Heat Generation in Electronics Thermal Management of Electronics Reference: San José State...
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Transcript of Heat Generation in Electronics Thermal Management of Electronics Reference: San José State...
Heat Generation in Heat Generation in ElectronicsElectronics
Thermal Management of ElectronicsThermal Management of ElectronicsReference: Reference:
San José State UniversitySan José State UniversityMechanical Engineering DepartmentMechanical Engineering Department
Heat in ElectronicsHeat in Electronics
Heat is an unavoidable by-product of Heat is an unavoidable by-product of operating electronicsoperating electronics
Effects of increased temperature in Effects of increased temperature in electronicselectronics Decreased reliability Decreased reliability Parametric changes may occur in an Parametric changes may occur in an
electronic device’s componentselectronic device’s components
Power DissipationPower Dissipation
Current flowing through active and passive Current flowing through active and passive components results in power dissipation components results in power dissipation and increased temperaturesand increased temperatures
The amount of power dissipated by a The amount of power dissipated by a device is a function of:device is a function of: The type of deviceThe type of device The geometryThe geometry The path from the device to the heat sinkThe path from the device to the heat sink
Components Where Power Components Where Power Dissipation OccursDissipation Occurs
Passive DevicesPassive Devices ResistorsResistors CapacitorsCapacitors InductorsInductors TransformersTransformers
Active DevicesActive Devices TransistorsTransistors Integrated Integrated
CircuitsCircuits
InterconnectionsInterconnections
General TheoryGeneral Theory
Power dissipated will be a function of the Power dissipated will be a function of the type of current that it receivestype of current that it receives
For DC:For DC:
VIP
device the across drop VoltageV
Amps in CurrentI
ondJoules/sec or Watts in PowerP
General TheoryGeneral Theory
For AC:For AC:
1
2
)()(1 t
tM
dttitvT
P
current the for conduction of limit Uppertcurrent the for conduction of limit Lowert
element the through voltage of value ousInstantanev(t)element the through current of value ousInstantanei(t)
Period Waveform TLoss Power MeanP
1
M
2
ResistorsResistors
SymbolSymbol
Power DissipatedPower Dissipated
LawsJouleRIPRIIP
VIPOhm's LawRIV
' )(
2
Temperature Coefficient of Temperature Coefficient of Resistance (TCR)Resistance (TCR)
TCR characterizes the TCR characterizes the amount of drift that amount of drift that takes place in takes place in resistance values over resistance values over temperature changetemperature change
TCR usually has such a TCR usually has such a small effect that (even small effect that (even over large temperature over large temperature gradients) that it can be gradients) that it can be ignored for resistorsignored for resistors
CapacitorsCapacitorsSymbolSymbol
The ideal capacitor would not dissipate The ideal capacitor would not dissipate any power under a DC current any power under a DC current
A real capacitor can be modeled with the A real capacitor can be modeled with the equivalent series circuit below:equivalent series circuit below:
CapacitorsCapacitors
There will be power There will be power dissipated due to the dissipated due to the equivalent series equivalent series resistance (ESR)resistance (ESR)
Power dissipation due Power dissipation due to equivalent series to equivalent series inductance is inductance is negligible compared negligible compared to ESRto ESR
Inductors and TransformersInductors and Transformers
Inductor symbolInductor symbol
Transistor symbolTransistor symbol
Two types of resistance associated with Two types of resistance associated with these devicesthese devices WindingWinding CoreCore
Resistance for Inductors and Resistance for Inductors and TransformersTransformers
Winding Resistance – Resistance that Winding Resistance – Resistance that occurs due to the winding on the componentoccurs due to the winding on the component
Core Resistance – Losses that occur due to Core Resistance – Losses that occur due to use of a ferromagnetic coreuse of a ferromagnetic core Hysteresis Loss – Power dissipation due to the Hysteresis Loss – Power dissipation due to the
reversal of the magnetic domains in the corereversal of the magnetic domains in the core Eddy Current Loss – Heat generated from the Eddy Current Loss – Heat generated from the
conductive current flowing in the metallic core conductive current flowing in the metallic core induced by changing fluxinduced by changing flux
Active DevicesActive DevicesPower dissipation for all standard-product Power dissipation for all standard-product active integrated circuits can be obtained active integrated circuits can be obtained from:from: Device data sheets Device data sheets Calculated from laboratory measurementsCalculated from laboratory measurements
