| 1. |
- Enmark, Markus, 1991, et al.
(author)
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A Critical Assessment of Nano Enhanced Vapor Chamber Wick Structures for Electronics Cooling
- 2021
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In: 2021 23rd European Microelectronics and Packaging Conference and Exhibition, EMPC 2021.
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Conference paper (peer-reviewed)abstract
- The increasing need for high thermal dissipation in small electronic products puts tough requirements on effective cooling solutions. Two of the most effective passive cooling devices in electronics today are vapor chambers and heat pipes. With new advancements in materials science and nanotechnology comes the possibility to further increase cooling capacity and at the same time make devices lighter. This study is a critical assessment on recent progress in the field of nanomaterial enhanced wick structures in vapor chambers and heat pipes. In this paper, nano-enhanced wick structures are divided into five different sub-categories based on material type. Publication trends for the different types of nano-enhanced wicks are studied by plotting them on a timeline. It is found that nanostructured metal wicks is the most studied field in recent years. A plot showing wick performance in terms of superheat temperatures for given heat flux is created to be used for benchmarking of new wick structures when pool boil experiments are carried out. An attempt to find correlation between publication trends, type of wick and performance is done. On the basis of the gathered data it is deemed difficult to find a distinct correlation, this is mainly due to difficulty in comparing performance between different studies, especially when different heat fluxes are used. There is no unambiguous answer to which category of nano-enhanced wicks that should be target for future studies. Graphene coating and pure carbon nanomaterials such as aerogels and graphene foam are still relatively unexplored and believed to have great potential if they can be attached to envelope materials.
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| 2. |
- Enmark, Markus, 1991
(author)
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Development and Characterization of Reliable Graphene-based Materials for Lightweight and Efficient Thermal Management in Electronics
- 2024
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Licentiate thesis (other academic/artistic)abstract
- The semiconductor industry continuously aims to increase the transistor density in integrated circuits to improve performance of electronics. As performance and transistor density increases, so does the power density of integrated circuits. To help solve the future demand of thermal management in electronics it is necessary to work with new innovative materials, engineer advanced material structures and develop new cooling concepts. The carbon nanomaterial graphene has the right properties to be used for this purpose as it has an extremely high thermal conductivity and is very lightweight. One challenge with using graphene in thermal management solutions is to engineer macroscopic materials from the nanomaterial graphene without losing too much of the extraordinary properties that are exhibited on nanoscale. High-performance graphene-based thermal management products are already commercialized today. Products like thermal interface materials (TIMs) and heat spreaders are still novel, and some knowledge gaps exist. More understanding of these products regarding reliability, aging properties and how to optimize production processes can enable them on a broader market. Further, it is believed that graphene-based materials can replace more conventional metals in applications where they have not been used before. In this thesis, the thermal conductivity and heat dissipation capacity of a graphene-assembled film heat spreader has been shown to be improved by a newly developed annealing process. The effect of the annealing process was demonstrated in a thermal test rig where a high-power light emitting diode (LED) was used as a hot spot while the temperature was monitored with an infrared (IR) camera. Furthermore, a vertically aligned graphene-based TIM was tested with a new test method to gain a better understanding of the long-term reliability and aging properties. The TIM was subjected to thermal aging, thermal cycling and damp heat while regularly measuring the thermal resistance to see how the performance changes with time. Generally, it could be seen that the thermal resistance was stable, a result that paves way for this type of TIM to be used in applications with a need for high performance over a long time. Additionally, a literature study on nano-enhanced wick structures was carried out to help determine the most promising nanomaterial-based wick to be used in a two-phase heat spreading device called vapor chamber. Lastly, prototypes of a novel graphene-enhanced vapor chamber were built with graphene assembled film as encapsulating material and they were characterized in a custom-made test rig. The lightweight prototype vapor chambers could outperform a conventional copper vapor chamber in terms of mass-based thermal resistance. However, leak tightness, working fluid and the wick structure were identified as three important future design improvements to further enhance performance and reliability.
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| 3. |
- Enmark, Markus, 1991, et al.
(author)
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Reliability Characterization of Graphene Enhanced Thermal Interface Material for Electronics Cooling Applications
- 2022
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In: 2022 IMAPS Nordic Conference on Microelectronics Packaging, NordPac 2022.
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Conference paper (peer-reviewed)abstract
- Graphene-based products are gaining popularity in thermal management applications in high performance electronics systems. The ultra-high thermal conductivity of graphene together with its relatively low density makes it a suitable material for reaching high cooling capability in lightweight applications. An example of products that are starting to enter the market is graphene enhanced thermal interface materials (TIMs). Pristine graphene enhanced TIMs are well characterized and show high thermal conductivity and low thermal interface resistance. Before these TIMs can take the next step from being a niche product to reach high volume sales on the market, it needs to be proven that they have stable performance over time when conditioned and aged according to industry reliability standards. In this work, a set of customized test rigs was designed, and graphene enhanced TIMs of three different thicknesses were tested. The TIMs were compressed by 30% and then subjected to three different industry standard reliability tests; thermal aging, temperature cycling and damp heat. The thermal resistance was measured sequentially during each test to monitor change over time. The reliability tests are still ongoing and so far the tested graphene enhanced TIMs have stable performance over time with some observable trends for the different tests. At the current test time the maximum degradation in thermal resistance is 13%, measured after 511 cycles in the thermal cycling test. The used test method is deemed promising for reliability comparison and future requirement standardization on thermal pads.
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| 4. |
- Guo, Sihua, et al.
(author)
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Toward ultrahigh thermal conductivity graphene films
- 2023
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In: 2D Materials. - : IOP Publishing. - 2053-1583. ; 10:1
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Journal article (peer-reviewed)abstract
- With increasing demands of high-performance and functionality, electronics devices generate a great amount of heat. Thus, efficient heat dissipation is crucially needed. Owing to its extremely good thermal conductivity, graphene is an interesting candidate for this purpose. In this paper, a two-step temperature-annealing process to fabricate ultrahigh thermal conductive graphene assembled films (GFs) is proposed. The thermal conductivity of the obtained GFs was as high as 3826 +/- 47 W m(-1) K-1. Extending the time of high-temperature annealing significantly improved the thermal performance of the GF. Structural analyses confirmed that the high thermal conductivity is caused by the large grain size, defect-free stacking, and high flatness, which are beneficial for phonon transmission in the carbon lattice. The turbostratic stacking degree decreased with increasing heat treatment time. However, the increase in the grain size after long heat treatment had a more pronounced effect on the phonon transfer of the GF than that of turbostratic stacking. The developed GFs show great potential for efficient thermal management in electronics devices.
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