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predictions show that carbon nanotubes have extremely highthermal conductivity, these computations are mainly basedon CNTs with assumed perfect atomic structures, which arevery difficult to achieve by current technology. Theexperimental works reporting high measurement thermalconductivity values of CNT are normally performed usingshort and single CNTs. It’s reasonable that these values aremuch higher than those results measured for macro- scaleCNT films or composites. Moreover, the contact thermalresistances between nanotubes and other substances, e.g. thepolymer matrix in composites and the substrates above orbelow the aligned CNT films, are very high and cause thelow overall performance of the materials. Another maintechnical barrier is the high difficulty of achieving highfilling ratio and dense alignment of CNTs in the TIMs. In thecase of using CNTs as fillers of composites, it is hard toobtain good dispersion of CNTs and high filling ratio. In thecase of aligned CNT films, the gaps between nanotubes inthe films are indeed quite significant compared to theirdiameters, causing a rather low effective filling content.Besides the research works on carbon nanotube-basedthermal interface materials, some other novel approaches arealso worthwhile to mention. Namics develops a kind ofthermal conductive adhesive by adding nano particles toimprove the heat transfer, achieving the thermal conductivityas high as 7 W/mK. Btechcorp claims they successfullydeveloped a TIM consisting of very densely filled verticallyaligned carbon fibers with a dramatically high thermalconductivity of 750 W/mK [91]. At Chalmers University ofTechnology, a unique kind of TIM with micro- andTIMs with carbon-based fillers24-26 September 2008, Rome, Italynanofibers as reinforcement and solder alloys as fillers hasbeen invented, obtaining good thermal properties andpossibly low manufacturing cost and difficulty [92].Another important problem in this field is the difficulty toevaluate and compare the results from different sources.Many similar experiments produce far different results. It ispartly due to the different preparation methods of materials.A more important reason is probably that the materials aretested by many different methods. A variety ofimplementations can be applied even using the same methodor standard. A sound discussion about this issue can befound from Lasance’s papers [88, 89].VI. CONCLUSIONSHigh performance thermal interface materials are animportant necessity in the IT industry to enable the higherdensity integration of electronics systems and furtherdownscaling of components. This review summaries andanalyzed the current status of TIM research anddevelopment. It’s pointed out that the modification of thematerials at micro- to nano- scale is the key to achieve greatprogresses. The main technical barriers in materialdevelopment and difficulties in testing are also discussed.ACKNOWLEDGMENTThe work was partly financially supported by the SeventhFramework Program of the European Union (Project name:Nano Packaging Technology for Interconnection and HeatDissipation under the contract No: 216 176).TABLE 1 Summary of recent research works on thermal interface materialsReference Material Structure FabricationMethod[13] VA-MWNT Dendrimer-assistedPECVDTest Method Results NotesPA 8-18 Kmm 2 /W -[14] SWNT-epoxy, 1wt% - Comparative method k: 70%↑@40K,125%↑@RT-[15] SWNT-PMMA, 7% - Double guardedplatek: 55%↑ -[16] VA-MWNT-PDMS TCVD Laser flash 1.8-3.8 W/mK 2-4 times larger acrossthe alignment direction[17, 18] VA-MWNT PECVD ASTM D5470 25 Kmm 2 /W “lift-off” transfer of CNTfilm[19] VA-MWNT-Cu TCVD,Electroplating ofCu[20] A-SWNT-epoxy, 3 wt% Magnetic fieldprocessingASTM D5470 20 Kmm 2 /W In viasComparative method 4-6 W/mK -[21] MWNT-poly(α-olefin) oil, 1 vol% - Transient hot wire k: 150%↑ -[22] VA-SWNT/MWNT/CNF TCVD/PECVD - R: 60%↓ Comparative study of 5systems[23] VA-MWNT PECVD PA Si-CNT-Ag : 15.8Kmm 2 /WSi-CNT-CNT-Cu : 4.0-©EDA Publishing/THERMINIC 2008 158ISBN: 978-2-35500-008-9