Intel EM64T - Celeron D 336 Boxed Ena, 640 - Pentium 4 640 3.2GHz 800MHz 2MB Socket 775 CPU, Pentium 4, Pentium 4 Extreme Edition User Manual

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Intel® Pentium® 4 Processor on
90 nm Process in the 775–Land
LGA Package

Thermal and Mechanical Design Guidelines

Supporting Intel® Pentium® 4 Processor 5xx and 6xx Sequences in
the 775-land LGA Package and Intel® Pentium® 4 Processor
Extreme Edition in the 775-land LGA Package

November 2005

Document Number: 302553-004

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THIS DOCUMENT AND RELATED MATERIALS AND INFORMATION ARE PROVIDED "AS IS” WITH NO WARRANTIES, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE,
NON-INFRINGEMENT OF INTELLECTUAL PROPERTY RIGHTS, OR ANY WARRANTY OTHERWISE ARISING OUT OF ANY PROPOSAL,
SPECIFICATION, OR SAMPLE. INTEL ASSUMES NO RESPONSIBILITY FOR ANY ERRORS CONTAINED IN THIS DOCUMENT AND HAS NO
LIABILITIES OR OBLIGATIONS FOR ANY DAMAGES ARISING FROM OR IN CONNECTION WITH THE USE OF THIS DOCUMENT. Intel
products are not intended for use in medical, life saving, life sustaining, critical control or safety systems, or in nuclear facility applications.

Intel Corporation may have patents or pending patent applications, trademarks, copyrights, or other intellectual property rights that relate to the
presented subject matter. The furnishing of documents and other materials and information does not provide any license, express or implied, by
estoppel or otherwise, to any such patents, trademarks, copyrights, or other intellectual property rights.

The hardware vendor remains solely responsible for the design, sale and functionality of its product, including any liability arising from product
infringement or product warranty. Intel provides this information for customer’s convenience only. Use at your own risk. Intel accepts no liability for
results if customer chooses at its discretion to implement these methods within its business operations. Intel makes no representations or
warranties regarding the accuracy or completeness of the information provided.

®

The Intel
product to deviate from published specifications. Current characterized errata are available on request.

Δ

different processor families. See www.intel.com/products/processor_number for details.

Φ

EM64T. Processor will not operate (including 32-bit operation) without an Intel EM64T-enabled BIOS. Performance will vary depending on your
hardware and software configurations. See
EM64T or consult with your system vendor for more information.

Intel, Pentium, and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States and other
countries.

*Other names and brands may be claimed as the property of others

Copyright © 2004–2005 Intel Corporation

Pentium® 4 Processor in the 775–Land LGA Package may contain design defects or errors known as errata, which may cause the

Intel processor numbers are not a measure of performance. Processor numbers differentiate features within each processor family, not across

®

Intel

EM64T requires a computer system with a processor, chipset, BIOS, operating system, device drivers and applications enabled for Intel

www.intel.com/info/em64t for more information including details on which processors support Intel

2 Thermal/Mechanical Design Guide

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Contents

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 T

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

CONTROL

................................................................................................ 20

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

Thermal/Mechanical Design Guide 3

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

5.2.1.2.1 Recommended Test Sequence........................... 43

5.2.1.2.2 Post-Test Pass Criteria ....................................... 43

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

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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

6.5 Interaction of Thermal Profile and T

CONTROL

......................................................... 59

Appendix A LGA775 Socket Heatsink Loading.................................................................................... 61

A.1 LGA775 Socket Heatsink Considerations ............................................................61

A.2 Metric for Heatsink Preload for ATX/µATX Designs Non-Compliant with Intel

Reference Design.................................................................................................

61

A.2.1 Heatsink Preload Requirement Limitations ..........................................61

4 Thermal/Mechanical Design Guide

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A.2.2 Motherboard Deflection Metric Definition .............................................62

A.2.3 Board Deflection Limits......................................................................... 63

A.2.4 Board Deflection Metric Implementation Example................................ 64

A.2.5 Additional Considerations ..................................................................... 65

A.2.5.1 Motherboard Stiffening Considerations............................... 65

A.3 Heatsink Selection Guidelines ............................................................................. 66

Appendix B Heatsink Clip Load Metrology ...........................................................................................67

B.1 Overview............................................................................................................... 67

B.2 Test Preparation ...................................................................................................67

B.2.1 Heatsink Preparation ............................................................................67

B.2.2 Typical Test Equipment ........................................................................70

B.3 Test Procedure Examples .................................................................................... 70

B.3.1 Time-Zero, Room Temperature Preload Measurement ....................... 71

B.3.2 Preload Degradation under Bake Conditions ....................................... 71

Appendix C Thermal Interface Management........................................................................................ 73

C.1 Bond Line Management .......................................................................................73

C.2 Interface Material Area......................................................................................... 73

C.3 Interface Material Performance............................................................................ 73

Appendix D Case Temperature Reference Metrology ......................................................................... 75

D.1 Objective and Scope ............................................................................................ 75

D.2 Definitions............................................................................................................. 75

D.3 Supporting Test Equipment.................................................................................. 76

D.4 Thermal Calibration and Controls ........................................................................77

D.5 IHS Groove........................................................................................................... 77

D.6 Thermocouple Attach Procedure .........................................................................80

D.6.1 Thermocouple Conditioning and Preparation....................................... 80

D.6.2 Thermocouple Attachment to the IHS .................................................. 80

D.6.3 Curing Process .....................................................................................84

D.7 Thermocouple Wire Management........................................................................ 86

Appendix E Board Level PWM and Fan Speed Control Requirements ...............................................87

Appendix F Balanced Technology Extended (BTX) System Thermal Considerations ........................ 91

Appendix G Mechanical Drawings........................................................................................................ 93

Appendix H Intel Enabled Reference Solution Information ................................................................105

Thermal/Mechanical Design Guide 5

Figures

Figure 1. Package IHS Load Areas ..................................................................................15

Figure 2. Processor Case Temperature Measurement Location ..................................... 19

Figure 3. Example Thermal Profile ...................................................................................20

Figure 4. Processor Thermal Characterization Parameter Relationships ........................ 26

Figure 5. Locations for Measuring Local Ambient Temperature, Active Heatsink ........... 29

Figure 6. Locations for Measuring Local Ambient Temperature, Passive Heatsink......... 29

Figure 7. Concept for Clocks under Thermal Monitor Control .......................................... 33

