This post authored by John Coonrod, Technical Marketing Manager, and team originally appeared on the ROG Blog hosted by Microwave Journal.

Circuit materials are evaluated by a number of different parameters, including dielectric constant (Dk) and dissipation factor (Df). Those two parameters also have temperature-based variants that provide insight into the expected behavior of a circuit material with changes in temperature, notably the thermal coefficient of dielectric constant (TCDk) and the thermal coefficient of dissipation factor (TCDf). The parameters detail the amounts of change in a material’s Dk and Df, respectively, as a function of temperature, with less change representing a material that is more stable with temperature.

A circuit material with an ideal TCDk, with a Dk that would remain at a fixed value even as the temperature changes, would have a TCDk of 0 ppm/°C. In the real world, however, circuit materials exhibit some change in Dk with changing temperature. A circuit material considered to have stable Dk with temperature will have a very low value of TCDk, typically less than 50 ppm/°C. When an application requires that a circuit board be subjected to a wide operating-temperature range and deliver stable performance all the while, a circuit board’s TCDk parameter is one of the key specifications to consider after determining the required Dk for that application’s circuits.

Although circuit temperature stability requirements for military and aerospace applications are well documented, due to the typically hostile operating conditions of military circuits and systems in the field, commercial applications can also endure conditions of changing temperatures that can require better-than-average circuit-board TCDk performance. Power amplifiers for wireless base stations or outdoor-mounted microcells may not experience the wide temperature swings of military environments, but they depend on circuit Dk stability with temperature to maintain stable gain and output power. Their active devices are impedance matched to a typical 50-Ω circuit/system environment for optimum gain, output power, and power-added efficiency, and changes in Dk will cause variations in amplifier performance. In addition to environmental temperatures, the self-heating effects of amplifiers can further complicate changes in a material’s Dk characteristics with temperature, especially for materials with high values of TCDk.

Similarly, passive components, such as filters, can suffer from unwanted frequency changes with changes in Dk, such as shifts in passbands and stopbands. Ideally, wireless base stations would be maintained in temperature-controlled environments but, again in the real world, this is often not the case, and circuit-board TCDk is then a key performance parameter of interest.

When performance with temperature is important, specifying a circuit-board material should be done deliberately and by taking a close look at available data sheets. Circuit designers should never assume that two materials from the same manufacturer or the same product line will have the same TCDk characteristics. Different materials based on PTFE, for example, can have widely different values of TCDk. PTFE, of course, is the basis for many excellent, low-loss, high-frequency circuit materials, but the TCDk characteristics of these materials can vary widely. Some PTFE-based circuit materials can suffer large changes in Dk with temperature, evidenced by TCDk values of 200 ppm/°C and even higher.

At the same time, some PTFE-based circuit based materials can provide near-ideal TCDk characteristics. PTFE-based RO3003™ circuit material from Rogers Corp. has outstanding TCDk of -3 ppm/°C, making it a strong candidate for temperature-sensitive circuit designs facing wide operating temperature ranges. The family of circuit laminates includes materials with Dk from 3.00 to just over 10.00 when measured through the z-axis (thickness) of the material at 10 GHz. The laminates are popular circuit choices for military and commercial applications through millimeter-wave frequencies of 77 GHz and higher, including in automotive radar systems which much maintain stable performance over wide temperature extremes.

Just as suppliers of circuit materials may test and specify the Dk values of their materials in different ways, such as at different test frequencies, any valid comparison of circuit materials for their TCDk performance levels calls for an understanding of the measurement methods used to determine TCDk for a particular material. Material measurements are often based on industry-standard IPC test methods for agreement of values among different material suppliers.

For example, measurements of circuit laminate TCDk at Rogers Corp. are performed by means of the clamped stripline test detailed in IPC test method IPC-TM-650 2.5.5.5c. Prior to testing a circuit laminate, all of the copper is etched from the substrate. The substrate is then clamped into a fixture, which behaves like a loosely coupled stripline resonator. The fixture and its material to be tested are placed into a laboratory temperature-controlled environment, such as an oven. The temperature is changed in steps and the fixture and material are allowed to reach thermal equilibrium with each change in temperature before the Dk is measured. Many measurements are performed to cover a wide operating temperature range and to measure the Dk at different points across that temperature range. The end result is a curve of Dk versus temperature for that material, which is the TCDk of that material.

