Professional Development Course (PDC)

Additional IssuesWhen DevelopingPackaging for 5GNormal ICPackagingIssuesChallenges of Packaging for 5G Add A Layer OfComplexity Choose compatible materials for reliabilityDie attach method and interconnect methodMetal systemSealing and die encapsulationDesign of the metal pattern and dielectric thickness to maintain50 ohmsShort interconnect lengths to minimize reflections.Careful material selection to minimize effect on electromagneticfields in integrated circuits and packagingCoupling between traces, package resonanceRF devices often have high dissipated power densityp.26

Section 1: Conclusions 5G Promises Significant Increases In Access 5G Physical Layer Leverages Two Main Items– Additional Spectrum at mmWave Frequencies– Phased Array Antennas The challenge of packaging at microwave andmillimeter wave frequencies for 5G– Components and interconnects are large compared to awavelength– Integration of 5G solutions is much more complexp.27

Section 2: Fundamentals Of 5G Packaging2.1 Transmission Lines2.2 Dispersion2.3 Package Resonances2.4 Skin Depth2.5 Coupling (both beneficial and detrimental)2.6 Interconnects2.7 Heat Dissipationp.28

Section 2.1 Transmission LinesTransmission Line Theory Transmission lines are used to carry alternatingcurrent signals such as radio frequency signals.Equivalent ModelSchematic Of Transmission Line,𝛽Coax Is A FamiliarTransmission Line TypeLine Z R j L0ImpedanceG j CPropagation2𝜋 𝛽 Constant𝜆p.29𝜆 𝑣 𝑐/ 𝜖𝑟 𝑓𝑓LCIf Losses Are Ignored

When Operating atMicrowave andespecially Millimeterwave Frequencies,Special Care Must BeTaken To Avoid HigherOrder ModePropagation.Therefore, thefollowing slides willdiscuss how to designtransmission linestaking into accounthigher order modepropagation.Adapted From: R. Sturdivant, “Fundamentals of packaging at microwave and millimeter-wave frequencies,” Chapter 1 of RF andMicrowave Microelectronics Packaging (Springer, 2010)p.30

Waveguide Transmission Lineba Waveguide is commonlyused in mmW systems. Normally, the goal is to havesingle mode propagation. Therefore, the TE10 mode isselected as the mode forthe transmission line.Approximate Electric FieldDistribution For TE10 Mode( Fc ) mn 12 12 m n a b c( Fc )10 2 a 0 0 2 ap.312Where: permeability in the waveguide permittivity in the waveguidec speed of light 3x108 m/s

Table Of Common Waveguide R10WR8WR6WR7WR5Frequency Range10.00 to 15 GHz12.40 to 18 GHz15.00 to 22 GHz18.00 to 26.50 GHz22.00 to 33 GHz26.50 to 40 GHz33.00 to 50 GHz40.00 to 60 GHz50.00 to 75 GHz60 to 90 GHz75 to 110 GHz90 to 140 GHz110 to 170 GHz110 to 170 GHz140 to 220 GHzCutoff Freq, Fc7.869 GHz9.488 GHz11.572 GHz14.051 GHz17.357 GHz21.077 GHz26.346 GHz31.391 GHz39.875 GHz48.373 GHz59.015 GHz73.768 GHz90.791 GHz90.791 GHz115.714 GHzDimension a inch(mm)0.75 [19.05]0.622 [15.7988]0.51 [12.954]0.42 [10.668]0.34 [8.636]0.28 [7.112]0.224 [5.6896]0.188 [4.7752]0.148 [3.7592]0.122 [3.0988]0.1 [2.54]0.08 [2.032]0.065 [1.651]0.065 [1.651]0.051 [1.2954]Dimension b inch(mm)0.375 [9.525]0.311 [7.8994]0.255 [6.477]0.17 [4.318]0.17 [4.318]0.14 [3.556]0.112 [2.8448]0.094 [2.3876]0.074 [1.8796]0.061 [1.5494]0.05 [1.27]0.04 [1.016]0.0325 [0.8255]0.0325 [0.8255]0.0255 [0.6477]Millimeter-wavecomponents usingwaveguide from SageMillimeterwww.sagemillimeter.comp.32

