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JJD: What is driving the growth in sales of RF/microwave circuit materials?
AA: Three segments have been driving RF and microwave market growth in 2014: wireless infrastructure, automotive, and defense. The deployment of wireless infrastructure in support of 4G services (LTE and LTE-A) in regions like Asia (China, Japan, and South Korea) and the U.S. has created significant opportunities, as these countries adopted 4G early. They are striving to lead the world when it comes to advanced wireless connectivity. (Both the US and China were seen as laggers when it came to 3G deployments.)
Automotive is not an area one first thinks of when it comes to microwave circuitry. But there are currently RF sensors operating at 24 GHz in vehicles (in essence, radar). These sensors aid the driver in making decisions pertaining to lane changes and on-coming traffic (as part of Advanced Driver Assistance Systems, or ADASs). Today, such systems are marketed as convenience features rather than safety options. We are seeing the adoption of these sensors beyond the traditional luxury vehicles like Mercedes, Acura, and Cadillac. They are now making their way to mid-size vehicles like VW, Ford, and Toyota, where volumes are much higher. In the defense industry, the current growth is a result of renewed government spending on several major programs. Those efforts were delayed in 2013 as a part of the effects of the sequestration on government spending.
JJD: What problems faced by today’s design engineers require new material solutions?
AA: Within the markets listed above, we are seeing changes that are driving design engineers toward new solutions. Those solutions require innovations in materials. One trend that affects both the automotive and wireless-infrastructure markets is the use of operating frequencies above 60 GHz—in particular, 77 to 79 GHz. The amount of data that is being transmitted wirelessly is doubling roughly every year, according to Cisco’s annual VNI report.
As a result, data usage is reaching the limits of available bandwidth for microwave backhaul. Limits for available bandwidth span the 7-to-40-GHz spectrum. A solution is to move to frequencies beyond 60 GHz, both licensed and unlicensed, where there is much greater availability.
To vacate the spectrum around 24 GHz, automotive sensors will be transitioning in the future to frequencies close to 79 GHz. This shift is a product of interference concerns. In the area of wireless infrastructure, power levels are increasing within base stations. This means that operating temperatures are increasing as well. Managing this increase in thermal density—along with the decrease in housing size—is creating new thermal-management issues for designers.
JJD: In which ways have traditional RF/microwave circuit materials changed to meet these needs?
AA: In the area of higher operating frequencies, reducing circuit losses is a key element in developing material solutions for use beyond E-band. Existing resin systems can still be used, such as polytetrafluoroethylene (PTFE) and possibly those used in low-loss thermoset materials. However, reducing the conductor loss component of the total circuit loss is critical. This is done by using copper with a lower surface roughness profile while maintaining good copper peel strength to the dielectric.
At frequencies above 60 GHz, conductor loss is much greater than dielectric loss. Smoother foils are now available on both thermoplastic and thermoset resins, resulting in reduction of the insertion loss of 30% to 50% (depending on material types). To better handle increased operating temperatures, heatsinks, metal plates for groundplanes, and metal alloy coins can be added. They offer increased thermal conductivity for areas below the power device.
Thermally, the circuit would also benefit significantly by having PCB materials with increased thermal conductivity. In the past, higher thermal conductivity was a “nice” bonus for substrate performance. But recent thermal-density increases in microwave circuits are necessitating higher thermal conductivity with the substrate.
Some designs have required little change, as they were already using thermoset materials with high ceramic loading. These materials have raised thermal conductivity over traditional RF/microwave materials. Now, the industry is seeing needs for thermal conductivity to increase by as much as 30% to 100% above current industry standards. As a solution, special ceramic fillers are being incorporated in existing resins. Their goal is to evolve the thermal behavior of substrate products in a controlled manner.
JJD: Operating frequencies continue to get higher in volume applications, such as 79 GHz for automotive and wireless backhaul. In those cases, what is critical about selecting circuit materials?
AA: There is always great emphasis on the electrical properties of the substrate materials at these frequencies. And they are important in both dielectric-constant control and low loss with the dielectric and conductor. However, one property that usually gets overlooked by RF designers is thickness control. Often, when a customer discusses material needs in this space, they ask about tightening Dk tolerance. Typically, Dk tolerances are already around ±1% to ±1.5%. Many designers forget that thickness tolerances can be as much as ±10%.
In many RF equations, the effect of Dk is a factor of the square root while the thickness impact is a direct product. If improved stability is truly needed, going through the analysis in the electromagnetic (EM) simulator may reveal that there is more of an advantage in circuit performance. The focus simply needs to be on thickness control improvements rather than on the dielectric constant.
This file type includes high resolution graphics and schematics when applicable.
Hot Markets
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JJD: What markets should we be watching as possible drivers of future growth?
AA: There are still many opportunities in several of the existing markets. Full-out 4G/LTE adoption is still confined to few countries, although the rest will eventually follow. Additionally, there is the discussion about 5G. With no standards set yet, the form that 5G will take is still quite fluid. We don’t know what it means for the materials industry yet.
Meanwhile, the automotive market is expanding from ADASs to cars as wireless-communications hubs. Ford and Volvo provided demonstrations of the “car of tomorrow” at World Mobile Congress in Barcelona this year. Eventually, organizations like Google will be pioneering self-driving vehicles.
The Internet has brought about many changes in the past 15 years. Without these changes, who knows if we would be seeing the explosions in broadband data that have driven so much of the infrastructure capital expenditures (CAPEX)? It is likely that the next technology wave will be driven by what is today called the Internet of Things/Internet of Everything (IoT/IoE). It is too early to say with any degree of confidence which applications will drive material development. But many potential market opportunities would benefit from the flow of wireless data to improve process yields, increase energy efficiencies, keep us safer, or just plain entertain us.