Figure 8. Random Vibration PSD...................................................................................... 42

Figure 9. Shock Acceleration Curve .................................................................................43

Figure 10. Intel® RCBFH-3 Reference Design.................................................................. 46

Figure 11. Intel® RCBFH-3 Reference Design (Exploded View) ...................................... 47

Figure 12. Upward Board Deflection during Shock .......................................................... 48

Figure 13. Reference Clip/Heatsink Assembly ................................................................. 49

Figure 14. Critical Parameters for Interfacing to Reference Clip ...................................... 51

Figure 15. Critical Core Dimension ................................................................................... 51

Figure 16. Thermistor Set Points ...................................................................................... 54

Figure 17. Example Acoustic Fan Speed Control Implementation ................................... 55

Figure 18. Fan Speed Control........................................................................................... 56

Figure 19. Temperature Range = 5 °C .............................................................................57

Figure 20. Temperature Range = 10 °C ...........................................................................58

Figure 21. Diode and Thermistor ...................................................................................... 59

Figure 22. Board Deflection Definition .............................................................................. 63

Figure 23. Example: Defining Heatsink Preload Meeting Board Deflection Limit............. 64

Figure 24. Load Cell Installation in Machined Heatsink Base Pocket (Bottom View) ...... 68

Figure 25. Load Cell Installation in Machined Heatsink Base Pocket (Side View)........... 69

Figure 26. Preload Test Configuration.............................................................................. 69

Figure 27. 775-Land LGA Package Reference Groove Drawing .....................................78

Figure 28. IHS Reference Groove on the 775-Land LGA Package ................................. 79

Figure 29. IHS Groove Orientation Relative to the LGA775 Socket................................. 79

Figure 30. Bending the Tip of the Thermocouple .............................................................80

Figure 31. Securing Thermocouple Wires with Kapton Tape Prior to Attach ...................81

Figure 32. Thermocouple Bead Placement ...................................................................... 81

Figure 33. Position Bead on the Groove Step .................................................................. 82

Figure 34. Detailed Thermocouple Bead Placement........................................................ 82

Figure 35. Using 3D Micromanipulator to Secure Bead Location .................................... 83

Figure 36. Measuring Resistance between Thermocouple and IHS ................................83

Figure 37. Applying the Adhesive on the Thermocouple Bead ........................................84

Figure 38. Thermocouple Wire Management in the Groove ............................................84

Figure 39. Removing Excess Adhesive from IHS............................................................. 85

Figure 40. Filling the Groove with Adhesive .....................................................................85

Figure 41. Thermocouple Wire Management ................................................................... 86

Figure 42. FSC Definitions Example................................................................................. 88

Figure 43. System Airflow Illustration with System Monitor Point Area Identified ............92

Figure 44. Thermal Sensor Location Illustration ...............................................................92

Figure 45. ATX/µATX Motherboard Keep-out Footprint Definition and Height Restrictions

for Enabling Components – Sheet 1..........................................................................

94

Figure 46. ATX/µATX Motherboard Keep-out Footprint Definition and Height Restrictions

for Enabling Components – Sheet 2..........................................................................

95

Figure 47. ATX/µATX Motherboard Keep-out Footprint Definition and Height Restrictions

for Enabling Components – Sheet 3..........................................................................

96

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6 Thermal/Mechanical Design Guide

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Tables

Figure 48. Reference Clip Drawings – Sheet 1 ................................................................

97

Figure 49. Reference Clip Drawings – Sheet 2 ................................................................98

Figure 50. Reference Fastener – Sheet 1 ........................................................................ 99

Figure 51. Reference Fastener – Sheet 2 ......................................................................100

Figure 52. Reference Fastener – Sheet 3 ......................................................................101

Figure 53. Reference Fastener – Sheet 4 ......................................................................102

Figure 54. Clip/Heatsink Assembly .................................................................................103

Figure 55. Intel(R) RCBFH-3 Reference Solution Assembly.......................................... 104

Table 1. Thermal Diode Interface .....................................................................................35

Table 2. ATX Reference Heatsink Performance Target ................................................... 39

Table 3. Fan Electrical Performance Requirements......................................................... 41

Table 4. Intel® RCBFH-3 Reference Design Performance ............................................... 46

Table 5. Board Deflection Configuration Definitions......................................................... 62

Table 6. Typical Test Equipment ......................................................................................70

Table 7. FSC Definitions ................................................................................................... 87

Table 8. ATX FSC Settings............................................................................................... 89

Table 9. Balanced Technology Extended (BTX) FSC Settings ........................................ 89

Table 10. Intel Representative Contact for Licensing Information.................................. 105

Table 11. Intel Reference Component Thermal Solution Provider ................................. 105

Thermal/Mechanical Design Guide 7

Revision History

Revision

Number

-001 • Initial Release. June 2004

-002 • Updated to add information for the Intel® Pentium® 4 processor 660,

-003 • Added information for Intel® Pentium® 4 processor 670

-004 • Added Intel® Pentium® 4 processors 662 and 672 to the list of

650, 640, and 630 in the 775-land LGA package and the Intel

®

Pentium

• Updated the Fan Speed Control tables

• Updated the Fastener Drawings

processors supported by this thermal/mechanical design guide.

• Added Intel
to the list of processors supported by this thermal/mechanical design
guide.

4 processor Extreme Edition in the 775-land LGA package

®

Pentium® 4 processors 571, 561, 551, 541, 531, and 521

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Description Date

®

February 2005

May 2005

November 2005

§

8 Thermal/Mechanical Design Guide

Introduction

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1 Introduction

1.1 Document Goals and Scope

1.1.1 Importance of Thermal Management

The objective of thermal management is to ensure that the temperatures of all components in a
system are maintained within their functional temperature range. Within this temperature range a
component is expected to meet its specified performance. Operation outside the functional
temperature range can degrade system performance, cause logic errors or cause component and/or
system damage. Temperatures exceeding the maximum operating limit of a component may result
in irreversible changes in the operating characteristics of this component.

In a system environment, the processor temperature is a function of both system and component
thermal characteristics. The system level thermal constraints consist of the local ambient air
temperature and airflow over the processor as well as the physical constraints at and above the
processor. The processor temperature depends in particular on the component power dissipation,
the processor package thermal characteristics, and the processor thermal solution.

All of these parameters are affected by the continued push of technology to increase processor
performance levels and packaging density (more transistors). As operating frequencies increase
and packaging size decreases, the power density increases while the thermal solution space and
airflow typically become more constrained or remains the same within the system. The result is an
increased importance on system design to ensure that thermal design requirements are met for
each component, including the processor, in the system.

