Darla Wellheuser Advanced System Logic Semiconductor Group SCZA00

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Package Thermal Considerations
Darla Wellheuser Advanced System Logic Semiconductor Group
SCZA002B
IMPORTANT NOTICE Texas Instruments (TI) reserves right make changes products discontinue semiconductor product service without notice, advises customers obtain latest version relevant information verify, before placing orders, that information being relied current. warrants performance semiconductor products related software specifications applicable time sale accordance with TI's standard warranty. Testing other quality control techniques utilized extent deems necessary support this warranty. Specific testing parameters each device necessarily performed, except those mandated government requirements. Certain applications using semiconductor products involve potential risks death, personal injury, severe property environmental damage ("Critical Applications"). SEMICONDUCTOR PRODUCTS DESIGNED, INTENDED, AUTHORIZED, WARRANTED SUITABLE LIFE-SUPPORT APPLICATIONS, DEVICES SYSTEMS OTHER CRITICAL APPLICATIONS. Inclusion products such applications understood fully risk customer. products such applications requires written approval appropriate officer. Questions concerning potential risk applications should directed through local sales office. order minimize risks associated with customer's applications, adequate design operating safeguards should provided customer minimize inherent procedural hazards. assumes liability applications assistance, customer product design, software performance, infringement patents services described herein. does warrant represent that license, either express implied, granted under patent right, copyright, mask work right, other intellectual property right covering relating combination, machine, process which such semiconductor products services might used.
Copyright 1996, Texas Instruments Incorporated
Contents
Title Page Abstract Introduction Reliability Power Consumption Power Calculations CMOS BiCMOS/Bipolar Thermal-Resistance Values Summary References
List Illustrations
Figure Title Page Advanced Packages Versus Frequency (One Switching, Unused Outputs Low) Versus Frequency (All Outputs Switching) Versus Frequency (All Switching, Duty Cycle Enabled) Versus Duty Cycle Enabled MHz) 48-Pin SSOP Versus Trace Length 48-Pin SSOP Versus Flow 48/56-Pin SSOP K-Factor Board Modeling
Abstract
meet current future system requirements increasing speed decreasing size, integrated circuit manufacturers pushing edge existing packaging technology. component's performance determined process technology thermal limitations package. leader package technology, Texas Instruments (TI) introduced number fine-pitch packages acutely aware thermal considerations that must examined systems designers. This paper intended create awareness understanding thermal issues explore factors that influence thermal performance.
Introduction
Thermal awareness became industry concern when surface-mount (SMT) packages began replacing through-hole (DIP) packages designs. Circuits operating same power enclosed smaller package meant higher power. issue, systems required increased throughput, which resulted higher frequencies, increasing power density even further. only these same concerns haunting designers today, they progressively getting more severe. Figure shows part reason increased attention thermal issues. baseline comparison, 24-pin small-outline integrated circuit (SOIC) shown along with several fine-pitch packages supplied including 24-pin SSOP (shrink small outline), 48-pin SSOP, 100-pin TQFP (thin quad flat pack). 24-pin SSOP bits) allows same circuit functionality 24-pin SOIC packaged less than half area, while 48-pin SSOP (16, bits) occupies just slightly more area twice functionality 24-pin SOIC. This same phenomena expanded even further with 100-pin TQFP bits), which functional equivalent four 24-pin 48-pin devices, with additional board savings over that SSOP packages. trend packaging technology continues toward smaller packages, attention must focused thermal issues that created.
