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I. Conventional Thermal Pads (1-12 W/m·K): The Foundational Line of Defense for Heat Dissipation
Traditional thermal pads, featuring a silicone base filled with various thermally conductive ceramic particles, are widely used in electronic heat dissipation due to their excellent insulation, flexibility, and process adaptability. Their thermal conductivity spans a broad range from 1 to 12 W/m·K, offering multiple options from basic to advanced levels for the H100 cooling system. However, their applicability varies significantly across different performance tiers.
Low Thermal Conductivity Range (1-3 W/m·K): Suitable Only for Peripheral Auxiliary Cooling
These entry-level materials primarily aim to fill interface voids and displace air (air's thermal conductivity is only 0.026 W/m·K). In the H100 system, even during low-load startup phases below 200 watts, heat transfer becomes noticeably sluggish. Once load climbs to full 750W power consumption, excessive interfacial thermal resistance causes heat to accumulate rapidly on the chip surface. Simulation analysis indicates this exacerbates “hotspot” effects at the center of the liquid cooling plate, potentially pushing core temperatures above 100°C within ten minutes and triggering protective throttling. Therefore, materials in this range must never be used for GPU core cooling and can only serve as auxiliary thermal interfaces for components like low-power power management units surrounding the H100.
Medium Thermal Conductivity Range (4-6 W/m·K): A Transitional Solution for Medium-Low Loads
By incorporating higher-performance fillers like aluminum nitride and aluminum oxide, these pads reduce thermal resistance by approximately 30% compared to low-end products. When the H100 performs light-to-medium AI inference tasks at around 300-400 watts, core temperatures can be maintained within the acceptable range of roughly 95°C. However, under sustained full load stress of 750 watts, their heat transfer rate cannot match the rate of heat generation. Under prolonged operation, both simulations and real-world testing indicate heat continues to accumulate in the central area. After approximately 30 minutes, core temperatures may exceed 110°C, with localized hotspots reaching higher levels, posing a risk of gradual circuit performance degradation. Therefore, this solution is only suitable as a temporary measure for non-sustained full-load conditions.
High Thermal Conductivity Range (7-12 W/m·K): The Mainstream Cost-Effective Choice for Full-Load Conditions
This category employs high-purity, thermally conductive composite fillers (e.g., graphene flakes combined with boron nitride) and exhibits excellent compression recovery (20%-40% compression ratio), effectively filling microscopic irregularities between the H100 chip and copper liquid cooling plate. Under 750W full-load conditions, it stabilizes chip junction temperatures within the safe window of 85-95°C while maintaining surface temperature differentials below 5°C. Its high electrical insulation (volume resistivity ≥10^9 Ω·cm) ensures electrical safety. With a significantly lower overall cost than indium sheets or high-performance graphite sheets, it stands as one of the most cost-effective mainstream choices for large-scale commercial deployment of H100 systems.
II. Indium Foil (81-86 W/m·K): A Niche Option Balancing High Performance and High Cost
As a soft metal thermal interface material, indium foil delivers near-ideal thermal interface connections through its exceptionally high intrinsic thermal conductivity and outstanding ductility.
Core Advantages and Thermal Performance
With thermal conductivity reaching 81-86 W/m·K, indium foil enables “near-instantaneous” heat transfer from the chip to the cold plate with extremely low thermal resistance (approximately one-fifth that of high-performance pads at 12 W/m·K). This proves particularly effective in addressing heat accumulation at the center of H100 chips, maintaining a stable temperature difference of less than 3°C between the chip and cold plate. In scenarios demanding extreme temperature stability for compute nodes (such as supercomputing clusters), indium foil significantly reduces thermal fluctuations, thereby mitigating hardware fatigue damage caused by thermal stress.
Application Limitations and Challenges
However, widespread adoption of indium sheets faces multiple constraints. First, their material cost is prohibitively high—reaching 5 to 8 times that of high-performance thermal pads priced at 12 W/m·K—significantly escalating system costs for large-scale deployment. Second, indium oxidizes rapidly in air, forming a surface oxide layer within 24 hours of exposure that degrades thermal conductivity by up to 30%, necessitating additional protective coatings. Furthermore, installation demands exceptionally stringent processes. Its low hardness means even minor surface irregularities on chips or cold plates can cause uneven deformation under mounting pressure, potentially creating new thermal barriers and triggering localized overheating. Consequently, indium sheets are only suitable for specific high-end scenarios with ample budgets and extremely precise process control.
