Innovative Metal TIMs for AI/GPU Processors
As artificial intelligence (AI) and high-performance computing (HPC) technologies evolve, their computational demands have skyrocketed, leading to a critical challenge in thermal engineering. AI and GPU processors, with their increased power density and expanded die areas, require advanced heat dissipation solutions to maintain peak performance and reliability. This rise in thermal design power (TDP) has driven researchers and manufacturers to push the boundaries of thermal interface materials (TIMs), with metal TIMs emerging as a promising innovation.
This blog explores the challenges associated with traditional TIMs, the development of novel metal TIMs, including hybrid liquid metal and phase-change alloys, and the experimental methods and outcomes that illustrate their effectiveness.
The Heat Dissipation Challenge in Modern Processors
Today’s high-performance AI/GPU processors must perform under increasingly demanding thermal loads. With power dissipation levels exceeding 850 watts for single dies, traditional cooling solutions struggle to meet these requirements. Adding to the complexity, modern server processors often integrate high-bandwidth memory (HBM) stacks alongside the CPU/GPU dies. These memory modules are highly sensitive to temperature fluctuations, requiring TIMs that can distribute heat not only across the die but also protect adjacent components.
These challenges underscore the limitations of traditional polymeric TIMs (greases, pastes, PCMs), which often fail to provide the thermal efficiency and reliability necessary to handle extreme heat challenges. Their susceptibility to issues like pump-out (material displacement under cyclic heat loads) and insufficient thermal conductivity has positioned metal TIMs as a more effective solution. If thermal performance drives system value or yield, metal TIMs are justified. If cost drives the design, polymeric TIMs may suffice.
Figure 1. Rising Thermal Design Power (TDP) for select processor families over the past decade [1].
Figure 1 illustrates the sharp increase in maximum thermal design power (TDP) for leading server and AI processor families, underscoring the need for next-generation thermal interface materials.
Why Metal TIMs?
Metal TIMs offer significantly higher thermal conductivity compared to their polymeric counterparts. These advanced materials are specifically engineered for high dissipation applications, like bare-die processors, where the TIM layer is in direct contact with the die or its interface. They come in a variety of forms, including:
- Hybrid Liquid Metal TIMs – These are made by combining liquid metals like gallium alloys and solid hybrid components to create tailored thermal properties, which improve heat dissipation while offering enhanced reliability and easier application. These materials are designed to leverage the high thermal conductivity of liquid metals, while offering easier containment and decreasing changes of pump out, resulting in a more user-friendly application. These are primarily used in TIM1 and TIM1.5 applications.
- Phase-Change Metal Alloys (PCMAs) – Alloys designed to combine the high thermal conductivity of metals with the ability to change phase from a solid to a liquid at a specific temperature. This allows them to fill microscopic gaps between components and facilitate heat transfer effectively. PCMAs are applied to a component in a preform state when solid at room temperature. As the device heats during operation, the PCMA melts and the liquid metal flows, maximizing thermal transfer. When the device cools, the alloy re-solidifies, creating a stable thermal joint over time.
- Metal Foils and Compressible Sheets – These metal TIMs are used to improve heat transfer between heat-generating components and a heat sink. Foils offer high thermal conductivity with the benefit of a thin profile, which offers lower thermal resistance. Compressible materials, such as Indium Corporation’s Heat-Spring®, are made from soft metal alloys, allowing them to conform to uneven surfaces under pressure to fill gaps and provide a low-resistance thermal path. These are primarily used in TIM2 applications.
Each category of metal-based TIM addresses unique challenges, from improving thermal conduction to accommodating die warpage and ensuring long-term stability.
Experimental Approaches to Metal TIM Development
The development of metal TIMs involves rigorous testing to ensure they meet the demanding requirements of high-performance applications. Key experimental methods include:
Application and Testing Techniques
- Thermal Test Vehicles (TTVs): These are simulated processor setups used for in-situ testing of TIMs under controlled conditions. TTV testing assesses thermal resistance, die warpage responses, and heat dissipation efficiency.
- Material Evaluations: Experimental efforts focus on assessing alloy compositions, thermal conductivity, surface adhesion, and phase-change properties. These evaluations often include power cycling tests to determine reliability over thousands of operating cycles.
- Environmental Factors: Metal TIMs, particularly those with gallium components, are tested for corrosion resistance and oxidation risks. Protective barriers and alloy modifications are explored to mitigate these issues.
