Appendix Alga775 Socket Heatsink Loading; Lga775 Socket Heatsink Considerations; Metric For Heatsink Preload For Atx/Uatx Designs Non-Compliant With Intel Reference Design; Heatsink Preload Requirement Limitations - Intel BX80571E7400 - Core 2 Duo 2.8 GHz Processor Manuallines

LGA775 Socket Heatsink Loading
Appendix A LGA775 Socket Heatsink
A.1

LGA775 Socket Heatsink Considerations

Heatsink clip load is traditionally used for:
• Mechanical performance in mechanical shock and vibration
⎯ Refer to Section 6.7.1 for the information on the structural design strategy for
the 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 (F
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.
A.2 Metric for Heatsink Preload for ATX/uATX
Designs Non-Compliant with Intel
Reference Design
A.3

Heatsink Preload Requirement Limitations

Heatsink preload by itself is not an appropriate metric for solder joint force across
various mechanical designs and does not take into account for example (not an
exhaustive list):
• Heatsink mounting hole span
• Heatsink clip/fastener assembly stiffness and creep
• Board stiffness and creep
• Board stiffness is modified by fixtures like backing plate, chassis attach, etc.
Thermal and Mechanical Design Guidelines
Loading
axial ) induced by the heatsink preload
®
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