ETC AMD-K5

®
TM
AMD-K5™
PROCESSOR
Thermal Considerations
Application Note
Publication # 20092
Issue Date: September 1996
Rev: B
Amendment/0
This document contains information on a product under development at Advanced Micro
Devices (AMD). The information is intended to help you evaluate this product. AMD reserves the right to change or discontinue work on this proposed product without notice.
© 1996 Advanced Micro Devices, Inc. All rights reserved.
Advanced Micro Devices reserves the right to make changes in its products
without notice in order to improve design or performance characteristics.
This publication neither states nor implies any representations or warranties
of any kind, including but not limited to any implied warranty of merchantability or fitness for a particular purpose.
AMD makes no representations or warranties with respect to the accuracy or
completeness of the contents of this publication or the information contained
herein, and reserves the right to make changes at any time, without notice.
AMD disclaims responsibility for any consequences resulting from the use of
the information included herein.
Trademarks
AMD, the AMD logo, and combinations thereof are trademarks of Advanced Micro Devices, Inc.
AMD-K5 is a 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.
20092B/0—Sep1996
AMD-K5 Processor Thermal Considerations
Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Definition of Thermal Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Heat Sinks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Heat Sink Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Types of Heat Sinks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Heat Sink Mechanical Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Thermal Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Thermal Grease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Thermal Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Thermal Grease with Aluminum Carrier . . . . . . . . . . . . . . . . . . . . . . 14
Thermal Adhesive Tape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
The AMD-K5 Processor Thermal and Power Specifications. . . . . . . 17
Physical Dimensions of the AMD-K5 Processor . . . . . . . . . . . . . . . . . 17
Personal Computer System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Thermal Measurement Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Thermal Characterization of the AMD-K5 Processor
296-Pin Ceramic PGA Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Thermal Resistance Calculations with No Heat Sink . . . . . . . . . . . . 24
Thermal Resistance Calculations with Pin Fin Heat Sink A . . . . . . 25
Thermal Resistance Calculations with Pin Fin Heat Sink B . . . . . . 28
Thermal Resistance Calculations with Pin Fin Heat Sink C . . . . . . 31
Conclusion (Final Checklist) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Vendors and Manufacturers for the AMD-K5 Processor . . . . . . . . . 35
Heat Sink Vendors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Other Manufacturers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Contents
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AMD-K5 Processor Thermal Considerations
iv
20092B/0—Sep1996
Contents
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
List of Tables
Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Table 6.
Table 7.
Table 8.
Table 9.
Table 10.
Table 11.
Table 12.
Table 13.
Table 14.
Table 15.
Table 16.
v
Heat Sink/Fan Module Specifications . . . . . . . . . . . . . . . 9
Thermal Conductivity Values for Materials
Used In Cooling Solutions . . . . . . . . . . . . . . . . . . . . . . . 13
Thermal Conductive Adhesive Tapes . . . . . . . . . . . . . . 15
Operating Range of the AMD-K5 Processor . . . . . . . . . 17
Test Heat Sink Characteristics for
Fifth-Generation Processors . . . . . . . . . . . . . . . . . . . . . . 22
Table of Thermal Measurements . . . . . . . . . . . . . . . . . . 23
Thermal Resistance Calculations with No Heat Sink . 24
Heat Sink A with Thermal Grease . . . . . . . . . . . . . . . . . 25
Heat Sink A with White Pad . . . . . . . . . . . . . . . . . . . . . 25
Heat Sink A with Rose Pad . . . . . . . . . . . . . . . . . . . . . . 25
Heat Sink B with Thermal Grease . . . . . . . . . . . . . . . . . 28
Heat Sink B with White Pad. . . . . . . . . . . . . . . . . . . . . . 28
Heat Sink B with Rose Pad. . . . . . . . . . . . . . . . . . . . . . . 28
Heat Sink C with Thermal Grease . . . . . . . . . . . . . . . . . 31
Heat Sink C with White Pad. . . . . . . . . . . . . . . . . . . . . . 31
Heat Sink C with Rose Pad. . . . . . . . . . . . . . . . . . . . . . . 31
List of Tables
AMD-K5 Processor Thermal Considerations
vi
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List of Tables
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
List of Figures
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7A.
Figure 7B.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
Figure 15.
Figure 16.
Figure 17.
Figure 18.
Figure 19.