1.1.2 Document Goals

Depending on the type of system and the chassis characteristics, new system and component
designs may be required to provide adequate cooling for the processor. The goal of this document
is to provide an understanding of these thermal characteristics and discuss guidelines for meeting
the thermal requirements imposed on single processor systems for the Intel
in the 775–Land LGA package.

®

Pentium® 4 processor

Thermal/Mechanical Design Guide 9

Introduction

1.1.3 Document Scope

This design guide supports the following processors:

• Pentium 4 processors 570/571, 560/561, 550/551, 540/541, 530/531, and 520/521 in the 775-

land LGA package

• Pentium 4 processor 670/672, 660/662, 650, 640, and 630 in the 775-land LGA package

• Pentium 4 processor Extreme Edition in the 775-land LGA package

In this document, when a reference is made to “the processor” and/or “the Pentium 4 processor in
the 775–Land LGA package”, it is intended that this includes all the processors supported by this
document. If needed for clarity, the specific processor will be listed.

In this document, when a reference is made to “the datasheet”, the reader should refer to either the

®

Pentium® 4 Processors 570571, 560/561, 550/551, 540/541, 530/531, and 520/521∆ – On

Intel
90 nm Process in the 775–Land LGA Package and Supporting Hyper-Threading Technology
Datasheet or the Intel
Extreme Edition Datasheet – On 90 nm Process in the 775-land LGA Package, supporting Intel
Extended Memory 64 Technology

appropriate. If needed for clarity, the specific processor datasheet will be referenced.

®

Pentium® 4 Processor 6xx∆ Sequence and Intel® Pentium® 4 Processor

Φ

, and supporting Intel® Virtualization Technology as

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®

Chapter

2 discusses package thermal mechanical requirements to design a thermal solution for the
Pentium 4 processor in the 775–land LGA package in the context of personal computer
applications. Chapter
recommendations to validate a processor thermal solution. Chapter

3 discusses the thermal solution considerations and metrology

4 addresses the benefits of the

processor’s integrated thermal management logic for thermal design.

Chapter
processor in the 775–land LGA package discussed in this document. Chapter

5 provides information on the common Intel reference thermal solution for the Pentium 4

6 discusses the

implementation of acoustic fan speed control.

THE PHYSICAL DIMENSIONS AND THERMAL SPECIFICATIONS OF THE PROCESSOR
THAT ARE USED IN THIS DOCUMENT ARE FOR ILLUSTRATION ONLY. REFER TO
THE DATASHEET FOR THE PRODUCT DIMENSIONS, THERMAL POWER DISSIPATION
AND MAXIMUM CASE TEMPERATURE. IN CASE OF CONFLICT, THE DATA IN THE
DATASHEET SUPERSEDES ANY DATA IN THIS DOCUMENT.

10 Thermal/Mechanical Design Guide

Introduction

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1.2 References

Material and concepts available in the following documents may be beneficial when reading this
document.

Document Document Link

Intel® Pentium® 4 Processor 6xx∆ and Intel® Pentium® 4
Processor Extreme Edition Datasheet – On 90 nm Process in
the 775-land LGA Package, supporting Intel
Memory 64 Technology
Technology.

Intel® Pentium® 4 Processors 570/571, 560/561, 550/551,
540/541, 530/531, and 520/521
Technology – On 90 nm Process in the 775–Land LGA
Package and Supporting Intel Extended Memory 64
Technology

LGA775 Socket Mechanical Design Guide http://developer.intel.com/design/Pentium

Boxed Intel® Pentium® 4 Processor in the 775-Land LGA
Package - Integration Video

Fan Specification for 4-wire PWM Controlled Fans http://www.formfactors.org/

Performance ATX Desktop System Thermal Design
Suggestions

Performance microATX Desktop System Thermal Design
Suggestions

Balanced Technology Extended (BTX) System Design Guide http://www.formfactors.org/

Φ

Datasheet

Φ

, and supporting Intel® Virtualization

∆

Supporting Hyper-Threading

®

Extended

http://intel.com/design/pentium4/datashts/

306382.htm

http://developer.intel.com/design/Pentium

4/datashts/302351.htm

4/guides/302666.htm

http://www.intel.com/go/integration

http://www.formfactors.org/

http://www.formfactors.org/

Thermal/Mechanical Design Guide 11

Introduction

1.3 Definition of Terms

Term Description

The measured ambient temperature locally surrounding the processor. The ambient

T

A

TC

T

E

T

S

T

C-MAX

ΨCA

ΨCS

ΨSA

TIM

P

MAX

TDP

IHS

LGA775 Socket

temperature should be measured just upstream of a passive heatsink or at the fan
inlet for an active heatsink.

The case temperature of the processor, measured at the geometric center of the
topside of the IHS.

The ambient air temperature external to a system chassis. This temperature is usually
measured at the chassis air inlets.

Heatsink temperature measured on the underside of the heatsink base, at a location
corresponding to

The maximum case temperature as specified in a component specification.

Case-to-ambient thermal characterization parameter (psi). A measure of thermal
solution performance using total package power. Defined as (T
Power.

Note: Heat source must be specified for

Case-to-sink thermal characterization parameter. A measure of thermal interface
material performance using total package power. Defined as (T
Power.

Note: Heat source must be specified for

Sink-to-ambient thermal characterization parameter. A measure of heatsink thermal
performance using total package power. Defined as (T

Note: Heat source must be specified for

Thermal Interface Material: The thermally conductive compound between the heatsink
and the processor case. This material fills the air gaps and voids, and enhances the
transfer of the heat from the processor case to the heatsink.

The maximum power dissipated by a semiconductor component.

Thermal Design Power: a power dissipation target based on worst-case applications.

Thermal solutions should be designed to dissipate the thermal design power.

Integrated Heat Spreader: A thermally conductive lid integrated into a processor
package to improve heat transfer to a thermal solution through heat spreading.

The surface mount socket designed to accept the Pentium 4 processor in the 775–
land LGA package.

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T

.

C

– TA) / Total Package

C

Ψ measurements.

– TS) / Total Package

C

Ψ measurements.

– TA) / Total Package Power.

S

Ψ measurements.

ACPI

Bypass

Thermal Monitor

TCC

T

Temperature reported from the on-die thermal diode.

DIODE

Advanced Configuration and Power Interface.

