®
AMD-K6
®
Processor
Thermal
Solution Design
Application Note
Publication # 21085
Rev: I
Issue Date: February 1999
Amendment/0
The contents of this document are provided in connection with Advanced
Micro Devices, Inc. ("AMD") products. AMD makes no representations or
warranties with respect to the accuracy or completeness of the contents of this
publication and reserves the right to make changes to specifications and
product descriptions at any time without notice. No license, whether express,
implied, arising by estoppel or otherwise, to any intellectual property rights
is granted by this publication. Except as set forth in AMD’s Standard Terms
and Conditions of Sale, AMD assumes no liability whatsoever, and disclaims
any express or implied warranty, relating to its products including, but not
limited to, the implied warranty of merchantability, fitness for a particular
purpose, or infringement of any intellectual property right.
AMD’s products are not designed, intended, authorized or warranted for use
as components in systems intended for surgical implant into the body, or in
other applications intended to support or sustain life, or in any other
application in which the failure of AMD’s product could create a situation
where personal injury, death, or severe property or environmental damage
may occur. AMD reserves the right to discontinue or make changes to its
products at any time without notice.
© 1999 Advanced Micro Devices, Inc.
All rights reserved.
Trademarks
AMD, the AMD logo, K6, and combinations thereof are trademarks, and AMD-K6 is a registered trademark of
Advanced Micro Devices, Inc.
Other product names used in this publication are for identification purposes only and may be trademarks of their
respective companies.
21085I/0—February 1999
AMD-K6® Processor Thermal Solution Design
Contents
Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
System Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Thermal Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Heatsink . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Heat Dissipation Path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Interface Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Layout and Airflow Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
4
5
6
Voltage Regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Heatsink and Fan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Airflow Management in a System Design . . . . . . . . . . . . . . . . . 8
Airflow Management in the ATX Form Factor . . . . . . . . . . . . . 9
Additional Box Fans. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Thermal Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Measuring Case Temperature . . . . . . . . . . . . . . . . . . . . . . . . . .
Thermal Power Utility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Recommended Thermal Solutions for the AMD-K6®
Processor Family . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Additional Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Contents
11
12
13
13
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AMD-K6® Processor Thermal Solution Design
iv
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Contents
AMD-K6® Processor Thermal Solution Design
21085I/0—February 1999
List of Figures
Figure 1. Passive Heatsink Thermal Model . . . . . . . . . . . . . . . . . . . . 4
Figure 2. Processor Heat Dissipation Path . . . . . . . . . . . . . . . . . . . . 4
Figure 3. CPGA Package Thermal Resistance Model. . . . . . . . . . . . 5
Figure 4. Voltage Regulator Placement . . . . . . . . . . . . . . . . . . . . . . . 7
Figure 5. Airflow for a Heatsink with Fan . . . . . . . . . . . . . . . . . . . . . 8
Figure 6. Airflow Path in a Dual-Fan System . . . . . . . . . . . . . . . . . . 8
Figure 7. Airflow Path in an ATX Form-Factor System . . . . . . . . . . 9
Figure 8. Standard Mid-Tower Case . . . . . . . . . . . . . . . . . . . . . . . . . 11
Figure 9. Measuring Case Temperature. . . . . . . . . . . . . . . . . . . . . . 12
List of Tables
Table 1.
AMD-K6 Processor Family TCASE Specifications . . . . . . . 1
Table 2.
Summary of Chassis Box Fan Configurations . . . . . . . . . 10
List of Figures and Tables
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AMD-K6® Processor Thermal Solution Design
vi
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List of Figures and Tables
21085I/0—February 1999
AMD-K6® Processor Thermal Solution Design
Revision History
Date
Rev
March 1998
E
Improved detail of Figure 1, “Passive Heatsink Thermal Model,” on page 4 and Figure 4, “Voltage
Regulator Placement,” on page 7.
March 1998
E
Added system design considerations for fansink implementations. See “Heatsink and Fan” on
page 7.