List of Figures
Series Resistance Representation of the
Thermal Resistance Path . . . . . . . . . . . . . . . . . . . . . . . . 4
Natural and Forced Convection Curves for a
Typical Heat Sink . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Extruded and Pin Fin Heat Sinks . . . . . . . . . . . . . . . . . 8
Heat Sink Impingement Airflow . . . . . . . . . . . . . . . . . 10
Mechanical Interface from AMD-K5 Processor to
Heat Sink Options (Personal Computer Power
System Fan Generates Airflow) . . . . . . . . . . . . . . . . . 11
Mechanical Interface from AMD-K5 Processor to
Heat Sink/Fan Module Options (Airflow
Generated by Fan on Module). . . . . . . . . . . . . . . . . . . 12
296-Pin Ceramic Staggered Pin Grid Array . . . . . . . . 18
296-Pin Ceramic Staggered Pin Grid Array
With Thermal Slug . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Airflow Through the Personal Computer Chassis . . . 20
Test Setup to Measure AMD-K5 Processor Case
and Heat Sink Temperature . . . . . . . . . . . . . . . . . . . . 21
AMD-K5 Processor With No Heat Sink. . . . . . . . . . . . 24
Heat Sink A with Thermal Grease . . . . . . . . . . . . . . . 26
Heat Sink A with White Pad . . . . . . . . . . . . . . . . . . . . 26
Heat Sink A with Rose Pad . . . . . . . . . . . . . . . . . . . . . 27
Heat Sink B with Thermal Grease. . . . . . . . . . . . . . . . 29
Heat Sink B with White Pad . . . . . . . . . . . . . . . . . . . . 29
Heat Sink B with Rose Pad . . . . . . . . . . . . . . . . . . . . . 30
Heat Sink C with Thermal Grease . . . . . . . . . . . . . . . 32
Heat Sink C with White Pad . . . . . . . . . . . . . . . . . . . . 32
Heat Sink C with Rose Pad . . . . . . . . . . . . . . . . . . . . . 33
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AMD-K5 Processor Thermal Considerations
viii
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List of Figures
20092B/0—Sep1996
AMD-K5 Processor Thermal Considerations
AMD-K5™ Processor
Thermal Considerations
Introduction
All semiconductor devices dissipate heat as a byproduct of normal operation. Prior to fourth-generation processors, these
devices were able to dissipate heat via the integrated circuit
package in most personal computer applications. Fifth-generation processors use sub-micron, CMOS VLSI integrated circuit
technology to support superscalar processor architecture like
the AMD-K5™ processor, which has integrated more than
3 million transistors on a single semiconductor die. Fifth-generation processors generally operate at a reduced supply voltage
to minimize power consumption. Reducing Vcc from +5 V to
+3.3 V decreases the power consumption by approximately 43
percent. Even with this power savings, fifth-generation processors can still exceed the maximum case temperature specification when operating at maximum clock frequency. External
integrated cooling solutions such as heat sinks, heat spreaders,
and heat sink/fan modules are required to maintain safe thermal margins for the processor junction temperature.
This application note discusses integrated circuit cooling solutions, thermal terms, and explains the thermal equations. This
information allows designers to select the best processor cooling solution for personal computer applications. These solutions should have the following attributes: maintain safe
Introduction
1
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
processor thermal margins, be a non-custom solution that is
readily available, be easy to attach to personal computer motherboards, have adequate mechanical attachment to withstand
personal computer shock and vibration specifications, and be
cost effective.
Definition of Thermal Terms
This section defines the thermal-related terms used in this
document.
Temperature (T) is the degree of hotness or coldness of a material. The temperature abbreviation, T, is used in the following
terms:
■
■
■
■
Tjunction is the junction temperature of the processor die
Tcase is the temperature of the processor case
Ts is the temperature of the heat sink
Ta is the ambient temperature. Ambient temperature is the
average or mean temperature of the surrounding air that
comes in contact with the unit under test. For personal computer applications, ambient temperature is the average
temperature inside the personal computer that comes in
contact with the heat sink and processor case.
Thermal Resistance (θ) is the opposition offered by a medium
to the passage of thermal energy and is expressed in units of
oC / watts. The thermal resistance abbreviation, θ, is used in
the following terms:
■
■
■
θjc is the thermal resistance from junction to processor case
θcs is the thermal resistance from case to heat sink
θsa is the thermal resistance from heat sink to ambient air
Heat Transfer is the process of thermal energy flowing from a
body of higher temperature to a body of lower temperature.
The means of transfer are conduction, convection, and radiation.
Natural Convection is the movement of ambient air over,
around, and through a heat sink that is induced by temperature differences generated as a byproduct of processor power
2
AMD-K5™ Processor Thermal Considerations
20092B/0—Sep1996
AMD-K5 Processor Thermal Considerations
dissipation, also known as buoyancy effects. When air is
heated around the processor, warm air rises and cool air sinks,
causing air circulation around the processor package.
Forced Air Convection is caused by an active power element
(e.g., a fan or a blower) that forces air to circulate around and
through the heat sink channels (extruded and pin fin heat
sinks). Heat sink/fan modules use impingement airflow to force
air into the top of the heat sink. A hot wire anemometer can be
used in wind tunnels to characterize heat sinks and heat
spreaders. The anemometer is generally located in front of the
heat sink (e.g., 2 inches) to minimize the effect of the air turbulence caused by the heat sink.
Heat Sinks are devices designed to transfer heat generated by
an electronic component to a gas or a liquid. They are usually
made of heat-conductive metal that has the ability to rapidly
transmit heat from the generating source to the ambient air.
Heat Conduction is the transmission of heat by random molecular motion or vibration from a hotter region to a cooler region
in the conducting media.
