LGA775 Socket Heatsink Loading
R
62 Thermal/Mechanical Design Guide
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 22):
d = dmax – (d1 + d2)/2
d’ = dmax – (d’1 + d’2)/2
Configurations in which the deflection is measured are defined in the
Table 5.
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 5. 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
BOL: Beginning of Life
EOL: End of Life
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