A.2.5.1 Motherboard Stiffening Considerations; Heatsink Selection Guidelines; Motherboard Stiffening Considerations - Intel QX9770 - Core 2 Extreme Quad-Core Processor Design Manual

A.2.5.1

Motherboard Stiffening Considerations

To protect LGA775 socket solder joint, designers need to drive their mechanical design
to:
• Allow downward board deflection to put the socket balls in a desirable force state
to protect against fatigue failure of socket solder joint (refer to sections A.2.1,
A.2.2, and A.2.3.)
• Prevent board upward bending during mechanical shock event
• Define load paths that keep the dynamic load applied to the package within
specifications published in the processor datasheet
Limiting board deflection may be appropriate in some situations like:
• Board bending during shock
• Board creep with high heatsink preload
However, the load required to meet the board deflection recommendation (refer to
Section A.2.3) with a very stiff board may lead to heatsink preloads exceeding
package maximum load specification. For example, such a situation may occur when
using a backing plate that is flush with the board in the socket area, and prevents the
board to bend underneath the socket.
A.3

Heatsink Selection Guidelines

Evaluate carefully heatsinks coming with motherboard stiffening devices (like backing
plates), and conduct board deflection assessments based on the board deflection
metric.
Solutions derived from the reference design comply with the reference heatsink
preload, for example:
• The Intel ALCT reference design available from licensed suppliers (refer to
Appendix H for contact information)
68
LGA775 Socket Heatsink Loading
§
Thermal and Mechanical Design Guidelines