Convection is the transmission of thermal energy by random
molecular motion or vibration and gross bulk motion of a fluid
from a hotter region to a cooler region through a moving
medium, such as air or water.
Radiation is the process of emission, transmission, and absorption of thermal energy by electromagnetic waves between bodies separated by empty space.
Thermocouples are sensing devices constructed of two dissimilar metals with a junction point. A thermocouple develops a
voltage proportional to the difference in temperature between
the hot junction and the lead wires. These devices are used to
measure the temperature of materials.
Heat Sinks
A heat sink is thermally connected to the AMD-K5 processor to
dissipate the heat it generates as a byproduct of its normal
operation. If this heat is not removed, the processor would
Heat Sinks
3
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
exceed its maximum operating temperature and fail. The junction temperature of the processor is a function of the thermal
resistance between the junction and the ambient air, the
amount of heat being dissipated, and the ambient air
temperature.
Heat Sink Equations
The total thermal resistance from junction to ambient air, θja,
is equal to the sum of the following: thermal resistance from
junction to case, thermal resistance from case to heat sink, and
thermal resistance from heat sink to ambient air (see Equation
1 and Figure 1 for more information).
Equation 1
θja = θjc + θcs + θsa
Figure 1. Series Resistance Representation of the Thermal Resistance Path
When the processor dissipates heat via the thermal interface
layer, the relationship of the temperatures at the different
thermal boundaries is found by using Equation 2:
Equation 2
Pmax = (Tj - Ta) / (θjc + θcs + θsa)
where
■
■
■
4
Pmax is the maximum power consumption (in watts) of the
AMD-K5 processor
Tj is the operating junction temperature of the processor
die
Ta is the average ambient temperature inside the personal
computer enclosure
AMD-K5™ Processor Thermal Considerations
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
■
■
■
θjc is the thermal resistance from junction to case
θcs is the thermal resistance from case to heat sink
θsa is the thermal resistance from heat sink to ambient air
The above relationship can also be stated in the following
forms:
Equation 3
Pmax = (Tc - Ta) / (θcs + θsa)
Equation 4
Pmax = (Ts - Ta) / (θsa)
where
■
■
Tc is the case temperature of the AMD-K5 processor
Ts is the heat sink temperature
The heat sink selection process requires knowledge of the following system variables:
■
■
■
■
■
Available volume of space to be occupied without interference of other system components (e.g., personal computer
expansion cards, side walls of enclosure, peripherals,
cables, etc.)
The maximum allowable device junction temperature of
the processor die
The maximum power dissipation of the processor
The device configuration (package size and orientation of
the package)
Ambient conditions (temperature, air velocity, and airflow
direction)
Types of Heat Sinks
The most frequently used heat sinks for processor cooling
applications are discussed in the following sections. These heat
sinks are designed to transfer heat from the processor into the
air inside a personal computer case. Several manufacturers
offer standard, cost effective, aluminum products (e.g.,
extruded, pin fin, die cast), composition products, and custom
products. Each heat sink should have the following items specified: thermal resistance (i.e., natural and forced air), size
(length, width, and height), and weight. Many heat sink product families have one standard shape and varying heights
Heat Sinks
5
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
(e.g., 0.25 in, 0.5 in, 0.75 in, 1.00 in, 1.25 in, etc.) to handle different processor speed grades. The speed of an AMD-K5 processor is directly proportional to its power consumption (see
The AMD-K5 Processor Thermal and Power Specifications on page
17 for more information). Larger heat sinks usually cost more
and can have reduced internal airflow. Airflow is a function of
the friction coefficient, channel size, surface conditions, and
heat sink shape. Closely examine the geometry of the heat sink
to determine the best heat sink orientation for reducing airflow resistance.
Heat sink thermal performance is expressed for both natural
and forced airflow. A typical heat sink performance curve (see
Figure 2) is shown with two curves. Natural convection is represented by the positive slope curve. This curve is read from
the left axis (heat sink temperature) and bottom axis (heat dissipation). Forced convection is represented by the negative
slope curve. This curve is read from the upper axis (air velocity) and the right axis (thermal resistance from sink to ambient). Airflow is often the biggest uncertainty for processor
designs and it is the most important variable on heat sink thermal performance.
6
AMD-K5™ Processor Thermal Considerations
20092B/0—Sep1996
AMD-K5 Processor Thermal Considerations
Figure 2. Natural and Forced Convection Curves for a Typical Heat Sink
Extruded Aluminum
Heat Sinks
The extruded aluminum heat sink is the least expensive processor cooling solution, but it must be aligned with an airflow
or have an attached fan. Many of the least expensive heat sink/
fan modules use aluminum extruded heat sinks.
