| 1. |
- Fu, Yifeng, 1984, et al.
(författare)
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Graphene related materials for thermal management
- 2020
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Ingår i: 2D Materials. - : IOP Publishing. - 2053-1583. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- Almost 15 years have gone ever since the discovery of graphene as a single atom layer. Numerous papers have been published to demonstrate its high electron mobility, excellent thermal and mechanical as well as optical properties. We have recently seen more and more applications towards using graphene in commercial products. This paper is an attempt to review and summarize the current status of the research of the thermal properties of graphene and other 2D based materials including the manufacturing and characterization techniques and their applications, especially in electronics and power modules. It is obvious from the review that graphene has penetrated the market and gets more and more applications in commercial electronics thermal management context. In the paper, we also made a critical analysis of how mature the manufacturing processes are; what are the accuracies and challenges with the various characterization techniques and what are the remaining questions and issues left before we see further more applications in this exciting and fascinating field.
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| 2. |
- Hansson, Josef, 1991, et al.
(författare)
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A review of recent progress of thermal interface materials: from research to industrial applications
- 2016
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Ingår i: IMAPS Nordic Annual Conference 2016 Proceedings; Tonsberg; Norway; 5 - 7 June 2016. - 9781510827226
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Konferensbidrag (refereegranskat)abstract
- The increasing trend of further scaling down electronic components put an increasing demand for more efficient cooling. A significant part of the thermal resistance from source to ambient occurs at the interface between materials, and thermal interface materials are crucial for efficient heat transfer. Recent years have seen a significant amount of progress various types of thermal interface materials. In this review, the field of thermal interface materials (TIMs) development is summarized and analyzed, focusing on three topics which have received attention at a research level, and their road towards market applicability. The first topic is development in particle laden polymers, which uses thermally conductive filler particles in a polymer matrix. New development is focused on novel fillers such as h-BN or carbon based fillers, and hybrid filler combinations. The next topic is continuous metal phase TIMs, which includes solder and liquid metal TIMs. The thermal performance is already very good, and development is largely focused on improving the mechanical properties. Finally, the last topic is carbon nanotube array TIMs, which used chemical vapor deposition-grown carbon nanotube arrays as bridging material. The concept has promise for great performance in both handling, mechanical stability and thermal performance, but is still at a research stage. In addition to these topics, a quantitative study on the progress of thermal interface materials development is made, both in terms of research papers published and in terms of patents filed. The study shows a stable trend of continuous development on all levels and concludes that significant improvements can be expected to continue in the future.
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| 3. |
- Hansson, Josef, 1991, et al.
(författare)
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Bipolar electrochemical capacitors using double-sided carbon nanotubes on graphite electrodes
- 2020
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 451
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Tidskriftsartikel (refereegranskat)abstract
- The electrochemical capacitor (EC) is a key enabler for the miniaturized self-powered systems expected to become ubiquitous with the advent of the internet-of-things (IoT). Vertically aligned carbon nanotubes (VACNTs) on graphite holds promise as electrodes for compact and low-loss ECs. However, as with all ECs, the operating voltage is low, and miniaturization of higher voltage devices necessitates a bipolar design. In this paper, we demonstrate a bipolar EC using graphite/VACNTs electrodes fabricated using a joule heating chemical vapor deposition (CVD) setup. The constructed EC contains one layer of double-sided VACNTs on graphite as bipolar electrode. Compared to a series connection of two individual devices, the bipolar EC has 22% boost in volumetric energy density. More significant boost is envisaged for stacking more bipolar electrode layers. The energy enhancement is achieved without aggravating self-discharge (71.2% retention after 1 h), and at no sacrifice of cycling stability (96.7% over 50000 cycles) owing to uniform growth of VACNTs and thus eliminating cell imbalance problems.
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| 4. |
- Hansson, Josef, 1991, et al.
(författare)
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Effect of Fiber Concentration on Mechanical and Thermal Properties of a Solder Matrix Fiber Composite Thermal Interface Material
- 2019
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Ingår i: IEEE Transactions on Components, Packaging and Manufacturing Technology. - 2156-3985 .- 2156-3950. ; 9:6, s. 1045-1053
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Tidskriftsartikel (refereegranskat)abstract
- Increased demand on the mechanical and thermal properties on the thermal interface and die attach material creates a demand for materials with tailored material properties. Solder matrix fiber composites (SMFCs) have been shown to address these challenges, but have, so far, required complicated procedures and components. In this paper, we present the fabrication of a new type of SMFC based on commercially available fiber networks infiltrated with Sn-Ag-Cu alloy (SAC305) or indium using equipment for large-volume production. The composite material exhibits similar thermal properties compared to pure solder, and mechanical properties that can be tailored toward specific applications. We also show that the handling properties of the SMFC allows it to be used in process flows where multiple reflow cycles are required and can achieve a well-defined bond line thickness (BLT) and good bonding using fluxless reflow under pressure.
