Thermal Management: TIM, Data Centers, EV Power Electronics

The flame is on the central processor that lies on the printed circuit board. Low-key photo.
Thermal management has gained significant attraction over the past few years, driven by industries such as high-performance computing in data centers and higher power density of EV power electronics. In this article, IDTechEx will summarize the main trends of thermal management in the data center and EV power electronics industries, as well as the recent developments of thermal interface materials used.
 
 
Thermal interface materials (TIM): Advancements, applications and prices
 
A TIM is a material used to improve heat transfer between two surfaces, typically a heat source, such as a chip, and a heat sink. TIMs play an important role in reducing the system's overall heat resistance.
 
Broadly speaking, depending on the locations of TIMs, they can be split into TIM1 and TIM2. TIM1s are typically used within the heat source packaging and often present significantly higher thermal conductivity; for instance, die-attach material is one of the most widely used TIM1s. TIM2, in contrast, is more widely seen outside of the heat source packaging. TIM2s have various forms, including grease, pads, gels, conductive adhesives, sheets, and phase change materials. During the formulation processes, there are two important components - TIM fillers and matrix materials. Thermal fillers are highly thermally conductive materials, and they often determine the TIM costs. Commonly used fillers include sphere alumina, ground alumina, and ATH.
 
For high-performance TIMs, other fillers such as AlN, MgO, ZnO, BN, and carbon-based materials also have a presence. However, as some of them are high cost (e.g., BN), have safety hazards (e.g., ZnO), and have difficulty achieving a high loading percentage (e.g., MgO), they are less commonly used as the primary fillers. In addition to the innate thermal conductivity of thermal fillers, the geometry, filler size, and filler loading percentage also significantly influence the overall TC. Spherical fillers often tend to have a higher maximum loading percentage. In contrast, fillers with flaky shapes can only achieve a relatively low loading percentage, ultimately affecting the thermal performance.
 
Fillers costs vary significantly depending on the factors mentioned above, along with the order volume, customer relations, and a few others. For instance, from IDTechEx's database, spherical alumina typically costs around US$5/kg, whereas ground alumina has a 40% reduction. ATH costs around US$5/kg, which is around ten times less than BN fillers. A full comprehensive analysis of filler costs and other parameters (e.g., dielectric strength, concerns, electrical conductivity, etc.) can be found in IDTechEx's latest research on Thermal Interface Materials.
 
TIMs are used in various industries, ranging from EV batteries, EV power electronics, data centers, consumer electronics, 5/6G base stations, and components in advanced driver-assistance systems (ADAS). The thermal conductivity requirement varies by industry and other properties such as dielectric strength, viscosity (if applicable), mechanical strength, and compressibility. Figure 1 summarizes some of the thermal conductivity requirements for different applications. The thermal conductivity is generally expected to increase over time due to the rising power and heat dissipation needed.
 
One interesting use case is that EV batteries, the largest application for TIMs as of 2024, will adopt TIMs with lower thermal conductivity. This is primarily driven by battery pack transitions from traditional modular design to cell-to-pack and cell-to-body design, making the heat transfer more efficiently, thereby reducing the demand for high thermal conductivity. These trends will also affect the types of thermal filler used as well as the costs. IDTechEx's research on Thermal Interface Materials forecasts that the yearly market size of TIMs will exceed US$8 billion by 2034, driven by industries such as telecommunication, electric vehicles, and data centers.
 
Figure 1. Thermal interface material: thermal conductivity trends for different applications. Source: IDTechEx
 
Thermal management for EV power electronics
 
The megatrend within the EV power electronics industry is the transition from Si IGBTs to SiC MOSFETs, which brings the maximum junction temperature from up to 150°C for IGBTs to up to 175°C or ever over 200°C for MOSFETs. This increase in junction temperature requires more efficient thermal management. IDTechEx's research on Thermal Management for EV Power Electronics investigates the most advanced cooling technologies, such as double-sided cooling, pin-fin cooling, sintering technology, TIM1s, and heat sinks.
 
