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5G Wafer Test and the New Age of ParallelismPresented by David Raschko

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Overview

• 5G – What do you know now? When will it arrive?• What Probing Technology can you use at these frequencies?• What should you think about for probe head inductance?

• Everything we know is wrong

• What is the Digital signal measurement capability of different probing technologies?• What is the RF measurement repeatability?

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What is 5G?

• Communication Network for 4th Industrial Revolutiono 5G RF, Optical, High Speed Digital

• Extremely Fast Data Rateso 10Gbps (5G) vs 100Mbps (4G)

• Ultra Low Latencyo 1ms (5G) vs 50ms (4G)

• Huge No. of Connectionso 100 billion (5G) vs 1000 (4G)

• Higher Energy Efficiencyo Always Stay Connected

• Connect Everyone, Everything

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5G Use Cases

• Enhanced Mobile Broadbando Enterprise/Team Collaborations, AR/VR,

Enhanced Wireless Broadband, Education, Mobile Computing, Enhanced Digital Signage.

• Massive Internet of Things (MIoT)o Smart Cities, Energy/Utility Monitoring, Asset

Tracking, Smart Agriculture, Physical Infrastructure, Smart Homes, Remote Monitoring, Beacons & Connected Shoppers.

• Mission Critical Services (Low Latency Requirement)o Autonomous Vehicles, Remote Patient

monitoring/TeleHealth, Industrial Automation, Smart Grid, Drones. 4G - braking command makes a car at

100kmph to stop after 1.4m. 5G - Same car stops within 2.8cm due to

ultra low latency.

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5G Industry Timeline

• 3GPP planned for a 2-part 5G roll out:• < 6GHz starting in 2020

• mmWave starting in 2021

• >200M mmWave Handsets in 2023

• Actual roll out is pulled in > 1year!

• Major IC suppliers are starting to move on initial mmWave handset IC production

• Multiple orders now for // device test

• Infrastructure still lags behind

*From EETimes

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What are we seeing with 5G devices?

• The efforts to develop 5G fall under 3 main categories:o Spectral Efficiency: Better use of the RF spectrum for greater bandwidth over farther

distances of communication 30 GHz, 40 GHz, and 60 GHz bands are being added

o Energy Efficiency: Reduce power usage for lower cooling costs and longer lifetimes of battery operated devices Beamforming for antenna gain, requiring more antenna channels

o Utilization: Infrastructure overhaul with more distributed, high speed digital devices More high speed devices with a larger number of base stations

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New 5G mmWave Probe Card Requirements

• New device architectures: o IF transceiver driving multiple antenna driverso Antenna drivers for multiple antenna arrays

• Antenna Driver chips pose special challengeso 9GHz to 20GHz IF, 28GHz, 39-43GHzo Emerging requirements for 60GHzo 18, 34, or even 50 RF IO per die

• Antenna Driver probe card challengeso Achieve Frequency and Isolation requirementso Ability to fit all mmWave RF lineso Multi-DUT Tester capabilityo Support loopback to reduce tester complication

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Supporting 5G from Lab to Fab

Analytical Probes>1.2THz

Pyramid>80GHz

• Highest performance production solution

Pyrana<10GHz

• RF performance• Replaceable spring head• Individual replaceable probes

ePyrana>40GHz

• New in 2H-19!

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ePyrana Overview

• Pyrana architecture has evolved to support applications beyond 10 GHz and smaller arrays (10 mm).

• Active probe area extended out to 75 x 12 mm o Thousands of pins o Hundreds of RF channelso Same robust contact and electrical performanceo Now available!

• Enhanced Pyrana supports applications >40GHzo Impedance Controlled Spring Heado Shorter probes (reduced inductance)o Beta opportunities now, release to mfg. targeting 2H’19.

