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Heatsink Clip Load Metrology
Appendix B Heatsink Clip Load Metrology
B.4
Overview
This section describes a procedure for measuring the load applied by the heatsink/clip/fastener
assembly to a processor package. This procedure is recommended to verify that the preload is
within the design target range for a design, and in different situations. For example:
•
Heatsink preload for the LGA775 socket.
•
Quantify preload degradation under bake conditions.
B.5
Test Preparation
B.5.6
Heatsink Preparation
Three load cells are assembled into the base of the heatsink under test in the area interfacing with
the processor Integrated Heat Spreader (IHS) using load cells equivalent to those listed in
B.5.8, "Typical Test Equipment" on page
To install the load cells, machine a pocket in the heatsink base as shown in
Figure
17. The load cells should be distributed evenly, as close as possible to the pocket walls.
Apply wax around the circumference of each load cell and the surface of the pocket around each
cell to maintain the load cells in place during the heatsink installation on the processor and board
(Refer to
The depth of the pocket depends on the height of the load cell used for the test. It is necessary that
the load cells protrude out of the heatsink base. However, this protrusion should be minimized as it
will create additional load by artificially raising the heatsink base. The measurement offset depends
on the whole assembly stiffness (i.e. board, clip, fastener, etc.). For example, the Intel RCBFH-3
Reference Heatsink Design clip and fastener assembly has a stiffness of around 380 N/mm [2180
lb/in]. In that case, a protrusion of 0.038 mm [0.0015"] will create an extra load of 15 N [3.3 lb].
Figure 16
Celeron D processor in the 775–land LGA package.
When optimizing the heatsink pocket depth, the variation of the load cell height should also be
taken into account to make sure that all load cells protrude equally from the heatsink base. It may
be useful to screen the load cells before installing to minimize variation.
B.5.7
Remarks: Alternate Heatsink Sample Preparation
Ensuring that the load cells have minimum protrusion out of the heatsink base is paramount to
meaningful results. An alternate method to make sure that the test setup measures loads
representative of the non-modified design is:
1. Machine the pocket in the heat sink base to a depth such that the tips of the load cells are just
flush with the heat sink base.
2. Machine back the heatsink base by approximately 0.25 mm [0.01"] so that the load cell tips
protrude beyond the base.
Intel
42
Figure
17).
shows an example using the Intel RCBFH-3 Reference Heatsink designed for the
®
®
Celeron
D Processor in the 775-Land LGA Package Thermal Design Guide
44.
Section
Figure 16
and
Order #303730
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