Advanced Chip Thermal Challenges and Solutions: Direct-to-Chip (D2C) Liquid Cooling Technology and Coolant
2025
Thermal Engineering
As AI and high-performance computing (HPC) drive unprecedented demand for compute density, thermal engineering has become one of the most critical bottlenecks in next-generation chip design. When electric charges flow rapidly through nanoscale metal interconnects, inevitable Joule heating raises the temperature of logic units and power modules. If this heat cannot be extracted promptly through effective interface materials and thermal architectures, the result is a sharp increase in thermal resistance, thermal throttling, reliability degradation, and ultimately a shortened operational lifespan of the chip.
With semiconductor process technologies advancing toward the 2 nm and 1 nm nodes, chip architectures are evolving toward higher-density 3D ICs, chiplets, and heterogeneous integration. Consequently, the heat flux per unit area is growing exponentially. This means that within an extremely compact package volume, power density has exceeded the limits of conventional air cooling and single-interface thermal solutions. Thermal management has therefore shifted from a secondary engineering concern to a core challenge in chip design validation and system-level architecture.
In this high-heat era, reducing interface thermal resistance, enhancing the effective thermal conductivity of heat-removal pathways, and improving overall PUE efficiency—while guiding heat along the shortest possible route to the substrate, heat spreader, or liquid-cooling loop—has become a decisive battleground for pushing the performance limits of advanced semiconductor devices.
Current air-cooling technology
Trend
Compared with ABF organic substrates, the FCBGA (Flip-Chip Ball Grid Array) packaging architecture delivers significantly better thermal performance. According to feedback from existing customers, resin-based ABF structures are prone to thermal warpage and exhibit lower thermal conductivity and reduced reliability. In contrast, FCBGA connects the die electrically to the substrate through solder bumps or micro-bumps, allowing the heat sink to be positioned precisely on top of the chip. To accommodate rapidly increasing heat flux requirements, the industry is increasingly adopting metal heat spreaders as top-level packaging materials. These spreaders, together with high-conductivity interface materials (TIM1 / TIM2), quickly homogenize heat from the die and transfer it to the spreader, after which it is dissipated by an external cooling module.
However, with next-generation AI accelerators and HPC processors reaching thermal design powers (TDP) of 700 W to 1000 W, conventional air cooling and standard liquid cooling are nearing their performance limits. As a result, the industry is shifting toward more direct and aggressive thermal solutions—most notably Direct Liquid Cooling, with the Micro-Channel Liquid Cooling Plate (MLCP) emerging as a breakthrough technology.
MLCP integrates multiple components—including the vapor chamber or heat spreader, cold plate, package lid, and bare die—into a highly modular structure. Inside the plate, micron-scale channels (50–200 μm) are etched or machined, enabling coolant to flow directly above the primary heat source at extremely close proximity. This transforms thermal management from the conventional:
“Indirect heat transfer (die → TIM → heat spreader → cooler)”
to:
“Direct heat transfer (coolant → micro-channels → above-die)”
With the heat conduction path dramatically shortened, interface thermal resistance reduced, and overall conduction losses minimized, MLCP can deliver 2–4× greater cooling performance than traditional cold plates within the same packaging height. This makes it one of the most revolutionary cooling technologies for next-generation AI GPUs, data-center accelerators, and high-heat-flux semiconductor packages.
Advantages of D2C (Direct-to-Chip) Cooling
As HBM4 (High Bandwidth Memory 4) and next-generation accelerator platforms continue to push power density higher, traditional air cooling and board-level liquid cooling can no longer manage thermal design powers (TDP) in the kilowatt range. Consequently, the data center industry is rapidly shifting toward Direct-to-Chip (D2C) liquid cooling, in which cold plates are directly coupled to primary heat sources—including CPUs, GPUs, AI ASICs, and stacked memory modules.
In a D2C system, cold plates are manufactured using high-thermal-conductivity materials such as copper, AlSiC, or CNT-reinforced composites. Inside these plates are precision-machined single-phase or two-phase heat-transfer channels. Engineering-grade coolants circulate through the cold plate in turbulent flow, absorbing heat directly at the point closest to the die. The coolant then returns to a Coolant Distribution Unit (CDU) for heat exchange before recirculating through the loop. By allowing the coolant to directly transport the processor’s thermal load, D2C dramatically reduces thermal resistance and improves overall PUE efficiency.
Advanced direct-liquid-cooling technologies not only change the thermal pathway but also redefine system-level design principles. Through direct-contact heat extraction, phase-change-enhanced cooling, or fluid-dynamics-optimized micro-channels, D2C delivers extremely high heat-transfer performance while maintaining the die within a tighter temperature operating window—preventing thermal runaway and avoiding frequency throttling.
