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CFA - Tours 2006
Acoustique
&
Techniques n° 45
onsumer demand for smaller products with more
functions, coupled with advances inmicroelectronic integration,
has driven the miniaturisation of electronic devices over the
past three decades. Thermal management has become a
critical issue in product design, however, due to increasing
power dissipation levels and decreasing space available for
cooling solutions. Components must be maintained below
temperatures (~100°C) which are critical for performance
and reliability. Heat is ultimately rejected to the ambient air
(~0-50°C), and it is customary to define thermal resistance
as a measure of heat transfer from source to sink. For heat
dissipation, Q (W), from a silicon junction at temperature, Tj
(°C), to ambient at temperature, Ta (°C), thermal resistance,
Rth, is defined as (1):
Power dissipation for microprocessors in contemporary server
applications is over 100W, and the design value of thermal
resistance is ~0.1°C/W. Most of today’s thermal management
solutions use air as the cooling medium, utilising heat sinks
and fans to overcome the high thermal resistances associated
with convective heat transfer. Cooling solutions must also be
capable of removing very high heat fluxes – at component
level, heat flux is now over 50 W/cm2 – and this is on the limit
of conventional air cooling. Although there has been recent
discussion about extending the performance of air cooling –
Rodgers et al [1], in particular – it is clear that the adaptation of
liquid cooling is imminent for many high power applications due
to increasing heat flux levels at die, package and substrate.
The theme of this paper is the emerging thermal management
techniques which act directly at the location of power
generation within electronic systems. These so-called point-
of-source technologies can be categorised in contrast with
conventional forced convection cooling schemes – see figure
1 – which predominantly achieve local energy removal using
heat sinks, utilising system-level airflow as the medium for
heat transfer.
Summary
This paper addresses a range of emerging cooling technologies for electronic systems
which are deployed at the location of power generation – in contrast with conventional
forced convection schemes which predominantly involve heat sinks cooled using fans.
A set of these ‘point-of-source’ technologies are outlined, ranging from small-scale
air movers and microchannel coolers, to heat pipes and thermoacoustic engines.
Recent research at the author’s Institute into two point-of-source thermal management
solutions is reviewed: micro fans; and microchannel coolers. Energy aspects of
point-of-source cooling technologies are considered, with specific reference to the
opportunities for efficient cooling schemes associated with low thermal resistance
paths from source to sink. Finally, three challenges in thermal management for the
acoustics community are outlined: noise minimisation; simulation; and the application
of thermoacoustic phenomena.
Résumé
Cet article présente une toute nouvelle gamme de technologies de refroidissement
pour systèmes électroniques dont l’utilisation s’effectue directement à la source
électrique – contrairement aux agencements conventionnels de type convection
forcée qui impliquent principalement des radiateurs refroidis à l’aide de ventilateurs.
Un ensemble de ces technologies de «point-de-source» sont décrits, depuis de petits
moteurs à air et refroidisseurs basés sur l’utilisation de micro-canaux, jusqu’aux
caloducs et autres moteurs thermo-acoustiques. De récentes recherches portant sur
deux solutions de gestion thermique de «point de source» et développées au Stokes
Institute sont passées en revue : les micro-ventilateurs et les refroidisseurs utilisant
de micro canaux. L’aspect énergétique de ces technologies de refroidissement «point
de source» est considéré, avec une référence particulière sur la possibilité d’obtenir
des refroidisseurs efficaces associés à de faibles résistances thermiques entre
source et drain. Enfin, trois défis dans la gestion thermique pour la communauté
acoustique sont décrits: minimisation de bruit; simulations; et application des
phénomènes thermo-acoustiques.
Jeff Punch
CTVR
Stokes Institute
University of Limerick
Limerick
IRLANDE
Tel. : +353 61 213004
Fax : +353 61 202393
E-mail : jeff.punch@ul.ie
Thermal Management of Electronic Systems :
Emerging Technologies and Acoustic Challenges
Gestion thermique des systèmes électroniques :
Technologies naissantes et défis acoustiques
C