Heatsink Clip Load Metrology
Thermal and Mechanical Design Guidelines 79
B.3.1 Time-Zero, Room Temperature Preload
Measurement
1. Pre-assemble mechanical components on the board as needed prior to mounting
the motherboard on an appropriate support fixture that replicate the board attach
to a target chassis
• For example: standard ATX board should sit on ATX compliant stand-offs. If
the attach mechanism includes fixtures on the back side of the board, those
must be included, as the goal of the test is to measure the load provided by
the actual heatsink mechanism.
2. Install relevant test vehicle (TTV, processor) in the socket.
3. Assemble the heatsink reworked with the load cells to motherboard as shown for
the reference design example in Figure 7-10, and actuate attach mechanism.
4. Collect continuous load cell data at 1 Hz for the duration of the test. A minimum
time to allow the load cell to settle is generally specified by the load vendors
(often of order of 3 minutes). The time zero reading should be taken at the end of
this settling time.
5. Record the preload measurement (total from all three load cells) at the target time
and average the values over 10 seconds around this target time as well, that is, in
the interval , for example over [target time – 5 seconds ; target time
+5 seconds].
B.3.2 Preload Degradation under Bake Conditions
This section describes an example of testing for potential clip load degradation under
bake conditions.
1. Preheat thermal chamber to target temperature (45 ºC or 85 ºC for example)
2. Repeat time-zero, room temperature preload measurement
3. Place unit into preheated thermal chamber for specified time
4. Record continuous load cell data as follows:
• Sample rate = 0.1 Hz for first 3 hrs
• Sample rate = 0.01 Hz for the remainder of the bake test
5. Remove assembly from thermal chamber and set into room temperature
conditions
6. Record continuous load cell data for next 30 minutes at sample rate of 1 Hz.
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