March 1998
E
Combined recommended fansink solutions into one table. See Table 2, “AMD-K6® Processor
Model 6 Fansink Recommendations.”
March 1998
E
Added new fansink manufacturers and models to Table 4, “Manufacturer Contact List.”
May 1998
F
Revised “Recommended Fansinks for the AMD-K6® Processor Model 7 and AMD-K6®-2 Processor
Model 8” to include AMD-K6-2 processor Model 8 information.
May 1998
F
Revised Table 2, “AMD-K6® Processor Model 6 Fansink Recommendations” and Table 4,
“Manufacturer Contact List.”
May 1998
F
Added Table 3, “Additional AMD-K6® Processor Models 7 and AMD-K6®-2 Processor Model 8
Fansink Recommendations.”
Aug 1998
G
Removed package thermal specifications tables. For thermal specifications, added reference to the
applicable AMD-K6 and AMD-K6-2 Processor Data Sheets.
Aug 1998
G
Revised Table 2, “AMD-K6® Processor Model 6 Fansink Recommendations” and Table 4,
“Manufacturer Contact List.”
Aug 1998
G
Added recommended 350 MHz AMD-K6-2 processor thermal solutions to Table 3, “Additional
AMD-K6® Processor Model 7 and AMD-K6®-2 Processor Model 8 Fansink Recommendations.”
Nov 1998
H
Revised Figure 9, “Measuring Case Temperature,” on page 12.
Nov 1998
H
Combined paragraphs “Recommended Fansinks for the AMD-K6® Processor Model 6” and
“Recommended Fansinks for the AMD-K6® Processor Model 7 and AMD-K6®-2 Processor Model
8” into one paragraph.
Nov 1998
H
Replaced Recommended Fansinks (Tables 2 and 3) and the Manufacturer Contact List (Table 4)
with a reference to the Recommended Thermal Solution section of the AMD website.
Feb 1999
I
Added references for the AMD-K6-III processor, where applicable.
Feb 1999
I
Added Table 1, “AMD-K6® Processor Family TCASE Specifications.”
Feb 1999
I
Revised “Thermal Power Utility” on page 12 to reflect the latest recommended utility.
Revision History
Description
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AMD-K6® Processor Thermal Solution Design
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Revision History
AMD-K6® Processor Thermal Solution Design
21085I/0—February 1999
Application Note
AMD-K6
®
Processor Thermal
Solution Design
Unless otherwise noted, the information in this application
note pertains to all processors in the AMD-K6® family, which
includes the AMD-K6 processor (Models 6 and 7), the
AMD-K6-2 processor (Model 8), and the AMD-K6-III processor
(Model 9).
Introduction
The operating specification for the AMD-K6 processor family
calls for the case temperature (TCASE) to be in the range of 0°C
to TCASE Max. It is important to maintain the case temperature
w i t h i n t h e s p e c i f ic a t i o n fo r n o rm a l o p e ra t io n . I f t h e
specification is exceeded, the result can be functional failures,
damage to the device, or reduction in long term reliability.
Table 1 on page 1, lists the TCASE specifications for the desktop
AMD-K6 processor family.
Table 1.
AMD-K6® Processor Family TCASE Specifications
Processor Family
Minimum
Maximum
AMD-K6®
0°C
70°C
AMD-K6-2
0°C
60°C, 65°C, or 70°C
AMD-K6-III
0°C
65°C
Note
*
Note:
* Refer to the AMD-K6®-2 Processor Data Sheet, order# 21850 for operating specifications
as they apply to each AMD-K6-2 offering.
Introduction
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AMD-K6® Processor Thermal Solution Design
21085I/0—February 1999
An effective thermal management system is the best way to
maintain the case temperature within specification. In addition
to the thermal characteristics and power dissipation of the
processor, the temperature of the processor case is dependent
on internal ambient temperature and air velocity. The internal
ambient temperature is affected by several variables —
electronic components, peripherals, thermal characteristics of
the chassis, and external ambient temperature.