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| 5. |
- Hansson, Josef, 1991, et al.
(författare)
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Effects of high temperature treatment of carbon nanotube arrays on graphite : Increased crystallinity, anchoring and inter-tube bonding
- 2020
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Ingår i: Nanotechnology. - : Institute of Physics Publishing (IOPP). - 0957-4484 .- 1361-6528. ; 31:45
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Tidskriftsartikel (refereegranskat)abstract
- Thermal treatment of carbon nanotubes (CNTs) can significantly improve their mechanical, electrical and thermal properties due to reduced defects and increased crystallinity. In this work we investigate the effect of annealing at 3000 degrees C of vertically aligned CNT arrays synthesized by chemical vapor deposition (CVD) on graphite. Raman measurements show a drastically reduced amount of defects and, together with transmission electron microscope (TEM) diffraction measurements, an increased average crystallite size of around 50%, which corresponds to a 124% increase in Young's modulus. We also find a tendency for CNTs to bond to each other with van der Waals (vdW) forces, which causes individual CNTs to closely align with each other. This bonding causes a densification effect on the entire CNT array, which appears at temperatures >1000 degrees C. The densification onset temperature corresponds to the thermal decomposition of oxygen containing functional groups, which otherwise prevents close enough contact for vdW bonding. Finally, the remaining CVD catalyst on the bottom of the CNT array is evaporated during annealing, enabling direct anchoring of the CNTs to the underlying graphite substrate.
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| 6. |
- Hansson, Josef, 1991
(författare)
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Exploration of Metal Composites and Carbon Nanotubes for Thermal Interfaces
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Modern microelectronics are perpetually pushing against limitations caused by inadequate heat dissipation. One of the critical bottlenecks is at the interfaces between different materials and components. Thermal interface materials (TIM) are used to improve the heat transfer at these interfaces, and to improve TIMs is one of the critical research areas in order to reduce the total thermal resistance for electronics systems. A TIM requires both high thermal conductivity, ability to conform to mating surfaces, and the ability to absorb stress from thermal expansion mismatch during thermal cycling. Solder based TIMs utilize solder to form a strong connection between the mating surfaces with high thermal conductivity, but their stiffness prevents adequate absorption of thermal expansion mismatch. In this thesis, the solder is combined with a fiber network phase, which modifies the mechanical properties, while maintaining the continuous heat paths within the solder. This solder matrix fiber network composite TIM allows for the tailoring of the mechanical properties of solder based TIM while retaining thermal performance. Another promising TIM candidate is based on arrays of vertically aligned CNTs. CNT arrays can achieve good thermal performance, but the reliability had not previously been investigated experimentally. A thorough investigation of the reliability of CNT array TIM revealed that reliability is not guaranteed, but requires careful matching between CNT array height, bonding method and substrate configuration. Furthermore, we developed a new joule self-heating chemical vapor deposition (CVD) method for the synthesis of double-sided CNT arrays on thin foils, which can be used both as TIM or as supercapacitor electrodes. Double-sided arrays are challenging with conventional CNT array synthesis methods, but the Joule heating CVD method allows for rapid, scalable and uniform synthesis of large area double-sided arrays. Finally, this method was used to study the effect of heat treatment of CNT arrays on graphite. The heat treatment serves to simultaneously improve the CNT crystallinity, eliminate catalyst residues, and form a seamless connection between CNT arrays and graphite.
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| 7. |
- Hansson, Josef, 1991, et al.
