LGA775 Socket Heatsink Loading
70 Thermal and Mechanical Design Guidelines
Simulation shows that the solder joint force (F
axial
) is proportional to the board
deflection measured along the socket diagonal. The matching of F
axial
required to
protect the LGA775 socket solder joint in temperature cycling is equivalent to
matching a target MB deflection.
Therefore, the heatsink preload for LGA775 socket solder joint protection against
fatigue failure can be more generally defined as the load required to create a target
board downward deflection throughout the life of the product
This board deflection metric provides guidance for mechanical designs that differ from
the reference design for ATX//µATX form factor.
A.3.1 Motherboard Deflection Metric Definition
Motherboard deflection is measured along either diagonal (refer to Figure 7-6):
d = dmax – (d1 + d2)/2
d’ = dmax – (d’1 + d’2)/2
Configurations in which the deflection is measured are defined in the Table 7–1.
To measure board deflection, follow industry standard procedures (such as IPC) for
board deflection measurement. Height gauges and possibly dial gauges may also be
used.
Table 7–1. Board Deflection Configuration Definitions
Configuration
Parameter
Processor + Socket
load plate
Heatsink Parameter Name
d_ref yes no BOL deflection, no preload
d_BOL yes yes BOL deflection with preload
d_EOL yes yes EOL deflection
NOTES:
BOL: Beginning of Life
EOL: End of Life
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