Chapter 13 Fundamentals of RF Packaging ECEN 5004 – Digital Packaging Mike Weimer Zach Allen

Chapter 13

Fundamentals of RF PackagingFundamentals of RF Packaging

ECEN 5004 – Digital Packaging

Mike WeimerZach Allen

IntroductionRF is the 2nd major technology in

microsystem revolution20th Century: Copper wire21st Century: Wireless/RF transmission

Potential to become the ultimate technology for giga/tera-bit communications

Packaging is a substantial issue


13.1 What is RF?Radio Frequency (3 kHz – 300 GHz)

Wavelengths of 1 mm – 30 cmFirst RF transmission was in 1901 with a

message sent in Morse code from England to Newfoundland

Titanic was assisted by sending an RF transmission to the Carpathia 58 miles away, saving 705 lives (1912)

Marconi earned Nobel Prize in PhysicsFirst mobile phone introduced prior to 1946First Cell Phone Commercial


13.2 RF ApplicationsCellular telephony, portable internet,

broadband communications, etc.Most financially significant market is in

wireless applications (duh)High-bandwidth transmission (i.e. Verizon’s

new TV service) demands improved RF devicesAll while reducing package size and cost


13.3 Anatomy of RF SystemsBase-mobile communication is standard

VHF: Very High Frequency [30 – 300 MHz]

UHF: Ultra High Frequency [300 – 3000 MHz]

SHF: Super High Frequency [3 – 30 GHz]

EHF: Extremely High Frequency [30 – 300 GHz]

Multiple-hop autonomous system networksIndividual mobiles act as repeaters


13.3 Anatomy of RF SystemsTransceiver

Based around Variable-frequency Oscillators (VFOs)

RepeaterIntercepts/retransmits transmissionsOperates at VHF, UHF, and microwave frequencies

DuplexerAllows duplex operation (two operators can

interrupt each other at any time)Generally uses two separate frequencies

AutopatchConnects radio transceiver to telephone control


13.3 Anatomy of RF SystemsPortable Telephone

Portable radio transceiverLong-range (10 – 20 miles)

Cordless TelephoneOld 900 MHz technologyShort-range (600 – 800 feet)

PagerActivated by a two-tone signal from base

stationOperates at 30 – 932 MHzUses a high-gain compact antenna


13.3 Anatomy of RF SystemsTransmission Quality

Dedicated frequency to minimize interferenceAdequate power to ensure high S/N ratioSufficient bandwidth for high voice qualityFM operation to minimize noise problems

Service QualityAccessibility and Usability

Cell Phone ExampleRF Transceiver Low-pass Filter Power

Amplifier A/D Converter D/A Converter Local oscillator Antenna


13.3 Anatomy of RF SystemsHigh quality filtering requirements

Low-pass (noise removal)Processing performed at Intermediate

FrequencyDSP is used in most modern cellular phones

Reprogrammable, fast, low power consumption


13.4 Fundamentals of RFRadio Wave

Radiation and propagation of waves (dropping stone into pool)

Transverse waves (wave occurs in directions perpendicular to propagation)

FrequencyNumber of cycles per secondTerm coined in 1967 after Heinrich Hertz (Hz)

In lieu of the term ‘cycles per second’ (cps) ‘cps’ is also a unit of viscosity (CentiPoise)


13.4 Fundamentals of RFAudio Frequencies

Range: 15 Hz – 20 kHzDefined by limits of human aural ability

Radio FrequenciesRange: 3 kHz – 300 GHzLargely used in radio transmission

WavelengthSpace occupied by one full cycle of a wave at

any timeWavelengths reduced at high frequencies

Passive component size comes into play


13.4 Fundamentals of RFVelocity

Speed of signal propagation through substrateAffected by

Barometric pressure Humidity Molecular content Density

Unaffected by frequencyFilters

Passes or rejects signals of certain frequenciesBased analog filters are Circuits II materialDSP Filtering is complex and precise


13.4 Fundamentals of RFAntenna

Interfaces RF systems with rest of worldRadiated power is a function of distance

Power density decreases by 1/r2 in all directions Why 850KOA (Denver) is a 50 kW system, but only

fractions of a W are received at your radioConductor and dielectric losses also are

considerationsGain and directivity (uni/onmi-directional)


