Heatsink Attach; General Guidelines; Heatsink Clip Load Requirement - Intel EM64T - Celeron D 336 Boxed Ena User Manual

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2.1.2

Heatsink Attach

2.1.2.1

General Guidelines

There are no features on the LGA775 socket to directly attach a heatsink; a mechanism must be
designed to attach the heatsink directly to the motherboard. In addition to holding the heatsink in
place on top of the IHS, this mechanism plays a significant role in the robustness of the system in
which it is implemented, in particular:
• Ensuring thermal performance of the thermal interface material (TIM) applied between the
IHS and the heatsink. TIMs based on phase change materials are very sensitive to applied
pressure: the higher the pressure, the better the initial performance. TIMs (such as thermal
greases) are not as sensitive to applied pressure. Designs should consider a possible decrease
in applied pressure over time due to potential structural relaxation in retention components.
• Ensuring system electrical, thermal, and structural integrity under shock and vibration events.
The mechanical requirements of the heatsink attach mechanism depend on the mass of the
heatsink and the level of shock and vibration that the system must support. The overall
structural design of the motherboard and the system have to be considered when designing
the heatsink attach mechanism. Their design should provide a means for protecting LGA775
socket solder joints. One of the strategies for mechanical protection of the socket is to use a
preload and high stiffness clip. This strategy is implemented by the reference design and
described in Section 5.7.
Note: Package pull-out during mechanical shock and vibration is constrained by the LGA775 socket
load plate (refer to the LGA775 Socket Mechanical Design Guide for further information).
2.1.2.2

Heatsink Clip Load Requirement

The attach mechanism for the heatsink developed to support the Pentium 4 processor in the
775–land LGA package should create a static preload on the package between 18 lbf and 70 lbf
throughout the life of the product for designs compliant with the Intel reference design
assumptions:
• 72 mm x 72 mm mounting hole span (refer to Figure 45)
• And no board stiffening device (backing plate, chassis attach, etc.).
The minimum load is required to protect against fatigue failure of socket solder joint in
temperature cycling.
It is important to take into account potential load degradation from creep over time when
designing the clip and fastener to the required minimum load. This means that, depending on clip
stiffness, the initial preload at beginning of life of the product may be significantly higher than the
minimum preload that must be met throughout the life of the product. For additional guidelines on
mechanical design, in particular on designs departing from the reference design assumptions refer
to Appendix A.
For clip load metrology guidelines, refer to Appendix B.
Thermal/Mechanical Design Guide
Processor Thermal/Mechanical Information
17