If the extruded aluminum heat sink is not used with an
attached fan module, the forced airflow must be generated by
the personal computer power supply fan or system fan. The
power supply fan usually blows warm air out of the system
enclosure. Personal computer airflow can be obstructed by any
of the following items: expansion cards, ribbon cables, internal
peripherals, power cables, and brackets. Extruded aluminum
heat sinks are specified usually with airflow entering the heat
sink from one of two open ends. Using the extruded aluminum
heat sink requires an in-depth knowledge of the airflow velocity and direction. To optimize heat sink efficiency, the airflow
should be aligned with the extruded length of the heat sink.
Extruded aluminum heat sinks for the AMD-K5 processor are
available with the following configuration variables: number
of fins, location and thickness of fins, fin heights, and thickness
Heat Sinks
7
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
of the base plate. For an example of an extruded aluminum
heat sink, see Figure 3A.
Figure 3. Extruded and Pin Fin Heat Sinks
The example in Figure 3A has a base plate and 15 fins. The
base plate would have a layer of thermal interface material
applied to it (e.g., thermal grease) and then be mounted
against the top of the AMD-K5 processor ceramic case top. The
dimensions of the heat sinks in Figure 3 are represented by x
and y for the base and h for the height.
Pin Fin Aluminum
Heat Sinks
The pin fin aluminum heat sink is cost effective (e.g., approximately 1.2 times the cost of the extruded aluminum heat sink)
and has the advantage of omnidirectional airflow. This means
that airflow can efficiently enter the heat sink from any side.
The airflow is maximized if it is in line with the row of pins. In
personal computer cases, airflow moves in many directions
because of mechanical restrictions. Therefore, pin fin heat sinks
are generally recommended. For an example of a pin fin heat
sink, see Figure 3B.
The pin fin aluminum heat sink can also be manufactured with
an attached fan module. If a fan is attached, the height of the
module is the combination of the heat sink height and the fan
height.
8
AMD-K5™ Processor Thermal Considerations
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
Heat Sink/Fan
Modules (Pin Fin Heat
Sinks with Attached
Fan)
In this type of module the following items are supplied: heat
sink, DC brushless fan, and fan cable with four-pin power connector. These modules may be purchased in a retail store without any instructions or specifications. It is a gamble for
personal computer system designers to select these modules by
appearance and cost only. The least expensive modules generally come with sleeve bearings in the fan. Such fans are not
noted for their reliability and durability, and are, therefore,
not recommended. Better heat sink/fan modules have ball
bearing fan motors and the following specifications:
Table 1. Heat Sink/Fan Module Specifications
Electrical Fan Specification
1) Type of DC motor
Recommended Specification for AMD-K5 Processors
Brushless DC motor, power supply voltage: +12 V or +5 V
2) Rated motor power consumption Application dependent (e.g., approximately 1 watt)
3) Fan motor should have
With cable and standard 4-pin power supply connector
4) Optional alarm available if fan
fails
When fan speed drops to less than 70% of rated speed
Mechanical Specification
1) Heat sink type
Pin fin, extruded, or die cast aluminum
2) Rated airflow
Application dependent (e.g., 9 cubic feet per minute)
3) Noise
Application dependent (e.g., 27 dB)
4) Size x, y, h
Base plate approximately 2-inch square, and height dependent on application.
See Figure 3 for more information.
5) Attachment means
Heat sink clip
6) Head clearance fan
Clearance height above fan air intake (e.g., 0.5 in to 1 in minimum)
7) Fan bearings
Sealed ball bearing
Thermal Performance
Thermal resistance
Application dependent: thermal specification of the personal computer operating temperatures, power specification of AMD-K5 processor, airflow and flow
direction of the processor
Sleeve bearing fans are less expensive but have as little as
1/10 the expected fan life as the more expensive sealed ball
bearing fan (cost increase for a fan with sealed ball bearing is
less than a $1.00). It is strongly recommended that sealed ball
bearing fan motors be used for heat sink/fan modules. A fan
failure is defined as a fan decreasing to less than 70 percent of
its initial rotational speed. Evox Rifa has a technical note on
Heat Sinks
9
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
fan operating life. See Heat Sink Fan Motor Manufacturer on
page 35 for more information.
The heat sink/fan module uses an attached fan that generates
airflow into the heat sink. This is referred to as impingement
airflow. (see Figure 4 for more information.)
Figure 4. Heat Sink Impingement Airflow
Heat Sink Mechanical Interface
The heat sink mechanical interface (e.g., heat sink clips) is
designed to withstand shock and vibration during shipping and
normal operation. These heat sink clips assert pressure against
the thermal interface and secure the heat sink to one of the following: the AMD-K5 processor, the AMD-K5 processor socket,
or the personal computer motherboard. Different options for
securing mechanical interfaces to the AMD-K5 processor are
shown in Figure 5 and Figure 6. In both figures, options 3 and 4
are recommended. The first two options are not recommended
because the processor can be dislodged from its socket due to
shock and vibration.