(författare)
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Fabrication and characterization of a carbon fiber solder composite thermal interface material
- 2017
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Ingår i: 2017 IMAPS Nordic Conference on Microelectronics Packaging (NordPac). - 9781538630556 ; , s. 97-100
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Konferensbidrag (refereegranskat)abstract
- One of the significant bottlenecks in thermal management is to develop thermal interface materials (TIMs) with lower thermal interface resistance while retaining good reliability, mechanical properties and handling capabilities. Recently, the combination of electrospun polymer fibers and solder matrix has gathered interest, combining the excellent thermal properties of metal with the mechanical properties of polymers. Carbon fibers are increasingly common as reinforcement in composites, owing to their high strength and thermal conductivity. Utilizing carbon fibers in a similar composite could allow for the fabrication of TIMs with so far unexplored properties such as increased thermal conductivity, strength and tunable CTE. In this work, we have fabricated and characterized a TIM based on a carbon fiber network infiltrated by an alloy of Sn-Ag-Cu, (CF-TIM). Commercially available carbon fibers are coated with a thin layer of Ag and infiltrated by molten alloy under high pressure. The result is a preform TIM, easy to handle and compatible with standard SMT assembly. A thermal interface resistance lower than 2 Kmm2/W between two ENIG coated Cu substrates was measured with laser flash. Comparing total thermal interface resistance to bond line thickness indicates a very low contact resistance consistent with good metallurgical bonding and a bulk thermal conductivity of 24 W/mK for the TIM. X-ray inspection and SEM of cross section of the assembled structure indicates good adhesion between fiber and matrix, and a very low degree of voiding. To demonstrate the handling capabilities of CF-TIM, a variety of reflow conditions were investigated. A consistent bond line thickness (BLT) of 45±5μm was achieved independent on applied pressure during reflow, and decreased less than 20% after 10 additional reflow cycles, without additional material leakage. This demonstrates the possibility of CF-TIM use in assembly line processes requiring additional reflow steps. Solder preforms are common in industry, and due to similar handling characteristics of the CF-TIM, it should be easily integrated into existing electronics assembly lines. The usage of commercial fibers not reliant on slow and expensive processes such as electrospinning further opens up the potential for mass production.
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| 8. |
- Hansson, Josef, 1991, et al.
(författare)
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Novel nanostructured thermal interface materials: a review
- 2018
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Ingår i: International Materials Reviews. - : Informa UK Limited. - 0950-6608 .- 1743-2804. ; 63:1, s. 22-45
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Forskningsöversikt (refereegranskat)abstract
- The trend of continuing miniaturisation of microelectronics leads to new thermal management challenges. A key point in the heat removal process development is to improve the heat conduction across interfaces through improved thermal interface materials (TIMs). We identify the key areas for state-of-the art TIM research and investigate the current state of the field together with possible future advances.
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| 9. |
- Hansson, Josef, 1991, et al.
(författare)
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Review of Current Progress of Thermal Interface Materials for Electronics Thermal Management Applications
- 2016
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Ingår i: 2016 Ieee 16th International Conference on Nanotechnology (Ieee-Nano). - 9781509014934 ; , s. 371-374
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Konferensbidrag (refereegranskat)abstract
- Increasing power densities within microelectronic systems place an ever increasing demand on the thermal management. Thermal interface materials (TIMs) are used to fill air gaps at the interface between two materials, greatly increasing the thermal conductance when solid surface are attached together. The last decade has provided significant development on high-performing TIMs, and this paper makes a summarized review on recent progress on the topic. Current state of the art commercial TIM types are presented, and discussed in regards to their advantages and disadvantages. Two main categories of TIMs with high interest are then reviewed: continuous metal phase TIMs and carbon nanotube array TIMs.
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| 10. |
- Hansson, Josef, 1991
(författare)
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Solder Matrix Fiber Composite Thermal Interface Materials
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Overheating has been a problem for microelectronics devices for decades, and the problem is exacerbated by the continued trend of miniaturization of features and the corresponding increase in power density. Thermal interface materials (TIMs) target one of the main bottlenecks in heat transfer: the interface between two materials, such as between a heat-generating microchip and a heatsink. By filling out microgaps caused by the roughness of the mating surfaces, TIMs improve the heat transfer over the interface by orders of magnitude. Nonetheless, even with a TIM the interface can be a limiting factor for the overall cooling. Thus, the development of new and improved TIMs is a big challenge for the electronics field. This thesis thoroughly reviews the overall status of the field of TIM research, and identifies three main tracks for novel research. First, particle laden polymers, which utilizes thermally conductive particles inside a polymer matrix which can conform to surfaces. Second, continuous metal phase TIM, which forms metallurgical bonds to both surfaces, and utilizes the inherently high thermal conductivity of metals. Third, carbon nanotube (CNT) array TIMs, which utilize the incredible thermal conductivity of CNTs. Here, an array of vertically aligned CNTs is used as nanosprings to connect the two surfaces together. In addition to these main tracks, various novel ideas based on polymers, metal and carbonaceous materials are explored. From the reviewed categories, continuous metal phase TIM in the form of solder is already widely used in industry, but comes with severe drawbacks in terms of mechanical properties and handling issues. Solder matrix fiber composites (SMFCs) have been shown to address these challenges, but have so far required complicated procedures and components. In this thesis, we present the fabrication of a new SMFCs based on commercially available polymer and carbon fiber networks infiltrated with Sn-Ag-Cu alloy (SAC) or Indium using equipment for large volume production. The composite material exhibits similar thermal properties compared to pure solder, and mechanical properties that can be tailored towards specific applications. We also show that the handling properties of the SMFC allows it to be used in process flows where multiple reflow cycles are required, and can achieve a well-defined bond line thickness and good bonding using fluxless reflow under pressure.
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