Thermal management consists of heatsinks, thermal interface
materials, heatsink clips, fans, chassis ventilation, and
component placement. This application note is intended to
guide the system designer through the process of developing an
effective thermal solution for the AMD-K6 processor.
For information about the thermal specifications for the
following AMD-K6 processors:
■
■
■
AMD-K6 processor Model 6 (0.35-µm process technology)
and the AMD-K6 processor Model 7 (0.25-µm process
technology), refer to the AMD-K6® Processor Data Sheet,
order# 20695.
AMD-K6-2 processor Model 8 (0.25-µm process technology),
refer to the AMD-K6®-2 Processor Data Sheet, order# 21850.
AMD-K6-III processor Model 9 (0.25-µm process technology),
refer to the AMD-K6®-III Processor Data Sheet, order# 21918.
System Conditions
The environmental specifications on most systems guarantee
o p era t io n fo r ex t e rna l a m b ie n t s u p t o 35 ° C. M o st P C
chassis/system boxes result in an internal 10°C increase in
temperature over the external ambient temperature. In
general, this means the thermal solution should be designed to
allow an internal ambient (TA) of 45°C.
2
Introduction
AMD-K6® Processor Thermal Solution Design
21085I/0—February 1999
Thermal Solutions
Heatsink
Figure 1 on page 4 shows the thermal model of a processor with
a passive thermal solution. The thermal resistance of a heatsink
is determined by the heat dissipation surface area, the material
and shape of the heatsink, and the airflow volume through the
heatsink. In general, the larger the surface area the lower the
thermal resistance. Heatsink designs use fins to increase the
amount of dissipating surface area in contact with the ambient
air. A larger surface area usually results in a lower thermal
resistance. Some designs implement cross-cutting along the fins
to allow omnidirectional airflow through the heatsink.
The required thermal resistance of a heatsink ( θ SA ) can be
calculated using the following example:
If:
TC = 65°C
TA = 45°C
PMAX = 29.5W
Then:
TC – TA
20°C - = 0.678°C ⁄ W
θ CA ≤ ------------------- = ---------------- P
29.5W
MAX
Where:
TC
= Processor case temperature
TA
= Ambient temperature
PMAX = Maximum power consumption
θCA = Case-to-ambient thermal resistance
Using an interface material with a low thermal resistance of
approximately 0.20 ° C/W (i.e. thermal grease), the required
thermal resistance of the heatsink (θSA) is calculated as follows:
θSA = θCA – θIF = 0.678 – 0.20 = 0.478 °C/W
Where:
θCA = Case-to-ambient thermal resistance
θIF = Interface material thermal resistance
θSA = Sink-to-ambient thermal resistance
Thermal Solutions
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AMD-K6® Processor Thermal Solution Design
21085I/0—February 1999
Ambient Air
Temperature Delta
(Case-to-Ambient)
TCA
θSA
Thermal
Resistance
(°C/W)
θCA
Sink
Case
θIF
Figure 1. Passive Heatsink Thermal Model
Heat Dissipation Path
Figure 2 illustrates the heat dissipation path of the processor.
Due to the lower thermal resistance between the processor die
junction and case, most of the heat generated by the processor
is transferred from the top surface of the case. The small
amount of heat transferred from the bottom side of the
processor can be safely ignored due to high thermal resistance
(the processor socket blocks convection).
Ambient Temperature
Thin Lid
Case Temperature
Figure 2. Processor Heat Dissipation Path
Figure 3 on page 5 illustrates the overall thermal resistance
model of a socketed AMD-K6 processor with a heatsink
att ached. The t herma l resistance of t he primary heat
dissipation path is much lower than the secondary heat
dissipation path. Therefore, most of the heat is transferred from
the top side of the processor. In Figure 3, θCA represents the
thermal resistance from the top of the case to ambient. It
includes the thermal resistance of the thermal interface
material and the heatsink, which must be considered when
designing a thermal solution for the AMD-K6 processor.