D2C cooling systems typically use water-based engineered coolants that exhibit low electrical conductivity, high boiling points, and low corrosivity. Compared with pure water, these fluids offer higher dielectric strength and superior material compatibility, enabling safe deployment in high-voltage, high-density packages and complex power-electronics modules.
Because the cold plate is tightly integrated with the package, D2C also improves rack density and enhances deployment flexibility in data centers, making it a core thermal strategy for enabling the next generation of AI supercomputing platforms.
Challenges of D2C (Direct-to-Chip) Cooling
1. Increased Packaging Integration Complexity
D2C requires the cold plate to be directly bonded above the die or the HBM stack, creating significant packaging challenges, including:
- TIM1 bondline and pressure control
- Risk of thermal warpage of the package lid
- Mechanical stress sensitivity of HBM stacks and TSV structures
2. Fluid Compatibility and Material Reliability
Because cold plates, tubing, and server boards are in extremely close proximity, the coolant must satisfy strict requirements:
- Low electrical conductivity
- Non-corrosive to aluminum, copper, nickel, solder, AlSiC, and ceramic components
- Non-reactive with plastics and elastomers (O-rings, EPDM, FKM, TPU, PPS)
Some customers are testing Brugarolas BRADOL IT-GR, a specialty engineered coolant.
3. Pumping Power and Pressure Drop Management
D2C cold plates usually contain very narrow channels (hundreds of micrometers). To enhance heat-transfer coefficients, high-velocity flow is required, which raises concerns such as:
- Sharp increase in pressure drop
- Higher pump power consumption
- System-level noise and vibration
In high-density racks, many cold plates operating in parallel significantly increase the complexity of managing the liquid distribution network.
4. CDU- and Rack-Level Redundancy, Maintenance, and Reliability
D2C systems rely on the CDU to circulate coolant and perform heat exchange, requiring:
- Dual-pump redundancy
- Redundant heat exchangers
- 24/7 monitoring of flow rate, pressure drop, conductivity, and coolant level
Any contamination, trapped gas, or particle deposition can cause rapid thermal resistance spikes, demanding frequent maintenance.
Key data-center concerns include:
- Leakage risks in cold plates
- Long-term durability of quick-disconnect fittings
- Coolant replacement cycles
- Environmental sustainability considerations
5. Deployment and Ecosystem Challenges
Unlike air cooling, D2C is not plug-and-play. It requires substantial data-center infrastructure upgrades:
- Liquid-ready racks
- Integration with facility water loops and cooling towers
- A supply chain still lacking unified standards (cold-plate dimensions, flow rates, and pressure specs vary widely)
- OCP is developing specifications, but full standardization has not yet been achieved
Furthermore, AI accelerators refresh every 12–18 months, far faster than the 5–10 year data-center infrastructure lifecycle, resulting in compatibility issues between cold plates and new platforms.
6. Additional Challenges for Two-Phase D2C Liquid Cooling
If two-phase cold plates are used, additional engineering barriers arise:
- Non-uniform vapor–liquid distribution
- Vapor lock and channel blockage
- Boiling point and pressure-vessel safety management
- Coolant phase-change durability and chemical stability
- These risks have prevented two-phase D2C systems from reaching large-scale commercial adoption to date.
Summary: The Core Challenges of D2C Cold-Plate Cooling
Although D2C introduces higher system-design complexity, packaging integration cost, and facility-level upgrade requirements compared with traditional air cooling, it offers compelling advantages:
- Significant energy-savings potential
- Improved rack-density capability
- A scalable path toward supporting future generations of higher-power compute units
D2C is becoming essential for next-generation platforms such as:
- HBM4 / HBM3E 3.5D packages
- AI GPUs and accelerators (e.g., Nvidia Blackwell, AMD MI300)
- Exascale HPC systems
Brugarolas Speciality Lubricants – one of the largest European thermal management solutions
Founded in 1885 and headquartered in Barcelona, Brugarolas Lubricants is committed to innovation in lubricant applications. All products comply with RoHS directives, ensuring import and export without concerns about restricted substances testing. Our solutions extend equipment lifespan and reduce overall operating costs. With a comprehensive product portfolio covering a wide range of industries—from cement, food processing, paper manufacturing, and aerospace to electronics and advanced semiconductor fabrication—we welcome inquiries for any specialized lubrication applications not listed below. Our engineers are ready to assist you.
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