Design Equation For Stripline And CommonImplementation With Vias rWb/2b/2 60 4bZ0 ln r 0.67 W 0.8 t W The vias suppress theundesired waveguide modethat can propagate in thestripline.p.33

top metalgroundbLsviasYt rWsXZbottom metalgroundap.34

Design Of The Stripline Section Requires CarefulAttention To Via Placement Detail rviaAvoiding the two undesiredmodes results in a limitedrange for acceptable valuesfor dimension a.Stripline Undesired Mode1Fsr1 rc2a r raStripline Undesired Mode2 raSimulate using quasi-static or fullwave simulator to determine changein impedance and effective dielectricconstant as a function of spacingbetween vias.p.35Line Impedance 2.53030.02027.51025.000.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0CavityWidth,CavityWidth,a b(mm)(mm)(for r 9.8, b 1mm, w 0.203mm)Onset Of TE01 Resonant Mode (GHz)Stripline Desired ModeAllowed Range ForDimension a

Design Procedure And Example For StriplineTransmission LineExample: Consider the example of a stripline transmission line in HTCC alumina with a dielectricconstant of 9.8 and allowed substrate thickness that must be a multiple of 0.125mm due toavailable green tape thicknesses with the fabricator. The frequency of operation is 20GHz.Using these design constraints, design a transmission line that is resonant free.Step 1. Choose the thickness of the dielectric using . In most cases, the dielectric material isalready determined which fixes r and r. The maximum operating frequency propagation onthe line is also known for most applications which will determine fsr2. To provide margin, it isgood design practice is set fsr2 at 10-20% higher than is required. We will use a margin of15% so that our maximum allows operation frequency which is the same as fsr2 1.15 x20GHz 23GHz. Use the equation for Fsr2 and solve for b which is the thickness of thedielectric.b c4 Fsr 2 r r 1.042mmSince, the fabricator can only fabricate a dielectric with a thickness that is a multiple of0.125mm, we will choose 1.0mm which means that the dielectric will be eight layers, each0.125mm thick. The signal line will be symmetrically placed in the middle so there will befour layers above and four layers below the signal strip.p.36

Design Procedure And Example For StriplineTransmission LineStep 2. Next is the determination of the required linewidth for 50 ohm operation. Using a quasi staticvariational method of analysis (or other method) itwas found that a line width of 0.203mm achievesabout .04032.53030.02027.51025.000.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0CavityWidth,CavityWidth,a b(mm)(mm)(for r 9.8, b 1mm, w 0.203mm)Onset Of TE01 Resonant Mode (GHz)Line Impedance (ohm)Step 3. The final step is to determine the width of thecavity. This is done by choosing the cavity width tobe narrow so that the TE10 mode does notpropagate, and at the same time, choosing thecavity width wide enough that the slot type modeis not excited on the strip which will increase theinsertion loss. A good trade off is to keep thechange in line impedance to be less than 5% andthe TE10 mode at least 15% above the desiredfrequency range as illustrated in the figure. Forthis example, a cavity width of 1.5mm will bechosen. This results in the TE10 mode beingpushed out to 30GHz and the change in lineimpedance is less than about 2%.Allowed Range ForDimension a

Coplanar Waveguide and Conductor BackedCoplanar Waveguide Transmission Lines Coplanar Waveguide–Not used very often.–Sometimes used forwaveguide components suchas filters Conductor BackedCoplanar Waveguide(CBCPW)– Used in planar circuits suchas printed circuit boards.GairW Gth rairWGGW GWGt rhp.38