24-Pin SOIC 24-Pin SSOP
24-Pin SOIC Area
Height 2.65 Volume Lead Pitch 1.27
24-Pin SSOP Area
Height Volume Lead Pitch 0.65
48-Pin SSOP
100-Pin TQFP
48-Pin SSOP Area
Height 2.74 Volume Lead Pitch 0.635
100-Pin TQFP 100-Pin Cavity TQFP Area
Height Volume Lead Pitch
Figure Advanced Packages
Reliability
overriding effect increased power densities integrated circuits decrease overall system reliability. direct relationship exists between junction temperature reliability. Table provides example device with initial junction temperature 150°C calculated failure-rate decrease in-use junction temperature lowered. data Table indicates that lower junction temperature results increased system reliability. Table TEMPERATURE 0.02
Failure rate 100,000 hours
better understanding factors that contribute junction temperature (TJ) provides system designer with more flexibility when attempting solve thermal issues. Device junction temperature determined equation Where: junction (die) temperature (°C) ambient temperature (°C) thermal resistance package from junction ambient (°C/W) total power device
Junction temperature altered lower chip power consumption, longer trace length, heat sinks, forced flow, package mold compound, lead-frame size material, surface area, size. Some these mechanically inherent particular package while others controlled designer application specific. Understanding which variables influenced practicing good thermal-design techniques requires more detailed investigation power considerations well thermal-resistance measurements.
Power Consumption
lower junction temperature (TJ) device, thus improving reliability, lower power consumption. variety options available help achieve this, such low-power process technologies, reduced output swing, reduced power-supply voltage. closer look power performance advantages several popular logic families assist designer when choosing what best fits needs. choices available from high-speed interfaces range from standard bipolar advanced CMOS (ACL /ACT) state-of-the-art BiCMOS (BCT) advanced BiCMOS (ABT). Figures through show comparisons current (ICC) consumption functions these technologies across frequency. expected, bipolar device consumes more current than CMOS device lower frequencies, frequency increases, this relationship longer holds true. fact, there region frequency range where CMOS device consumes more current than bipolar device. point where they equal referred crossover frequency.
Frequency
Figure Versus Frequency (One Switching, Unused Outputs Low)
Frequency
Figure Versus Frequency (All Outputs Switching)
Frequency
Figure Versus Frequency (All Switching, Duty Cycle Enabled)
Typical applications bus-interface devices require them disabled standby mode during certain periods time, instance, while other devices access bus. This result large decrease current consumption ABT, BCT, devices, which have low-standby current. These values given data sheets ICCZ (250 mA). Current-consumption data versus percent duty cycle enabled shown Figure frequency data held constant outputs switching.
Duty Cycle Enabled
Figure Versus Duty Cycle Enabled MHz) power-consumption data provided limited small range variations. However, using this data, along with standard formulas, power consumption calculated specific applications.
Power Calculations
When calculating total power consumption circuit, both static dynamic currents must taken into account. Both bipolar BiCMOS devices have varying static-current levels, depending state output (ICCL, ICCH, ICCZ), while CMOS device single value ICC. These values found individual data sheets. inputs, when driven levels, also consume additional current because they driven GND; therefore, input transistors completely turned off. This value known provided data sheet. Dynamic power consumption results from charging discharging both internal parasitic capacitances external load capacitance. parameter devices that accounts parasitic capacitances known Cpd. obtained using equation found data sheet. [ICC (dynamic)/(VCC fi)] Where: input frequency (Hz) supply voltage load capacitance measured value current into device
Although value provided ABT, BCT, devices, versus frequency curves display essentially same information. slope curve provides value form /(MHz bit), which when multiplied number outputs switching desired frequency, provides dynamic power dissipated device without load current. Equations through used calculate total power CMOS, bipolar, BiCMOS devices: PS(static) PD(dynamic) CMOS (CMOS-level inputs) [(Cpd VCC2 (TTL-level inputs) [ICC (NTTL DCd)] [(Cpd VCC2 f1]Nsw BiCMOS/Bipolar [DCen(NH ICCH/NT ICCL/NT) (1-DCen)Iccz] (NTTL DCd) Note: bipolar devices [DCen (VOH VOL) [DCen (mA/MHz bit)] Where: ICCL ICCH ICCZ DCen mA/(MHz bit) Supply voltage Power-supply current (from data sheet) Power-supply current when outputs state (from data sheet) Power-supply current when outputs high state (from data sheet) Power-supply current when outputs high-impedance state (from data sheet) Power-supply current when inputs level (from data sheet) duty cycle enabled (50% 0.5) duty cycle data (50% 0.5) Number outputs high state Number outputs state Total number outputs switching Total number outputs Operating frequency (Hz) Operating frequency (MHz) Output voltage high state Output voltage state External load capacitance Slope versus frequency curve
Thermal-Resistance Values
Design trends requiring board size reduction have made circuit manufacturers produce fine-pitch packages that appear threaten reliability systems further thermal constraints. leader packaging technology, done considerable research into validity traditional thermal measurements data provided circuit manufacturers.
