Optimizing Power Electronics Reliability: Advanced Thermal Management & Wire Bond Lifetime Testing

As the demand for reliable power systems comprised of parallel-connected converter units continue to increase the need for optimized load sharing techniques rises accordingly. This fact is emphasized by a power system minimization trend that tends to shrink the available PCB area set aside for the power system. These contradictive trends feed the research in topics such as advanced thermal management and dynamic thermal management. Implementation of the latter topic usually requires the use of complicated controllers that continuously monitors the thermal working environment and key components within the system. If the thermal stress exceeds preset limits the controller react according to a predetermined sequence to minimize the damaging effects of excessive thermal stress. This paper combines the dynamic thermal management with the load sharing. It is hereby effectively ensured that the parts count is kept to a minimum while providing a dynamic optimization of parameters such as average and absolute system temperatures as well as overall system reliability. The latter aspect is achieved by redistributing the current throughput of each converter, which in turn results in equal thermal conditions as opposed to well-known and widely used current sharing technique's intent to establish equal currents.

Significant improvements in thermal management technologies will be required to support NASA’s planned Lunar and Mars missions. The developments needed include the application of advanced materials to reduce radiator system masses, enhanced survivability, and the use of alternative working fluids. Current thermal management systems utilize one of two heat rejection alternatives; either single phase pumped loops, or two phase heat pipes constructed with thick walled metal casings. These two technologies have proven themselves to be reliable performers in the transport and rejection of waste heat from spacecraft. As thermal management needs increase with increased power consumption and activity required on spacecraft, these metal based thermal management systems will become mission limiting. Investigations into the use of light weight ceramic materials for high temperature thermal management systems have been conducted by NASA, the Department of Energy, and the Department of Defense since the early 1980s, with results showing that significant mass savings can be obtained by replacing some of the metallic functions with ceramic materials.

<title>ABSTRACT</title> <p>Lithium-ion (Li-ion) batteries are increasingly targeted for electrical energy storage due to their exceptional energy and power density. However, Li-ion batteries operating in the hostile military environments are prone to catastrophic thermally induced failures or reduced lifetime if not maintained within narrow operating windows. There is great interest in advanced thermal management to optimize battery pack performance and enhance safety. In this numerical study, we examine the performance and safety benefits afforded by thermal management systems with effective thermal conductivities beyond the limits of traditional conductive cooling. Thermal runaway simulations based on NREL’s multi-scale multi-domain (MSMD) model illuminate how advanced thermal management can improve power density, while mitigating thermal runaway and cell fratricide potential. More efficient cooling increases the margin of safety, allowing end users to extend the pack operating envelope over an interrelated three parameter space encompassing the maximum permissible discharge rate, ambient operating temperature, and/or thermal runaway pack protection thresholds. Enhanced battery cooling will make Li-ion batteries safer for next generation military vehicles.</p>

The major factor defining the wear and tear in power electronic components is temperature swing. The paper presents an insight to failure mechanisms and the benefits that can be gained if a holistic approach considering devices, adequate design-in and advanced thermal management is considered.

Lithium-ion battery packs are essential in aviation, particularly for aircraft like the Cessna, Cirrus, and Piper models usually with 24V, and 16Ah to 35Ah capacities, depending on the specific model and avionics package installed, due to their high energy density and weight efficiency, which are critical for optimizing performance and fuel economy.This paper makes an exploration when it comes to spreading the heat from Auxiliary Power Unit (APU) battery packs with various cooling methods.This study addresses thermal management challenges, including the risk of thermal runaway, which can jeopardize safety challenges by optimizing heat dissipation in a 7s4p battery pack used in these aircraft, employing cooling techniques such as air cooling, phase change materials (PCMs), and aluminum-based heat spreaders (Al 3003-H18 and Al 6063-T83) to meet typical aviation requirements for reliability and efficiency.The simulations proved by COMSOL Multiphysics pointed out that the aluminum variants especially the Al 3003-H18 significantly reduced peak temperatures (64.27 C) compared to air cooling (82.36C) at 8C, thus offered best thermal regime capability and managed the peak temperature as well as the voltage across the different rates of discharged.Pearson's correlation coefficient analysis also showed positive higher order linear regression between aluminum-based models highlighting their efficiency in dealing with the heat generation or thermal runaway.This work extends existing literature by applying aluminum heat spreaders for aviation-specific applications, offering new insights into the relationship between thermal properties and cooling strategies under high discharge conditions, thereby enhancing both safety and battery longevity in critical aviation operations.