10
AMD-K5™ Processor Thermal Considerations
20092B/0—Sep1996
AMD-K5 Processor Thermal Considerations
Figure 5. Mechanical Interface from AMD-K5 Processor to Heat Sink Options (Personal Computer
Power System Fan Generates Airflow)
Heat Sinks
11
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
Figure 6. Mechanical Interface from AMD-K5 Processor to Heat Sink/Fan Module Options (Airflow
Generated by Fan on Module)
12
AMD-K5™ Processor Thermal Considerations
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
Thermal Interfaces
Thermal interface between the case and heat sink is controlled
in a variety of ways using different heat conducting materials.
The interface resistance between the case and the heat sink is
dependent on three variables: p (the thermal resistance of the
interface material in units of (oC · inch2) / (watts · thickness in
inches)), t (the average material thickness in inches), and A
(the area of contact in square inches). These variables are
related in the following equation:
Equation 5
θcs = (p · t ) / A
Table 2 contains typical thermal resistance values for materials used in cooling solutions for semiconductors.
Table 2. Thermal Conductivity Values for Materials Used In Cooling
Solutions
Thermal Interface Materials
Thermal Conductivity
(Watts / (Meter · oC)
Copper (pure)
389
Aluminum (1100 series)
200
Aluminum (6000 series)
220
Beryllia
240
Carbon Steel
60.5
Alumina
21
Anodized Finish
0.5-1.0
Silicone RTV
0.2
Polyimide
0.15
Silicone Grease
0.5-1.0
Dead Air
0.026
The thermal interface material is placed between the top of
the AMD-K5 processor case and the bottom plate of the heat
sink. It is recommended that the heat sink plate have a flatness
tolerance of 0.002′′ to 0.003′′ per inch. The thickness of the
thermal interface material should be minimized to obtain the
lowest possible thermal resistance. The thermal grease compounds are the best materials for the thermal interface, followed by thermal compounds, and then thermal adhesive
Thermal Interfaces
13
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
tapes. (The latter is the least desirable from a thermal standpoint, but the most desirable from a user installation standpoint.)
Thermal Grease
Thermal grease is a compound composed of a carrier, conductor, and binder. The carrier is used to support the conductive
material. The conductor is a material of relatively low thermal
resistance and is added to the carrier as a filter. The binder is a
material that controls the viscosity of the compound. Thermal
grease is applied to both the heat sink and processor case to fill
air gaps between the two surfaces. When using thermal grease,
a heat sink clip is required. An example of thermal grease is
the Thermalcoate I manufactured by Thermalloy, Inc. The
thermal resistance of this material is p, expressed in units of
(oC · inch2) / watts.
Thermal Compounds
An alternative to silicone-based thermal greases (e.g., Sil-Free
by Aavid) is silicone-free thermal joint compound, which is
filled with metal oxide filler. These compounds were developed as an alternative to silicone grease and they do not
exhibit the deterioration or contamination associated with silicone-based products. This material efficiently fills the air gaps
between the top of the processor case and the bottom of the
heat sink. When using these compounds, a heat sink clip is
required.
Thermal Grease with Aluminum Carrier
These products use an aluminum carrier with a typical thickness of 0.004 inches and have uniform droplets of silicone
grease applied to both sides of the aluminum carrier. Both
sides have a protective paper coating that is removed prior to
installation. An example of this product is Conducta-Cote by
Thermalloy, Inc.
14
AMD-K5™ Processor Thermal Considerations
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
Thermal Adhesive Tape
Thermal tapes consist of the following: thermally conductive
carrier, adhesive material coated on both sides, and a clear
release liner used to protect the adhesive surface during shipping and handling. These tapes provide a thermal interface
between the processor case and the heat sink. The adhesive
material provides the mechanical attachment between the
heat sink and processor case. This interface is prone to
mechanical failures if one or more of the following conditions
exist:
■
■
■
■
Foreign material on the heat sink, processor case, or thermal interface tape
Incorrect thickness of thermal interface tape. If the tape is
too thin, air pockets may form. If the tape is too thick, the
thermal resistance increases.
Insufficient pressure applied during installation of tape.
Failure to prepare the surface of the processor case with
ceramic sealer.
For these reasons, thermal tapes are not recommended. But, if
the personal computer design requires the use of thermal tape,
the materials and procedures described below should be used.
Table 3. Thermal Conductive Adhesive Tapes
Typical Properties
Thermal Interfaces
Chomerics
T405
Chomerics
T412
Test Method
Carrier
Aluminum
Expanded
Aluminum
n/a
Color
White
Gray
n/a
Thermal Resistance,
(oC · inch2) / Watt
0.5
1.40
MIL-l-49456A
Thermal Conductivity,
Watt / (Meters · oC)
0.5
0.25
MIL-I-49456A
Thickness (in inches)
0.006
0.009
n/a
Shear Adhesion,
psi @ 25oC
125
135
Chomerics
T.P. 54
Shear Adhesion,
psi @ 150oC
55
25
Chomerics
T.P. 54
15
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
When using thermal conductive adhesive tape it is important
to select one tape that fills the gap between the two surfaces
(tolerance of both processor case top and heat sink is worst
case of 0.003 inch). Therefore, tape thickness of a minimum of
0.006 inch should be used to fill the microscopic holes in the
surfaces.
