Thermal Management Fundamentals and Design Guides in Electronic Packaging

Power semiconductors and chips are essential in modern electronics, driving applications from personal devices and data centers to energy technologies, vehicles, and Internet infrastructure. However, efficient heat dissipation remains a critical challenge, directly affecting their performance, reliability, and lifespan. High-power electronics based on wide- and ultrawide-bandgap semiconductors can exhibit power densities exceeding 10 kW/cm2, hundreds of times higher than digital electronics, posing significant thermal management challenges. Addressing this issue requires advanced materials and interface engineering, alongside a comprehensive understanding of materials physics, chemistry, transport dynamics, and various electronic, thermal, and mechanical properties. Despite progress in thermal management solutions, the complex interplay of phonons, electrons, and their interactions with material lattices, defects, boundaries, and interfaces presents persistent challenges. This Account highlights key advancements in thermal management for power semiconductors and chips, with a focus on our group's recent contributions. Our approach addresses several critical issues: (1) developing materials with ultrahigh thermal conductivity for enhanced heat dissipation, (2) reducing thermal boundary resistance between power semiconductors and emerging 2D materials, (3) improving thermal and mechanical contacts between chips and heat sinks, (4) innovating dynamic thermal management solutions, and (5) exploring novel principles of thermal transport and design for future technologies. Our research philosophy integrates multiscale theoretical predictions with experimental validation to achieve a paradigm shift in thermal management. By leveraging first-principles calculations, the recent studies redefined traditional criteria for high-thermal-conductivity materials. Guided by these insights, we developed boron arsenide and boron phosphide, which exhibit record-high thermal conductivities of up to 1300 W/mK. Through phonon band structure engineering, we reduced TBR in GaN/BAs interfaces by over 8-fold compared to GaN/diamond interfaces. The combination of low TBR and high thermal conductivity significantly reduced hotspot temperatures, setting new benchmarks in thermal design for power electronics. We further explored the anisotropic TBR properties of two-dimensional materials and Moiré patterns in twisted graphene, expanding the thermal design landscape. To address challenges at device-heat sink interfaces, we developed self-assembled boron arsenide composites with a thermal conductivity of 21 W/mK and exceptional mechanical compliance (∼100 kPa). These composites provide promising solutions for thermal management in flexible electronics and soft robotics. In dynamic thermal management, we pioneered the concept of solid-state thermal transistors, enabling electrically controlled heat flow with unparalleled tunability, speed, reliability, and compatibility with integrated circuit fabrication. These innovations not only enhance thermal performance but also enable the exploration of novel transport physics, improving our fundamental understanding of thermal energy transport under extreme conditions. Looking forward, we reflect on remaining challenges and identify opportunities for further advancements. These include scaling up the production of high-performance materials, integrating thermal solutions with existing manufacturing processes, and uncovering new physics to inspire next-generation power electronics technologies. By addressing these challenges, we aim to inspire future codesign strategies that enable the development of more efficient, reliable, sustainable, and high-performance electronic systems.

Evaluation of analytical models for thermal analysis and design of electronic packages

A variety of new advanced composite materials are now available that provide great advantages over conventional materials for electronic packaging thermal control, including extremely high thermal conductivities (more than twice that of copper); low tailorable coefficients of thermal expansion; weight savings up to 80 percent; extremely high strength and stiffness; low-cost, net-shape fabrication processes; and cost reductions as high as 65 percent. In addition, composites are in a state of continual development that will provide even greater benefits. This article provides an overview of advanced composites used in thermal management, including properties, applications, and future trends. The focus is on materials having thermal conductivities at least as high as those of aluminum alloys. Future trends and the potential for composites in other aspects of the electronics industry, such as high-speed assembly machine materials of construction, are also examined.

