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? amd-k6 processor thermal solution design publication # 21085 rev: i amendment/ 0 issue date: february 1999 application note ?
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. 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.
contents iii 21085i/0february 1999 amd-k6 ? processor thermal solution design contents revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 system conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 thermal solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 heatsink . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 heat dissipation path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 interface materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 layout and airflow considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . . . . . . . . . . 11 thermal power utility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 recommended thermal solutions for the amd-k6 ? processor family . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 additional information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
iv contents amd-k6 ? processor thermal solution design 21085i/0february 1999
list of figures and tables v 21085i/0february 1999 amd-k6 ? processor thermal solution design 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 t case specifications . . . . . . . 1 table 2. summary of chassis box fan configurations . . . . . . . . . 10
vi list of figures and tables amd-k6 ? processor thermal solution design 21085i/0february 1999
revision history vii 21085i/0february 1999 amd-k6 ? processor thermal solution design revision history date rev description 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 t case specifications. feb 1999 i revised thermal power utility on page 12 to reflect the latest recommended utility.
viii revision history amd-k6 ? processor thermal solution design 21085i/0february 1999
21085i/0february 1999 amd-k6 ? processor thermal solution design introduction 1 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 (t case ) to be in the range of 0c to t case max. it is important to maintain the case temperature within the specification for normal operation. if the 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 t case specifications for the desktop amd-k6 processor family. table 1. amd-k6 ? processor family t case specifications processor family minimum maximum note amd-k6 ? 0c 70c amd-k6-2 0c 60c, 65c, or 70c * amd-k6- iii 0c 65c note: * refer to the amd-k6 ? -2 processor data sheet, order# 21850 for operating specifications as they apply to each amd-k6-2 offering. ?
2 introduction amd-k6 ? processor thermal solution design 21085i/0february 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: n amd-k6 processor model 6 (0.35- m m process technology) and the amd-k6 processor model 7 (0.25- m m process technology), refer to the amd-k6 ? processor data sheet , order# 20695. n amd-k6-2 processor model 8 (0.25- m m process technology), refer to the amd-k6 ? -2 processor data sheet , order# 21850. n amd-k6-iii processor model 9 (0.25- m m process technology), refer to the amd-k6 ? -iii processor data sheet, order# 21918 . system conditions the environmental specifications on most systems guarantee operation for external ambients up to 35c. most pc chassis/system boxes result in an internal 10c increase in temperature over the external ambient temperature. in general, this means the thermal solution should be designed to allow an internal ambient (t a ) of 45c.
thermal solutions 3 21085i/0february 1999 amd-k6 ? processor thermal solution design 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 ( q sa ) can be calculated using the following example: if: t c = 65c t a = 45c p max = 29.5w then: where: t c = processor case temperature t a = ambient temperature p max = maximum power consumption q ca = 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 ( q sa ) is calculated as follows: q sa = q ca C q if = 0.678 C 0.20 = 0.478 c/w where: q ca = case-to-ambient thermal resistance q if = interface material thermal resistance q sa = sink-to-ambient thermal resistance q ca t c t a C p max ------------------ - ? ?? 20 c 29.5w ----------------- - 0.678 cw ==
4 thermal solutions amd-k6 ? processor thermal solution design 21085i/0february 1999 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). 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 attached. the thermal resistance of the 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, q ca 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. temperature delta thermal q sa q ca q if (c/w) (case-to-ambient) case sink t ca resistance ambient air thin lid case temperature ambient temperature
thermal solutions 5 21085i/0february 1999 amd-k6 ? processor thermal solution design 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 print-circuit board zif socket heat sink thermal interface material die thin lid ceramic substrate heat sink clip radiation convection radiation convection print-circuit board and socket heat sink thermal interface material thin lid and grease sil icon c4 bumps cerami c substrate package pins underfill chip junction primary heat dissipation path secondary heat dissipation path pga package external resistance external resistance ambient case temperature junction temperature q jc q ca
6 layout and airflow considerations amd-k6 ? processor thermal solution design 21085i/0february 1999 trapped beneath the heatsink during assembly. amd 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 0.3c/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 10C15 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.
layout and airflow considerations 7 21085i/0february 1999 amd-k6 ? processor thermal solution design 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: n to avoid impeding airflow within the chassis to the fansink, route ribbon cables between the system motherboard and chassis drive bays. n to provide a sufficient volume of air to the fansink, maintain a 1/2 inch clearance above the fansink. heatsink fins aligned airflow voltage regulator (v cc core) voltage regulator (v cc i/o) with airflow
8 layout and airflow considerations amd-k6 ? processor thermal solution design 21085i/0february 1999 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. figure 6. airflow path in a dual-fan system airflow ideal areas for voltage regulator drive bays p/s vents v e n t s fan fan main board front
layout and airflow considerations 9 21085i/0february 1999 amd-k6 ? processor thermal solution design 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. 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. p/s main board drive bays f a n air vents
10 layout and airflow considerations amd-k6 ? processor thermal solution design 21085i/0february 1999 for the given chassis, different combinations of fans were tested. the tests were performed in an oven with a constant temperature of 35c, and the internal ambient temperature of the chassis was measured with a thermocouple. the 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 48.2c. 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 48.2c to 43.6c. see table 2 for a complete summary of fan and chassis combinations. also, note that the best case temperature (t case ) for the processor was obtained when the internal ambient temperature was held to approximately 44.4c. 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 t case . table 2. 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, t case 68.8c 69c 64.1c 65.9c internal ambient temperature 48.2c 48.7c 44.4c 43.6c
thermal evaluation 11 21085i/0february 1999 amd-k6 ? processor thermal solution design figure 8. standard mid-tower case thermal evaluation measuring case temperature the processor case temperature is measured to ensure that the thermal solution meets the processors operational 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. fan power supply box fan amd-k6 ? processor regulator heatsink drive bays box fan inside ambient thermocouple front rear intake vent
12 thermal evaluation amd-k6 ? processor thermal solution design 21085i/0february 1999 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 t case 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 processors 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. thermocouple thermally conductive epoxy
additional information 13 21085i/0february 1999 amd-k6 ? processor thermal solution design the maxpwr99.exe utility is available under a nondisclosure agreement. contact your local amd sales office for 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: n amd-k6 processor models 6 and 7, see the amd-k6 ? processor data sheet , order# 20695 or contact your local amd sales representative. n amd-k6-2 processor model 8, see the amd-k6 ? -2 processor data sheet , order# 21850 or contact your local amd sales representative. n amd-k6-iii processor model 9, see the amd-k6 ? -iii processor data sheet, order# 21918 or contact your local amd sales representative.
14 additional information amd-k6 ? processor thermal solution design 21085i/0february 1999

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