10
Intel
®
Celeron
®
D Processor in the 775-Land LGA Package
Thermal Design Guide
Order #303730
Processor Thermal/Mechanical Information
The IHS also features a step that interfaces with the LGA775 socket load plate, as described in
LGA775 Socket Mechanical Design Guide. The load from the load plate is distributed across two
sides of the package onto a step on each side of the IHS. It is then distributed by the package across
all of the contacts. When correctly actuated, the top surface of the IHS is above the load plate
allowing proper installation of a heatsink on the top surface of the IHS. The post-actuated seating
plane of the package is flush with the seating plane of the socket. Package movement during socket
actuation is along the Z direction (perpendicular to substrate) only. Refer to the LGA775 Socket
Mechanical Design Guide for further information about the LGA775 socket.
The processor datasheet gives details on the IHS geometry and tolerances, and IHS material.
The processor package has mechanical load limits that are specified in the processor datasheet. The
specified maximum static and dynamic load limits should not be exceeded during their respective
stress conditions. These include heatsink installation, removal, mechanical stress testing, and
standard shipping conditions.
•
When a compressive static load is necessary to ensure thermal performance of the thermal
interface material (TIM) between the heatsink base and the IHS, it should not exceed the
corresponding specification given in the processor datasheet.
•
When a compressive static load is necessary to ensure mechanical performance, it should not
exceed the corresponding specification given in the processor datasheet.
•
The heatsink mass can also add additional dynamic compressive load to the package during a
mechanical shock event. Amplification factors due to the impact force during shock must be
taken into account in dynamic load calculations. The total combination of dynamic and static
compressive load should not exceed the processor datasheet compressive dynamic load
specification during a vertical shock. For example, with a 0.454 kg [1 lbm] heatsink, an
acceleration of 50G during an 11 ms trapezoidal shock with an amplification factor of 2 results
in approximately a 445 N [100 lbf] dynamic load on the processor package. If a 178 N [40 lbf]
static load is also applied on the heatsink for thermal performance of the TIM the processor
package could see up to a 623 N [140 lbf]. The calculation for the thermal solution of interest
should be compared to the processor datasheet specification.
No portion of the substrate should be used as a load-bearing surface.
Finally, the processor datasheet provides package handling guidelines in terms of maximum
recommended shear, tensile and torque loads for the processor IHS relative to a fixed substrate.
These recommendations should be followed in particular for heatsink removal operations.
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 support the heatsink. 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 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.
