Intel 640 User Guide - Page 73

Thermal Interface Management

R

Thermal/Mechanical Design Guide

73

Appendix C Thermal Interface

Management

To optimize a heatsink design, it is important to understand the impact of factors related to the

interface between the processor and the heatsink base. Specifically, the bond line thickness,

interface material area and interface material thermal conductivity should be managed to realize

the most effective thermal solution.

C.1

Bond Line Management

Any gap between the processor integrated heat spreader (IHS) and the heatsink base degrades

thermal solution performance. The larger the gap between the two surfaces, the greater the

thermal resistance. The thickness of the gap is determined by the flatness and roughness of both

the heatsink base and the integrated heat spreader, plus the thickness of the thermal interface

material (for example thermal grease) used between these two surfaces and the clamping force

applied by the heatsink attach clip(s).

C.2

Interface Material Area

The size of the contact area between the processor and the heatsink base will impact the thermal

resistance. There is, however, a point of diminishing returns. Unrestrained incremental increases

in thermal interface material area do not translate to a measurable improvement in thermal

performance.

C.3

Interface Material Performance

Two factors impact the performance of the interface material between the processor and the

heatsink base:

•

Thermal resistance of the material

•

Wetting/filling characteristics of the material

Thermal resistance is a description of the ability of the thermal interface material to transfer heat

from one surface to another. The higher the thermal resistance, the less efficient the interface

material is at transferring heat. The thermal resistance of the interface material has a significant

impact on the thermal performance of the overall thermal solution. The higher the thermal

resistance, the larger the temperature drop is across the interface and the more efficient the

thermal solution (heatsink, fan) must be to achieve the desired cooling.

The wetting or filling characteristic of the thermal interface material is its ability, under the load

applied by the heatsink retention mechanism, to spread and fill the gap between the processor and

the heatsink. Since air is an extremely poor thermal conductor, the more completely the interface

material fills the gaps, the lower the temperature drops across the interface. In this case, thermal

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

Intel 640 User Guide - Page 73

Appendix C Thermal Interface, Management

Page 73 highlights