Gain pattern of 9 element Yagi-Uda antenna

13.4 Fundamentals of RFBandwidth

Affect performance of communications systemIdeal resonant circuit only resonates at one

frequencyCircuit ‘quality’ affects resonanceWidth of frequency band centered around the

resonant frequency is the ‘bandwidth’Noise

Affect accurate reproduction of transmissionsReceivers must have bandpass response to

limit noise


13.4 Fundamentals of RFExternal Noise

Generated outside of the receiverCaused by atmospheric conditions, space,

solar, cosmetic-noise, lightingMan-Made Noise

EMI traceable to non-natural sourcesIgnition and impulse noise, which originates

from car engines and electrical appliances


13.4 Fundamentals of RFInternal Noise

Caused by passive/active devices inside a receiver

Thermal Noise Generated in resistances or impedances

Shot Noise Generated by the shot effect present in all active

devices

Noise EvaluationSignal/noise ratio

Radio of signal power to noise power Higher is better for improved sound quality


13.4.11 RF Components and DevicesActive, resistive, and reactive componentsPassive RF components have parasitics at raised

frequenciesUsed primarily for building filters and oscillators

Microwave Discrete Circuits (MDCs)Separate elements connected by conductive wiresMeans ‘separately discrete’

Microwave Monolithic Integrated Circuits (MMICs)Single integrated circuit of all components‘monolithic’ comes from monos (meaning single)

and ‘lithos’ (meaning stone)


13.4.11 RF Components and DevicesMicrowave Integrated Circuits (MICs)

Combination of active/passive elements manufactured by successive diffusion processes on a semiconductor in monolithic or hybrid form

Very high integration densitiesVery useful in low-power and low-density

systems such as digital circuits and military applications


13.4.12 Noise EvaluationSignal to Noise Ratio

Ratio of Signal Power to Noise Power

n

s

n

s

P

PN

S

P

PN

S

log10

powernoise

powersignal

13.4.13 RF CircuitsPassive RF components exhibit parasitics at

higher frequenciesInductors have stray capacitanceCapacitors have stray inductance

13.4.14 Fundamentals of RF Transmission Lines Summary of Maxwell’s Equations:

Electric charges generate electric fields Electric currents generate magnetic fields

There are no magnetic “charges” Time-varying magnetic field generates a spatially-

dependent electric field Time-varying electric field generates a spatially-

dependent magnetic field When both electric and magnetic fields vary with time,

electromagnetic waves are generated that travel in space with a velocity determined by the constitutive parameters of the medium

History of Radio1873- James Clerk Maxwell formulated

Maxwell’s Equations 1887- Heinrich Hertz proved the existence of

electromagnetic waves by using an antenna 1901- Marconi received first wireless

message to cross the Atlantic

13.4.14 Fundamentals of RF Transmission LinesWave propagation in a transmission line:

Voltage and Current assume spatial and temporal variations described by the propagating waves

Parameters of interest: Propagation velocity Wavelength

13.4.14 Fundamentals of RF Transmission Lines

13.4.14 Fundamentals of RF Transmission LinesWavelength and Conductivity in Selected

Media

Equations

fv

Frequency and Velocity,,Wavelength

lengthunitperecapacitanc

lengthperinductance

/

:ImpedancesticCharacteri

0

C

L

CLZ

constant dielectricrelativeε

conductors the ofdiameter d

conductorsthebetweendistance

impedancesticcharacteriZ

log138

Z

:ImpedanceCoaxial

r

0

100

D

dD

r

d

DZ

r

2log276

line wire-two a of ImpedancesticCharacteri

100

13.4.14 Fundamentals of RF Transmission LinesUniform Transmission Lines

Include two or more conductors that maintain the same cross-sectional dimensions

Coaxial line Two-wire (twin lead) line

Planar Transmission LinesConductors lie on flat dielectric sheets

Microstrip Slot-line Fin-line

13.4.14 Fundamentals of RF Transmission LinesTypes of Transmission Lines

13.4.14 Fundamentals of RF Transmission LinesCharacteristic impedance of a two-wire line

ReflectionAny mismatch in impedance will generate a

reflectionFrom a packaging standpoint, reflections are

unwantedReflections cause non-optimized transfer of

power‘Good’ designs terminate the transmission line

with an impedance equal to the line wave impedance

Crosstalk Noise Crosstalk Noise occurs as a result of coupling energy

between two transmission lines Result of capacitive and inductive coupling between

lines Generates unwanted signals in transmission lines

resulting in false and corrupted information Coupling is proportional to the time rate of change of

signals more serious at higher frequencies Present-day high frequency designs require more

compactness that compounds noise coupling problems

Crosstalk Noise (continued)Mixed-signal analog/digital circuits on the

same substrate are susceptible to crosstalk noise from digital to analog sections

System-on-chip (SOC) or system-on-package (SOP) designs must have crosstalk noise solution in place to be viable

Crosstalk Noise (continued)

