Electronics Protection - Summer 2014 - (Page 14)
How Thermal Ground Plane and Compact Air-Cooled
Heat Sinks are Revolutionizing Thermal Management
Nelson J. Gernert, Vice President, Engineering and Technology
Electronic devices used in military and aerospace equipment
are subject to temperatures ranging from -40°C to 100°C and in
radar applications, even as high as 150°C. These temperatures
tend to drift higher as designers increase device density by putting more processing power inside a smaller package. As a result,
device designers are looking for advanced, cost-effective thermal
management and heat rejection technologies that can improve
performance while reducing size and weight.
Two recently developed technologies, a planar, two-phase heat
pipe known as a Thermal Ground Plane (TGP) and compact, high
performance air-cooled heat sink, that can be combined in a
compact assembly to overcome the constraints encountered with
conventional thermal management methods.
Designing New Devices for More Power and Control
Increases in power and control have revolutionized the level of
performance obtainable in semiconductor devices such as amplifiers, lasers, microprocessors, graphics processors, thyristors, insulated gate bipolar transistors (IGBTs), symmetric gate commutated
turnoff thyristors, silicon controlled rectifiers (SCRs) and intelligent power modules (IPMs). But the most demanding arena for
designers in modern electronics is the world of military applications, where electronics must not only operate flawlessly in harsh
environments, but also meet demanding size, weight and power
(SWaP) constraints in current and future generation equipment.
For example, naval onboard power conversion systems and
aerospace power electronics offer a variety of harsh thermal and
environmental challenges: rugged environments involving exposure to salt water, heavy weather, extreme temperatures and
vibration; extremely high power loads (sometimes in excess of
3,000 W) and high heat fluxes due to concentrations of electronic
components. The technical challenge, however, is that increases
in power and decreases in size also require designers to deal with
tremendous increases in heat generation and heat fluxes, all within
the context of smaller and smaller areas for thermal solutions.
Thus, the combination of smaller footprint (thanks to increased
miniaturization) and greater power makes life much more difficult
for thermal engineers who need to develop solutions that protect
the life and performance of these high-performance devices.
Of course, the challenge of increased heat loads doesn't involve
just the amount of space available for thermal solutions. The configuration and the location of powerful electronics systems also
are factors that make solutions more difficult.
As a result, design engineers need to consider the following
thermal solution constraints:
Limited space availability due to packaging and other space
competing electronic components nearby
Operation in oddly shaped or situated spaces
Near maintenance-free operation
Thermal solutions that operate independently of gravity
Resistance to shock & vibration and environmental corrosion
Avoiding drawbacks associated with liquid-based cooling
(pipes, storage of chemicals, short circuit potential, ongoing or continuous maintenance is required, high cost, etc.)
Summer 2014 * www.ElectronicsProtectionMagazine.com
Conventional Materials Face Thermal
Cooling of electronics has traditionally been performed using
air-cooled (forced or natural convection) metallic conductors in
the form of extruded heat sinks and heat spreaders. Typically,
aluminum or copper extrusions are bonded to the electronics case
and air is blown over the extrusion using a fan or blower.
Passive two-phase heat transfer devices such as heat pipes are
another thermal management technology often used in military
and aerospace applications because of their thermal efficiency,
simplicity and reliability. Heat pipes employ three components: a
vacuum-tight containment shell or vessel, a working fluid, and a
capillary sintered-powder metal wick structure. Without moving
parts, the wick generates a capillary action that circulates a heated
liquid from the evaporator side to the condenser side of the heat
pipe where heat is ejected. Although heat pipes provide effective heat removal over long distances and are bendable, flexible,
and withstand high-g conditions, shock/vibration and freeze/thaw
cycles, conventional heat pipes also have thermal transport and
Another challenge for conventional heat pipes is harmonizing
the CTE between the heat source material and the heat sink material. If there are disparities in CTE between materials, then temperature changes will cause the devices to expand and contract,
which create mechanical stresses on the interface bond that will
eventually induce thermal failure. Using a solid conductor at the
interface, like diamond, can improve thermal conductivity and CTE
matching, but it is very expensive.
Another cooling challenge for heat sinks is achieving adequate
air side heat transfer directly at the electronic component level.
Factors that limit the effectiveness of air as a cooling medium include: lack of available volume for the heat sink, required surface
area is too high and the pressure drop is too large.
The alternative to air cooling is a pumped-liquid or refrigerantbased cooling system. This solution creates its own set of challenges by adding complexity, weight and the potential for failure, a
major issue where heat sink maintenance is difficult or impossible.
Adding components such as pumps, compressors, nozzles and
other components can also significantly increase cost.
TGP and Compact Air-Cooled Heat Sinks: Extending
The Benefits of Passive Thermal Technology
To overcome these challenges,
a new form of heat pipe, known
as a Thermal Ground Plane (TGP),
was developed employing a planar
The heat-pipe TGP, uses the
same reliable components and
sintered powder metal wick struc- Figure 1. Thermal Ground Plane A planar heat pipe in 30 by 30 by
ture of a regular heat pipe. It is a
3 mm thick dimensions.
passive heat transfer device using
a two-phase cooling approach. But
instead of a cylindrical shape, the form is a thin, planar structure
known as a vapor chamber, sometimes referred to as a flat heat
pipe, that makes an ideal substrate for mounting electronic de-
Table of Contents for the Digital Edition of Electronics Protection - Summer 2014
New High Efficiency LED Technology Benefits From Best Practice Thermal Management Design
Passive Thermal Management of Lithium-ion Batteries Using Phase Change Materials
Considerations for Powering Military Applications
How Thermal Ground Plane and Compact Air-Cooled Heat Sinks are Revolutionizing Thermal Management
Access Control Solutions for Railway Infrastructure
20 Data Center Downtime Study Puts Focus on Maximum Protection
Cooling and Shielding in the Right-Sized Enclosure
Calendar of Events
Electronics Protection - Summer 2014