Intel E6750 Design Guidelines - Page 21

Processor Thermal/Mechanical Information 2.3 TCONTROL will dissipate more power than a part with lower value (farther from 0, e.g., more negative number) of TCONTROL when running the same application. This is achieved in part by using the CA vs. RPM and RPM vs. Acoustics (dBA) performance curves from the Intel enabled thermal solution. A thermal solution designed to meet the thermal profile would be expected to provide similar acoustic performance of different parts with potentially different TCONTROL values. The value for TCONTROL is calculated by the system BIOS based on values read from a factory configured processor register. The result can be used to program a fan speed control component. See the appropriate processor datasheet for further details on reading the register and calculating TCONTROL. See Chapter 7, Intel® Quiet System Technology (Intel® QST), for details on implementing a design using TCONTROL and the Thermal Profile. Heatsink Design Considerations To remove the heat from the processor, three basic parameters should be considered: The area of the surface on which the heat transfer takes place. Without any enhancements, this is the surface of the processor package IHS. One method used to improve thermal performance is by attaching a heatsink to the IHS. A heatsink can increase the effective heat transfer surface area by conducting heat out of the IHS and into the surrounding air through fins attached to the heatsink base. The conduction path from the heat source to the heatsink fins. Providing a direct conduction path from the heat source to the heatsink fins and selecting materials with higher thermal conductivity typically improves heatsink performance. The length, thickness, and conductivity of the conduction path from the heat source to the fins directly impact the thermal performance of the heatsink. In particular, the quality of the contact between the package IHS and the heatsink base has a higher impact on the overall thermal solution performance as processor cooling requirements become stricter. Thermal interface material (TIM) is used to fill in the gap between the IHS and the bottom surface of the heatsink, and thereby improve the overall performance of the stack-up (IHS-TIMHeatsink). With extremely poor heatsink interface flatness or roughness, TIM may not adequately fill the gap. The TIM thermal performance depends on its thermal conductivity as well as the pressure applied to it. Refer to Section 2.3.4 and Appendix C for further information on TIM and on bond line management between the IHS and the heatsink base. The heat transfer conditions on the surface on which heat transfer takes place. Convective heat transfer occurs between the airflow and the surface exposed to the flow. It is characterized by the local ambient temperature of the air, TA, and the local air velocity over the surface. The higher the air velocity over the surface, and the cooler the air, the more efficient is the resulting cooling. The nature of the airflow can also enhance heat transfer using convection. Turbulent flow can provide improvement over laminar flow. In the case of a heatsink, the surface exposed to the flow includes in particular the fin faces and the heatsink base. Active heatsinks typically incorporate a fan that helps manage the airflow through the heatsink. Thermal and Mechanical Design Guidelines 21