III. Graphite Sheets (800-2500 W/m·K): Specialized Solutions for Enhanced Planar Heat Dissipation
The core value of graphite sheets lies in their exceptionally high in-plane thermal conductivity and ultra-thin physical form. Specifically designed to compensate for the limited in-plane thermal diffusion capabilities of copper and other metal cold plates, they effectively dissipate heat from chip “hotspots” laterally, preventing localized temperature spikes.
Natural Graphite Sheets (800-1200 W/m·K): The Cost-Effective Choice
Natural graphite sheets offer in-plane thermal conductivity 2 to 3 times that of copper. In H100 cooling systems, they are typically paired with high-performance 10-12 W/m·K pads responsible for vertical heat transfer. Serving as an intermediate layer, the graphite sheet rapidly spreads heat from the GPU core area across the entire cold plate surface. At 750W full load, it effectively reduces local hotspot temperatures by 10-15°C. Costing approximately one-third of synthetic graphite sheets, it has become a common auxiliary solution for enhancing thermal performance while balancing costs in large-scale commercial H100 servers.
Synthetic Graphite Sheets (1500-2000 W/m·K): Addressing High Sustained Loads
Synthetic graphite sheets produced via high-temperature graphitization offer superior in-plane thermal conductivity (1500-2000 W/m·K) and moderate vertical thermal transfer capability (30-50 W/m·K). Their ultra-thin profile (0.01-0.1 mm) enables seamless integration between chips and cold plates. In continuous full-load scenarios like 7×24 AI training on H100 systems, paired with high-performance thermal pads, they maintain core temperature fluctuations within an extremely narrow ±2°C range while achieving highly uniform heat distribution across the cold plate surface. However, their cost is approximately 3 to 5 times that of natural graphite sheets, requiring careful balancing between thermal performance and budget constraints.
Nano-composite graphite sheets (1800-2500 W/m·K): Cutting-edge technology for extreme demands
These materials achieve extreme in-plane thermal conductivity through specialized processes, reaching 8 to 10 times that of copper while maintaining stable performance across a wide temperature range of -50°C to 200°C. It represents one of the ultimate technical solutions for addressing the most severe hotspot issues in H100. However, its manufacturing process is extremely complex, with costs reaching 2 to 3 times that of synthetic graphite sheets, and it is often produced through customized manufacturing. Currently, it is primarily applied in specialized computing fields with extreme thermal management requirements, such as military-grade or specific supercomputing units, and does not yet possess the universality for civilian or large-scale commercial applications.
IV. Combination Logic for H100 (750W) Thermal Solutions
In summary, no single “best” TIM material exists for liquid cooling of NVIDIA H100 GPUs. The key lies in selecting the “most suitable” material combination based on application scenarios, performance requirements, and cost constraints.
Mainstream Commercial Scenarios (Cost-Effectiveness Priority): Employ a combination of “high-performance thermal pads (7-12 W/m·K, responsible for vertical heat transfer) + natural graphite sheets (responsible for lateral diffusion).” This solution directly addresses the shortfall of insufficient lateral heat diffusion in copper cold plates. It meets the demands of over 90% of commercial data center AI inference and general training tasks at the most competitive cost, achieving the optimal balance between thermal efficiency and economy.
High-End Computing Scenarios (Performance Stability Priority): Opt for a “top-tier thermal pad (e.g., 12 W/m·K) + synthetic graphite sheet” combination to handle intensive AI training highly sensitive to temperature fluctuations. Alternatively, for extreme performance pursuit within budget constraints, adopt an “indium sheet” solution suitable for supercomputing and other scenarios demanding stringent precision and stability. These two options typically incur 3 to 5 times the cost of mainstream solutions.
Special Extreme Scenarios: The “Nano-composite graphite sheet + Indium foil” combination represents the pinnacle of current thermal management technology. It serves only customized, high-budget special requirements—such as specific defense or cutting-edge scientific computing systems—and is not a mainstream market direction.
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