[EEPN In Electronic Design]
For More Efficient Cooling, Try Splayed Pin-Fin Heatsinks
Barry Dagan
ED Online ID #18391
March 27, 2008
Copyright © 2006 Penton Media, Inc., All rights reserved.
Printing of this document is for personal use only.
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The immense processing power generated by
today’s cutting-edge ICs enables engineers to
design extremely powerful applications. Unfortunately,
the higher processing power comes
with a dramatic increase in the magnitude of heat dissipation
that makes heatsink selection a very complex task.
Splayed pin-fin heatsinks consist of a base and an array of
embedded round pins splayed outwards (Fig. 1). Forged from
aluminum or copper, they range in size from 0.27 by 0.27 in.
to 2 by 2 in. and in heights from 0.3 to 1.1 in.
Splayed pin fins are derivatives of traditional
pin-fin heatsinks
that contain an array
of vertical round
pins (Fig. 2).
Traditional
pin fins generate
substantial cooling
power and
are widely used in
a variety of applications
requiring considerable
cooling power. Pin fins use
round pins, which boost
the cooling power generated by a heatsink by improving air
turbulence inside the pin array and providing lower resistance
to incoming airstreams.
Compared to traditional pin fins, splayed pin fins generate
superior cooling power in limited-airspeed environments as
well as lower pressure drop in any given airspeed environment.
In limited-airspeed environments, splayed pin fins offer up
to a 20% cooling premium over traditional pin fins and significantly
larger cooling premiums over most other existing
heatsink technologies.
The performance premiums offered by splayed pin fins
come from the unique splay structure that produces larger
distances between the pins while preserving large surface areas.
The larger spacing enables airstreams to enter and exit the pin
array more efficiently.
From a cooling perspective, the large surface area of the
heatsink is exposed to a large air volume and therefore able to
provide more effective cooling. From a pressure-drop perspective,
the wider spacing enables more air to exit the pin array,
reducing pressure drop.
LOW-AIRSPEED COOLING
The challenge of cooling devices in low-airspeed environments
stems from the fact that slow-moving air cannot penetrate the fin arrays on most standard heatsinks. To ensure that surrounding
airspeeds do penetrate through fin arrays, designers
have traditionally opted to use sparsely configured heatsinks.
Although they generally perform better than standard heatsinks,
their cooling ability depends on their surface area.
Placing a splayed pin-fin heatsink in a low-airspeed environment
generates a substantial cooling premium. Its structure
features considerable spacing between the pins, which reduces
the resistance to incoming air and allows air to flush through
the pin array. At the same time, splayed pin fins still possess a
large surface area.
COOLING HEAVILY POPULATED BOARDS
The heatsink selection process for boards hosting a large number
of devices is tedious. Designers not only must consider the
performance of a given heatsink but also must ensure that surrounding
airstreams are efficiently allocated across the board.
Splayed pin fins provide a significant premium for densely
populated applications. In addition
to substantial cooling power for
individual devices, they also exhibit
low pressure-drop characteristics
that allow more air to
flush through
their pin arrays,
leaving stronger
airflows for other
devices that reside
on the board.
In other words,
devices residing downstream
from the sources
will receive stronger airflow. The larger the
number of heatsinks that reside on the board, the more significant
the impact of the splayed technology will be.
EXTREME COOLING NEEDS
Devices dissipating heavy thermal loads require additional
cooling power, usually in the form of a heatsink much larger
than the device it cools. Splayed copper pin fins are highly recommended
as an alternative for such extreme applications.
Copper enables quick and efficient spreading of the heat
along the heatsink’s base, eliminating local hot spots. The added
value generated by a splayed copper heatsink can be as high
as 35% over a traditional pin-fin heatsink of the same size.
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