Intel Pentium 4 Processor in the 478-Pin Package Thermal Design Guidelines

Intel

Pentium

4 Processor in the 478-Pin Package Thermal Design Guidelines

12 Design Guide

2.1.2 Heatsink Attach

There are no features on the mPGA478 socket to directly attach a heatsink: a mechanism must be

designed to support the heatsink. In addition to holding the heatsink into 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 used between the IHS and the

heatsink. Some of these materials are very sensitive to pressure applied to them, the higher the

pressure, the better the performance.

• Ensuring system electrical, thermal and structural integrity under shock and vibration events.

The mechanical requirements of the attach mechanism depend on the weight of the heatsink

and the level of shock and vibration that the system has to support. The overall structural

design of the motherboard and the system has to be considered as well when designing the

heatsink attach mechanism, in particular their impact on motherboard stiffening needed to

protect mPGA478 socket solder joint, and prevent package pull-out from the socket.

A popular solution for heatsink attach mechanism is to use a retention mechanism and attach clips.

In that case, the clips should be designed to the general guidelines given above, and more

specifically:

• To hold the heatsink in place under shock and vibration events and apply force to the heatsink

base to maintain desired pressure on the thermal interface material. The load applied by the

clip also plays a role in ensuring that the package does not disengage from the socket during

mechanical shock testing. Note that the load applied by the clips must comply with the

package specifications described section 2.1.1 along with the dynamic load added by the

shock and vibration requirements.

• To engage easily with the retention mechanism tabs, if possible without the use of special

tools. This should also take into account that, in general, heatsink and clip are installed once

the motherboard has been installed into the chassis.

• To minimize contact with the motherboard surface during clip attach to the retention

mechanism tab features; the clip should not scratch the motherboard.

The Intel Reference design for the Intel

Pentium

4 processor in the 478-pin package is using

such a retention mechanism and clip assembly. Refer to section 3.3 and the document Mechanical

Enabling for the Intel

Pentium

4 processor in the 478-Pin Package for further information

regarding the Intel Reference mechanical solution.