When ceramic packages are used, some manufacturers recommend using a primer (e.g., 1088 Primer by Chomerics) on the
ceramic package before the adhesive tape is applied. The
primer fills the porous ceramic surface to allow the adhesive
tape to obtain a greater bond surface.
The procedure for applying thermal tape to the AMD-K5 processor and the heat sink is:
1. Cut the tape to a size that can cover the entire area between
the AMD-K5 processor and the heat sink.
2. Make sure that all oils and dust are removed from the
AMD-K5 processor case top and the bottom of the heat sink
to ensure maximum adhesion. This is done by using a lintfree cloth with an industrial cleaner (e.g., toluene, acetone,
or isopropyl alcohol) and rubbing both surfaces.
3. Peel away the clear release liner from the non-embossed
side of the thermal adhesive tape.
4. Apply tape to the AMD-K5 processor case top.
5. Smooth over the entire surface of the tape with moderate
pressure, using the applicator provided.
6. Remove the blue liner from the embossed side of the tape.
7. Align both the AMD-K5 processor and the heat sink and
apply pressure (e.g., 10 psi).
Note: Improved surface contact can be achieved by heating the
tape with a conventional heat gun, not to exceed 100oC,
prior to applying pressure.
8. Approximately 70% of the ultimate adhesion is achieved at
initial contact. At least 36 hours is required before ultimate
adhesive strength is achieved.
16
AMD-K5™ Processor Thermal Considerations
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
The AMD-K5 Processor Thermal and Power Specifications
Table 4 contains target data believed to be accurate, but consult the AMD-K5 processor data sheet for the latest
specifications.
Table 4. Operating Range of the AMD-K5 Processor
Symbol
Parameter
Description
Min.
Typical
Max.
Comments
Tcase
Case Temperature
0 oC
70oC
Temperature measured at the
top center of case
Vcc
Power Supply Voltage
3.135 V
3.465 V
Vcc = 3.3 V +/- 5%
Icc
Power Supply Current
44 mA / MHz
Vcc = 3.6 V
Icc
Power Supply Current
36 mA / MHz
Vcc = 3.3 V
Physical Dimensions of the AMD-K5 Processor
This section defines the mechanical specification for the
AMD-K5 processor case, shown in Figure 7A and Figure 7B.
The top of the ceramic package, approximately 4 square inches
in area, is where the primary heat transfer occurs. Very little
heat transfers from the bottom or sides of the package. The
thermal interface is applied to the top of the package and care
should be taken not to get foreign material on the interface or
the heat sink surface.
Note: Use the information in Figure 7A and Figure 7B for thermal
reference only.
The AMD-K5 Processor Thermal and Power Specifications
17
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
Figure 7A. 296-Pin Ceramic Staggered Pin Grid Array
Figure 7B. 296-Pin Ceramic Staggered Pin Grid Array With Thermal Slug
18
AMD-K5™ Processor Thermal Considerations
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
Both the ceramic and the ceramic thermal slug PGA packages
have the same overall dimensions (see Figure 7A and Figure
7B). Thus, the same cooling solution can be used for both processor packages. The heat sink clip that mechanically attaches
the heat sink and processor to the processor ZIF socket is not
affected by the package. The thermal interface layer (i.e., the
silicon grease) has a cross sectional area of 3.8 square inches
(1.95 inch squared) for the ceramic package, and 1.56 square
inches (1.25 inch squared) for the ceramic thermal slug package. The copper slug has greater thermal conductivity than
the ceramic package, allowing the processor junction to operate at a lower temperature for the same power levels. Vibration and shock testing have shown that the same heat sink clips
perform equally for both processor packages.
Physical Dimensions of the AMD-K5 Processor
19
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
Personal Computer System
To ensure good airflow in the personal computer, air vents
should be inserted into the chassis. These vents bring in cooler
ambient air from outside the chassis and cool the AMD-K5 processor inside the chassis. Refer to Figure 8 for more
information.
Figure 8. Airflow Through the Personal Computer Chassis
20
AMD-K5™ Processor Thermal Considerations
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
Thermal Measurement Procedure
The operating temperature range for the AMD-K5 processor
case temperature is typically 0oC to 70oC. (Check the OPN and
data sheet for the exact temperature range.) This temperature
should be measured on the top of the case in the middle of the
package (see Figure 9). In order to measure this temperature, a
hole must be drilled into the heat sink and a thermocouple
placed in contact with the case. Recommended thermocouple
types include J, K, and T manufactured by Omega Engineering, Inc. Thermal epoxy is usually used to secure the thermocouple to the heat sink. Only the thermal bead at the end of
the thermocouple should make contact with the AMD-K5 processor case. The leads of the thermocouple should be kept at a
90o angle to the processor case top. The thermocouple leads
should not be allowed to short out against the metal heat sinks.
