Reference Thermal Solution

R

6.5.4.1Effect of Pressure on TIM Performance

As mechanical pressure increases on the TIM, the thermal resistance of the TIM decreases. This phenomenon is due to the decrease of the bond line thickness (BLT). BLT is the final settled thickness of the thermal interface material after installation of heatsink. The effect of pressure on the thermal resistance of the Honeywell* PCM45F TIM is shown in Table 6-1. The heatsink clip provides enough pressure for the TIM to achieve a thermal conductivity of 0.17 °C inch2/W.

Table 6-1 Honeywell PCM 45F TIM Performance as a Function of Attach Pressure

Pressure (psi)

Thermal Resistance (°C × in2)/W

 

 

5

0.049

 

 

10

0.046

 

 

20

0.045

 

 

30

0.044

 

 

Note: All measured at 50 °C.

6.5.5Heatsink Clip

The retention mechanism in this reference solution includes two different types of clips; one is ramp clip and the other is wire clip. Each end of the wire clip is attached to the ramp clip that in turn attaches to anchors to fasten the overall heatsink assembly to the motherboard. See Appendix B for a mechanical drawing of the clip.

6.5.6Clip Retention Anchors

For 955X Express chipset-based platforms that have very limited board space, a clip retention anchor has been developed to minimize the impact of clip retention on the board. It is based on a standard two-pin jumper and is soldered to the board like any common through-hole header. A new anchor design is available with 45° bent leads to increase the anchor attach reliability over time. See Appendix A for the part number and supplier information.

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Intel® 955X Express Chipset Thermal/Mechanical Design Guide