Metric For Heatsink Preload For Atx/Uatx Designs Non-Compliant With Intel Reference Design; Heatsink Preload Requirement Limitations; Motherboard Deflection Metric Definition - Intel QX9770 - Core 2 Extreme Quad-Core Processor Design Manual

A.2 Metric for Heatsink Preload for ATX/uATX
Designs Non-Compliant with Intel
Reference Design
A.2.1

Heatsink Preload Requirement Limitations

Heatsink preload by itself is not an appropriate metric for solder joint force across
various mechanical designs and does not take into account for example (not an
exhaustive list):
• Heatsink mounting hole span
• Heatsink clip assembly stiffness and creep
• Board stiffness and creep
• Board stiffness is modified by fixtures like backing plate, chassis attach, etc.
Simulation shows that the solder joint force (F
deflection measured along the socket diagonal. The matching of F
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 26):
d = dmax – (d1 + d2)/2
d' = dmax – (d'1 + d'2)/2
Configurations in which the deflection is measured are defined in the Table 10.
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.
64
LGA775 Socket Heatsink Loading
®
) is proportional to the board
axial
axial
Thermal and Mechanical Design Guidelines
required to