A week ago, Microsoft adjusted
its warranty policy on the Xbox 360 to cover general hardware failure signaled
by the E74 error message.
The Xbox 360 has been a huge success since its launch in
2005, notching sales of more than 28 million worldwide, but there have been
thermal management problems with the high-tech gaming device. In the course of developing
new technology to dissipate heat from microprocessors, Microsoft was awarded
two U.S.
patents.
The power in the Xbox 360 was more than doubled from the
original Xbox, going from under 100 to more than 200W, and several other
important features were added, including an online capability. The box is
smaller, and had to be cost competitive. The Xbox mechanical engineering team
took steps to deal with thermal management, but overheating and reliability
problems dogged some of the models.
The original engineering of the Xbox 360 was coordinated by
Jeff Reents, the lead mechanical engineer. In an interview called "Xbox 360:
The Guts," posted on the xbox.com Web site, Reents provides insight into how
thermal issues were attacked.
"We
originally wanted to put in a single 80-mm fan. But we couldn't fit it in the
final form factor chassis," said Reents. "We couldn't just go with one 60-mm
fan because it would not provide the required cooling - as the diameter of the
fan increases the air flow performance per revolution increases exponentially.
So we ended up putting in two 60-mm fans, and we came up with a water-cooled heat
sink, as well, for the CPU."
The
heat sink includes a copper base, aluminum-stamped fins and a copper heat pipe,
which contains water. A vacuum is pulled on the pipe prior to sealing. Water boils
faster under a vacuum. The steam rises and moves the heat higher into the fins
where the air flow from the fans can extract the heat more efficiently. The
steam condenses and flows back to the copper base of the heat sink, which is
attached to the processor.
Copper
and other conductive materials have replaced aluminum as the material of choice
for heat sinks.
The
required cooling capacity of the Xbox 360 is determined by system electronics. Fans
cool the unit, but can be noisy. "We use thermal sensing diodes in the main ICs
(GPU and CPU) and thermal algorithm firmware that reads the diode temperatures
and adjust the fan RPMs by altering the fan voltage to a predetermined minimum
requirement that minimizes the fan speed (minimizes the acoustics) while
providing the required cooling capacity for the system," says Reents.
There
have been significant revisions to the Xbox 360 since its release. They include
the mundane,
such as surrounding the CPU and GPU with epoxy to prevent board movement during
heat expansion. More importantly, a second heat sink was added.
Two Patents issued
Microsoft and Reents have been issued two patents on new
thermal management concepts for electronics devices since engineering work
began on the Xbox 360.
A patent
was awarded last December for an integrated heat sink that provides efficient
transfer of heat from a non-planar surface. In an example, one of the heat
sinks is compressively coupled to an integrated circuit via an integral spring
assembly. The spring assembly pushes one of the heat sinks against one of the
integrated circuits while allowing the other heat sink to remain positioned
against the other integrated circuit. The integrated heat sink compensates for
variations in circuit height, which occur due to manufacturing tolerance
issues.
In 2006, Microsoft was awarded a patent
for Reents' invention of a system in which a heat sink is mounted to a processor
using a spring fastener. It's an interesting way to boost heat release from the
processor.
A plastic clip had typically been used to provide a tight
connection of the heat sink to the processor. As a result, a poor conducting
material (plastic) is placed over the hottest section of the heat sink. Use of
a metal fastener would prevent the use of fins across a portion of the surface
of the heat sink.
Reents' design goal was to develop a heat sink mounting
system that could avoid placing excessive forces on the PCB, while still
allowing the heat sink to tightly press against the CPU.
In Reents' invention, the spring element includes a thrust
plate made of an insulating material located between the spring element and the
PCB and presses on the bottom of the PCB to create a force that keeps the CPU
and the heat sink together.
It's not known to what extent the invention was used in the Xbox
360 because Microsoft turned down an interview request from Design News. "It is our policy not to
discuss specific details of internal components or manufacturing processes,"
said Jeremy Bartram, a company spokesman.
The Xbox 360 is available in three models: the "Arcade," the "Premium" and the
"Elite" console, each with its own accessories. The central
processing unit (CPU) is a 3.2-GHz PowerPC Tri-Core Xenon.
The majority of the heat problem in electronics, such as the
Xbox 360, is caused by the electrical leakage of the transistors that make up a
CPU. Efforts to reduce the heat output of CPUs have been mostly unsuccessful
because the number of transistors on a CPU increased from about 6,000
transistors on an Intel.RTM.8080 in 1974 to more than 50 million resistors on
CPUs in recent years.
The maximum die temperature for a silicon-based CPU is around
90C. Temperatures that high, however, will cause a short operating life.
Reents was one of the original dozen Microsoft employees
recruited by Todd
Holmdahl to work on the first Xbox.
Holmdahl is corporate vice president of the Gaming and Xbox Product Group at
Microsoft Corp., and is responsible for the design, engineering, testing and
manufacturing of all Xbox consoles worldwide.
Other Design News stories on the Xbox 360:
"Learning
from Failure" by Dean Takahashi
"Software-Defined
Instrumentation" by Kevin Bisking
Tweet This
0 