Electronic thermal packaging design continues to look for novel solutions for enhancing the performance of microelectronic cooling solutions. Driven by increasing thermal performance requirements, particularly in densely packaged militarized electronic systems and other high density or extreme use products, thermal designers are showing that to achieve the necessary cooling, combinations of existing technologies may offer further enhancement than has already been demonstrated. This paper discusses the performance characteristics of a single phase, pumped liquid cooling system (LCS) employed in cooling microprocessors and considers the effects of including solid state cooling (a.k.a thermoelectric cooling) in conjunction with the pumped liquid system. The thermal performance of a baseline LCS without TEC is compared to the performance of a LCS with a TEC combined with two alternative "flux transformer" heat spreaders. The two alternative flux transformers included a solid copper plate and vapor chamber heat pipe. Each "flux transformer" was sandwiched between the concentrated thermal load of the microprocessor and the TEC. The paper discusses the predicted thermal performance for the various systems as well as presenting experimental results. In demonstration, the experimental results show that the addition of TEC's coupled with the vapor chamber heat pipe "flux transformer" provided the most favorable improvement in system performance over the power dissipation range tested. As the TEC electrical power was increased, the temperature gradient across the TEC's increased reducing their coefficient of performance. Eventually, the combined TEC and vapor chamber heat pipe flux transformer solution matched, and then exceeded the heat sink temperature achievable with a conventional single phase pumped liquid cooling system. For microprocessor and ASIC heat dissipations of up to 175 watts, this particular pumped liquid system incorporating TEC's coupled with a vapor chamber heat pipe flux transformer can significantly reduce processor temperatures.

This paper describes the use of ANSYS ICEPAK software in teaching a senior level capstone thermal systems design course in a Mechanical Engineering curriculum. The use of ANSYS ICEPAK software tools in the thermal design course allows our undergraduates the preparation they need to become competitive and productive in today’s private industry sector. The paradigm of learn-by-doing adopted by the college is used in the thermal design course by exposing students to the use of ANSYS ICEPAK software in order to complete a design project in the thermal design course. The senior level capstone thermal design course is a three-unit semester course. Students are broken into teams and are tasked to solve a variety of thermal-fluid, heat transfer related design problem scenarios. The student teams are tasked to design an electronic systems thermal management system using PCBS, fans, heat sinks, heat pipes, etc. in order to meet a set of pre-defined requirements. In this manner, the use of the ICEPAK projects serves to build the soft skills (report writing and technical presentation) of the students. This paper will include examples of ANSYS ICEPAK based thermal design projects and methods of assessment and illustrations of how the thermal design course addresses the Mechanical Engineering program’s ABET objectives and outcomes related to senior design capstone design courses.

In this study, thermal design and thermal management for a low-cost photonic integrated circuits (PIC) platform is proposed and analyzed. The involved PIC platform is targeted for various applications including optical communications, optical interconnects, signal processing and sensing. The module considered in this study consists of a rigid PCB made of FR4 material and a silicon photonics ICs platform on which a laser diode chip, a driver chip, and a trans-impedance amplifier (TIA) chip are jointed using solder balls. A kovar case is chosen for the module. For the thermal design and thermal management, two objectives are involved in this study. The first one is to reduce the thermal resistance from junction to ambient and the other one is to reduce the thermal cross talk between the driver/TIA chips and laser source chip. The following accomplishments are achieved in this study. The overall junction to ambient thermal resistance is reduced to a certain level and meets the design target. The thermal cross effect between the driver/TIA chips and the laser source chip is reduced by cutting a slot in the silicon photonic platform and implementing separated heat spreaders for these chips.

