Accelerating the Arrival of 5G with Post-Fab Turnkey Services

GF’s expertise in RF/mmWave, testing, and packaging helps clients bring their products to market faster and more cost-effectively

by Gary Dagastine

The world was never the same after the brilliant physicist Heinrich Hertz proved the existence of radio waves in 1888. His discoveries led to new communications technologies that revolutionized how people lived and worked, and spawned many new industries.

Now, more than 130 years later, radio waves are once again revolutionizing the world, as new RF/millimeter-wave (mmWave)-based technologies drive growing interest and investments in 5G, mobile, and wireless infrastructure applications.

Semiconductors are at the heart of this latest revolution in communications, and GLOBALFOUNDRIES (GF) is playing a key role as the world’s leading foundry for RF/mmWave solutions. But in addition to a portfolio of differentiated and proven RF platforms for wafer fabrication, GF also offers clients unparalleled expertise in an array of post-fab turnkey services – along every step of the way, from finished wafer to tape-and-reel.

Post-Fab Functions are Critical to Success

Post-fab assembly, test, and advanced packaging functions are critical to the successful production of RF/mmWave integrated circuits (ICs) because the physics at these frequencies is complex, which makes it extremely difficult to accurately characterize and test these devices. These post-fab functions play a key role in keeping costs low while simultaneously delivering the high production volumes, high quality, and high reliability needed to meet growing market demands.

GF offers post-fab turnkey services to clients of all sizes who may have very different business models. The two extremes are startups focused primarily on product design and have very little capability in resourcing post-fab functions, and larger companies who also are focused on design but may not have the expertise or capability in complex post-fab activities for RF/mmWave. Clients of both types, and those in between, often engage GF to manage these post-fab activities for them.

GF’s services are based on extensive in-house RF expertise and include proprietary RF/mmWave testing technology, flexible engagement models to fit a client’s particular needs, and expert supply chain management based on decades of experience with RF technologies gained as part of the IBM Microelectronics acquisition in 2015.

In particular, GF’s in-house RF/mmWave test capability, called tester-on-board (ToB), represents a new testing paradigm for mmWave ICs. Traditional high-volume manufacturing test equipment is unable to cost-effectively perform the required testing of mmWave ICs in production environments – including, for example, measuring linearity and output power, verifying phase shifter performance, and validating noise figures. GF has invested millions of dollars developing its ToB solution, a modular plug-and-play system based on technology developed at IBM that reduces the cost of testing by 3-5 times versus rack-and-stack systems.

A Unified Approach

The increased complexity that comes with 5G mmWave applications calls for a unified design/production approach, taking into account front- and back-end considerations holistically in order to get the desired performance and reliability from a mmWave IC.

Packaging is a critical component in determining the performance of mmWave devices, said Peter Rabbeni, GF’s vice president of Mobile and Wireless Infrastructure. If packaging is regarded just as a back-end function, he said, clients may get bogged down in post-fab complexities, which could require additional time and, in turn, potentially result in missing a window of opportunity in the market.

“It’s not sufficient to simply test product performance at the wafer level at these frequencies. The specifications must be met in actual over-the-air operation through finished, packaged products,” he said. GF’s expertise with RF technologies and the company’s unique in-house RF testing capabilities are powerful tools that help clients meet this requirement. Rabbeni gave as an example a typical challenge faced by 5G base station designers: how to optimally design the power amplifier (PA) in a base station to balance reliability and achievable output power so that a handset can pick up its transmitted signal.

“Signal strength is key, of course, but there are modulation peaks and valleys that make it hard to know exactly how hard to drive the PA,” Rabbeni said. “Drive the PA too hard and you not only compromise signal quality but also PA lifetime. Drive the PA too weak and you leave efficiency on the table. There’s a ‘sweet spot’ that balances optimum power and reliability for optimum coverage. This also helps optimize the number of base stations needed to get the required coverage,” and ultimately minimizes operator capital expenditures and operating expenses, he said.

“The key to determining this sweet spot quickly and cost-effectively is having the ability to accurately simulate the performance of the PA and to characterize its reliability under any set of modulation conditions,” Rabbeni said. “GF’s process design kits incorporate our extensive RF intellectual property for device reliability and performance modeling and enable clients to perform these simulations quickly and easily.”

In addition, GF’s post-fab turnkey services enable clients to tap into the expertise of in-house experts to develop the best possible solutions. Jeff Pauza, RF turnkey business line manager for GF’s Mobile and Wireless Infrastructure unit, explained: “Let’s say a client’s design has the solder ball placements located on the bottom of the die, which is common. This could result in an unreliable or even unsafe product, depending on thermal and other effects that may relate to a specific application. Maybe the client isn’t aware of this, or simply hasn’t taken it into consideration in laying out the I/O.

“From our extensive experience with RF designs, we know what types of layouts are required to mitigate such effects, and our technical experts are available to clients to advise them and get their product to market faster,” Pauza said. “When clients realize that we, their foundry, are actually also expert in the testing and packaging of RF devices, and that they don’t have to go out and find someone else to do this for them, or set up separate relationships with OSATs [outsourced semiconductor assembly and test providers] and manage the complexities of global supply chains themselves, they see the advantages.”

Looking Ahead

Beyond 5G, GF’s post-fab turnkey services are likely to become even more important in the years to come. Guido Uberreiter, GF’s vice president of Tapeout, Mask and Postfab Operations, sees a future where RF/mmWave capabilities increasingly are added to state-of-the-art logic chips for AI, cloud computing, automotive, and other applications.

“As you look to the future you see an increasing number of applications that have to do with AI and cloud computing. This next wave of clients – many of which will be small and mid-sized companies – will want to combine RF with logic for such things as automotive radar, and they will need to find a solution to build RF SoCs (system-on-chip) in a way that is both the most cost-effective and very fast,” he said.

“They don’t want to have to send chips around the world many times, and this plays exactly to our strengths. In Dresden, for example, we have a center of excellence for bump-and-test, until now essentially dedicated to logic chips, given our 20-year history of producing advanced logic ICs in Dresden for clients. Today, we take the output from GF Fab 1 in Dresden, and Fab 8 in Malta, then bump, test, and send the tested wafers to clients. We will evolve these services to include the specialized RF expertise, and deliver them in an exceptional way for the 40-80 GHz range,” he said

GF’s post-fab turnkey services are also attractive to clients, Uberreiter said, because many customers require a secure supply chain. “Testing involves working with a lot of IP, and many customers ask us to do it because they know us and trust us. That is one of the reasons why we have become the largest test facility in Europe.”

Overall, post-fab turnkey services are another way in which GF differentiates itself and its technology as the world’s leading specialty foundry.

“Not only do we offer differentiated technology solutions for our clients, we offer differentiated services that provide a quick, high-quality, and cost-effective path to production and – ultimately – help them get to market faster,” Uberreiter said.