Design Equations For The Line Impedance ofConductor Backed Coplanar Waveguide704.4654.2604.0553.8503.645WGW G3.4WGt40a W/2b W/2 GK(k) complete ellipticalintegral of the first kindG rEffective Dielectric ConstantWhere:k a/bk3 tanh( a/2h)/tanh( b/2h)Line Impedance (ohm)Comparison of Zo and Ereff calculatedvalue and HFSS simulated value.3.2h353.00.050.150.250.350.45Line Width (mm)Use closed form approximations for the complete elliptical integralof the first kind for the calculations.p.39

Avoid Undesired Modes In CoplanarYWaveguideXDesired CBCPWMode r rControlled using viasconnecting groundstogetherUndesired Parallel rPlate ModeControlled using viasconnecting groundstogetherUndesired SlotModep.40

Avoid Undesired Modes In Conductor BackedCoplanar Waveguide By Using ViasWGLGhWWGDPY r rXZp.41

It Is Possible To Predict The Excitation OfUndesired Resonances From The TopsideGrounds rWGmode indexResonant FrequencymnFrom TheAbove EquationSimulatedHFSSSimulatedMoM0112.17 GHz12.5 GHz12.9 GHz0224.35 GHz24.55 GHz25.46 GHz0336.52 GHz36.55 GHz37.74 GHzLGhAgreement is within 2.7%WWGDPY r rXZComparison of the equation and HFSS for the prediction of resonantmodes on the topside ground plane of CBCPW with r 6.0, h 0.2mm,WG 1.016mm, LG 5.03mm , W 0.203mm, G 0.152mmp.42

Guidelines For Designing CBCPWTransmission Lines Use either closed form design equations that were presented orcommercially available software for the design of the transmission lines toachieve the desired line impedance. The transmission line will support three modes: the desired CBCPW mode,the slot like mode and the parallel plate (or also called the microstrip like)mode. It is important to use vias to connect the topside grounds to thebottom side grounds to inhibit the excitation of the undesired modes. Proper placement of vias connecting the topside ground to the bottom sideground is critical to achieve the bandwidth required. The vias pitch Dpshould be chosen to avoid the onset of a patch antenna type mode whichresonates along the length of the line. In general, place the vias as close asis allowed by the design rules of the circuit board process. However, as agood rule of thumb, place the vias no more than a quarter wavelength away(this is half the distance that is predicted by the equation on the previouspage with Lg replaced by Dp). Use multiple vias on the topside ground at the edge near the gap and theoutside edge of the top metal.p.43

Excellent References On Designing CBCPWTo Avoid Undesired ModesLiu, Y., Itoh, T., “Leakage phenomena in multilayer conductor-backed coplanar waveguides,” IEEEMicrowave and Guided Wave Letters, Vol. 3, No. 11, 1993, pp. 426-427.Jackson, R.W., "Mode Conversion at Discontinuities in Finite-Width Conductor-Backed CoplanarWaveguides," IEEE Trans. Microwave Theory Tech., Vol. 37, No. 10, 1989, pp. 1582-1589.Beilenhoff, K., Heinrich, W., “Excitation of the parasitic parallel-plate line mode at coplanardiscontinuities,” IEEE MTT-S International Microwave Symposium Digest, Denver, CO, June 813, 1997, pp. 1789-1792.Schnieder, F., Tischler, T., Heinrich, W., “Modeling dispersion and radiation characteristics ofconductor backed CPW with finite ground width,” IEEE Trans. Microwave Theory Tech., Vol.51, No. 1, 2003, pp. 137-143.Heinrich, W., Schnieder, F., Tischler, T., “Dispersion and radiation characteristics of conductorbacked CPW with finite ground width,” IEEE MTT-S International Microwave SymposiumDigest, Boston, MA, June 11-16, 2000, pp. 1663-1666.p.44

Design Of Microstrip LinesWthLmsY rXZp.45 Design equations forcalculating the lineimpedance and effectivedielectric constant ofmicrostrip. Suggestion: Usecommercially availabletransmission line impedancesolvers.