Bypass is the area between a passive heatsink and any object that can act to form a
duct. For this example, it can be expressed as a dimension away from the outside
dimension of the fins to the nearest surface.

A feature on the Pentium 4 processor in the 775–land LGA package that attempts to
keep the processor die temperature within factory specifications.

Thermal Control Circuit: Thermal Monitor uses the TCC to reduce die temperature by
lowering effective processor frequency when the die temperature has exceeded its
operating limits.

12 Thermal/Mechanical Design Guide

Introduction

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Term Description

Fan Speed Control: Thermal solution that includes a variable fan speed which is

FSC

T

CONTROL_BASE

T

CONTROL_OFFSET

T

CONTROL

PWM

Health Monitor

Component

BTX

TMA

driven by a PWM signal and uses the on-die thermal diode as a reference to change
the duty cycle of the PWM signal.

Constant from the processor datasheet that is added to the T

results in the value for

Value read by the BIOS from a processor MSR and added to the T

results in the value for

T

Pulse width modulation is a method of controlling a variable speed fan. The enabled 4
wire fans use the PWM duty cycle % from the fan speed controller to modulate the fan
speed.

Any standalone or integrated component that is capable of reading the processor
temperature and providing the PWM signal to the 4 pin fan header.

Balanced Technology Extended: BTX is an enhanced form factor specification for
desktop platforms.

Thermal Module Assembly. The heatsink, fan and duct assembly for the BTX thermal
solution.

is the specification limit for use with the on-die thermal diode.

CONTROL

T

CONTROL

T

CONTROL

CONTROL_OFFSET

CONTROL_BASE

that

that

§

Thermal/Mechanical Design Guide 13

Introduction

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14 Thermal/Mechanical Design Guide

Processor Thermal/Mechanical Information

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2 Processor Thermal/Mechanical

Information

2.1 Mechanical Requirements

2.1.1 Processor Package

The Pentium 4 processor is packaged in a 775–land LGA package that interfaces with the
motherboard via a LGA775 socket. Refer to the processor datasheet for detailed mechanical
specifications.

The processor connects to the motherboard through a land grid array (LGA) surface mount
socket. The socket contains 775 contacts arrayed about a cavity in the center of the socket with
solder balls for surface mounting to the motherboard. The socket is named LGA775 socket. A
description of the socket can be found in the LGA775 Socket Mechanical Design Guide.

The package includes an integrated heat spreader (IHS) that is shown in
only. Refer to the processor datasheet for further information. In case of conflict, the package
dimensions in the processor datasheet supersedes dimensions provided in this document.

Figure 1. Package IHS Load Areas

Substrate

Substrate

to install a heatsink

to install a heatsink

Top Surface of IHS

Top Surface of IHS

Figure 1 for illustration

IHS Ste p

IHS Ste p

to interface w ith LGA775

to interface w ith LGA775

Socket Load Plate

Socket Load Plate

Thermal/Mechanical Design Guide 15

Processor Thermal/Mechanical Information

The primary function of the IHS is to transfer the non-uniform heat distribution from the die to
the top of the IHS, out of which the heat flux is more uniform and spread over a larger surface
area (not the entire IHS area). This allows more efficient heat transfer out of the package to an
attached cooling device. The top surface of the IHS is designed to be the interface to the heatsink.

The IHS also features a step that interfaces with the LGA775 socket load plate, as described in
LGA775 Socket Mechanical Design Guide. The load from the load plate is distributed across two
sides of the package onto a step on each side of the IHS. It is then distributed by the package
across all of the contacts. When correctly actuated, the top surface of the IHS is above the load
plate allowing proper installation of a heatsink on the top surface of the IHS. After actuation of
the socket load plate, the seating plane of the package is flush with the seating plane of the socket.
Package movement during socket actuation is along the Z direction (perpendicular to substrate)
only. Refer to the LGA775 Socket Mechanical Design Guide for further information about the
LGA775 socket.

The datasheet gives details on the IHS geometry and tolerances, and material.

The processor package has mechanical load limits that are specified in the processor datasheet.
The specified maximum static and dynamic load limits should not be exceeded during their
respective stress conditions. These include heatsink installation, removal, mechanical stress
testing, and standard shipping conditions.

• When a compressive static load is necessary to ensure thermal performance of the thermal

interface material between the heatsink base and the IHS, it should not exceed the
corresponding specification given in the processor datasheet.

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• When a compressive static load is necessary to ensure mechanical performance, it should

remain in the minimum/maximum range specified in the processor datasheet

• The heatsink mass can also generate additional dynamic compressive load to the package

during a mechanical shock event. Amplification factors due to the impact force during shock
must be taken into account in dynamic load calculations. The total combination of dynamic
and static compressive load should not exceed the processor datasheet compressive dynamic
load specification during a vertical shock. For example, with a 0.454 kg [1 lb] heatsink, an
acceleration of 50G during an 11 ms trapezoidal shock with an amplification factor of
2 results in approximately a 445 N [100 lbf] dynamic load on the processor package. If a
178 N [40 lbf] static load is also applied on the heatsink for thermal performance of the
thermal interface material the processor package could see up to a 623 N [140 lbf]. The
calculation for the thermal solution of interest should be compared to the processor datasheet
specification.

No portion of the substrate should be used as a load-bearing surface.

Finally, the datasheet provides package handling guidelines in terms of maximum recommended
shear, tensile and torque loads for the processor IHS relative to a fixed substrate. These
recommendations should be followed in particular for heatsink removal operations.

16 Thermal/Mechanical Design Guide

Processor Thermal/Mechanical Information

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2.1.2 Heatsink Attach

2.1.2.1 General Guidelines

There are no features on the LGA775 socket to directly attach a heatsink; a mechanism must be
designed to attach the heatsink directly to the motherboard. In addition to holding the heatsink in
place on top of the IHS, this mechanism plays a significant role in the robustness of the system in
which it is implemented, in particular:

• Ensuring thermal performance of the thermal interface material (TIM) applied between the

IHS and the heatsink. TIMs based on phase change materials are very sensitive to applied
pressure: the higher the pressure, the better the initial performance. TIMs (such as thermal
greases) are not as sensitive to applied pressure. Designs should consider a possible decrease
in applied pressure over time due to potential structural relaxation in retention components.

• Ensuring system electrical, thermal, and structural integrity under shock and vibration events.

