Guidelines

Intel
®
7500 Chipset Thermal Mechanical Design Guide 29
Reference Thermal Solution
6.5.4.1 Effect 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 PCM45 F
TIM is shown in Table 6-2.
Intel provides both End of Line and End of Life TIM thermal resistance values of
Honeywell PCM45F. End of Line and End of Life TIM thermal resistance values are
obtained through measurement on a Test Vehicle similar to Boxboro’s physical
attributes using an extruded aluminum heatsink. The End of Line value represents the
TIM performance post heatsink assembly while the End of Life value is the predicted
TIM performance when the product and TIM reaches the end of its life. The heatsink
clip provides enough pressure for the TIM to achieve End of Line thermal resistance of
0.19°C cm
2
/W and End of Life thermal resistance of 0.39°C cm
2
/W.
6.5.5 Heatsink Clip
The reference solution uses a wire clip with hooked ends. The hooks attach to wire
anchors to fasten the clip to the board. See Appendix B for a mechanical drawing of the
clip.
Table 6-2. Honeywell PCM45 F* TIM Performance as a Function of Attach Pressure
Pressure on Thermal solution
and package interface (PSI)
Thermal Resistance (°C × cm
2
)/W
End of Line(Mean+2.3Sigma) End of Life(Mean+2.3Sigma)
40 0.19 0.39
Table 6-3. Target load for Intel 7500 Chipset Heatsink Spring Clip Design
Minimum load(lbf) Maximum load(lbf)
9 15