Intel QX9770 Design Guidelines - Page 63
Appendix A, LGA775 Socket Heatsink, Loading, LGA775 Socket Heatsink Considerations
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LGA775 Socket Heatsink Loading Appendix A LGA775 Socket Heatsink Loading A.1 LGA775 Socket Heatsink Considerations Heatsink clip load is traditionally used for: • Mechanical performance in mechanical shock and vibration ⎯ Refer to Section 5.6 above for information on the structural design strategy for the Intel ALCT Reference Design • Thermal interface performance ⎯ Required preload depends on TIM ⎯ Preload can be low for thermal grease In addition to mechanical performance in shock and vibration and TIM performance, LGA775 socket requires a minimum heatsink preload to protect against fatigue failure of socket solder joints. Solder ball tensile stress is originally created when, after inserting a processor into the socket, the LGA775 socket load plate is actuated. In addition, solder joint shear stress is caused by coefficient of thermal expansion (CTE) mismatch induced shear loading. The solder joint compressive axial force (Faxial) induced by the heatsink preload helps to reduce the combined joint tensile and shear stress. Overall, the heatsink required preload is the minimum preload needed to meet all of the above requirements: Mechanical shock and vibration and TIM performance AND LGA775 socket protection against fatigue failure. Thermal and Mechanical Design Guidelines 63