Unlike data-sheet parameters, where industry adopted standard load measurement measurement standard which manufacturers comply. problem facing designer wishing make comparisons thermal data from several manufacturers that this could apples-to-oranges type comparison. result, software package been developed allow designers obtain thermal data based their specific application. validity usefulness traditional approach presenting values became pressing issue when another manufacturer measured identical package obtained results that varied 40%. Extensive research conclusion that methodology used measure cause discrepancy physical aspects such trace length, trace width, number devices board, proximity other devices did. demonstrate extreme impact trace length alone, Figure shows values TI's 48-pin SSOP LFMP LFMP with varying trace lengths. 48-pin SSOP shown Figure side-by-side comparison with standard 24-pin SOIC, 24-pin SSOP, 100-pin TQFP. data Figure clearly shows need more complete thermal data, simply single data point.
°C/W LFPM
LFPM Trace Length
Figure 48-Pin SSOP Versus Trace Length There other methods lower device. Using heat sinks blowing across device certainly improves ability remove heat from surface. Figure provides data 48-pin SSOP with trace lengths mils inch while varying amount flow. Although many applications tend limit amount flow, excellent benefits possible with increased flow.
°C/W Mils 1000 Mils Flow LFPM
Figure 48-Pin SSOP Versus Flow
Several variables that have direct effect values were compared results shown Figure Surprisingly, major contributing factor trace length, flow. Once again, this validates need improvement necessarily test methodology used calculate values, certainly those values provided.
VARIABLE Trace Length Flow
Board Extension After Trace Board Extension After Package Trace Thickness Trace Width Power
Total Interactions Between Factors
Figure 48-/56-Pin SSOP K-Factor Board Modeling
provides values variety packages (including SOIC, SSOP, QSOP) user-friendly software package. program allows designers specify their conditions, such trace length, flow, proximity other devices, trace width order obtain realistic thermal solutions.
RANGE mils mils
CONTRIBUTION 41.4 28.8 16.3
mils 2000 mils mils mils mils mils
Summary
system avoid being reliability nightmare today's world where:
Eight-bit devices being replaced bits single package, increasing power. Higher operating frequencies increase power. Fine-pitch packages reducing amount available surface area remove heat from device.
Semiconductor manufacturers must take first step provide realistic useful thermal information that will provide designers variables focus thermal management.
References
Thermal Software Contact factory (903) 868-7682. Power Dissipation Advanced CMOS Logic Designer's Handbook, Texas Instruments Incorporated, 1988, literature number SCAA001B SSOP Designer's Handbook, Texas Instruments Incorporated, 1991, literature number SCYA00
IMPORTANT NOTICE Texas Instruments (TI) reserves right make changes products discontinue semiconductor product service without notice, advises customers obtain latest version relevant information verify, before placing orders, that information being relied current. warrants performance semiconductor products related software specifications applicable time sale accordance with TI's standard warranty. Testing other quality control techniques utilized extent deems necessary support this warranty. Specific testing parameters each device necessarily performed, except those mandated government requirements. Certain applications using semiconductor products involve potential risks death, personal injury, severe property environmental damage ("Critical Applications"). SEMICONDUCTOR PRODUCTS DESIGNED, INTENDED, AUTHORIZED, WARRANTED SUITABLE LIFE-SUPPORT APPLICATIONS, DEVICES SYSTEMS OTHER CRITICAL APPLICATIONS. Inclusion products such applications understood fully risk customer. products such applications requires written approval appropriate officer. Questions concerning potential risk applications should directed through local sales office. order minimize risks associated with customer's applications, adequate design operating safeguards should provided customer minimize inherent procedural hazards. assumes liability applications assistance, customer product design, software performance, infringement patents services described herein. does warrant represent that license, either express implied, granted under patent right, copyright, mask work right, other intellectual property right covering relating combination, machine, process which such semiconductor products services might used.
Copyright 1996, Texas Instruments Incorporated

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