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AP-480
APPLICATION
NOTE
Pentium PROCESSOR
THERMAL DESIGN
GUIDELINES REV 2 0
November 1995
Order Number 241575-003
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COPYRIGHT INTEL CORPORATION 1996
Pentium PROCESSOR THERMAL DESIGN GUIDELINES
REV 2 0
CONTENTS PAGE CONTENTS PAGE
4 4 Thermal Resistance 7
1 0 INTRODUCTION 4
1 1 Document Goal 4 5 0 DESIGNING FOR THERMAL
PERFORMANCE 8
2 0 IMPORTANCE OF THERMAL 5 1 Heat Sinks 9
MANAGEMENT 4
5 2 Airflow 13
3 0 Pentium PROCESSOR POWER 5 3 Fans 13
SPECIFICATIONS 5
5 4 Thermal Performance Validation 13
4 0 THERMAL PARAMETERS 5
6 0 CONCLUSION 13
4 1 Ambient Temperature 5
4 2 Case Temperature 6 APPENDIX A A-1
4 3 Junction Temperature 6
APPENDIX B B-1
AP-480
1 0 INTRODUCTION 1 1 Document Goal
In a system environment the Pentium processor's The goal of this document is to provide thermal per-
temperature is a function of both the system and com- formance information for the Pentium processor and
ponent thermal characteristics The system level ther- recommendations for meeting the thermal requirements
mal constraints imposed on the package are local ambi- imposed on systems This application note attempts to
ent temperature and thermal conductivity (i e airflow provide an understanding of the thermal characteristics
over the device) The Pentium processor thermal char- of the Pentium processor and some examples of how
acteristics depend on the package (size and material) the thermal requirements can be met
the type of interconnection to the printed circuit board
(PCB) the presence of a heat sink and the thermal
conductivity and the power density of the PCB 2 0 IMPORTANCE OF THERMAL
MANAGEMENT
All of these parameters are aggravated by the continued
push of technology to increase the operating speeds and Thermal management of an electronic system encom-
the packaging density As operating frequencies in- passes al of the thermal processes and technologies that
crease and packaging size decreases the power density must be employed to remove and transfer heat from
increases and the heat sink size and airflow become individual components to the system's thermal sink in a
more constrained The result is an increased impor- controlled manner
tance on system design to ensure that thermal design
requirements are met for each component in the sys- The objective of thermal management is to ensure that
tem the temperature of all components is maintained within
functional and absolute maximum limits The function-
In addition to heat sinks and fans there are other solu- al temperature limit is the range within which the elec-
tions for cooling integrated circuit devices A few of trical circuits can be expected to meet their specified
these solutions are fan mounted on heat sink heat performance requirements Operation outside the func-
pipes thermoelectric (peltier) cooling liquid cooling tional limit can degrade system performance or cause
etc While these alternatives are capable of dissipating logic errors The absolute maximum temperature limit
additional heat they have disadvantages in terms of is the highest temperature that a portion of the compo-
system cost complexity reliability and efficiency nent may be safely exposed Temperatures exceeding
These techniques are more expensive than a passive the limit can cause physical destruction or may result in
heat sink and fan The introduction of active devices irreversible changes in operating characteristics Higher
can also decrease reliability Finally the power efficien- temperatures result in earlier failure of the devices in
cy of some of these techniques is poor and gets worse the system Every 10 C rise above the operating range
as the amount of power being dissipated increases De- means a halving of the mean time between failures
spite these disadvantages each of these solutions may
be the right one for particular system implementations
However for the purpose of this application note Intel
has focused its efforts on describing solutions using pas-
sive heat sinks and fans
4
AP-480
3 0 Pentium PROCESSOR POWER tem level accounting for the thermal requirements of
SPECIFICATIONS each component
The Pentium processor's power dissipation and case
temperature specs for 60 MHz and 66 MHz are shown 4 0 THERMAL PARAMETERS
in Table 1
Component power dissipation results in a rise in tem-
To ensure functionality and reliability of the Pentium perature relative to the temperature of a reference
