Recent Research in Thermal Interface Materials
1.Highly Thermal Conductive Copper Nanowire Composites with Ultra low Loading: Toward Applications as Thermal Interface Materials
Thermal interface materials (TIMs) are of ever-rising importance with the development of modern microelectronic devices. However, traditional TIMs exhibit low thermal conductivity even at high loading fractions. The use of high-aspect-ratio material is beneficial to achieve low percolation threshold for nanocomposites. In this work, single crystalline copper nanowires with large aspect ratio were used as filling materials for the first time. A thermal conductivity of 2.46 W/mK was obtained at an ultralow loading fraction, ∼0.9 vol %, which was enhanced by 1350% compared with plain matrix. Such an excellent performance makes copper nanowires attractive fillers for high-performance TIMs.
2.Application of graphene as filler to improve thermal transport property of epoxy resin for thermal interface materials
Thermal interface materials (TIMs) play an important role in the electronic components area due to the continued miniaturization and lightweight. As a novel material with a thermal conductivity as high as ∼5000 W m−1 K−1, graphene is regarded as a promising filler to improve the thermal performance of the TIMs. In this study, graphene prepared by varied approaches are employed as filler to modified epoxy resin. All the resulting TIMs not only show excellent thermal conductivity under room temperature (the maximum value reaches 4.9 W m−1 K−1 with 30 wt% loading, thermal conductivity enhancement factor is up to 1900%), but also demonstrate great stability at high temperature. Experimental and calculated results manifest a strong coupling of phonon modes between graphene and the matrix.
The influences from graphene on thermal conductivity of composites are discussed. Larger size graphene sheets and surface functional groups would further reduce the Kapitza thermal resistance between the interfaces of graphene and epoxy resin. Moreover, the tested mechanical properties demonstrate that adding of graphene does not influence the outstanding mechanical performance of the matrix.
3.Metallic thermal interface material testing and selection for IC, power, and RF semiconductors
Thermal interface materials (TIM) are integral for adequate heat transfer from a semiconductor source to an external environment. Specialized TIM materials can be characterized as “well-performing” when measured against challenging requirements for critical applications. A range of metallic thermal interface materials have been developed and described, for specialized applications requiring performance and reliability in challenging conditions. Selection of a specialized TIM must be considered against a range of specific application requirements, as described.
4.Thermal-mechanical Co-design of Cold Plate, Second Level Thermal Interface Material (TIM2) and Heat Spreaders for Optimal Thermal Performance for High-end Processor Cooling
Cooling high-end system processors has become increasingly more challenging due to the increase in both total power and peak power density in processor cores. Junction peak temperature at worst case corner conditions often establish the limits on the maximum supportable circuit speed as well as processor chip yield. While significant progress has been made in cooling technology (e.g., cold plate design and thermal interface materials at first and the second level package), a systematic approach is needed to optimize the entire thermal and mechanical stack to achieve the overall (optimal) thermal performance objectives. The necessity and importance of this is due to the thermal and mechanical design interdependencies contained with the overall stack. This paper reports an in-depth study of the thermal-mechanical interactions associated with the cold plate, second level thermal interface material (TIM2) and heat spreaders.
Thermal test results are reported for different cold plate designs and TIM2 pad sizes. Thermal and mechanical modeling results are provided to quantify the TIM2 thermal performance as a function of the TIM2 mechanical stress, the TIM2 dimensions and cold plate design. As described via both modeling and testing results, an optimal TIM2 pad size results as a trade-off between heat transfer area for conduction and TIM2 compressive pressure. In addition, pressure sensitive film study results are also provided revealing that heat spreader design affects the module level and TIM2 thermal performance. Results from this set of work clearly demonstrate the close interactions between cooling hardware in the stack hence the importance of thermal-mechanical co-design to achieve optimal thermal performance for the high-end processors.