The mechanical requirements of the heatsink attach mechanism depend on the mass of the
heatsink and the level of shock and vibration that the system must support. The overall
structural design of the motherboard and the system have to be considered when designing
the heatsink attach mechanism. Their design should provide a means for protecting LGA775
socket solder joints. One of the strategies for mechanical protection of the socket is to use a
preload and high stiffness clip. This strategy is implemented by the reference design and
described in Section

5.7.

Note: Package pull-out during mechanical shock and vibration is constrained by the LGA775 socket

load plate (refer to the LGA775 Socket Mechanical Design Guide for further information).

2.1.2.2 Heatsink Clip Load Requirement

The attach mechanism for the heatsink developed to support the Pentium 4 processor in the
775–land LGA package should create a static preload on the package between 18 lbf and 70 lbf
throughout the life of the product for designs compliant with the Intel reference design
assumptions:

• 72 mm x 72 mm mounting hole span (refer to

• And no board stiffening device (backing plate, chassis attach, etc.).

The minimum load is required to protect against fatigue failure of socket solder joint in
temperature cycling.

It is important to take into account potential load degradation from creep over time when
designing the clip and fastener to the required minimum load. This means that, depending on clip
stiffness, the initial preload at beginning of life of the product may be significantly higher than the
minimum preload that must be met throughout the life of the product. For additional guidelines on
mechanical design, in particular on designs departing from the reference design assumptions refer

Appendix A.

to

For clip load metrology guidelines, refer to

Appendix B.

Figure 45)

Thermal/Mechanical Design Guide 17

Processor Thermal/Mechanical Information

2.1.2.3 Additional Guidelines

In addition to the general guidelines given above, the heatsink attach mechanism for the Pentium
4 processor in the 775–land LGA package should be designed to the following guidelines:

• Holds the heatsink in place under mechanical shock and vibration events and applies force to

the heatsink base to maintain desired pressure on the thermal interface material. Note that

the load applied by the heatsink attach mechanism must comply with the package
specifications described in the processor datasheet. One of the key design parameters is the
height of the top surface of the processor IHS above the motherboard. The IHS height from
the top of board is expected to vary from 7.517 mm to 8.167 mm. This data is provided for
information only, and should be derived from:

⎯ The height of the socket seating plane above the motherboard after reflow, given in the

LGA775 Socket Mechanical Design Guide with its tolerances

⎯ The height of the package, from the package seating plane to the top of the IHS, and

accounting for its nominal variation and tolerances that are given in the corresponding
processor datasheet.

• Engages easily, and if possible, without the use of special tools. In general, the heatsink is

assumed to be installed after the motherboard has been installed into the chassis.

• Minimizes contact with the motherboard surface during installation and actuation to avoid

scratching the motherboard.

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2.2 Thermal Requirements

Refer to the datasheet for the processor thermal specifications. The majority of processor power is
dissipated through the IHS. There are no additional components (e.g., BSRAMs) that generate
heat in this package. The amount of power that can be dissipated as heat through the processor
package substrate and into the socket is usually minimal.

Intel has introduced a new method for specifying the thermal limits for the Pentium 4 Processor in
the 775–land LGA package. The new parameters are the Thermal Profile and T
Thermal Profile defines the maximum case temperature as a function of power being dissipated.
T

CONTROL

thermal diode. Designing to these specifications allows optimization of thermal designs for
processor performance and acoustic noise reduction.

2.2.1 Processor Case Temperature

For the Pentium 4 processor in the 775–land LGA package, the case temperature is defined as the
temperature measured at the geometric center of the package on the surface of the IHS. For
illustration,
[1.474 in x 1.474 in] FCLGA4 package. Techniques for measuring the case temperature are
detailed in Section

Note: In case of conflict, the package dimensions in the processor datasheet supersedes dimensions

provided in this document.

is a specification used in conjunction with the temperature reported by the on-die

Figure 2 shows the measurement location for a 37.5 mm x 37.5 mm

3.4.

CONTROL

. The

18 Thermal/Mechanical Design Guide

Processor Thermal/Mechanical Information

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Figure 2. Processor Case Temperature Measurement Location

37.5 mm

37.5 mm

37.5 mm

37.5 mm

2.2.2 Thermal Profile

The Thermal Profile defines the maximum case temperature as a function of processor power
dissipation. The TDP and Maximum Case Temperature are defined as the maximum values of the
thermal profile. By design the thermal solutions must meet the thermal profile for all system
operating conditions and processor power levels.

Measure TCat this point

Measure TCat this point

(geometric center of the package)

(geometric center of the package)

The slope of the thermal profile was established assuming a generational improvement in thermal
solution performance of about 10% based on previous Intel reference designs. This performance
is expressed as the slope on the thermal profile and can be thought of as the thermal resistance of

Ψ

the heatsink attached to the processor,

(Refer to Section 3.1). The intercept on the thermal

CA

profile assumes a maximum ambient operating condition that is consistent with the available
chassis solutions.

To determine compliance to the thermal profile, a measurement of the actual processor power
dissipation is required. Contact your Intel sales representative for assistance in processor power
measurement. The measured power is plotted on the Thermal Profile to determine the maximum
case temperature. Using the example in

Figure 3 for a processor dissipating 70 W the maximum

case temperature is 61 °C.

For the Pentium 4 processor in the 775–land LGA package, there are two thermal profiles to
consider. The Platform Requirement Bit (PRB) indicates which thermal profile is appropriate for
a specific processor. This document will focus on the development of thermal solutions to meet
the thermal profile for PRB=1. See the processor datasheet for the thermal profile and additional
discussion on the PRB.

Thermal/Mechanical Design Guide 19

Processor Thermal/Mechanical Information

Figure 3. Example Thermal Profile

75

70

65

60

55

50

45

Case Temperature (C)

40

35

30

30 40 50 60 70 80 90 100 110

R

Heatsink
Design Point

Thermal Profile

TDP

Watts

2.2.3 T

T
thermal solution fan speed is being controlled by the on-die thermal diode. The T
parameter defines a very specific processor operating region where fan speed can be reduced.

This allows the system integrator a method to reduce the acoustic noise of the processor cooling
solution, while maintaining compliance to the processor thermal specification.

The value of T
the processor idle power. As a result, a processor with a high T
power than a part with lower value of T

The value of T
value, the thermal solution should perform similarly. The higher power of some parts is offset by

a higher value of T
acoustically.

This is achieved in part by using the
curves from the Intel enabled thermal solution. A thermal solution designed to meet the thermal

profile should perform virtually the same for any value of T

The value for T
configured processor register. The result can be used to program a fan speed control component.