The traditional thermal architecture of a power module consists of around seven layers, including chip (e.g., IGBT, MOSFET, etc.), chip solder/die attach (e.g., SnPb solder, Ag sinter paste, etc.), DBC/AMB substrate, substrate attach/solder, baseplate (Cu or Al), TIM2 (e.g., thermal grease, etc.), and heatsinks. While this architecture traditionally works well for Si IGBT modules, to achieve better overall thermal performance and reduce the thermal resistance, a few improvements on the architecture level have been identified:
  • Baseplate elimination and pin-fin cooling: the traditional "baseplate + TIM2 + heat sink" structure gets integrated where the baseplate is eliminated, and the DBC/AMB is sintered directly to the heat sink. This approach reduces the overall thermal resistance due to the decreased number of layers.
  • Die attach materials transition from solders to sintered pastes. Compared with traditional solders, sinter pastes have much higher electrical and thermal conductivity and high-temperature stability. The low coefficient of thermal expansion (CTE) and good tensile strength give them advantages in thermal and power recycling tests. Driven by these benefits, there has been a strong trend transitioning to Ag sintered pastes. Leading companies such as Tesla, Hyundai, VW, and BYD are already using it, and IDTechEx believes more vehicles will adopt it. In addition to Ag sintering, Cu sintering is another technology emerging. However, as of 2024, IDTechEx has not seen large-scale adoption of Cu sintering in EV power electronics because of the immature technology. The benefit of Cu sintering is its low costs. Some Cu sintered paste suppliers report to IDTechEx that they are aiming to achieve around 30-50% cost reduction. Some suppliers reported that they aim to release their automotive-qualified Cu sintered pastes by late 2024 or 2025. However, IDTechEx believes that Cu sintering will not be adopted at scale in the next two to three years due to the immaturity status of the technology.
  • Wire bonding to lead frame/ribbon bonding. Wire bonding is widely used as of 2024. Wire bonds can only cover around 20% of the die surface, and the heat is not well spread across the die pad. Therefore, wire bonding tends to be one of the most common failure points. The increasing current and heat will further exacerbate this. Ribbon bonding or lead frame gets increasingly used to mitigate these issues. Compared with wires, ribbons or lead frames have large cross-sectional areas, allowing for a higher thermal dissipation and current carrying capacity.
  • Heat sink materials: There is no clear trend on this, but IDTechEx has noticed that Al heat sinks are more widely used in vehicles from Asia (e.g., China, Japan, and Korea, etc.), whereas Cu heat sinks are popular in vehicles from Europe (Germany, France, etc.). Cu has higher thermal conductivity than Al, therefore presenting a greater thermal dissipation ability. However, high performance comes with high costs. Cu can be a few times more expensive than Al, and IDTechEx sees that an increasing number of vehicles are planning to use more cost-effective solutions that are made of Al.
 
Figure 2. Thermal management technologies in EV power electronics. Source: IDTechEx
 
Thermal management for data centers
 
Data center and high-performance computing (HPC) are driving the growth of the AI and data center industry. With Nvidia's B200 with a thermal design power (TDP) over 1000W, the chip cooling industry is transitioning from traditional air cooling to liquid cooling. Liquid cooling can be split into direct-to-chip (D2C) cooling and immersion cooling. Depending on the cooling principle, liquid cooling can also be split into single-phase cooling, where heat is extracted via convection, and two-phase cooling, where heat is extracted via the latent heat during phase change. Historically, the average TDP has experienced a 3.5-fold increase over the past 16 years. This trend will likely continue, and for high-end GPUs, single-phase D2C cooling is also adopted, such as GB200. IDTechEx believes that 1500W and 2000W TDP would be a critical range where single-phase D2C cooling will struggle, and IDTechEx believes that two-phase D2C cooling is very likely needed for 2000W+ TDP.
 
D2C Cooling Roadmap
 
D2C cooling is believed to take off very soon, driven by Nvidia's GB200, which has already adopted single-phase cold plates. Thanks to their flexibility and lower complexity of retrofitting compared with immersion cooling, IDTechEx believes that cold plate will likely be the mainstream for mid-to-high-end GPUs in the short-term future. However, as mentioned above, a single-phase cold plate is expected to reach its limit around 2000W, and this is where a two-phase cold plate will likely take off. A two-phase cold plate system tends to cost slightly more than its single-phase counterpart.
 
IDTechEx believes that a typical single-phase cold plate system (including hoses, fluid distribution manifolds within servers, and pipes) costs between US$200 and US$400, with the CPU cold plate on the lower end and the GPU cold plate on the higher end. A two-phase cold plate system has a slight premium, costing around US$450 per cold plate system. It is worth noting that these costs only indicate the general range, and depending on the configuration, the cost per system varies. IDTechEx forecasts that by 2035, the total addressable market (TAM) of D2C cooling will reach around US$4.8 billion.
 
Immersion Cooling Roadmap
 
Immersion cooling, unlike D2C, is at its early stage of commercialization. Some pilot projects exist, but IDTechEx has not seen any large-scale adoption yet as of 2024. Despite offering higher overall capacity, immersion cooling presents challenges such as a lack of expertise, difficulty in retrofitting server boards and infrastructure, and fluid loss. Hyperscalers value flexibility and sustainability, and IDTechEx believes that one of their overarching priorities is avoiding vendor locking-in. Immersion cooling lacks flexibility, therefore making them less favorable to hyperscalers. Single-phase immersion cooling typically relies on hydrocarbon oil (e.g., PAO oil, etc.) with costs between US$8.5/L and US$11/L, whereas two-phase immersion cooling uses specialized engineered fluids. However, a two-phase immersion coolant is susceptible to regulations, particularly PFAS.
 
Given the technical barriers and commercial considerations, IDTechEx believes that D2C cooling will likely dominate, although it will still take a few years before immersion is largely adopted. Figure 3 summarizes the roadmap of different cooling technologies.
 
Figure 3. Roadmap of cooling technologies and components on the IT equipment level. Source: IDTechEx
 
To learn more about thermal management developments and trends, please refer to the IDTechEx research portfolio at www.IDTechEx.com/Research/Thermal. Downloadable sample pages are available for all IDTechEx reports.

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