Intel 740, Design Manual

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Application Note 653
19
Intel740™ Graphics Accelerator Thermal Design Considerations
5.0 Measurements for Thermal Specifications
To appropriately determine the thermal properties of the system, measurements must be made.
Guidelines have been established for the proper techniques to be used when measuring the Intel740
graphics accelerator case temperatures.
Section 5.1, “Case Temperature Measurements” on
page 19 provides guidelines on how to accurately measure the case temperature of the Intel740
graphics accelerator. Section 5.2, “Power Simulation Software” on page 20 contains information
on running an application program which will emulate anticipated thermal design power. The
flowchart in
Figure 12 as well as Section 4.2, “Thermal Enhancements” on page 10 offer useful
guidelines for performance and evaluation.
5.1 Case Temperature Measurements
To ensure functionality and reliability, the Intel740 graphics accelerator is specified for proper
operation when T
case
(case temperature) is maintained at or below the maximum case temperatures
listed in Table 1 . The surface temperature of the case in the geometric center of the mold cap is
measured. Special care is required when measuring the T
case
temperature to ensure an accurate
temperature measurement.
Thermocouples are often used to measure T
case
. Before any temperature measurements are made,
the thermocouples must be calibrated.
When measuring the temperature of a surface which is at a different temperature from the
surrounding local ambient air, errors could be introduced in the measurements. The measurement
errors could be due to having a poor thermal contact between the thermocouple junction and the
surface of the package, heat loss by radiation, convection, by conduction through thermocouple
leads, or by contact between the thermocouple cement and the heat-sink base for those solutions
which implement a heat-sink. To minimize these measurement errors, the following approach is
recommended:
Attaching the Thermocouple
•
Use 36 gauge or smaller diameter K type thermocouples.
•
Ensure that the thermocouple has been properly calibrated.
•
Attach the thermocouple bead or junction to the top surface of the package (case) in the center
of the mold-cap using high thermal conductivity cements. An alternative for tape attach users
is to use the tape itself to mount the thermocouple. It is Critical that the thermocouple be
intimately attached across the entire moldcap.
•
The thermocouple should be attached at a 0° angle if there is no interference with the
thermocouple attach location or leads (refer to
Figure 10 ). This is the preferred method and is
recommended for use with both unenhanced packages as well as packages employing Thermal
Enhancements.
•
For solutions where a heat-sink is preferred, the thermocouple should be attached at a 90°
angle if a heat sink is attached to the case and the heat sink covers the location specified for
T
case
measurement (refer to Figure 11 ).
•
The hole size through the heat sink base to route the thermocouple wires out should be smaller
than 0.150” in diameter.
•
Make sure there is no contact between the thermocouple cement and heat sink base. This
contact will affect the thermocouple reading.