Intel Pentium 4 Processor on 90 nm Process Thermal and Mechanical Design Guidelines

Intel® Thermal/Mechanical Reference Design Information
R
38 Intel
®
Pentium
®
4 on 90 nm Process Thermal Design Guide
4.1.1.2 Acoustics
To optimize acoustic emission by the fan heatsink assembly, it is recommended to develop a
solution with a variable speed fan. A variable speed fan allows higher thermal performance at
higher fan inlet temperatures (T
A
) and lower thermal performance with improved acoustics at
lower fan inlet temperatures. The required fan speed necessary to meet thermal specifications can
be controlled by the fan inlet temperature and should comply with requirements below:
1. Fan set points for a loadline A compliant solution:
• High set point: T
A
= 38 °C; Ψ
CA
= 0.34 °C/W (per Table 2 above)
• Low set point: T
A
= 28 °C; Ψ
CA
= 0.47 °C/W
Note: The temperature rise (T
R
) between external ambient (T
E
) and local ambient temperature (T
A
)
may be greater than 3 °C at the low set point.
2. Fan heatsink assembly acoustic performance:
• Acoustic performance is defined in term of declared sound power (LwAd) as defined in ISO
9296 standard, and measured according ISO 7779.
• LwAd should not exceed 5.7 BA at the high set point temperature.
• LwAd should not exceed 4.5 BA at the low set point temperature.
Note that any form of variable performance thermal solution that relies on the on-die thermal
diode must react fast enough to handle any sudden increases in processor workload. Refer to
Section 3.4.8.1 for more details.
4.1.1.3 Altitude
The reference heatsink solutions will be evaluated at sea level. However, many companies design
products that must function reliably at high altitude, typically 1500 m [5000 ft] or more. Air-
cooled temperature calculations and measurements at sea level must be adjusted to take into
account altitude effects like variation in air density and overall heat capacity. This often leads to
some degradation in thermal solution performance compared to what is obtained at sea level, with
lower fan performance and higher surface temperatures. The system designer needs to account for
altitude effects in the overall system thermal design to make sure that the T
C
requirement for the
processor is met at the targeted altitude.
4.1.1.4 Reference Heatsink Thermal Validation
The Intel reference heatsink is validated within specific boundary conditions based on the
methodology described Section 3.3, and using a thermal test vehicle.
Testing is done on bench top test boards at ambient lab temperature. In particular, for the
reference heatsink, the Plexiglas* barrier is installed 81 mm [3.2 in] above the motherboard (refer
to Section 3.3.2).
The test results, for a number of samples, are reported in terms of a worst-case mean + 3σ value
for thermal characterization parameter using real processors (based on the thermal test vehicle
correction factors).