5G mmWave check builds on RF greatest practices

The excessive degree of integration in immediately’s mmWave cellphone means conventional check strategies now not apply.

By David Vondran and Rodrigo Carrillo-Ramirez, Teradyne 

5G, the primary mobile technology to make use of the mmWave spectrum, can ship quicker knowledge charges (as much as 10x higher than LTE). Plus, 5G can accommodate extra simultaneous subscribers with greater reliability providers. These enhancements make 5G very best for particular deployments comparable to dense city environments — airports, stadiums, and metropolitan areas.

mmWave smartphones comprise extremely built-in parts. In contrast to at decrease frequencies, check methods can now not carry out carried out checks in any respect manufacturing steps. Whereas testing on the wafer degree can use methods discovered at sub-6 GHz frequencies, mmWave parts comparable to antenna-in-package (AiP) should use over-the-air (OTA) check procedures.

Why mmWave?
Within the US, the community operators have procured mmWave bands and deployed mmWave networks. Desk 1 outlines the 4 major mmWave bands (i.e., 24 GHz, 28 GHz, 39 GHz, and 47 GHz) by service.

In accordance with a cell knowledge visitors outlook report from Ericsson, the standard US subscriber in 2028 will eat 55 GB month-to-month. Why a lot in comparison with immediately’s roughly 15 GB averages? This predicted visitors progress comes from estimates for prolonged reality-type providers (XR) — augmented actuality (AR), digital actuality (VR), and blended actuality (MR). On prime of that, elevated and higher-resolution video visitors, at the moment about 70% of all knowledge visitors, can even contribute to this progress.

mmWave hasn’t but seen the accelerated progress that usually accompanies new connectivity applied sciences. The information-traffic outlooks point out that it gained’t be lengthy earlier than congestion and starvation for throughput open the floodgates. The preliminary technology of mmWave-capable units will assist develop the mmWave ecosystem, which incorporates manufacturing checks.

Whereas the US has allotted 39 GHz and 47 GHz for mobile use, the 26 GHz to twenty-eight GHz mmWave band appears poised to grow to be the usual for world protection. Due to this fact, we count on the goal marketplace for mmWave will quickly grow to be ten occasions bigger, measured in billions of subscribers.
Ahead-looking producers have risen to satisfy this rising demand. Since 2019, greater than 400 5G mmWave succesful cell units have come to market, which signifies that mmWave is catching on. Desk 2 breaks down these system capabilities based on their supported mmWave bands.

Now that we’ve seen issues from the community operators’ perspective, these smartphones are price a better look to know the opposite half of the wi-fi equation.

Inside immediately’s 5G smartphone
The practical block diagram in Determine 1 reveals how 5G smartphones organizes the intricate constellation of parts to allow wi-fi communication between subscribers and community operators. The applying processor, which controls all
smartphone operations, joins all the pieces. Generally, the connectivity bands are served by separate RF sign paths for unlicensed band operations comparable to within the 2.4 GHz, 5 GHz, and 6 GHz bands. Equally, separate RF and mmWave paths serve licensed-band operations for the mobile bands.

Consider every wi-fi sign path as consisting of a modem,
transceiver, and path to an antenna(s), which may embrace
different RF front-end parts comparable to switches, tuners, and
multiplexers. On this organized method, the wi-fi sign
paths between the applying processor and the antennas grow to be
the numerous pathways from RF to bits. And these paths set up the
wi-fi hyperlinks that ship wi-fi providers for the
subscriber.

Specializing in the mobile path, the modem is the hub for the
wi-fi mobile linkages. Moreover, the RF transceiver
handles all of the sub-6 GHz actions for knowledge transmission and
reception. Likewise, the mmWave transceiver handles all mmWave
knowledge transmission and reception. The precise variety of wi-fi
bands relies on the community operator’s plan to ship providers
to their subscribers.

RF and mmWave transceivers
The RF transceiver should help all operational bands for the community operator. Throughout the transceiver are separate transmit and obtain paths for every band. The full variety of bands relies on a community operator’s unfold throughout 1G/2G/3G/4G/5G and will whole as many as 70 bands. Moreover, antenna expertise has developed to accommodate huge enter, and big output (MIMO) options that concurrently transmit and obtain on 4 antennas. Thus, the transceiver should carry out persistently at excessive ranges and throughout all supported bands. This important performance, flexibility, and reliability relaxation on exceptional integration and complexity that wants testing.

Just like the RF transceiver, the mmWave transceiver should additionally help all of a community operator’s operational bands. Within the mmWave spectrum, these bands are the 24 GHz, 28 GHz, 39 GHz, and finally, 47 GHz bands. On condition that mmWave communication entails shorter wavelengths relative to sub-6 GHz, its sign paths are additionally smaller. In truth, the Semiconductor ecosystem appears to have standardized on an antenna in package deal (AiP) module to mix the mmWave transceiver, energy administration IC (PMIC), beamformer, and antenna array right into a single modular package deal. Determine 2 illustrates this miniaturization pattern by exhibiting AiP modules, the place probably the most trendy is at proper. This makes the AiP module simple to combine right into a sign path however makes testing them tougher.

As Desk 3 summarizes, AiP has undergone 4 generations thus far. The present AiP modules help a number of mmWave bands. This achievement has accelerated mmWave expertise adoption. It additionally reveals how extra band help has an inevitable ripple impact as a result of all of the sign paths should align to help the wi-fi hyperlink.