A multifunctional carbon-base phase change composite inspired by "fruit growth"

Over the past two decades, 3D techniques combined with heterogeneous integration, combining different functions and materials, have emerged as a key enabler for overcoming the physical and scaling limits of traditional 2D integration. These approaches are now expanding across multiple domains, including CMOS, memories, photonics, imagers, and RF systems, with the aim of delivering next-generation integrated systems for advanced computing (AI), analog/RF, and imaging applications. In this presentation, we will explore the fundamental techniques, recent advancements, and some challenges associated with achieving integration. Special emphasis will be placed on the role of hybrid bonding and sequential 3D integration schemes, as well as their implications for energy efficiency, device performance, and system-level innovations.3D integration has transitioned from a niche research area to a cornerstone technology in microelectronics, driven by its potential to address high density interconnect and traditional 2D scaling bottlenecks for several applications and enable heterogeneous integration at unprecedented scales. At the heart of this technological evolution are advanced schemes such as wafer thinning, Through-Silicon Vias (TSVs), hybrid bonding, and sequential 3D integration techniques. These techniques have been pivotal in shrinking the interconnect length, reducing latency, and enhancing data bandwidth in computing systems. In parallel, developments in wafer-to-wafer, die-to-wafer, and chiplet integration are enabling the seamless merging of diverse materials enabling functionalities such as logic, memory, photonics, and RF. Compact form factors are achieved enabling to boost performances of the most demanding applications such as Artificial Intelligence or Tb/s transceiver applications [1].Recent studies highlight significant progress in hybrid bonding technology, which achieves high-density interconnects at the submicron scale, thereby optimizing power delivery and thermal management in stacked devices [2]. Meanwhile, sequential 3D integration [3][4] where layers of transistors are fabricated sequentially on the same substrate, is emerging as a game-changing paradigm. It promises ultra-high-density integration with minimal parasitics, creating new opportunities for energy-efficient and high-performance systems. Several applications are foreseen including C-FETS, memories and imagers [5] .Photonic interconnects will enter in next generation 3D IC integration, addressing challenges in data bandwidth, power consumption and signal integrity and enabling photonic interposers for next generation of components for data centers and communication systems [7]. Similarly, RF [8] and analog domains [9] benefit from 3D stacking by improving front-end module integration with specific materials (III-V, HR, ...), leading to enhanced performance and higher frequencies.Despite these achievements, significant challenges remain. Thermal dissipation is a critical bottleneck [10] , particularly in densely 3D stacked architectures where hotspots can severely impact reliability and performance. Moreover, the mechanical stresses induced during bonding and processing can affect device yield and long-term stability. Our recent work in advanced thermal management and stress engineering underscores the need for interdisciplinary approaches to address these challenges. Solutions such as microfluidic cooling, novel materials for thermal interface layers and specific bonding technologies are being actively explored. Furthermore, while heterogeneous integration is currently feasible at the wafer scale—such as wafer-to-wafer hybrid bonding, which is already in mass production—expanding application fields will require advancements in die-to-wafer integration techniques.Looking ahead, the convergence of 3D integration with emerging paradigms such as neuromorphic computing, quantum technologies, multispectral and smart imagers, and advanced packaging promises to redefine system design at all levels. The synergy between 3D technologies and heterogeneous integration of advanced materials, such as 2D semiconductors, III-V, ferroelectric or oxide semiconductor [11] materials, further expands the horizon for innovation.In conclusion, 3D integration has proven to be a transformative force in microelectronics, offering pathways to overcome traditional limitations and unlock new performance dimensions. Intensive researches worldwide continues contribute to push the boundaries of what is possible, paving the way for smarter, more efficient, and highly integrated systems.