Avoid The Transverse Higher Order Modec 0 r Z02Fc 2h reffChoose h so that Fc 2 times yourmax operating frequencyWthLmsY rXZ This is the mode that exists whenthe microstrip line width is equalto a half wavelength. Example: alumina substrate ( r 9.8) and 0.5mm thickness with50 ohm line and reff 6.839. Fc 47GHz. However, a good rule of thumb isto set the maximum operatingfrequency to half the valuecalculated using this equation toaccommodate the range of lineimpedances that may be needed.p.46

Summary For Microstrip Design Step 1: Choose substrate thickness so that the cutoff frequency is twice your maximum operatingfrequency. Step 2: Design transmission line width to achievethe desired line impedances using the providedequations or a commercially available transmissionline solver.p.47

Section 2.2: Dispersion What is dispersion and why is it important topackaging for 5G solutions?58Dispersion in transmission lines causethe line impedance and propagationconstant to change as a function offrequency. Stated another way, thegroup delay of the signal will not beconstant as a function of frequency ifthere is dispersion.Line Impedance (ohm)5756555453525150494802468 10 12 14 16 18 20 22 24 26 28 30 32Frequency (GHz)Dispersion in microstrip for h 635 m, w 635 m, r 9.8 (alumina ceramic)p.48

332210In-1MicrostripOut-2Output Voltage (V)Input Voltage (V)Dispersion Is Also A Concern For Wide BandSignals10-1-2-320253035Time (ps)404550w 0.422mm,h 0.381mm, r 9.8 andFREQ 0.08 GHzline length of 3.81mm-3202530354045Time (ps)Output Eye DiagramInput Eye Diagram Dispersion reduces signal integrity and is particularlydifficult for wideband signals. Causes– Overshoot– Eye closing– Increased jitterp.4950

Design Guideline For Microstrip To AvoidDispersionhh 0.05 But, 0.05f r c1Therefore,hf r 0.05 ch For microstrip, dispersioneffects increase as thethickness of the substrateincreases. A guideline for microstriplines is that the substratethickness must be less than5% of a wavelength.Solving for h, we obtain0.05ch f rWhere:c velocity of light in free spaceh substrate thickness r dielectric constant of substratef max frequency of operationTo avoid dispersion,choose substrate thicknessthat obeys this guidelinep.50

Section 2.3: Package ResonancesIn Packages And Housings Cause Energy To Be Sucked Outof The Desired Signal0Cavity Width aIntegrated CircuitsAnd Other Components-5Insertion Loss (dB)AirdbtDielectric Substrate-107.00 GHz-19.69 dB-15-20-25Approximate ElectricField Distribution02468101214161820Frequency (GHz)XYResonance FrequencyIs Approximated Bycfr 2aWhere:fr cavity resonance frequencya width of the cavityc velocity of light in free spaceThe cavity resonancefrequency can beapproximated as a TE10waveguide moderesonancep.51

A Better Approximation Of The ResonantFrequency Is The LSM11 Mode The Logitudinal SectionMagnetic (LSM) modepropagates in adielectric filledwaveguide.baPropagationconstant for theLSM11 mode isgive by T Q Q 2 2 P 4 PP 0.522LSM 11The full solution to the equation for the LSM11 mode is given in either of these referencesR. Sturdivant, Microwave and Millimeter-wave Electronic Packaging (Artech House, 2014), pp. 8-9.R.E. Collin, Field Theory of Guided Waves, 2nd Edition (IEEE Press, 1991), pp. 428-429.p.52

One Method To Reduce The Cavity ResonanceEffect Is To Use Absorber In The Lid0-5-1Insertion Loss (dB)Insertion Loss (dB)Without Absorber On The Lid0-107.00 GHz-19.69 dB-15Without Absorber On The Lid7.00 GHz-0.35 dB-2-3-4-20-25-502468101214161820024Frequency (GHz)68101214161820Frequency (GHz)AirIntegrated CircuitsAnd Other ComponentsDielectric SubstrateAirDielectric SubstrateMetal housing enclosurep.53Integrated CircuitsAnd Other ComponentsAbsorber