See the processor datasheet for further details on reading the register and calculating T

CONTROL

CONTROL

defines the maximum operating temperature for the on-die thermal diode when the

CONTROL

CONTROL

CONTROL

CONTROL

CONTROL

CONTROL

CONTROL

is driven by a number of factors. One of the most significant of these is

will dissipate more

CONTROL

CONTROL

when running the same application.

is calculated such that regardless of the individual processor’s T

in such a way that they should behave virtually the same

Ψ

vs. RPM and RPM vs. Acoustics (dBA) performance

CA

CONTROL

.

is calculated by the system BIOS based on values read from a factory

.

See Chapter

6, Acoustic Fan Speed Control, for details on implementing a design using T

CONTROL

and the Thermal Profile.

20 Thermal/Mechanical Design Guide

Processor Thermal/Mechanical Information

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2.3 Heatsink Design Considerations

To remove the heat from the processor, three basic parameters should be considered:

• The area of the surface on which the heat transfer takes place. Without any

enhancements, this is the surface of the processor package IHS. One method used to improve
thermal performance is by attaching a heatsink to the IHS. A heatsink can increase the
effective heat transfer surface area by conducting heat out of the IHS and into the
surrounding air through fins attached to the heatsink base.

• The conduction path from the heat source to the heatsink fins. Providing a direct

conduction path from the heat source to the heatsink fins and selecting materials with higher
thermal conductivity typically improves heatsink performance. The length, thickness, and
conductivity of the conduction path from the heat source to the fins directly impact the
thermal performance of the heatsink. In particular, the quality of the contact between the
package IHS and the heatsink base has a higher impact on the overall thermal solution
performance as processor cooling requirements become stricter. Thermal interface material
(TIM) is used to fill in the gap between the IHS and the bottom surface of the heatsink, and
thereby improve the overall performance of the stack-up (IHS-TIM-Heatsink). With
extremely poor heatsink interface flatness or roughness, TIM may not adequately fill the gap.
The TIM thermal performance depends on its thermal conductivity as well as the pressure
applied to it. Refer to Section
bond line management between the IHS and the heatsink base.

2.3.4 and Appendix C for further information on TIM and on

• The heat transfer conditions on the surface on which heat transfer takes place.

Convective heat transfer occurs between the airflow and the surface exposed to the flow. It is
characterized by the local ambient temperature of the air, T

, and the local air velocity over

A

the surface. The higher the air velocity over the surface, and the cooler the air, the more
efficient is the resulting cooling. The nature of the airflow can also enhance heat transfer via
convection. Turbulent flow can provide improvement over laminar flow. In the case of a
heatsink, the surface exposed to the flow includes in particular the fin faces and the heatsink
base.

Active heatsinks typically incorporate a fan that helps manage the airflow through the heatsink.

Passive heatsink solutions require in-depth knowledge of the airflow in the chassis. Typically,

passive heatsinks see lower air speed. These heatsinks are therefore typically larger (and heavier)
than active heatsinks due to the increase in fin surface required to meet a required performance.
As the heatsink fin density (the number of fins in a given cross-section) increases, the resistance
to the airflow increases: it is more likely that the air travels around the heatsink instead of through
it, unless air bypass is carefully managed. Using air-ducting techniques to manage bypass area can
be an effective method for controlling airflow through the heatsink.

Thermal/Mechanical Design Guide 21

Processor Thermal/Mechanical Information

2.3.1 Heatsink Size

The size of the heatsink is dictated by height restrictions for installation in a system and by the
amount of space available on the motherboard and other considerations for component height and
placement in the area potentially impacted by the processor heatsink. The height of the heatsink
must comply with the requirements and recommendations published for the motherboard form
factor of interest. Designing a heatsink to the recommendations may preclude using it in systems
adhering strictly to the form factor requirements, while still in compliance with the form factor
documentation.

For the ATX/microATX form factor, it is recommended to use:

• The ATX motherboard keep-out footprint definition and height restrictions for enabling

components, defined for the platforms designed with the LGA775 socket in
this design guide.

• The motherboard primary side height constraints defined in the ATX Specification V2.1 and

the microATX Motherboard Interface Specification V1.1 found at

http://www.formfactors.org/.

The resulting space available above the motherboard is generally not entirely available for the
heatsink. The target height of the heatsink must take into account airflow considerations (for fan
performance for example) as well as other design considerations (air duct, etc.).

R

Appendix G of

2.3.2 Heatsink Mass

With the need for pushing air cooling to better performance, heatsink solutions tend to grow
larger (increase in fin surface) resulting in increased mass. The insertion of highly thermally
conductive materials like copper to increase heatsink thermal conduction performance results in
even heavier solutions. As mentioned in Section
consideration the package and socket load limits, the heatsink attach mechanical capabilities, and
the mechanical shock and vibration profile targets. Beyond a certain heatsink mass, the cost of
developing and implementing a heatsink attach mechanism that can ensure the system integrity
under the mechanical shock and vibration profile targets may become prohibitive.

The recommended maximum heatsink mass for the Pentium 4 processor in the 775–land LGA
package is 450g. This mass includes the fan and the heatsink only. The attach mechanism (clip,
fasteners, etc.) is not included.

2.3.3 Package IHS Flatness

The package IHS flatness for the product is specified in the processor datasheet and can be used
as a baseline to predict heatsink performance during the design phase.

Intel recommends testing and validating heatsink performance in full mechanical enabling
configuration to capture any impact of IHS flatness change due to combined socket and heatsink
loading. While socket loading alone may increase the IHS warpage, the heatsink preload
redistributes the load on the package and improves the resulting IHS flatness in the enabled state.

2.1, the heatsink mass must take into

22 Thermal/Mechanical Design Guide

Processor Thermal/Mechanical Information

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2.3.4 Thermal Interface Material

Thermal interface material application between the processor IHS and the heatsink base is
generally required to improve thermal conduction from the IHS to the heatsink. Many thermal
interface materials can be pre-applied to the heatsink base prior to shipment from the heatsink
supplier and allow direct heatsink attach, without the need for a separate thermal interface
material dispense or attach process in the final assembly factory.

All thermal interface materials should be sized and positioned on the heatsink base in a way that
ensures the entire processor IHS area is covered. It is important to compensate for heatsink-to­processor attach positional alignment when selecting the proper thermal interface material size.