13.4.15 Transmission Line Losses and Skin Effect3 major types of losses that commonly occur

in practical transmission lines:Conductor lossDielectric lossRadiation loss

Conductor Loss I2R power dissipation due to heating that occurs in

the pure resistance of the conductor Copper loss is usually greater in a line having a low

characteristic impedance Lower-impedance higher current = higher power

dissipation (I2R) Reduced current in a high-impedance line results in

reduced copper loss without causing a reduction in transmitted power

Skin EffectA type of conductor lossAs frequency of applied current is increased,

more of the electron flow is on the surface (skin) of the conductor

H/cm 10 1.26 ty,permeabili

Hertz in frequency

10cm ohm in metal the of yresistivit

10

8-0

6

0

3

f

fs

Skin Effect

Skin Effect

Dielectric Loss I2R power dissipation due to heating that occurs in

the dielectric between conductors in a transmission line

Proportional to the voltage across the dielectric Standing waves of voltage on a line increase dielectric

loss Dielectric material stores energy in the form of

electric charge Naturally polarized dipoles realign by rotating in

direction of applied field Rotation causes part of electrical energy to be

converted into heat (lost)

Dielectric LossLost energy in a dielectric may be

characterized by its Dielectric Loss Tangent:

component) phase-(in energy stored'

component) phase-of-(out energylost '''

''tan

Radiation LossRadiation from circuit increases rapidly with

frequencyConfining the fields to the interior of metallic

enclosures (packaging/shielding) may prevent radiative power loss

Mode GenerationGenerated by discontinuities, unmatched

terminations, and controlled by type of feeding

Single-mode propagation is desired for higher bandwidth and optimum power transfer

Mode Generation (continued) Three types of modes:

TEM: Transverse-electromagnetic modes Often called transmission line modes Transmission lines that have at least two separate conductors

and a homogeneous dielectric can support one TEM mode Quasi-TEM Modes

Inhomogeneous dielectric such as microstrip transmission line Propagation characteristics exhibit a slight dependence with

frequency when compared with TEM Waveguide Modes

Can transport energy or information only when operated above distinct cutoff frequencies.

One of the most important aspects in the RF packaging design since any package operates as a waveguiding structure

DispersionIf phase velocity is different for different

frequencies individual frequency components will not maintain their original phase relationshipsSignal distortion will occurThis is Dispersion

Microwave FundamentalsMicrowave frequencies range from

approximately 1 GHz to 300 GHzTravel essentially straight through atmosphereNot effected by ionized layers of the

atmosphereUsed for short-range, high-reliability radio and

television linksCommonly used for satellite communication

and control

Microwave RepeatersA Microwave Repeater is a

receiver/amplifier/transmitter combination used for relaying signals at microwave frequencies

Used in long distance, overland communication links

Waveguides Used to carry microwave energy at frequencies above

3 GHz Feedline used at microwave frequencies Waveguide wall resistance is made as low as possible Are often purged with dry air or nitrogen to drive

moisture from inside Attractive option because of wide-bandwidth and low-

loss transmission characteristics

13.5.1 Digital vs. RF PackagingBy contrast with digital designs, RF

interconnects scale with frequency rather than technology (not directly subject to Moore’s Law)

RF packaging is dominated by transmission lines and reactive elements

Successful implementation of RF systems requires a departure from conventional circuit theory and design techniques

13.5.2 RF Packaging Design Problems that may arise include:

Rise-time degradation Attenuation due to losses Coupling between adjacent pins Radiation of signals

Major task: determine electrical parameters of the package at microwave frequency Lumped model consisting of inductors, capacitors, and

possibly resistors represents the package at RF frequencies

13.5.3 Flip ChipFlip chip has emerged as one of the most

successful packaging technologiesBeing used for RF systems where parasitic

minimization is essentialUsing ball arrays minimizes parasitic

inductance

13.5.4 Passive and Microwave Components Many components such as band select, channel

select, and tuning elements of the Voltage Controlled Oscillator VCO must still remain external to the chip Inductors with high quality factors are not available in

standard silicone processes Development of the following items will be a major

step toward low-cost, fully-monolithic RF and microwave transceivers: Better active device models Active inductors MEMS filter building blocks

13.6 RF Measurement TechniquesRF components, devices and systems are

measured using high frequency network analyzers

Measurements involve extraction of scattering parameters (S parameters)Describe interactions between incident and

reflected waves from device under testModern network analyzers cover frequency

range up to 110 GHz

13.7 Future TrendsCell phone manufacturing goal: reduce

power consumption and price of cell phones by 30% every year

Ubiquitous Blue Tooth

Ball Aerospace Antenna ProductsFor some really neat pictures of advanced

antenna packaging, go to this address on the Ball website:

http://www.ballaerospace.com/file/media/antennatech.pdf

Documents

Chapter 13 Fundamentals of RF Packaging ECEN 5004 – Digital Packaging Mike Weimer Zach Allen