Three-dimensional integrated circuits (3D IC) technology has emerged in the past few decades, driven in part by the techno-economic difficulties of dimensional scaling and the increasing interconnect delay in microelectronics. In a 3D IC, vertical integration of multiple transistor planes, either through monolithic integration or through bonding of multiple strata offers reduced interconnect delay and enhanced design flexibility. However, vertical integration in a 3D IC also results insevere thermal management challenges. Thermal management of a 3D IC is exacerbated by the multi-layer nature of the 3D IC. Further, new components such as Through Silicon Vias (TSVs) offer opportunities for novel thermal management. This paper presents a critical review of research literature related to heat transfer in 3D ICs, focusing specifically on thermal modeling, thermal-electrical co-design and thermal management of a 3D IC. Key literature from recent years is categorized and summarized. A discussion on the future outlook for research in these areas is presented. It is expected that this review paper will be helpful for researchers in academia and industry for understanding the state-of-the-art in various areas related to heat transfer in 3D ICs.

The venting of hot gases due to rupture of a Li-ion cell during thermal runaway may rapidly transfer thermal energy to neighboring cells in a battery pack and cause propagation of thermal runaway. While thermal runaway has been studied extensively through both measurements and simulations, there is a relative lack of research on the impact of the venting process on thermal runaway propagation. This work presents a non-linear thermal-fluidic simulation of supersonic turbulent flow of hot gases ejecting from a trigger cell and spreading to neighboring cells. Assuming isentropic flow, temperature and speed of the gas flow as functions of time are estimated based on past measurements. These data are used in simulations to determine the thermal impact of the venting process on neighboring cells. The impact of various geometrical parameters of the battery pack on the spreading of venting gases is investigated. Results indicate that cell-to-cell gap, overhead gap and the location of the vent hole on the cell body strongly influence the nature of propagation of thermal runaway to neighboring cells. This work develops a fundamental understanding of an important process during thermal runaway, and may help in the design and optimization of safe Li-ion battery packs for energy conversion and storage.

The performance, safety, and reliability of electrochemical energy storage and conversion systems based on Li-ion cells depend critically on the nature of heat transfer in Li-ion cells, which occurs over multiple length scales, ranging from thin material layers all the way to large battery packs. Thermal phenomena in Li-ion cells are also closely coupled with other transport phenomena such as ionic and charge transport, making this a challenging, multidisciplinary problem. This review paper presents a critical analysis of recent research literature related to experimental measurement of multiscale thermal transport in Li-ion cells. Recent research on several topics related to thermal transport is summarized, including temperature and thermal property measurements, heat generation measurements, thermal management, and thermal runaway measurements on Li-ion materials, cells, and battery packs. Key measurement techniques and challenges in each of these fields are discussed. Critical directions for future research in these fields are identified.

The rastering of discrete polymer filaments during Fused Filament Fabrication (FFF) results in the formation of voids between filaments, leading to poor properties and performance of the printed part. Minimising voids and improving filament-to-filament adhesion remains a key technological challenge for FFF. While mechanical rolling is commonly used in traditional manufacturing, its use in polymer 3D printing has not been explored much. This paper discusses the in situ compression of just-deposited filament using a roller that is integrated with the filament-dispensing nozzle. The roller travels with the filament nozzle, and compresses the filament immediately after deposition when it is still soft. The rolling process is characterised using high speed imaging and infrared (IR) thermography. The effects of compression force and roller temperature on print quality is investigated. In situ compression of the filaments is shown to result in 10X reduction in void formation. Tensile test results show 154% improvement in Ultimate Tensile Stress (UTS) and 417% improvement in material toughness due to compressive rolling. It is expected that implementation of the rolling technique discussed in this work may help print parts with improved properties and functionality.

Strategies to prevent or minimize propagation of thermal runaway in a pack of Li-ion cells are critically needed to ensure safe operation, storage and transportation. While significant literature already exists on thermal runaway simulations, several key questions of practical relevance have remained unaddressed. This work presents multi-mode heat transfer simulations to predict the onset and propagation of thermal runaway in a pack of cylindrical Li-ion cells. The impact of inter-cell gap and thermal properties of the interstitial material on onset and propagation of thermal runaway is studied. It is shown that high interstitial thermal conductivity promotes thermal runaway propagation. However, too low a thermal conductivity results in heat localization in the trigger cell, also leading to thermal runaway. An optimum range of interstitial material thermal conductivity is thus identified. The impact of trigger cell position on propagation is investigated. It is shown that, depending on external conditions, either the center or the corner position may be more susceptible to propagation. Finally, it is shown that radiation and natural convection play a key role in thermal runaway propagation. It is expected that the trade-offs identified here will help minimize the onset and propagation of thermal runaway in Li-ion battery packs.

Accurate understanding of propagation of thermal runaway is of much importance for developing safe battery pack designs. Combustion of vent gases emerging from a trigger cell undergoing thermal runaway has not been studied in sufficient detail, even though the additional heat generated during combustion likely plays an important role in thermal runaway propagation. This work presents comprehensive numerical modeling and simulations of thermal runaway propagation in a pack of cylindrical cells. The model accounts for multiple coupled non-linear phenomena, including vent gas flow and combustion, radiation and thermal runaway. Non-premixed combustion of venting gas is modeled using k - ε turbulence model and finite rate chemical kinetics. Simulation results are shown to be in good agreement with experimental data for a benchmark turbulent non-premixed jet flame. Simulations show that hot combustion products are rapidly transported in gaps between cells, potentially leading to self-sustained thermal runaway propagation to adjacent cells. Results demonstrate the critical importance of combustion in determining the nature of propagation of thermal runaway. The vent hole location is identified as an important parameter that influences whether and the extent to which thermal runaway propagation occurs. This work contributes towards the practical understanding of thermal runaway safety of Li-ion battery packs.