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RF Performance of ePyrana

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Pyramid, Katana-RF, Pyrana & ePyrana Comparison:

Pyramid Probe Card Katana-RFX Probe Card Pyrana Probe Card Pyrana Probe CardRF Performance 80 GHz <10 GHz <10GHz >40GHzSpace Transformer Membrane to CBI MLO or Direct Attach Membrane to CBI Membrane to CBIMax Probe Area 10 x 38mm ~ 75 x 75mm 12 x 75mm 12 x 75mmCommon PCB Yes (standard CBI) No Yes YesPin repair No Yes Yes YesPin-Pin Compliance <10μm +/- 150μm +/- 150μm +/- 75μm

Pyrana Probe Card

PCB

Core Mechanics

ProbeHead

MembraneVertical MEMS

CBI

pProbe Probe CardCore

Mechanics

MembranepProbe tips

CBIPCB

Katana-RF Probe Card

PCB

ProbeHead Vertical MEMS

MLO

ePyrana Probe Card

Impedance Controlled MEMS

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Probe Inductance – Define Residual Inductance

• Delay and Inductanceo Inductance can be defined by the delay in

the output signal vs. input signalo But even with a delay, a properly designed

transmission line will not have a substantially degraded signal

o A good 50 Ohm cable can have inductance of µH, but we do not worry about this since it is compensated with capacitance

• Residual Inductanceo Here, inductance can be looked at the

amount of voltage drop from the system ‘uncompensated’ inductance

o This is what affects the overall signal integrity

When you are looking at inductance, people confuse the definition of the time delay with residual inductance

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How to Calculate the Ground Inductance?

• We then looked at the voltage drop due to the inductance from the two sides of the probe heado We use the definition of voltage drop, not phase delay

∆𝑉𝑉=−𝐿𝐿 𝑑𝑑𝐼𝐼/𝑑𝑑𝑡𝑡 The phase delay of a perfect conductor is limited by the speed of light, even if there is no net drop

of voltage of the sine wave magnitude in the materialo By looking at the frequency dependent voltage drop of the magnitude of the signal, we have estimated

that the inductance is ~50 pH

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Inductance of the Ground Returns

• In order to estimate the ground return inductance we built a model to look at the ground currents from the DUT to the membrane

• For this, we assumed that the membrane is a perfect ground, and looked at only the inductance from the contactor to the membrane

• Based on simulations, the residual inductance is:o Pyramid Probe: ~ 40 pHo Pyrana: ~500 pHo ePyrana: ~ 50 pH

• The residual inductance is what is contributed to signal degradation from the pin

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0 0.05 0.1Time (ns)

Pyramid

-0.2

0

0.2

0.4

0.6

0.8

p2

0 0.05 0.1Time (ns)

Pyrana Eye

-0.2

0

0.2

0.4

0.6

0.8

p1

p3

Eye Diagram• Here, we look at how the different probe technologies affect an eye diagram

o We picked a representative one with the following characteristics: Rise Time/Fall Time: 20 ps Fundamental frequency of 30 GHz V_high : 1.5 V V_low: 0.0 V

Pyrana has a reduction in eye size of ~14%

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Production RF Calibration comparison

• There a multiple ways to do RF calibration. We have picked two of the simpler methods that can be used in a full production environmento 1-port SOL o Automatic Fixture Removal (AFR) from Keysight

• Both methods can be used to generate 2-port S-parameters for the Probe Cardo Note: AFR can be done three different ways:

Use Short only, Open only, and Short-Open

• We compared the absolute value of the measurements and repeatability of each measurement

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Comparison of the RF Measurements

Pyramid Pyrana

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RF Repeatability of SOL

• One key consideration post calibration is how repeatable are the measurements from touchdown to touchdown

• These measurements are done with a single SOL calibration, and then remeasuring the standards 10 times each

• Each plot is the std dev of the measurements

Load Open Short

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Repeatability of AFR

• AFR, in comparison, has similar, if not better repeatability• This indicates that the cal method doesn’t necessarily dictate the repeatability, but accuracy

is degraded

Load Open Short

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Calibration and IL-RL difference

• One key point is the sudden roll-off in the performance of the measurements at ~37 GHz in the H-row Pyrana

• What is the cause?o At 37 GHz, the IL and RL difference just reached

the critical point of about 3 dB difference It appears to be that this might be a significant ratio

that once you reach this, the ability for repeatably measurements will be degraded and continue to get worse

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Summary

• 5G is an all encompassing communication network that will reach everyone and everything• Arrival of 5G is coming quickly and is accelerating

• 5G will require greater parallelism with uncompromised fidelity for wafer Testo Wafer Probe technologies will need to combine mechanical compliance with reduced residual

inductance Beginning to see “transmission line” probes

• The increased frequency requirements for 5G will place greater emphasis on the need for RF calibration in order to reduce system noise from RF measurements