Figure 9. Test Setup to Measure AMD-K5 Processor Case and Heat Sink Temperature
Thermal Measurement Procedure
21
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
Thermal Characterization of the AMD-K5 Processor
296-Pin Ceramic PGA Package
A thermal study was conducted to determine the thermal resistance of the AMD-K5 processor 296-pin grid array ceramic
package. Three heat sinks were evaluated (i.e., heat sinks A, B,
and C). All heat sinks were of the extruded aluminum pin fin
design and were attached with a single clip to the AMD-K5 processor socket (AMP Socket 5). The socket was soldered to a sixlayer printed circuit board.
Thermal test dies were mounted inside the processor ceramic
package and were used as the source of the heat dissipation,
simulating heat from the processor. These thermal dies have
power resistors and PN junctions that are used to sense the
junction temperature. The PN junctions were calibrated at the
beginning of the test by accurately measuring voltage drops at
different temperatures.
Type K (alumel/chromel) 40 AWG thermocouples were used to
sense the case, heat sink, and ambient temperatures. Ambient
temperatures were measured away from the processor to avoid
local heating errors. Results of the measurements include calculations of steady state thermal resistance (see Table 6 for
more information).
The heat sinks used in this study were supplied by manufacturers and are representative of fifth-generation pin fin designs.
See Table 5 for heat sink characteristics.
Table 5. Test Heat Sink Characteristics for Fifth-Generation Processors
Dimensions
(inches)
Manufacturer
Part Number
Comments
Heat Sink A
Base = 1.96 x 2.67
Height = 0.45
Aavid
022694
124 pin fins
Heat Sink B
Base = 1.96 x 2.675
Height = 0.7
Aavid
363324B
132 pin fins
Heat Sink C
Base = 2.1 x 2.1 Height = 1
Wakefield
698-100AB
Penguin Cooler with 132
pin fins
Three types of thermal interface material were used in this
test. The first material was standard silicon oil-based thermal
grease. The second material was fiberglass-reinforced silicone
22
AMD-K5™ Processor Thermal Considerations
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
interface material (ADUX White Pad by Thermagon, Inc.). The
third material was thermally conductive elastomer (AS-210
Rose Pad by Thermagon, Inc.).
The steady state test results are detailed in Tables 7 through
16. Each table is accompanied by a figure that represents the
test results graphically. Thermal grease is clearly the best thermal interface material. The variation in thermal interface
resistance was caused by the heat sink flatness. Having a heat
sink improved thermal resistance over not having a heat sink.
Heat sinks B and C show similar performance. Heat sink B has
a greater area in contact with the processor case, but heat sink
C is taller. The volume of heat sink B is 3.7 cubic inches and
the volume of heat sink C is 3.8 cubic inches.
Table 6. Table of Thermal Measurements
Parameter
Symbol
Units
Junction to Air
θja
oC / Watt
Junction to Airflow
θja @ 200 linear feet/min (lfpm)
oC / Watt
Junction to Airflow
θja @ 400 lfpm
o
C / Watt
Junction to Case
θjc
o
C / Watt
Case to Ambient
θca
o
C / Watt
Heat Sink to Ambient
θsa
o
C / Watt
Case to Heat Sink
θcs
o
C / Watt
Thermal Measurement Procedure
23
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
Thermal Resistance Calculations with No Heat Sink
Table 7. Thermal Resistance Calculations with No Heat Sink
Airflow (lfpm)
θca
0
12.6
200
9.3
400
8.5
Figure 10. AMD-K5 Processor With No Heat Sink
Note: The AMD-K5 processor requires a heat sink in most personal
computer applications. The thermal data with no heat sink
provides a point of reference for comparing the reduction of
thermal resistance from case to ambient when a heat sink is
used.
