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Appendix A LGA775 Socket Heatsink, Loading

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LGA775 Socket Heatsink Loading R Appendix A LGA775 Socket Heatsink Loading A.1 A.2 A.2.1 LGA775 Socket Heatsink Considerations Heatsink clip load is traditionally used for: • Mechanical performance in mechanical shock and vibration ⎯ Refer to Section 5.7.1 above for information on the structural design strategy for the Intel RCBFH-3 Reference Design • Thermal interface performance ⎯ Required preload depends on TIM ⎯ Preload can be low for thermal grease In addition to mechanical performance in shock and vibration and TIM performance, LGA775 socket requires a minimum heatsink preload to protect against fatigue failure of socket solder joints. Solder ball tensile stress is originally created when, after inserting a processor into the socket, the LGA775 socket load plate is actuated. In addition, solder joint shear stress is caused by coefficient of thermal expansion (CTE) mismatch induced shear loading. The solder joint compressive axial force (Faxial) induced by the heatsink preload helps to reduce the combined joint tensile and shear stress. Overall, the heatsink required preload is the minimum preload needed to meet all of the above requirements: Mechanical shock and vibration and TIM performance and LGA775 socket protection against fatigue failure. Metric for Heatsink Preload for ATX/µATX Designs Non-Compliant with Intel Reference Design 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/fastener assembly stiffness and creep • Board stiffness and creep • Board stiffness is modified by fixtures like backing plate, chassis attach, etc. Thermal/Mechanical Design Guide 61

Section	Page
Contents	3
Figures	6
Tables	7
Revision History	8
1 Introduction	9
1.1 Document Goals and Scope	9
1.1.1 Importance of Thermal Management	9
1.1.2 Document Goals	9
1.1.3 Document Scope	10
1.2 References	11
1.3 Definition of Terms	12
2 Processor Thermal/Mechanical Information	15
2.1 Mechanical Requirements	15
2.1.1 Processor Package	15
2.1.2 Heatsink Attach	17
2.1.2.1 General Guidelines	17
2.1.2.2 Heatsink Clip Load Requirement	17
2.1.2.3 Additional Guidelines	18
2.2 Thermal Requirements	18
2.2.1 Processor Case Temperature	18
2.2.2 Thermal Profile	19
2.2.3 TCONTROL	20
2.3 Heatsink Design Considerations	21
2.3.1 Heatsink Size	22
2.3.2 Heatsink Mass	22
2.3.3 Package IHS Flatness	22
2.3.4 Thermal Interface Material	23
2.4 System Thermal Solution Considerations	23
2.4.1 Chassis Thermal Design Capabilities	23
2.4.2 Improving Chassis Thermal Performance	23
2.4.3 Summary	24
2.5 System Integration Considerations	24
3 Thermal Metrology	25
3.1 Characterizing Cooling Performance Requirements	25
3.1.1 Example	26
3.2 Processor Thermal Solution Performance Assessment	27
3.3 Local Ambient Temperature Measurement Guidelines	27
3.4 Processor Case Temperature Measurement Guidelines	30
4 Thermal Management Logic and Thermal Monitor Feature	31
4.1 Processor Power Dissipation	31
4.2 Thermal Monitor Implementation	31
4.2.1 PROCHOT# Signal	32
4.2.2 Thermal Control Circuit	32
4.2.3 Operation and Configuration	33
4.2.4 On-Demand Mode	34
4.2.5 System Considerations	34
4.2.6 Operating System and Application Software Considerations	35
4.2.7 On-Die Thermal Diode	35
4.2.7.1 Reading the On-Die Thermal Diode Interface	35
4.2.7.2 Correction Factors for the On-Die Thermal Diode	36
4.2.8 THERMTRIP# Signal	37
4.2.8.1 Cooling System Failure Warning	37
5 Intel® Thermal/Mechanical Reference Design Information	39
5.1 Intel Validation Criteria for the Reference Design	39
5.1.1 Heatsink Performance Target	39
5.1.2 Acoustics	40
5.1.3 Altitude	40
5.1.4 Reference Heatsink Thermal Validation	41
5.1.5 Fan Performance for Active Heatsink Thermal Solution	41
5.2 Environmental Reliability Testing	42
5.2.1 Structural Reliability Testing	42
5.2.1.1 Random Vibration Test Procedure	42
5.2.1.2 Shock Test Procedure	42
5.2.2 Power Cycling	44
5.2.3 Recommended BIOS/Processor/Memory Test Procedures	44
5.3 Material and Recycling Requirements	44
5.4 Safety Requirements	45
5.5 Geometric Envelope for ATX Intel® Reference Thermal Mechanical Design	45
5.6 ATX Reference Thermal Mechanical Solution for the Intel® Pentium® 4 Processor in the 775–Land LGA Package	46
5.7 Reference Attach Mechanism	48
5.7.1 Structural Design Strategy	48
5.7.2 Mechanical Interface to the Reference Attach Mechanism	49
6 Acoustic Fan Speed Control	53
6.1 Acoustic Fan Speed Control	53
6.2 Thermal Solution Design	53
6.2.1 Compliance to Thermal Profile	53
6.2.2 Determine Thermistor Set Points	53
6.2.3 Minimum Fan Speed Set Point	54
6.3 Board and System Implementation	55
6.3.1 Choosing Fan Speed Control Settings	55
6.3.1.1 Temperature to begin Fan Acceleration	56
6.3.1.2 Minimum PWM Duty Cycle	58
6.4 Combining Thermistor and Thermal Diode Control	59

Match case Limit results 1 per page

LGA775 Socket Heatsink Loading

Thermal/Mechanical Design Guide

Appendix A LGA775 Socket Heatsink

A.1

LGA775 Socket Heatsink Considerations

Heatsink clip load is traditionally used for:

•

Mechanical performance in mechanical shock and vibration

⎯

Refer to Section 5.7.1 above for information on the structural design strategy for the

Intel RCBFH-3 Reference Design

•

Thermal interface performance

⎯

Required preload depends on TIM

⎯

Preload can be low for thermal grease

In addition to mechanical performance in shock and vibration and TIM performance, LGA775

socket requires a minimum heatsink preload to protect against fatigue failure of socket solder

joints.

Solder ball tensile stress is originally created when, after inserting a processor into the socket, the

LGA775 socket load plate is actuated. In addition, solder joint shear stress is caused by

coefficient of thermal expansion (CTE) mismatch induced shear loading. The solder joint

compressive axial force (F

axial

) induced by the heatsink preload helps to reduce the combined

joint tensile and shear stress.

Overall, the heatsink required preload is the minimum preload needed to meet all of the above

requirements: Mechanical shock and vibration and TIM performance and LGA775 socket

protection against fatigue failure.

A.2

Metric for Heatsink Preload for ATX/μATX 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/fastener assembly stiffness and creep

•

Board stiffness and creep

•

Board stiffness is modified by fixtures like backing plate, chassis attach, etc.