Thermal Metrology
R
Intel
®
848P Chipset Thermal Design Guide
13
3 Thermal
Metrology
The system designer must measure temperatures to accurately determine the thermal performance of
the system. Intel has established guidelines for proper techniques of measuring chipset component
case temperatures.
3.1
Case Temperature Measurements
To ensure functionality and reliability, the MCH is specified for proper operation when T
C
is
maintained at or below the maximum temperature listed in Table 2. The surface temperature at the
geometric center of the die corresponds to T
C
. Measuring T
C
requires special care to ensure an
accurate temperature reading.
Temperature differences between the temperature of a surface and the surrounding local ambient air
can introduce errors in the measurements. The measurement errors could be due to a poor thermal
contact between the thermocouple junction and the surface of the package, heat loss by radiation
and/or convection, conduction through thermocouple leads, or contact between the thermocouple
cement and the heatsink base (if a heatsink is used). To minimize these measurement errors a
thermocouple attach with a zero-degree methodology is recommended.
Although the basic metrology is the same for a clip-attached heatsink and a Wave Solder Heatsink
(WSHS), the removal and replacement of the WSHS requires additional guidelines for accurate
thermal measurements. Refer to the WSHS rework procedure in Section 4.3.3 for guidelines on
installing a WSHS modified for a zero-degree attach. Physical modifications to a WSHS are
identical to modifications for a clip-attached heatsink. Sections 3.1.1 details the modifications
required to measure package case temperature using both clip-attached heatsinks and WSHS.
3.1.1
Thermocouple Attach Methodology
1. Mill a 3.3 mm [0.13 in] diameter hole centered on the bottom of the heatsink base. The milled
hole should be approximately 1.5 mm [0.06 in] deep.
2. Mill a 1.3 mm [0.05 in] wide slot, 0.5 mm [0.02 in] deep, from the centered hole to one edge of
the heatsink. The slot should be in the direction parallel to the heatsink fins (see Figure 3).
3. Attach thermal interface material (TIM) to the bottom of the heatsink base.
4. Cut out portions of the TIM to make room for the thermocouple wire and bead. The cutouts
should match the slot and hole milled into the heatsink base.
5. Attach a 36 gauge or smaller calibrated K-type thermocouple bead or junction to the center of
the top surface of the die using a high thermal conductivity cement. During this step, make sure
no contact is present between the thermocouple cement and the heatsink base because any
contact will affect the thermocouple reading.
It is critical that the thermocouple bead makes
contact with the die
6. Attach heatsink assembly to the MCH and route thermocouple wires out through the milled slot.
For the Wave Solder Heatsink, refer to Section 4.3.3 for guidelines on proper heatsink removal
and installation. Following the guidelines is critical to ensure an accurate and repeatable
metrology.