4
Thermal Solutions
AMD-K6® Processor Thermal Solution Design
21085I/0—February 1999
Heat Sink
Thin Lid
Thermal Interface Material
Ceramic substrate
Die
Heat Sink Clip
ZIF Socket
Print-Circuit Board
Primary Heat Dissipation Path
Ambient
Radiation
Convection
Heat Sink
External Resistance
Case Temperature
Thermal Interface Material
Thin Lid and Grease
Silicon
C4 Bumps
PGA Package
θCA
Chip Junction
Junction Temperature
θJC
Underfill
Ceramic Substrate
Package Pins
Print-Circuit Board and Socket
External Resistance
Radiation
Convection
Secondary Heat Dissipation Path
Figure 3. CPGA Package Thermal Resistance Model
Interface Materials
The interface material used between the heatsink and
processor is important. The purpose of this material is to fill any
microscopic air gaps and ensure a thermally efficient path is
established for heat to flow from the package into the heatsink.
There are several different types of thermally conductive
interface material in use today. The most common are grease,
wax, thermal pads/tapes, and epoxy. While dry interfaces (pads
and tapes) are often the easiest to use, they have the poorest
thermal resistance. They are not recommended because small
pockets of air can be trapped during installation. Wet or paste
interfaces (grease, gel, wax, and epoxy) have lower thermal
resistances and allow air bubbles to migrate out of the interface
material.
Although epoxy, when handled correctly, can provide a
reasonable thermal interface, it is not a reliable mechanical
attachment. Caution should also be taken with pre-applied
waxes, because pockets of air (a poor thermal conductor) can be
Thermal Solutions
5
AMD-K6® Processor Thermal Solution Design
21085I/0—February 1999
trap p e d b en eath the heats i nk d ur i ng as s embly. AM D
recommends the use of grease and gels as thermal interfaces.
These materials are able to maintain the lowest thermal
resistance more consistently. In general, these materials can
achieve a thermal resistance of 0.15 to 0.3°C/W.
The application of interface material, in addition to material
type, is also important. Its purpose is simply to fill microscopic
air gaps and ensure a thermally efficient path for heat transfer.
Only a thin layer of interface material is desired between the
heatsink and processor. Excessive amounts of interface
material will restrict the flow of heat to the heatsink and
thereby make the thermal solution less effective.
Due to the light weight of most heatsinks, mechanical clips are
the recommended method of attachment. In addition to
providing stability, clips provide approximately 10–15 pounds
of downward pressure on the heatsink to minimize the thermal
resistance of the thermal interface material.
Layout and Airflow Considerations
Voltage Regulator
Voltage regulators, typically power transistors, are used to
provide the core and I/O voltages to the processor. In most
designs, separate heatsinks are also required to dissipate the
heat from the power transistors. The processor heatsink fins
should be aligned parallel to the chassis airflow and the voltage
regulators as shown in Figure 4 on page 7. With this alignment,
the heat generated by the voltage regulators has minimal effect
on the processor.
6
Layout and Airflow Considerations
AMD-K6® Processor Thermal Solution Design
21085I/0—February 1999
Voltage Regulator (VCC Core)
Heatsink Fins Aligned
With Airflow
Airflow
Voltage Regulator (VCC I/O)
Figure 4. Voltage Regulator Placement
Heatsink and Fan
A heatsink and fan combination, or fansink, can deliver even
better thermal performance than a heatsink alone. More
importantly, airflow requirements in a system design are not as
critical with a fansink. The fan pulls air from above the fan,
through the heatsink, and out the heatsink sides. When using a
fansink solution, the best location for the voltage regulators is
on the side of the processor, in the path of the air exiting the
fansink (See Figure 5 on page 8). Such a location guarantees
that the heatsinks on both the processor and the regulator
receive adequate airflow.