At this year’s MWC event, Bruno Jacobfeuerboin, CTO of Deutsche Telekom AG, said that we will go from “smartphones to smart things, from data consumption to data production.” To get there, Intel presented projections by IDC, which stated that there could be 50 billion connected devices in the next few years. These devices won’t operate like typical data-hungry applications, such as mobile video. Yet they do pose a problem—network loading, which has simply been optimized for broadband data like LTE. I don’t know about you, but I’m eager to find out what real benefits there are in having my refrigerator connected to the Internet.
JJD: What is changing about how material properties are characterized compared to the past?
AA: Obviously, what makes these materials unique are their properties in the RF and microwave frequency bands. Most common test methods were developed in the 1970s, when the only markets were defense and aerospace. This has led to materials being characterized at X-band frequencies (10 GHz), as that is where many of these applications operated. Today, we have wireless communications from 800 MHz to 2.5 GHz, microwave backhaul radios from 7 to 40 GHz, and now millimeter-wave backhaul to 60 GHz and beyond.
Additionally, automotive sensors as high as 77 GHz are being developed. And there is demand for data specific to their frequency bands. This frequency-specific data is not only for circuit modeling. Ultimately, this information also is used for standardized quality testing.
Unfortunately, there is no standard test method. Material suppliers have had to rely on their knowledge of testing and microwave theory. The data on these materials is out there now. But I would caution designers to have discussions with their suppliers and ask questions about testing protocols, signal launch schemes, and calibration methods. Ultimately, the best approach is to look at the data and verify if it matches what you are seeing in the applications and if it make sense.
JJD: What can you say about regional RF/microwave design activity around the world?
AA: I have been involved in this industry for 25 years and I have seen many changes that have impacted the RF and microwave market. The first wave of change, in the early 1990s, came about as we saw the demise of the Soviet Union and end of the Cold War. This industry transitioned from aerospace and defense programs, mainly U.S. and some European, to a new market called commercial RF and microwaves. The new aspects of the industry were spearheaded by activity in pagers and analog cell-phone networks. We saw much more design activity coming from Europe with companies like Ericsson and Nokia. There also was a refocusing of companies like Motorola and Alcatel. By the early 2000s, activity was evenly split between these markets and regions.
During this timeframe, the PCB industry also was transitioning to Asian manufacturing—the adoption of RF materials similar in process to FR4 that were now being fabricated overseas. These trends opened the window for RF design activity in China and for companies like Huawei and ZTE to begin to move into the industry. What started as activity for the Asian region is now a full global transition.
Today, we don’t only see “Western” companies doing design activity in Asia; We are also seeing Chinese companies doing research in Europe and North America. I would say that the amount of design activity is equal between North America, Europe, and Asia. Some regions having greater focus in certain markets, such as the defense focus in North America and mobile-network-infrastructure focus in Asia and Europe.
JJD: Over the last couple of years, we are seeing new PCB material suppliers coming into this market. (Some are more established suppliers to the traditional FR4 world.). Where does this interest stem from?
AA: When one talks about PCB materials, unless you are an RF engineer, one usually thinks of FR4 (epoxy glass). That is a product of FR4 materials controlling about 95% of the market, and this market is a commodity market. There is very little that differentiates one product from another, so it is an extremely competitive market. Some suppliers (in particular those that come from outside of China and Taiwan) are finding it quite difficult to compete and are losing share.
Such factors have encouraged these companies to focus their attention on the 5% of the market in which materials are differentiated. This area of the market treats PCB materials as more than just a mechanical support for connectivity. They are considered an essential part of the circuit itself, as a component that impacts electrical performance.
Many of these suppliers first pushed into what is known as the high-speed digital market in the early 2000s. These companies targeted operating data rates of 2.5, 9.8, and now up to 24 Gbps. As organizations, their logical next step is to try to move into the RF/microwave materials market. But there is a big difference in markets here. In high-speed digital applications, the primary performance characteristic is still fabrication (at 24 Gbps, that is a bit different).
Most of the discussion happens with the PCB facility. For RF/microwave applications, however, the issue is electrical and the discussions happen with the designers. The focus for RF/microwave applications must be on designers and applications. If split between traditional FR4 and the RF world, the resulting divided focus can lead to inefficiencies.
JJD: Rogers Corp. has been a supplier of high-frequency materials for several decades. What main features are customers in this space looking for in their materials?
AA: When a designer begins work on a new project, the basic value that is being addressed is “peace of mind.” What I mean is this: Designers are not looking just at what is the “best” material in the lab. The designer is trying to answer a much broader question, such as, “Which material will position my company in a more favorable way than my competition?”
Datasheets are an important part of the decision. When you compare datasheets, though, it is quickly found that no two companies present data the same way. This is a product of there being many test methods, conditions, and frequency ranges used for scale. So the experienced designer uses datasheet information as a starting point only.
There is also reliability testing to consider—mainly answering questions like, how is the performance affected by environmental changes like temperature and humidity over the short and long term? In addition, the designer must consider the supplier itself and if that company can supply the quantities needed in a timely manner. Can the supplier support PCB boardshops regardless of the region? And when issues arise, how does the supplier support their product?
A designer is not just making a laminate selection. That designer is putting his or her reputation on the line. Knowing that a whole team stands behind the designer to provide support through the product life cycle gives peace of mind. From the mid-1960s, Rogers has focused on sales, technical support, marketing, R&D, and production teams focused on not just laminates, but on solutions.
This file type includes high resolution graphics and schematics when applicable.