When pre-applied material is used, it is recommended to have a protective application tape over
it. This tape must be removed prior to heatsink installation.

2.4 System Thermal Solution Considerations

2.4.1 Chassis Thermal Design Capabilities

The ATX Intel reference thermal solution assumes that the chassis delivers a maximum TA of
38 °C at the inlet of the processor fan heatsink (refer to Section

5.1.1).

2.4.2 Improving Chassis Thermal Performance

The heat generated by components within the chassis must be removed to provide an adequate
operating environment for both the processor and other system components. Moving air through
the chassis brings in air from the external ambient environment and transports the heat generated
by the processor and other system components out of the system. The number, size, and relative
position of fans and vents determine the chassis thermal performance, and the resulting ambient
temperature around the processor. The size and type (passive or active) of the thermal solution
and the amount of system airflow can be traded off against each other to meet specific system
design constraints. Additional constraints are board layout, spacing, component placement,
acoustic requirements and structural considerations that limit the thermal solution size. For more
information, refer to the Performance ATX Desktop System Thermal Design Suggestions or
Performance microATX Desktop System Thermal Design Suggestions documents available on the

http://www.formfactors.org/

In addition to passive heatsinks, fan heatsinks and system fans are other solutions that exist for
cooling integrated circuit devices. For example, ducted blowers, heat pipes and liquid cooling are
all capable of dissipating additional heat. Due to their varying attributes, each of these solutions
may be appropriate for a particular system implementation.

To develop a reliable, cost-effective thermal solution, thermal characterization and simulation
should be carried out at the entire system level, accounting for the thermal requirements of each
component. In addition, acoustic noise constraints may limit the size, number, placement, and
types of fans that can be used in a particular design.

web site.

Thermal/Mechanical Design Guide 23

Processor Thermal/Mechanical Information

To ease the burden on thermal solutions, the Thermal Monitor feature and associated logic have
been integrated into the silicon of the Pentium 4 processor in the 775–land LGA package. By
taking advantage of the Thermal Monitor feature, system designers may reduce thermal solution
cost by designing to TDP instead of maximum power. Thermal Monitor attempts to protect the
processor during sustained workload above TDP. Implementation options and recommendations
are described in Chapter

2.4.3 Summary

In summary, considerations in heatsink design include:

• The local ambient temperature T

• The thermal design power (TDP) of the processor, and the corresponding maximum T

calculated from the thermal profile. These parameters are usually combined in a single
cooling performance parameter, Ψ
information on the definition and the use of Ψ

• Heatsink interface to IHS surface characteristics, including flatness and roughness.

• The performance of the thermal interface material used between the heatsink and the IHS.

4.

at the heatsink, which is a function of chassis design.

A

(case to air thermal characterization parameter). More

CA

is given Section 3.1.

CA

C

R

as

• The required heatsink clip static load, between 18 lbf to 70 lbf throughout the life of the

product (Refer to Section

2.1.2.2 for further information).

• Surface area of the heatsink.

• Heatsink material and technology.

• Volume of airflow over the heatsink surface area.

• Development of airflow entering and within the heatsink area.

• Physical volumetric constraints placed by the system

2.5 System Integration Considerations

Boxed Intel® Pentium® 4 Processor in the 775-Land LGA Package - Integration Video provides
best known methods for package and heatsink installation and removal for LGA775 socket based
platforms and systems manufacturing. The video is available on the Web, from

http://www.intel.com/go/integration

.

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24 Thermal/Mechanical Design Guide

Thermal Metrology

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3 Thermal Metrology

This chapter discusses guidelines for testing thermal solutions, including measuring processor
temperatures. In all cases, the thermal engineer must measure power dissipation and temperature
to validate a thermal solution. To define the performance of a thermal solution the “thermal
characterization parameter”, Ψ (“psi”) will be used.

3.1 Characterizing Cooling Performance Requirements

The idea of a “thermal characterization parameter”, Ψ (“psi”), is a convenient way to characterize
the performance needed for the thermal solution and to compare thermal solutions in identical
situations (same heat source and local ambient conditions). The thermal characterization
parameter is calculated using total package power.

Note: Heat transfer is a three-dimensional phenomenon that can rarely be accurately and easily modeled

by a single resistance parameter like Ψ.

The case-to-local ambient thermal characterization parameter value (Ψ

) is used as a measure of

CA

the thermal performance of the overall thermal solution that is attached to the processor package.
It is defined by the following equation, and measured in units of °C/W:

= (TC - TA) / PD (Equation 1)

Ψ

CA

Where:

= Case-to-local ambient thermal characterization parameter (°C/W)

Ψ

CA

= Processor case temperature (°C)

T

C

= Local ambient temperature in chassis at processor (°C)

T

A

= Processor total power dissipation (W) (assumes all power dissipates through the

P

D

IHS)

The case-to-local ambient thermal characterization parameter of the processor, Ψ
of Ψ

, the thermal interface material thermal characterization parameter, and of ΨSA, the sink-to-

CS

, is comprised

CA

local ambient thermal characterization parameter:

= ΨCS + ΨSA (Equation 2)

Ψ

CA

Where:

= Thermal characterization parameter of the thermal interface material (°C/W)

Ψ

CS

= Thermal characterization parameter from heatsink-to-local ambient (°C/W)

Ψ

SA

Thermal/Mechanical Design Guide 25

Thermal Metrology

Ψ

is strongly dependent on the thermal conductivity and thickness of the TIM between the

CS

heatsink and IHS.

is a measure of the thermal characterization parameter from the bottom of the heatsink to the

Ψ

SA

local ambient air. Ψ
It is also strongly dependent on the air velocity through the fins of the heatsink.

Figure 4 illustrates the combination of the different thermal characterization parameters.

Figure 4. Processor Thermal Characterization Parameter Relationships

Heatsink

Heatsink

TIM

TIM

Processor

Processor

is dependent on the heatsink material, thermal conductivity, and geometry.

SA

T

T

A

A

T

T

S

S

T

T

C

IHS

IHS

C

Ψ

Ψ

CA

CA

R

3.1.1 Example

The cooling performance, Ψ
parameter described above:

• The case temperature T

datasheet.

• Define a target local ambient temperature at the processor, T

Since the processor thermal profile applies to all processor frequencies, it is important to identify
the worst case (lowest Ψ
strategy such that a given heatsink can cover a given range of processor frequencies.

