Intel QX9770 Design Guidelines - Page 67

LGA775 Socket Heatsink Loading Figure 27. Example: Defining Heatsink Preload Meeting Board Deflection Limit A.2.5 Additional Considerations Intel recommends to design to {d_BOL - d_ref = 0.15 mm} at BOL when EOL conditions are not known or difficult to assess The following information is given for illustration only. It is based on the reference keep-out, assuming there is no fixture that changes board stiffness: d_ref is expected to be 0.18 mm on average, and be as high as 0.22 mm As a result, the board should be able to deflect 0.37 mm minimum at BOL Additional deflection as high as 0.09 mm may be necessary to account for additional creep effects impacting the board/clip assembly. As a result, designs could see as much as 0.50mm total downward board deflection under the socket. In addition to board deflection, other elements need to be considered to define the space needed for the downward board total displacement under load, like the potential interference of through-hole mount component pin tails of the board with a mechanical fixture on the back of the board. NOTES: 1. The heatsink preload must remain below the maximum load limit of the package at all times (Refer to processor datasheet) 2. Board deflection should not exceed motherboard manufacturer specifications. Thermal and Mechanical Design Guidelines 67