: Requires integration of pumps, heat exchangers, and sensors, accounting for 5-10% of total equipment costs.
4. Material Selection
- Copper (C101/C102): Thermal conductivity of 390 W/m·K, used in high-power scenarios but requires anti-oxidation coating.
- Aluminum 6061/6063: Lightweight (density 2.7g/cm³), thermal conductivity of 160-200 W/m·K, low cost.
- Stainless Steel 316L: Resistant to acid and alkali corrosion, suitable for acidic environments in etching machines.
- Titanium Alloy (Gr.2/5): Excellent biocompatibility, used in ultra-pure water systems, but with high processing costs.
5. Design Optimization
Flow Channel Design:
- Serpentine Channels: High pressure drop (ΔP≈10-50kPa), but excellent temperature uniformity (σ<1℃).
- Parallel Channels: Lower pressure drop (ΔP≈5-20kPa), requires flow distributors.
- Microchannels: Channel width 0.1-1mm, heat transfer coefficient increased by 3-5 times, but prone to clogging.
Turbulence Enhancement: Built-in vortex generators or fins increase the Nusselt number (Nu) by 20-30%.
Multi-Zone Cooling: Independent control of flow in different zones to adapt to non-uniform thermal loads (e.g., 3D packaging).
6. Future Trends
New Materials:
- Nanofluids: Adding Al₂O₃ or CuO nanoparticles increases thermal conductivity by 10-30%.
- Phase Change Materials (PCM): Such as paraffin, used for transient thermal shock buffering.
Intelligence:
- Digital Twin: Real-time optimization of flow distribution through CFD simulation.
- AI Control: Machine learning algorithms predict thermal load and dynamically adjust pump speed (e.g., an upgraded version of PID algorithm).
Sustainable Development:
- Natural Cooling: Utilizing two-phase flow (e.g., pump-driven two-phase systems) to reduce pump power consumption.
- Eco-friendly Coolants: Switching to low GWP coolants like HFO-1234yf.
7. Comparison with Other Cooling Technologies
- vs. Air Cooling: Liquid cooling offers more than 5 times higher heat dissipation capacity, but costs increase by about 30%.
- vs. Heat Pipes: Heat pipes are suitable for point-to-point heat transfer (thermal conductivity of 5000 W/m·K), but liquid cooling is better for surface heat dissipation.
- vs. Immersion Cooling: No complex piping is required, but compatibility is poor (e.g., high equipment modification costs).
8. Practical Cases
- ASML EUV Lithography Machine: Uses copper tube cold plates to cool CO₂ lasers, maintaining optical system temperature fluctuations within <±0.1℃.
- Tesla Dojo Chip Testing: Multi-zone aluminum cold plates support continuous testing of kilowatt-level chips.
Conclusion
Tubed liquid cold plates, with their high-efficiency heat dissipation and precise temperature control, have become a core cooling solution for semiconductor manufacturing equipment. In the future, with advancements in materials and intelligent technologies, they will further develop towards higher efficiency, compactness, and sustainability, supporting the continued evolution of Moore’s Law.
