LGA775 Socket Heatsink Loading
76 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.2.2 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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