Section 2.4: Skin EffectSkin Effect Tells Us That The RF Current OnlyPenetrates A Small Distance Into The MetalXAirRegionEx(z)J0Skin effect is the tendency of an alternatingelectric current (AC) to become distributedwithin a conductor such that the currentdensity is largest near the surface of theconductor, and decreases with greater depthsin the conductor.MetalRegion ( , )Jx(z) Joe z/ Skin Depth Z1 fWhere: permeability metal conductivityf frequency of concernp.54

Skin Depth For A Few Different Metal TypesAs A Function Of Frequency6.05.5Conductivity107 (S/m)Silver6.21Copper5.85Gold4.425.0Skin Depth (10-6 m)MetalTypeSkin Depth @ 5GHzSkin Depth @ 10GHz4.54.0Skin Depth @ 20GHzFe3.5Skin Depth @ Al AuCuAg2.00.50.001234567Metal Conductivity (107 S/m)p.558910

Section 2.5 CouplingCoupling (Both Desired and Undesired)Coupling Can Be Used For Desired FunctionsLange CouplerDirectional CouplerFilterCoupling Can Also Cause Significant Undesired Effects Coupling can cause oscillationsCoupling can cause undesired circuit resonancesCoupling can cause undesired electromagnetic resonancesCoupling can cause voltage spikesp.56

The Simple Model Of Coupling Uses ACapacitorW S100MHzWAir rhLRFINRFOUTC(L)p.57 At low frequencies,coupling can bemodeled as asimple capacitor. On this approach,coupling increasesas the length of thecoupling structureincreases.

A Higher Fidelity Model Of Coupling UsesEven and Odd Mode Analysis0Even Mode AirOdd Mode Air rGNDGNDPort4Port2AirhPort3Port1 rC112C122C127.40 GHz-0.70 dB-5Coupling (dB) rS21S31-107.40 GHz-8.30 dB-15-20C22L-25Line OfSymmetry02468101214161820Frequency (GHz)Length L bLPort1Port2Port3Port4 Coupling is frequencydependent. Coupling also depends upon thelength of the coupled sectionp.58

The Importance Of Grounding For IsolationAnd Avoiding “Ground” Layer ResonancesGround Metal Via ConnectionVias For IsolationYArray ofGround ViasRF InputXXZZGround PadRF OutputFence OfGround Vias Via arrays are essential for achieving acceptable groundcontact. Otherwise ground metal will resonate Via fence is used to increase isolation betweentransmission lines and other circuits.p.59

Section 2.6 InterconnectsLevel 1 Interconnects A Few Options1) Wire Bonding (Face-Up Die Mounting)1) Wire BondsBenefits:MMIC Low cost and low barrier to entry This is the industry standard for die attach. Extensive installed manufacturing baseDrawbacks:2) Flip ChipBumpInterconnects Wire bond inductance and variability. This creates variability in performance Wire bond radiation into the module can cause resonances at millimeter-wavefrequencies2) Flip ChipMMICBenefits: Low inductance and highly repeatable interconnect Low radiation and some cost benefit (compared to wire bonds) at very high volumeproductionDrawbacks:3) Chips FirstGround Pad andThermal Path Requires modified manufacturing and design processes(IC & module) Requires changes to design methods (CPW versus microstrip)3) Chips FirstBenefits: Moderate/low inductance and highly repeatable interconnectDrawbacks: Over molding affects MMIC performance Costly and module rework is difficult Requires modified manufacturing and design processes(IC & module)p.60

Wire Bonds Are Used Extensively InMicroelectronicsType1: Ball BondsType2: Wedge BondsWedgeBallStitchICICMother BoardWedgeMother BoardBroadly speaking, there are at least two types of wire bondsExample of a wire bonding machine Wire bonds are the back bone f

What Are The Implications For Electronic Packaging Technologies? 2.0 Fundamentals of uWave and mmWave Packaging Transmission Lines Dispersion Package Resonances Skin Depth Coupling (both beneficial and detrimental) Interconnects Heat Dissipation 3.0 Materials for 5G Packaging 4