24
AMD-K5™ Processor Thermal Considerations
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
Thermal Resistance Calculations with Pin Fin Heat Sink A
Table 8. Heat Sink A with Thermal Grease
θca
θsa
θcs
0
6.10
5.58
0.52
200
3.60
3.40
0.20
400
2.80
2.58
0.22
Airflow (lfpm)
Table 9. Heat Sink A with White Pad
θca
θsa
θcs
0
7.60
5.48
2.12
200
5.30
3.27
2.04
400
4.50
2.42
2.08
Airflow (lfpm)
Table 10. Heat Sink A with Rose Pad
θca
θsa
θcs
0
7.60
5.48
2.13
200
5.20
3.22
1.98
400
4.40
2.44
1.90
Airflow (lfpm)
Thermal Measurement Procedure
25
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
Figure 11. Heat Sink A with Thermal Grease
Figure 12. Heat Sink A with White Pad
26
AMD-K5™ Processor Thermal Considerations
20092B/0—Sep1996
AMD-K5 Processor Thermal Considerations
Figure 13. Heat Sink A with Rose Pad
Thermal Measurement Procedure
27
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
Thermal Resistance Calculations with Pin Fin Heat Sink B
Table 11. Heat Sink B with Thermal Grease
θca
θsa
θcs
0
5.00
4.44
0.56
200
3.10
2.72
0.38
400
2.20
1.90
0.30
Airflow (lfpm)
Table 12. Heat Sink B with White Pad
θca
θsa
θcs
0
7.30
4.52
2.78
200
6.00
2.49
3.51
400
5.20
1.69
3.51
Airflow (lfpm)
Table 13. Heat Sink B with Rose Pad
θca
θsa
θcs
0
7.30
4.40
2.90
200
5.10
2.63
2.47
400
4.30
1.82
2.48
Airflow (lfpm)
28
AMD-K5™ Processor Thermal Considerations
20092B/0—Sep1996
AMD-K5 Processor Thermal Considerations
Figure 14. Heat Sink B with Thermal Grease
Figure 15. Heat Sink B with White Pad
Thermal Measurement Procedure
29
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
Figure 16. Heat Sink B with Rose Pad
30
AMD-K5™ Processor Thermal Considerations
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
Thermal Resistance Calculations with Pin Fin Heat Sink C
Table 14. Heat Sink C with Thermal Grease
θca
θsa
θcs
0
4.80
4.08
0.71
200
3.00
2.65
0.35
400
2.10
1.76
0.34
Airflow (lfpm)
Table 15. Heat Sink C with White Pad
θca
θsa
θcs
0
7.60
4.15
3.45
200
5.80
2.49
3.31
400
4.80
1.55
3.25
Airflow (lfpm)
Table 16. Heat Sink C with Rose Pad
θca
θsa
θcs
0
7.40
4.23
3.17
200
5.50
2.47
3.03
400
4.60
1.55
3.05
Airflow (lfpm)
Thermal Measurement Procedure
31
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
Figure 17. Heat Sink C with Thermal Grease
Figure 18. Heat Sink C with White Pad
32
AMD-K5™ Processor Thermal Considerations
20092B/0—Sep1996
AMD-K5 Processor Thermal Considerations
Figure 19. Heat Sink C with Rose Pad
Thermal Measurement Procedure
33
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
Conclusion (Final Checklist)
When selecting a cooling solution for the AMD-K5 processor it
is important to know the following:
1. Maximum operating clock frequency and maximum case
temperature for the processor. Check the OPN and data
sheet for the latest information.
2. Thermal specification of the desktop personal computer for
both the maximum case inside temperature (e.g., 30oC) and
the airflow above the processor socket on the motherboard
(200 lfpm).
3. Select a heat sink or heat sink/fan module that assures a
safe thermal margin (see Heat Sink Equations on page 4)
and that fits within the maximum size requirements with a
secure mechanical attachment (e.g., heat sink clip or thermal adhesive tape) to withstand the vibration and shock
requirements of a personal computer system.
4. Select fans that have sealed ball bearings to ensure long life
(e.g., greater than 5 years).
5. Make sure that there are no mechanical restrictions above a
fan heat sink module (e.g., 0.5 in or more).
6. If thermal adhesive tape is used, the following items should
be specified: the tape should be approximately 0.006 and
the top of the ceramic case should be primed to ensure maximum bond strength (see Thermal Adhesive Tape on page
15).
7. Thermal system measurements are required to ensure that
the processor case doesn’t exceed the maximum case temperature specification (lower case temperatures ensure safe
thermal margins).
34
AMD-K5™ Processor Thermal Considerations
AMD-K5 Processor Thermal Considerations
20092B/0—Sep1996
Vendors and Manufacturers for the AMD-K5 Processor
Heat Sink Vendors
Aavid Thermal Technologies, Inc.
One Kool Path
P.O. Box 400
Laconia, NH 03247-0400
603-528-3400
IERC
135 W. Magnolia Blvd.
Burbank, CA 91502
818-842-7277
PC Power & Cooling, Inc.
5995 Avenida Encinas
Carlsbad, CA 92008
800-722-6555
Thermalloy, Inc.
2021 W. Valley View Lane
Dallas, TX 75234-0839
214-243-4321
Wakefield Engineering
60 Audubon Rd.
Wakefield, MA 01880
617-245-5900
Other Manufacturers
Heat Sink Fan Motor
Manufacturer
Evox Rifa
708-948-9511
Processor Socket
Manufacturer
AMP
2800 Fulling Mill Road
Middleton, PA 17057-3198
1-800-522-6752
Vendors and Manufacturers for the AMD-K5 Processor
35
AMD-K5 Processor Thermal Considerations
Thermal Interface
Material
Manufacturers
20092B/0—Sep1996
Chomerics, Inc.
77 Dragon Court
Woburn, MA 01888-4014
617-935-4850
Thermagon, Inc.
3256 W. 25th Street
Cleveland, OH 44109-1668
216-741-7659
Aavid Thermal Technologies, Inc.
One Kool Path
P.O. Box 400
Laconia, NH 03247-0400
603-528-3400
Thermalloy, Inc.
2021 W. Valley View Lane
Dallas, TX 75234-0839
214-243-4321
Thermocouple
Manufacturer
36
Omega Engineering, Inc.
One Omega Drive
Stamford, CT 06907
1-800-826-6342
AMD-K5™ Processor Thermal Considerations