The following provides an illustration of how one might determine the appropriate performance
targets. The example power and temperature numbers used here are not related to any Intel
processor thermal specifications, and are for illustrative purposes only.

Assume the TDP, as listed in the processor datasheet, is 100 W and the maximum case
temperature from the thermal profile for 100 W is 67 °C. Assume as well that the system airflow

LGA775 Socket

LGA775 Socket

System Board

System Board

is then defined using the principle of thermal characterization

CA,

and thermal design power TDP given in the processor

C-MAX

.

A

) for a targeted chassis characterized by TA to establish a design

CA

26 Thermal/Mechanical Design Guide

Thermal Metrology

R

has been designed such that the local ambient temperature is 38 °C. Then the following could be
calculated using Equation 1 from above:

= (TC – TA) / TDP = (67 – 38) / 100 = 0.29 °C/W

Ψ

CA

To determine the required heatsink performance, a heatsink solution provider would need to
determine Ψ
heatsink solution were designed to work with a TIM material performing at Ψ

performance for the selected TIM and mechanical load configuration. If the

CS

≤ 0.10 °C/W,

CS

solving for Equation 2 from above, the performance of the heatsink would be:

= ΨCA − ΨCS = 0.29 − 0.10 = 0.19 °C/W

Ψ

SA

3.2 Processor Thermal Solution Performance Assessment

Thermal performance of a heatsink should be assessed using a thermal test vehicle (TTV)
provided by Intel. The TTV is a stable heat source from which the user can take accurate power
measurements, whereas actual processors can introduce additional factors that can impact test
results. In particular, the power level from actual processors varies significantly due to variances
in the manufacturing process. The TTV provides consistent power and power density for thermal
solution characterization and results can be easily translated to real processor performance.

Once the thermal solution is designed and validated, it is strongly recommended to verify
functionality of the thermal solution on real processors and on fully integrated systems.

Contact your Intel field sales representative for further information on TTV or regarding accurate
measurement of the power dissipated by an actual processor.

3.3 Local Ambient Temperature Measurement Guidelines

The local ambient temperature TA is the temperature of the ambient air surrounding the processor.
For a passive heatsink, T
cooled heatsink, it is the temperature of inlet air to the active cooling fan.

It is worthwhile to determine the local ambient temperature in the chassis around the processor to
understand the effect it may have on the case temperature.

is best measured by averaging temperature measurements at multiple locations in the heatsink

T

A

inlet airflow. This method helps reduce error and eliminate minor spatial variations in
temperature. The following guidelines are meant to enable accurate determination of the localized
air temperature around the processor during system thermal testing.

For active heatsinks, it is important to avoid taking measurement in the dead flow zone that
usually develops above the fan hub and hub spokes. Measurements should be taken at four
different locations uniformly placed at the center of the annulus formed by the fan hub and the fan
housing to evaluate the uniformity of the air temperature at the fan inlet. The thermocouples

is defined as the heatsink approaches air temperature; for an actively

A

Thermal/Mechanical Design Guide 27

Thermal Metrology

should be placed approximately 3 mm to 8 mm [0.1 to 0.3 in] above the fan hub vertically and
halfway between the fan hub and the fan housing horizontally as shown in

Figure 5 (avoiding the
hub spokes). Using an open bench to characterize an active heatsink can be useful, and usually
ensures more uniform temperatures at the fan inlet. However, additional tests that include a solid
barrier above the test motherboard surface can help evaluate the potential impact of the chassis.
This barrier is typically clear Plexiglas*, extending at least 100 mm [4 in] in all directions beyond
the edge of the thermal solution. Typical distance from the motherboard to the barrier is 81 mm
[3.2 in]. For even more realistic airflow, the motherboard should be populated with significant
elements like memory cards, graphic card, and chipset heatsink. If a barrier is used, the
thermocouple can be taped directly to the barrier with a clear tape at the horizontal location as
previously described, half way between the fan hub and the fan housing. If a variable speed fan is
used, it may be useful to add a thermocouple taped to the barrier above the location of the
temperature sensor used by the fan to check its speed setting against air temperature. When
measuring T
is likely that the T

in a chassis with a live motherboard, add-in cards, and other system components, it

A

measurements will reveal a highly non-uniform temperature distribution

A

across the inlet fan section.

For passive heatsinks, thermocouples should be placed approximately 13 mm to 25 mm
[0.5 to 1.0 in] away from processor and heatsink as shown in

Figure 6. The thermocouples should
be placed approximately 51 mm [2.0 in] above the baseboard. This placement guideline is meant
to minimize the effect of localized hot spots from baseboard components.

R

Note: Testing an active heatsink with a variable speed fan can be done in a thermal chamber to capture

the worst-case thermal environment scenarios. Otherwise, when doing a bench top test at room
temperature, the fan regulation prevents the heatsink from operating at its maximum capability.
To characterize the heatsink capability in the worst-case environment in these conditions, it is
then necessary to disable the fan regulation and power the fan directly, based on guidance from
the fan supplier.

28 Thermal/Mechanical Design Guide

Thermal Metrology

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Figure 5. Locations for Measuring Local Ambient Temperature, Active Heatsink

Note: Drawing Not to Scale

Figure 6. Locations for Measuring Local Ambient Temperature, Passive Heatsink

Note: Drawing Not to Scale

Thermal/Mechanical Design Guide 29

Thermal Metrology

3.4 Processor Case Temperature Measurement Guidelines

The Pentium 4 processor in the 775–land LGA package is specified for proper operation when TC
is maintained at or below the thermal profile as listed in the datasheet. The measurement location

is the geometric center of the IHS. Figure 2 shows the location for TC measurement.

for T

C

Special care is required when measuring T
Thermocouples are often used to measure T
the thermocouples must be calibrated, and the complete measurement system must be routinely
checked against known standards. When measuring the temperature of a surface that is at a
different temperature from the surrounding local ambient air, errors could be introduced in the
measurements. The measurement errors could be caused by poor thermal contact between the
thermocouple junction and the surface of the integrated heat spreader, heat loss by radiation,
convection, by conduction through thermocouple leads, and/or by contact between the
thermocouple cement and the heatsink base.

Appendix D defines a reference procedure for attaching a thermocouple to the IHS of a 775-land
LGA processor package for T

measurement. This procedure takes into account the specific

C

features of the 775-land LGA package and of the LGA775 socket for which it is intended.

to ensure an accurate temperature measurement.

C

. Before any temperature measurements are made,

C

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§

30 Thermal/Mechanical Design Guide