Fansinks are more effective when the following design
techniques are employed:
■
■
To avoid impeding airflow within the chassis to the fansink,
route ribbon cables between the system motherboard and
chassis drive bays.
To provide a sufficient volume of air to the fansink, maintain
a 1/2 inch clearance above the fansink.
Layout and Airflow Considerations
7
AMD-K6® Processor Thermal Solution Design
21085I/0—February 1999
Airflow
Ideal areas for voltage regulator
Figure 5. Airflow for a Heatsink with Fan
Airflow Management in a System Design
Complete airflow management in a system is important. In
addition to the speed and volume of air, the path of the air is
also important. Figure 6 shows the airflow in a dual-fan system.
The fan in the front end pulls cool air into the system through
intake slots in the chassis. The power supply fan acts as an
exhaust and forces the hot air out of the chassis. The thermal
performance of the heatsink can be maximized if it is located in
the shaded area with the fins oriented parallel to the airflow
path.
Fan
P/S
Main Board
V
e
n
t
s
Drive Bays
Fan
Vents
Front
Figure 6. Airflow Path in a Dual-Fan System
8
Layout and Airflow Considerations
AMD-K6® Processor Thermal Solution Design
21085I/0—February 1999
Airflow Management in the ATX Form Factor
Figure 7 shows the airflow management in a system using the
ATX form-factor. The orientation of the power supply fan and
the motherboard are modified in the ATX platform design. The
power supply fan generates airflow through the chassis and
across the processor. The processor is located near the power
supply fan where it can receive maximum airflow without an
auxiliary fan. This arrangement significantly improves the
airflow across the processor with minimum installation cost.
Main Board
F
a
n
P/S
Air Vents
Drive
Bays
Figure 7. Airflow Path in an ATX Form-Factor System
Additional Box Fans
Additional box fans can enhance the effectiveness of the
airflow within the chassis. Table 2 on page 10 summarizes the
effect of different numbers and configurations of box fans in
the chassis. The purpose of the box fans is to improve
circulation of air within the chassis. The box fans used in this
experiment were chosen to fit the existing mountings in the
chassis. The front fan is an 80-mm 35-CFM fan and the rear fan
is a 60-mm 25-CFM fan. The goal of better circulation is to
reduce the ambient temperature inside the chassis.
Layout and Airflow Considerations
9
AMD-K6® Processor Thermal Solution Design
21085I/0—February 1999
For the given chassis, different combinations of fans were
tested. The tests were performed in an oven with a constant
temperature of 35°C, and the internal ambient temperature of
t h e ch a s s i s wa s m e a s u re d w i t h a t h e r m o c o u p l e . Th e
thermocouple was located two inches from the processor as
shown in Figure 8 on page 11. A control case was run with no
added fans in the chassis and it resulted in an internal ambient
of 48.2°C. The best improvement in ambient temperature was
observed with the configuration of a single box fan added to the
chassis as an intake fan in the rear wall of the system chassis.
This fan placement resulted in a decrease in ambient
temperature from 48.2°C to 43.6°C. See Table 2 for a complete
summary of fan and chassis combinations. Also, note that the
best case temperature (TCASE) for the processor was obtained
w h e n t h e i n t e r n a l a m b i e n t t e m p e ra t u re wa s h e l d t o
approximately 44.4°C. As shown in the test, the lowest ambient
temperature is not always an indicator of the lowest T CASE .
Ambient temperature is very dependent on the airflow path
and how it is measured. The only way to completely verify a
thermal solution is to measure TCASE.
Table 2.