This paper describes six advanced cryogenic thermal management devices/subsystems developed by Swales Aerospace for ground/space‐based applications of interest to NASA, DoD, and the commercial sector. The devices/subsystems described herein include the following: (a) a differential thermal expansion cryogenic thermal switch (DTE‐CTSW) constructed with high purity aluminum end‐pieces and an Ultem support rod for the 6 K Mid‐Infrared Instrument (MIRI) on the James Webb Space Telescope (JWST); (b) a quad‐redundant DTE‐CTSW assembly for the 35 K science instruments (NIRCam, NIRSpec, and FGS) mounted on the JWST Integrated Science Instrument Module (ISIM); (c) a cryogenic diode heat pipe (CDHP) thermal switching system using methane as the working fluid for the 100 K CRISM hyperspectral mapping instrument on the Mars Reconnaissance Orbiter (MRO); and (d) three additional devices/subsystems developed during the AFRL‐sponsored CRYOTOOL program, which include a dual DTE‐CTSW/dual cryocooler test bed, a miniaturized neon cryogenic loop heat pipe (mini‐CLHP), and an across gimbal cryogenic thermal transport system (GCTTS). For the first three devices/subsystems mentioned above, this paper describes key aspects of the development efforts including concept definition, design, fabrication, and testing. For the latter three, this paper provides brief overview descriptions as key details are provided in a related paper.This paper describes six advanced cryogenic thermal management devices/subsystems developed by Swales Aerospace for ground/space‐based applications of interest to NASA, DoD, and the commercial sector. The devices/subsystems described herein include the following: (a) a differential thermal expansion cryogenic thermal switch (DTE‐CTSW) constructed with high purity aluminum end‐pieces and an Ultem support rod for the 6 K Mid‐Infrared Instrument (MIRI) on the James Webb Space Telescope (JWST); (b) a quad‐redundant DTE‐CTSW assembly for the 35 K science instruments (NIRCam, NIRSpec, and FGS) mounted on the JWST Integrated Science Instrument Module (ISIM); (c) a cryogenic diode heat pipe (CDHP) thermal switching system using methane as the working fluid for the 100 K CRISM hyperspectral mapping instrument on the Mars Reconnaissance Orbiter (MRO); and (d) three additional devices/subsystems developed during the AFRL‐sponsored CRYOTOOL program, which include a dual DTE‐CTSW/dual cryocooler test bed, a miniaturiz...

Heat transfer in semi-permeable channels using ternary hybrid nanofluids: Effects of melting and radiation

Germanium telluride (GeTe) is an important functional material that has been attracting extensive research attention. Challenges such as phase transition processes and crystallization of amorphous GeTe cannot yet be accurately calculated using ab initio molecular dynamics because of the time limitations of density functional theory calculations. Molecular dynamics simulation using empirical potentials can address the aforementioned issues. However, their accuracy relies on the validity of the empirical interatomic potential. With the advancement of computational methodologies within materials science and engineering, machine learning potentials (MLPs) have garnered substantial interest. In this paper, we review the applications of MLPs, including neural network potential, Gaussian approximation potentials, and neuroevolution potential, in studying the phonon properties of GeTe. Our focus includes the crystallization of amorphous GeTe, the mechanisms underlying structural phase transitions, and thermal conductivity. These advancements can offer valuable guidance for the utilization of GeTe in advanced thermal management and contribute to the exploration of MLPs in phonon physics.

Polymer composites with excellent thermal conductivity and superior mechanical strength are in high demand in the electrical engineering systems. However, achieving superior thermal conductivity and mechanical properties simultaneously at high loading of fillers will still be a challenging issue. In this work, a facile method was proposed to prepare the epoxy composite with carbon fibers (CFs) and alumina (Al2O3). This CF and Al2O3 hybrid structure can effectively reduce the interfacial thermal resistance between the matrix and the CFs. The thermal conductivity of epoxy composite with 6.4 wt % CFs and 74 wt % Al2O3 hybrid filler reaches 3.84 W/(m K), which is increasing by 2096% compared with that of pure epoxy. Meanwhile, the epoxy composite still retains outstanding thermal stability and mechanical performance at high filler loading. A cost-effective avenue to prepare highly thermally conductive and superior mechanical properties of polymer-based composites may enable some prospective application in advanced thermal management.

Self-assembly carbon nanotube nanoporous coatings with great durability for highly efficient boiling heat transfer

In this paper, we report a thermal conductive polymer composite that consists of silicone rubber (SR) and branched Al2O3 (B-Al2O3). Owing to the unique two-dimensional branched structure, B-Al2O3 particles form a continuous three-dimensional network structure by overlapping each other in the matrix, serving as a continuous heat conductive pathway. As a result, the polymer composite with a 70 wt% filler achieves a maximum thermal conductivity of 1.242 Wm−1 K−1, which is equivalent to a significant enhancement of 521% compared to that of a pure matrix. In addition, the composite maintains a high volume resistivity of 7.94 × 1014 Ω·cm with the loading of 70 wt%, indicating that it meets the requirements in the field of electrical insulation. Moreover, B-Al2O3 fillers are well dispersed (no large agglomerates) and form a strong interfacial adhesion with the matrix. Therefore, the thermal decomposition temperature, residual mass, tensile strength, modulus and modulus of toughness of composites are significantly improved simultaneously. This strategy provides new insights for the design of high-performance polymer composites with potential application in advanced thermal management in modern electronics.

Advanced thermal management via directional freezing for high-strength infrared-modified alumina aerogels

This study presents the development of high-performance power modules with advanced 3D printed ceramics, integrated cooling channels and Cu pinfins for thermal management. Thick film printed electronics was employed for circuit metallization. SiC dies were then attached using Sinter Silver process for improved thermal performance and reliability. Thermal and electrical testing was performed to demonstrate the module’s capability.