Since the invention of the integrated circuit increasing transistor integration density has been the main path to increased performance of microelectronic devices. With traditional transistor scaling approaching fundamental limitations, the field of electronic packaging has seen increasing effort towards increased integration density, e.g. three-dimensional packaging. Overall, this has led to tremendous power densities in the order of 100 W/cm2. Consequently, thermal management of electronic packages has attracted increasing research interest and has been identified as a research priority by industry consortia iNEMI and ITRS [1–3]. There is a wide consensus within the microelectronics industry that current thermal interface materials constitute a bottleneck hindering a reduction of junction to ambient thermal resistances to future required levels (< 0.2 K7W) [1]. Hence, there has been a significant increase in research towards improved thermal interface materials. A clear trend observed in thermal interface materials research is the shift from traditional particulate composites, i.e. randomly dispersed high thermal conductivity particles in polymer matrices relying on percolation mechanisms, towards structured composites providing thermal conductivity through a continuous high thermal conductivity phase. In combination with the application of nanotechnology a number of interesting composite materials have been realized, based on e.g. vertically aligned silver and nickel nanowires and carbon nanotubes [4–6]. In this paper we introduce and discuss a new type of composite based on nanotechnology for thermal management applications. The core technology behind the composite is electrospun nanofibers. Electrospinning is a method for fabrication of polymeric fibers with diameters in the nano- and micrometer range, offering high flexibility in terms of choice of materials. A huge number of polymeric materials have been electrospun and documented in literature, including various polymeric precursors (e.g. to carbon fibers). In this work we present films of electrospun fibers based on a flexible thermoplastic polyurethane elastomer (Desmopan 9370A, Bayer Material Science AG) and high temperature resistant polyimide (Matrimid 5218, Huntsman Advanced Materials). A typical electrospun polyimide film is exhibited in figure 1. As seen in the image, the film is composed of randomly oriented fibers (mean diameter 780 run) forming a three-dimensional porous polymer structure. The porous polymer film is liquid phase infiltrated with a metal (typically In, Sn, InSnBi and similar alloy systems) under high pressure (30 MPa), leading to the formation of a topologically connected metal network within the polymeric structure (see figure 2). High thermal conductivity is achieved via the continuous metal phase, while the polymeric phase defines geometry (bondline thickness) and composition. In contrast to pure solder interfaces, the inclusion of a polymeric phase lowers stiffness, indicating a potential for lower bondline-thicknesses while still absorbing CTE-mismatch in assemblies. Results from xenon flash thermal characterization of a representative composite; polyimide infiltrated with pure indium, sandwiched between two copper plates is exhibited in figure 3. As seen, the composite exhibits a total contact resistance (2 interfaces) of 8 Kmm2/W. The thermal conductivity is found to be 28 W/mK, approximately 1/3 of the inherent thermal conductivity of the indium metal phase (83.7 W/mK). This clearly indicates the potential of the material in thermal management applications.

Originally published in IEEE Transactions on Components and Packaging Technology Vol. 20 No. 2. IEEE holds all copyright of this article. IEEE allows the final published version of author's own work to be deposited in institutional repositories.

This article presents a comprehensive review of the modern thermo-conductive materials that have potential to improve the heat extraction in electrical machines by conduction. Currently, there is a significant interest in thermal design and analysis of electrical machines as the demand for high power/torque density is substantially raised in applications such as marine, aerospace, e-mobility and rail. Thermal design engineering has become very important to develop smaller and more efficient electric motors, therefore electrical machine designers need to be more informed with the recent development in novel thermo-conductive (insulation) materials. Such developments can provide enhanced thermal characteristics for high power dense electrical machines. It is reported that high voltage electrical insulations can have more sophisticated thermal properties with the recent advancements in materials science. This study aims to inform electrical machine designers with and without a thermal background about recent thermo-conductive materials. Thus, a profound understanding can be gained in thermally conductive materials for the use of numerous applications in electrical machines for which thermal management is a crucial aspect of the overall multi-physics design and optimization process.