Bipolar devices – power dissipation is Bipolar devices – power dissipation is constant with frequencyconstant with frequency
CMOS devices – power dissipation is a 1CMOS devices – power dissipation is a 1stst order function of frequency and 2order function of frequency and 2ndnd order order function of device geometryfunction of device geometry
Power Dissipation in a CMOS GatePower Dissipation in a CMOS Gate
Power consumption is composed of three Power consumption is composed of three components:components:
Switching powerSwitching powerResults from charging and discharging of the Results from charging and discharging of the capacitance of transistor gates and interconnect capacitance of transistor gates and interconnect lines during the changing of logic stateslines during the changing of logic states
Comprises 70-90% of the power dissipatedComprises 70-90% of the power dissipated
Power Dissipation in a CMOS GatePower Dissipation in a CMOS Gate
Dynamic short-circuit powerDynamic short-circuit powerOccurs when pull-up or pull-down transistors are Occurs when pull-up or pull-down transistors are briefly on during a change of state in the output briefly on during a change of state in the output nodenode
Comprises 10-30% of dissipated powerComprises 10-30% of dissipated power
DC LeakageDC LeakageComprises 1% of dissipated powerComprises 1% of dissipated power
InterconnectionsInterconnections
Interconnections are the connections Interconnections are the connections between componentsbetween components
Power dissipated can be found with Power dissipated can be found with Joule’s Law where resistance of the Joule’s Law where resistance of the interconnection is given by:interconnection is given by:
A
LR
material onarea sectionalCrossA
cm in material of LengthL
cmohm iny Resistivit
Ohms in ResistanceR
Wire BondsWire Bonds
Low power devices (i.e. logic and small analog Low power devices (i.e. logic and small analog devices) usually have bonds fabricated from gold or devices) usually have bonds fabricated from gold or aluminum with a diameter of .001 inchaluminum with a diameter of .001 inch Negligible power is dissipated by a single bond but when Negligible power is dissipated by a single bond but when
many bonds exist these elements should not be ignoredmany bonds exist these elements should not be ignored
High power devices usually have aluminum bond High power devices usually have aluminum bond with diameters ranging from .005 to .025 incheswith diameters ranging from .005 to .025 inches Large amounts of power are dissipated from these bondsLarge amounts of power are dissipated from these bonds
Wire BondsWire Bonds
Ribbon BondsRibbon Bonds
Package PinsPackage Pins
Package pins are the physical connector Package pins are the physical connector on an integrated circuit package that on an integrated circuit package that carries signals into and out of an carries signals into and out of an integrated circuit integrated circuit Pins are made from low-resistance metal Pins are made from low-resistance metal and may be enclosed in glass or ceramic and may be enclosed in glass or ceramic beadbeadPower dissipate can still be calculate with Power dissipate can still be calculate with the relationship outlined for other the relationship outlined for other interconnectionsinterconnections
Package PinsPackage Pins
SubstratesSubstrates
Many different metallizations can be used Many different metallizations can be used for interconnections on substratesfor interconnections on substrates
Each metallization will have its own Each metallization will have its own resistance that will dissipate powerresistance that will dissipate power
Sheet resistivity is used in calculation due Sheet resistivity is used in calculation due to the fact that conductors are much wider to the fact that conductors are much wider than they are thickthan they are thick
SubstratesSubstrates
The resistance of a The resistance of a substrate can be substrate can be found with the sheet found with the sheet resistivityresistivity
Resistivity of the Resistivity of the conductors will vary conductors will vary with temperature with temperature (TCR may be (TCR may be important in some important in some substrate substrate calculations)calculations)
tB
s
W
LR s
film of thicknesst
hohms/lengttivity in Bulk resisρ
re ohms/squastivity inSheet resi
B
s
Various Substrate ConstructionsVarious Substrate Constructions
Substrate Metallization PropertiesSubstrate Metallization Properties
High-Frequency LossHigh-Frequency Loss
DC is evenly distributed DC is evenly distributed throughout a cross throughout a cross section of wiresection of wire
When frequency When frequency increases charge carrier increases charge carrier move to the edges move to the edges because it is easier to because it is easier to move in a conductor in move in a conductor in the edgethe edge
Resistance increases due Resistance increases due to the distribution of to the distribution of charge carrierscharge carriers