Example Testing Results
One study highlighted in this development involves the comparison of PCMAs with traditional graphite film TIMs and compressible metal foils during power cycling tests. The PCMAs demonstrated superior surface wetting and consistent die temperatures across 1,800 power cycles at varying thermal loads. However, oxidation at material interfaces was identified as a challenge, especially in scenarios where phase change occurred repeatedly.
Figure 2. Temperature Measurements with TTV and PCMA as TIM1.5.
Figure 2 compares temperature gradients across a die with significant warpage: (A) before initial heating when gradients are present, and (B) after achieving phase change, showing uniform surface wetting and sharply reduced gradients using development PCMA.
Results like these underscore the need for barrier seals and careful material composition targeting specific operational environments.
Key Advantages of Metal TIMs
Metal TIM innovations have brought a new level of performance to thermal management in AI/GPU processors. Better thermal management results in faster heat removal, cooler operating temperatures, and higher, more stable performance for the device long term. Their advantages include:
1. Superior Thermal Conductivity
High thermal conductivity alloys like gallium-indium-tin mixtures and phase-change reactive alloys effectively transfer heat away from the die surface. This can result in significant performance gains for processors operating under heavy loads.
2. Excellent Surface Wetting
Materials like PCMAs achieve 100% surface wetting, even on large or warped die surfaces. This ensures minimal thermal resistance across the interface, reducing hotspots and improving overall processor reliability.
3. Adaptability to Die Warpage
Advanced metal TIMs are engineered for compliance with die warpage, a growing challenge as die sizes expand. The ability to maintain uniform adhesion despite surface irregularities sets these TIMs apart from their polymeric counterparts.
Challenges and Solutions in Metal TIM Development
While metal TIMs excel in many areas, their adoption isn’t without hurdles. There are several practical- and manufacturing-based challenges that must be considered when thinking about adopting metal TIM materials. These challenges include:
- Corrosion and Oxidation: Gallium-based alloys can cause intermetallic reactions and degrade surfaces over time. Protective coatings and alloy modifications are ongoing areas of research.
- Material Dispersion: Ensuring a uniform thickness of metal TIMs across the die requires precise application processes.
- Cost and Scalability: Metal TIMs are often more expensive and require specialized equipment for application and testing.
Despite these challenges, their increasing specialization allows engineers to customize metal TIMs for specific processor packages and TDP requirements. This is why metal-based TIMs are frequently used on high-performance and mission critical applications such as data centers, high-end GPUs, or aerospace electronics.
Current State of Metal TIM Technology
The modern thermal engineering toolbox has been significantly enhanced by the introduction of metal-based TIMs. Their ability to handle high power densities and adapt to rapidly changing processor designs positions them as critical components in the future of AI and GPU technologies.
Advances in hybrid liquid metal TIMs and PCMAs illustrate the growing potential of these materials. By addressing persistent challenges like oxidation and barrier effectiveness, these TIMs are set to define the next generation of thermal solutions.
Future Outlook for Metal TIMs
The continued evolution of AI and server processors ensures that thermal challenges will remain at the forefront of electronic packaging design. With limitless possibilities for alloy customization, the metal TIM market has the flexibility to meet the diverse demands of modern processors, from maximizing thermal efficiency to ensuring robust reliability.
For engineers and manufacturers, the task ahead involves integrating these innovative metal-based TIMs effectively, refining their formulations, and optimizing application methods to support the higher performance thresholds of tomorrow’s processors.
Final Thoughts
Metal TIMs are reshaping the landscape of thermal management for AI/GPU processors and ASICs. With their superior thermal conductivity, adaptability to die warpage, and innovative phase-change capabilities, these materials answer the call for specialized solutions in an age of rapid technological advancement. While challenges like corrosion and material dispersion remain, ongoing research and development continue to close these gaps.
By adopting metal TIMs with the appropriate engineering and application strategies, manufacturers can ensure their processors meet the rigorous demands of modern computing—paving the way for the next wave of advancements in AI and HPC.
Explore Tailored Solutions with Indium Corporation
For more information about Indium Corporation’s full range of metal TIMs including liquid metal, compressible Heat-Spring®, and solder TIMs, connect with a metal TIM specialist or visit our thermal interface materials page.
References
[1] Dell’Oro Group, “Direct-to-Chip Liquid Cooling for the AI Data Center,” Open Compute Project, Educational Webinar Series, May 16, 2024, https://www.opencompute.org/events/past-events/ocp-educational-webinar-direct-to-chip-liquid-cooling-for-the-ai-data-center?utm_source=chatgpt.com.