Temperature-Dependent Loss

Just as TCDk is a barometer of how a material’s Dk changes with temperature, TCDf is a measure of a circuit material’s dissipation factor (Df) or loss tangent and how it changes with changing temperature, typically with loss increasing as temperature increases. As with TCDk, the temperature effects of TCDf can impact the performance of both active and passive circuits. At higher temperatures, a circuit material with high value of TCDf can compromise the gain and output power of an amplifier, and increase losses in passive circuits, such as filters or passive antennas.

The TCDf values of circuit materials from Rogers Corp. are characterized with a measurement method that is the same as that used for testing TCDk. The measurements are complicated by the variations in the loss properties of the resonator circuit, which is integral to the clamped stripline fixture and the fact that copper conductivity changes with temperature. Rather than attempting to measure and report Df versus temperature to derive a TCDf value for the material, loss versus temperature is measured, where it is the loss of the resonator in the form of its inverse quality factor (1/Q). As with TCDk, an ideal value of TCDf would be close to zero, to indicate little or no change in dissipation factor with temperature. In the real world, circuit materials with the lowest possible values of TCDf are to be preferred for temperature-sensitive circuit applications, whether for active or passive circuits.

All of the information shown above is in regards to the effect of temperature on the Dk and Df properties (TCDk and TCDf) of material when considering a short-term thermal event.  How a laminate responds to long-term thermal exposure is a different subject than TCDk and TCDf, even though these properties can be involved with long-term thermal aging evaluations.  These aging evaluations are critical to understand if the circuit material is the proper choice for the conditions it will be exposed to in the end-use environment and that it will meet the needs of the intended application over the life of the product.  More information on long-term thermal aging can be found a in two-part series blog, Picking A PCB For High Reliability and PCB Formulated for Reliability.

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A DC link is a connection between a rectifier and an inverter found in converter and VFD circuits. The DC capacitor helps prevent transients from the load side from going back to the distributor side. It also serves to smooth pulses in the rectified DC.

This webinar by the our Power Electronics Solutions group reviews the design of a DC Link System using optimized solutions based on integrated capacitor-busbar technology from Rogers Corporation.

Due to lower overshoot voltages and less uF/kW of required total capacitance, this solution offers lower total system cost and increased power density. The integrated capacitor-busbar assemblies are developed for critical DC link applications in traction drive inverters for HEV/EV, and inverter systems for solar and wind power.

View the webinar now.

Integrated Capacitor-Busbar Technology

The ROLINX® CapEasy and ROLINX® CapPerformance capacitor-busbar assemblies combine extremely low inductance and high power density to create small, lightweight devices. They feature a unique Power Ring Film Capacitor™ technology from SBE Inc. and the well-known ROLINX Laminated Busbars from Rogers Corporation. The result is reduced total system cost, improved reliability, and increased power density compared to currently available solutions.

ROLINX® CapEasy and ROLINX® CapPerformance advantages:

  • Ability to handle higher ripple currents
  • Lowest industry ESL with an integrated busbar structure
  • Increase system reliability and lifetime
  • Low system weight and volume

Download the data sheet.

View the product overview video.

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Today’s manufacturers of automotive fleets and mass transportation systems are motivated to meet fuel efficiency and emission requirements, as well as market demands for reduced costs. e-Mobility (electro mobility or advanced mobility) refers to clean and efficient electric and hybrid vehicles that use electric powertrain technologies, in-vehicle information, communication technologies, and connected infrastructures.

e-Mobility efforts are gaining traction around the world. According to EURACTIV, Europe is making major gains:

Metros and tramways are electric and provide high-capacity, zero-emission public transport systems in many European cities. Likewise, about 80% of Europe’s mainline rail traffic is powered by electricity. Several EU member states are now pushing towards a 100% electrified rail network, with the potential to reduce the CO2 emissions of rail to zero if they achieve it.