Desk 3. Qualcomm’s AiP modules hold including bands and rising knowledge charges as every successive modem hits the market.

We will now see how the applying processor, mobile modem, and transceivers have grow to be built-in, advanced semiconductor units. Even this digital tear-down dangers oversimplification. Many of those units have separate PMICs that regulate their energy to enhance battery life. In addition they comprise customized antennas that streamline the sign paths to the bottom station with extremely optimized signal-to-noise ratios to attain quicker and extra dependable knowledge charges.

Implications for automated check
As we’ve seen, the primary practical blocks of a 5G smartphone embrace the applying processor, modem, transceiver, RF entrance finish, and antenna. Each successive technology of those units has ripple results within the superior packaging essential to attain greater efficiency and extra advanced integration. Automated check tools (ATE) Satisfies the manufacturing want for high quality.

Check workflow for high-volume manufacture of Sub-6 GHz parts has grow to be ubiquitous. Check engineers try to get rid of defects as early within the manufacturing course of as attainable. As a rule of thumb, defects get ten occasions costlier to seize at every successive manufacturing step.

The wafer check insertion makes use of ATE to separate good and unhealthy die. These checks are normally electrical in nature (not RF). This primary check insertion, termed wafer kind, is designed to get rid of as many defects as attainable. In consequence, this step usually has the bottom yield.

Subsequent, package-level check additionally makes use of ATE to make sure operation and efficiency that meets statistical expectations to keep away from transport defects and outliers. These RF checks encompass each CW and modulated indicators and might embrace calibration procedures. This insertion is designed to usually have a a lot better yield than the wafer check.

Lastly, the RF chip integrates right into a module (or system meeting) to finalize the RF sign chain and fulfill its mission within the smartphone structure, together with antenna connection(s). On this manufacturing step, the module undergoes one final system-level check (SLT) insertion for a carried out check (not over the air, OTA), together with attainable calibration procedures. This insertion usually offers the very best attainable yield.

This workflow ensures high quality and consistency all through the availability chain for the RF sign chain, whether or not this package deal serves a singular perform or affords built-in capabilities. Notice that check protection is the sum of all three insertions and variations on the check technique are attainable relying on the basis reason behind defect mechanisms. The manufacturing purpose is defect-free shipments. In follow, the standard metric describing the ultimate SLT output is measured by faulty components per million (DPPM).

This Sub-6 GHz workflow additionally represents the very best practices to comply with for manufacturing the AiP module within the mmWave sign chain.

Superior packaging within the AiP module allows miniaturization inside the 5G smartphone. It additionally imposes on the manufacturing course of, which should adapt to the complexity and integration of the mmWave sign chain into this single package deal. As we evaluate the RF and mmWave sign chains, two predominant variations summarize these mmWave check challenges for AiP modules.

• Within the curiosity of miniaturization, the AiP module doesn’t make use of the identical conventional packaging methods employed within the beforehand described RF workflow. As an alternative, superior packaging to combine die with substrate and antenna array introduces new challenges to discovering defects associated to the elimination of packaging components to attain miniaturization.
• Given the small wavelengths in mmWave, shut coupling between the transceiver and antenna array (by way of a substrate) affords superior wi-fi efficiency in comparison with utilizing separate, discrete components. This tight coupling eliminates extreme transmission loss. Sadly, it additionally eliminates typical check factors and greatest practices for the carried out check. A brand new check technique that measures variations between antenna array — over the air (OTA) and accessible carried out check interface at 5G-IF — is critical for calibration and defect detection.

In comparison with the RF greatest practices, the mmWave workflow illustration in Determine 3 reveals the brand new rising simplification and complexity in testing AiP modules.

Check workflow for high-volume manufacture of mmWave parts has but to grow to be as ubiquitous as with RF. Certainly, it’s nonetheless evolving with each new technology of AiP modules. Like RF, check engineers try to get rid of defects as early within the manufacturing course of as attainable.

As with sub-6 GHz, wafer-test insertion makes use of ATE to separate good and unhealthy die. These checks make use of wafer probes and check with each electrical and mmWave indicators. This primary check insertion, termed wafer kind, eliminates as many defects as attainable and, as with the RF check, usually has the bottom yield. The output is a recognized good die (KGD).

Lastly, the KGD integrates into the AiP module to finalize the mmWave sign chain. On this manufacturing step, the module is positioned in an optimum anechoic chamber that's handler-friendly and undergoes one final system-level check (SLT) insertion utilizing OTA strategies, together with attainable calibration procedures utilizing each CW and modulated indicators. This insertion is designed to usually present the very best attainable yield.

Just like the RF sign chain, this workflow ensures high quality and consistency within the mmWave sign chain. Notice that check protection is the sum of all three insertions and variations on the check technique are attainable relying on the basis reason behind defect mechanisms.

Conclusion
With so many variables and applied sciences at play, testing the RF-to-bits parts inside a 5G smartphone is not any small process. Any check technique for 5G smartphones should account for greater frequency, larger bandwidth, elevated website density, and enhanced efficiency whereas additionally sustaining automated check tools (ATE) expectations for modularity and flexibility. This requires experience in lots of disciplines to succeed, particularly when that check leaves no room for guide intervention. If profitable, nevertheless, it might probably gas innovation, high quality, and profitability by assembly manufacturing volumes and reducing check price.