10
Summary of Chassis Box Fan Configurations
Thermal Test Condition
Test #1
Test #2
Test #3
Test #4
Rear Wall System Fan
Off
Off
Exhaust
Intake
Front Wall System Fan
Off
Intake
Intake
Off
Processor, TCASE
68.8°C
69°C
64.1°C
65.9°C
Internal Ambient Temperature
48.2°C
48.7°C
44.4°C
43.6°C
Layout and Airflow Considerations
AMD-K6® Processor Thermal Solution Design
21085I/0—February 1999
Rear
Front
Fan
Power
Supply
Drive Bays
Box Fan
AMD-K6® Processor
Regulator
Heatsink
Inside Ambient
Thermocouple
Box Fan
Intake Vent
Figure 8. Standard Mid-Tower Case
Thermal Evaluation
Measuring Case Temperature
The processor case temperature is measured to ensure that the
t h e r m a l s o l u t i o n m e e t s t h e p ro c e s s o r ’s o p e ra t i o n a l
specification. This temperature should be measured on the top
center of the package where most of the heat is dissipated.
Figure 9 on page 12 shows the correct location for measuring
the case temperature. If a heatsink is installed while
measuring, the thermocouple must be installed into the
heatsink via a small hole drilled through the heatsink base (for
example, 1/16 of an inch). The thermocouple is then attached to
the base of the heatsink and the small hole filled using thermal
epoxy, allowing the tip of the thermocouple to touch the top of
the processor case.
Thermal Evaluation
11
AMD-K6® Processor Thermal Solution Design
21085I/0—February 1999
Thermally Conductive Epoxy
Thermocouple
Figure 9. Measuring Case Temperature
Thermal Power Utility
A software utility has been developed to assist in testing
thermal solutions. This utility executes a tight loop of
instructions whose addressing and data have been defined to
put the AMD-K6 processor in a state that dissipates the
maximum thermal power. This utility can be used to determine
if a given thermal solution is sufficient to maintain the
specified TCASE limit.
To use this utility, execute the DOS program, Maxpwr99.exe as
follows: (Note: Do not execute the utility in a DOS window or with
a memory manager loaded.)
c:\>Maxpwr99.exe
The program executes in an infinite loop until exited. While
executing, the processor’s case temperature can be measured.
In addition, the actual power dissipation should be determined
by measuring the voltage and current supplied to the processor.
Note: Use a daughter card to allow the processor current to be
measured in series with an Ohmmeter. Take all
measurements close to the processor (use short lead wires).
If the processor power is less than the maximum thermal power
specification, a linear estimate must be used to determine if the
thermal solution maintains the case temperature below its
specified limit.
12
Thermal Evaluation
AMD-K6® Processor Thermal Solution Design
21085I/0—February 1999
The Maxpwr99.exe utility is available under a nondisclosure
a g re e m e n t . C o n t a c t yo u r l o c a l A M D s a l e s o f f i c e fo r
information.
Recommended Thermal Solutions for the AMD-K6® Processor Family
AMD continually works with heatsink and fan manufacturers to
identify thermal solutions for the AMD-K6 processor family. A
list of solutions that maintain the case temperature of the
AMD-K6 processor below the specified maximum temperature
is available in the Recommended Thermal Solutions section of
the AMD website, www.amd.com.
Most of the solutions listed are available as-is and can be
ordered as a combination or kit from the manufacturer. These
solutions are available as a heatsink and fan combination.
Other solutions require the use of a specific fan, mounted on
top of the heatsink, capable of sufficient air flow (for example,
24 CFM for the 233-MHz AMD-K6 processor). In such cases, the
fan and heatsink can be ordered separately from each
manufacturer.
Additional Information
For more information about the following AMD-K6 processors:
■
■
■
Additional Information
AMD-K6 processor Models 6 and 7, see the AMD-K6®
Processor Data Sheet, order# 20695 or contact your local AMD
sales representative.
AMD-K6-2 processor Model 8, see the AMD-K6®-2 Processor
Data Sheet, order# 21850 or contact your local AMD sales
representative.
AMD-K6-III processor Model 9, see the AMD-K6®-III
Processor Data Sheet, order# 21918 or contact your local AMD
sales representative.
13
AMD-K6® Processor Thermal Solution Design
14
21085I/0—February 1999
Additional Information