processor maximum device junction temperature must point The amount of rise in temperature depends on
remain below 90 C Considering the power dissipation the net thermal resistance between the junction and the
levels and typical ambient environments of 40 C to reference point Thermal resistance is the key factor in
45 C the Pentium processor's junction temperatures determining the power handling capability of any elec-
cannot be maintained below 90 C without additional tronic package
thermal enhancement to dissipate the heat generated by
this level of power consumption Thermal resistance from junction to case (iJC) and
from junction to ambient (iJA) are the two most often
The thermal characterization data described in Table 2 specified thermal parameters for integrated circuit
illustrates that both a heat sink and airflow are needed packages
The size of heat sink and the amount of airflow are
interrelated and can be traded off against each other
For example an increase in heat sink size decreases the 4 1 Ambient Temperature
amount of airflow required In a typical system heat
sink size is limited by board layout spacing and com- Ambient temperature is the temperature of the undis-
ponent placement Airflow is limited by the size and tributed ambient air surrounding the package Denoted
number of fans along with their placement in relation TA ambient temperature is usually measured at a spec-
to the components and the airflow channels In addi- ified distance away from the package In the laboratory
tion acoustic noise constraints may limit the size or test environment ambient temperature is measured 12
types of fans limiting the airflow inches upstream from the package under investigation
In a system environment ambient temperature is the
To develop a reliable thermal solution all of the above temperature of the air upstream to the package and in
variables must be considered Thermal characterization its close vicinity
and simulation should be carried out at the entire sys-
Table 1 Pentium Processor Power Dissipation
Package Total Pin Package Power Power Max Case
Type Pins Array Size (Typical) (Max) Temp ( C)
Pentium Processor 60 MHz PGA 273 21 x 21 2 16 x 2 16 11 9W 14 6W 80
Pentium Processor 66 MHZ PGA 273 21 x 21 2 16 x 2 16 13W 16W 70
5
AP-480
4 2 Case Temperature If the case temperature is measured with a heat sink
attached to the package drill a hole through the
Case temperature denoted TC is measured at the cen- heat sink to route the thermocouple wire out
ter of the top surface (on top of the heat spreader see
Figure 1) of the package typically the hottest point on
the package case Special care is required when measur- 4 3 Junction Temperature
ing the case temperature to ensure an accurate tempera-
ture measurement Thermocouples are often used to Junction temperature denoted TJ is the average tem-
measure TC Before any temperature measurements perature of the die within the package
the thermocouples have to be calibrated When measur-
ing the temperature of a surface which is at a different The junction temperature for a given junction-to-ambi-
temperature from the surrounding ambient air errors ent thermal resistance power dissipation and ambient
could be introduced in the measurements The mea- temperature is given by the following formula
surement errors could be due to having a poor thermal
contact between the thermocouple junction and the sur- TJ e PD iJA a TA
face heat loss by radiation or by conduction through
thermocouple leads To minimize the measurement er- If a heat sink with thermal resistance of iSA (sink-to-
rors it is recommended to use the following approach ambient) is used then the thermal resistance from the
junction-to-case iJC is given by the following formula
Use 36 gauge or finer diameter K T or J type ther-
mocouples The laboratory testing was done using a TJ e PD (iJC a iCS a iSA) a TA
thermocouple made by Omega (part number
5TC-TTK-36-36) where
Attach the thermocouple bead or junction to the
center of the package top surface using high thermal iCS is the thermal resistance from the component
conductivity cements The laboratory testing was (case) to the heat sink
done by using Omega Bond (part number OB-100)
The thermocouple should be attached at a 90 angle
as shown in Figure 1 When a heat sink is attached a
hole (no larger than 0 15 ) should be drilled
through the heat sink to allow probing the center of
the package as shown in Figure 1
241575