Improved hollow cathode magnetron deposition for producing high thermal conductivity graphite-copper composite

Three dimensional (3D) integration offers numerous electrical advantages like shorter interconnection distances between different dies in the stack, reduced signal delay, reduced interconnect power and design flexibilities. The main enabler of 3D integration is through-silicon-vias (TSVs) and stacking of multiple dies. Irrespective of these advantages, thermal management in 3D stacks poses significant challenges for the implementation of 3D integrated circuits. Even though extensive research work has been done in understanding the thermal management in two dimensional (2D) planar circuits for the past several decades, 3D integration offers a new set of challenges in terms of thermal management, which makes it difficult to readily apply the thermal management strategies available for 2D planar circuits. Over the past decade, some work has been done in thermal analysis and management of 3D stacks but still, knowledge is scattered and a comprehensive understanding is lacking. This research work focuses on bringing together the limited work on thermal analysis and thermal management in 3D vertically integrated circuits available in the literature. A compilation and analysis of the results from investigations on thermal management in 3D stacks is presented in this review with special emphasis on experimental studies conducted on different thermal management strategies. Furthermore, 3D integration technologies, thermal management challenges, and advanced 2D thermal management solutions are discussed.

The materials selection for thermal management of electronic packaging is influenced by thermal, electrical, physical and thermomechanical requirements of the device and its surrounding electrical system and by the environment to which the device will be exposed. The reliability of the finished device and electric system will depend not only on the characteristics of the individual materials but also on the interaction of package and thermal management materials at interfaces during exposure to such stresses as thermal gradients, temperature cycling, moisture, and contamination. This chapter will introduce general characterization methodologies of thermal management materials for assessing performance and reliability of electronic packaging, including thermal properties, electrical properties, thermomechanical analysis, as well as material microstructure and interface characterization, surface finish and contact interface compatibility, and reliability analysis and environmental evaluation.

The backbone of modern telecommunications is optical fibers. For each end of every optical fiber, there is one laser or laser diode transmitting the light and one photo detector to decode the signals. As Internet traffic expands and the transmission distance increases, more and more designs are using higher and higher power lasers or laser diodes. Once again this development calls for better thermal management designs and better thermal management materials. This chapter serves as a layman’s introduction to lasers, laser diodes, and laser diode packaging. Within the thermal management scope, the use of copper tungsten is examined in detail. As technology evolves, the introduction of newer and more advanced material will take place copper tungsten materials.

Electric motorcycles feature a smaller size and lower weight than electric cars, meaning they have greater manoeuvrability and energy efficiency, which translate to a dynamic riding experience and reduced environmental footprint. From a thermal management perspective, one major challenge is how to maximise the heat dissipation efficiency of the battery system within the limited space available onboard since the battery system represents one of the largest thermal loads onboard. This paper investigates electric motorcycle modelling to facilitate prototype development, emphasising a compact, integrated cooling system for high-voltage powertrain components, including the battery, inverter, and motor. Particularly, the proposed battery model is structured across the pack–module–cell hierarchy, which makes it capable of distinguishing the thermal state of each individual cell and the cell-to-cell performance variations resulting from temperature effects. The integrated cooling system and multi-scale battery modelling method proposed in this paper allow for a quick comparison of performances between different battery module thermal designs, which is specifically suited for early-stage investigation of different concepts. A series and a parallel battery module thermal design are proposed and compared, with a focus on evaluating their impacts on system-level and component-level thermal performances as well as cell-level performance variations, including but not limited to temperature, state of charge, voltage, and state of power. Specifically, the serial thermal design provides better overall cooling efficiency and lower battery pack temperatures, while the parallel design significantly reduces cell-to-cell variations.

Thermal management technology is the important means to optimize the design of thermal control system and maintain the manned thermal environment within the docking spacecraft combination. Through the thermal characteristic analysis of com- bination between target spacecraft and manned spacecraft, the thermal management design and simulated model basing on inter cabin ventilation were proposed. Results of simulation and thermal balance tests and orbital data show that velocity distribution satisfied the need and the air temperature and humidity were in target area. Base on simulation and tests, the thermal management design of manned combination was proved. The paper concluded the thermal management technology for space station.