Heinz Herwig Institute of Thermo-Fluid Dynamics, Harnburg University of Technology, Denickestraße 17, Harnburg 21073, Germany e-mail: h
[email protected]
High Heat Flux Cooling of Electronics: The Need for a Paradigm Shift In a discussion initiated by the German Research Faundarion (DFG) about cooling of electronics, two aspects turned out tobe important: The need for a paradigm shift from an "add on" to an "integrated multidisciplinary" solution and the definition of generic demonstrators for cooling strategies. [DOI: 10.1115/1.4024621] Keywords: paradigm shift, generic demonstrator, cooling strategy \
1 Introduction Sponsored by the German Research Foundation DFG (Deutsche Forschungsgemeinschaft) there recently was a discussion within an interdisciplinary group of scientists about the future perspectives of research with respect to the problern of cooling electronic devices. Some of the crucial aspects of this discussion and the conclusions drawn will be reported here since they may be of general interest and can help to focus the further discussions about the best strategy. The starting point of the discussion was the statement that the problern of cooling electronic devices is all but new since it is on the agenda for more than 30 yr-and that due to this fact funding agencies, always keen on innovative and more or less spectacular topics, will never strongly support research in this area which often is characterized as development and research (D & R) instead ofR&D. Then, however, the discussion revealed that a new situation arises right now: The way the problern could be handled in the past is not appropriate for the future. The thermal management tums out to become the Iimiting factor in the future as far as the increase in e1ectronics performance is concemed. All this culminates in the need for a drastic change of handling those problems which was called the need for a paradigm shift.
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In recent years, the heat fluxes became so high, however, (with peak values of 103 W/cm2 ) and in the near future with 3D electronic system design, the volumetric density of heat tobe removed will become so high that these add-on solutions will no Ionger be appropriate and sufficient. As an alternative, an "integrated approach" needs to be developed which is characterized by • a thermal management that from the beginning is part of the design process for electronic parts and systems, • multidisciplinary with respect to the scientists involved in the design process (coming from physics, material sciences, thermodynamics, fluid mechanics, ...), • physical/technical solutions that cope with the electrica1 and thermal challenges alike, as for example electrically and thermally conducting materials. Even if this integrated approach is not yet developed sufticiently (for some ideas, see Ref. [6], for example) the need for it and the need to replace the conventional add-on approach is beyond all questions. It should be discussed whenever new strategies are developed with respect to High Heat Flux Cooling of electronics [7 ,8]. Also, it clearly is a research topic again since fundamentally new questions arise when electrical and thermal processes are to be treated simultaneously instead of consecutively.
The Paradigm Shift
For the last two or three decades thermal management of electronic devices was an "add on"-problem: devices were developed and improved according to criteria related to their electronic performance and then, afterward, the problern of "heat removal" was addressed, however, with always increasing demand in performance with respect to the heat transfer solutions. On that way high performance and phase-change solutions appeared [1-4] and even water as cooling fluid is accepted nowadays [5]. All these solutions, however, still follow the general philosophy of an "add on"solution, i.e., there is a thermal problern that has to be solved after the electronic parts and systems have been designed. These conventional solutions are characterized by an "inner" and an "outer" heat transfer in the following sense, see also Fig. 1:
3 Challenge for an Integrated Approach: Two Generic Demonstrators A further outcome of the discussion about future strategies was that there should be a common Iist of demands with respect to the cooling technologies. This was rea1ized by defining so-called generic demonstrators which are models of typical racks with high heat Ioads. Figure 2 shows two such demonstrators which might be used as guidelines. Demonstrator I is achallenging set of technical demands for today and the near future. Once the trend that can be observed in the telecommunication applications today,
• Inner heat transfer: From the chip to the outer surface of the cap with a contact resistance CR1 mainly by heat conduction, • Outer heat transfer: With a contact resistance CR2 to the heat sink which serves as a spreader of heat and can include channels, rips, heat pipes, cold plates, etc. Contributed by the Heat Transfer Division of ASME for publication in the JouRNAL OF HEAT TRANSFER. Manuscript received June 28, 20 12; final manuscript received August 8, 20 13; published online September 23, 20 13. Assoc. Editor: Sujoy Kumar Saha.
Journal of Heat Transfer
outer heat transfer
Fig. 1 Conventional cooling strategy (add-on solution) for a chip as an example
Copyright © 2013 by ASME
NOVEMBER 2013, Vol. 135 I 111013-1
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