And road transport is catching up. Last year, the number of electric vehicles (EVs) purring up and down the world’s roads surpassed two million. This may not seem a lot when set against the total number of cars on the road (which is probably in excess of a billion) but it does represent remarkable and sustained growth. EV sales climbed by nearly 40% in the US last year, while China has become the largest single market in the world for EVs and plug-in hybrids, with sales only expected to grow as government-backed investment presses on.

You can find Rogers’ advanced materials in a wide variety of eMobility platforms: power electronics solutions for electrical oil pumps and battery packs, high-frequency PCB laminates for electrical power steering and antennas, and gaskets and vibration management foams for airbag sensors and sound systems. Let’s take a closer look at the electronics inside these vehicles.

 

High frequency PCB substrates are found in Adaptive Cruise Control, Antenna Boosters, Automated Tolling Tags, Blind Spot Detection, Collision Avoidance and Mitigation, GPS, Rear Cross Traffic Alert, Telematics, and V2X Antennas.

Ceramic substrates are found in Air Conditioning Compressors, Battery (Fast) Chargers, Converters, Electrical Power Steering, Inverters, Liquid Heater PTC, Oil Pumps, Start-Stop Systems, and Vacuum Pumps.

Power distribution systems are found in AC-DC Converters/DC-DC Converters, Battery Modules, Motors, Power Steering, and Start-Stop Systems.

Active Safety Systems

New cars are increasingly equipped with robust crash avoidance technologies. These active safety technologies are enabled by innovative Advanced Driver Assistance Systems using sensor technologies, such as radar, to detect collisions.

Rogers’ Advanced Connectivity Solutions group provides high performance PCB laminates for 24 GHz and 77 GHz automotive radar sensor applications. The RO4000® and RO3000® series materials enable radar sensors to detect upcoming collisions to prevent road accidents. In addition, RO4000® high frequency circuit materials are successfully used in 24 GHz radar sensors for blind spot detection or rear cross traffic alert.

Forward collision warning, emergency brake assist, adaptive cruise control, and traffic jam pilots require radar sensors that operate in the 76-81 GHz range. RO3000® High Frequency Laminates have an excellent Dk tolerance of ± 0.04 and at this high frequency concerns with insertion loss are paramount. These laminates also offer an extremely low dissipation factor, ensuring the dielectric loss component of insertion loss will be very low.

Vehicle to vehicle (V2V) or vehicle to infrastructure (V2I) communications systems send information via dedicated short range at 5.9GHz (DSRC) or intelligent transportation system G5 (ITS-G5) and 3G/4G cellular network. Rogers’ high frequency materials help antenna´s and modules to achieve high performance and reliable connections between cars and infrastructure even at high speed and under harsh vehicle environments.

Power Connectivity and Distribution

As power from a battery is expensive, the challenge is to use the electric power as efficiently as possible. The primary inverter needs to minimize switching losses and maximize thermal efficiency. Auxiliary inverters are used to power vehicle electrification solutions. The range of the vehicle is directly related to the efficiency of these inverters.

Semiconductor-based power systems are able to optimize overall system cost, minimize power losses, increase power density, maximize power savings, extend mileage, and improve battery efficiency.

RO-LINX® busbars from the Power Electronics Solutions group focus on efficient power distribution and lower energy losses, increasing the range of electric vehicles. These laminated busbars provide a customized liaison between the power source and capacitors, resistors, integrated circuits (ICs), integrated gate bipolar transistors (IGBTs), or complete modules. 

Within the circuit board, power substrates provide interconnections and cool components. curamik® ceramic substrates are designed to carry higher currents, provide higher voltage isolation, and operate over a wide temperature range.

 

 

Part of being a conscious global citizen is realizing that it’s possible to make a difference. Rogers is well aware of the impact a company can have. Our goal is to encourage our employees to be socially conscious and strive to improve the lives of those they touch.  We are immensely proud of the work they do on the job and in the local community. Here are a few recent stories about how our employees are making a difference.

Helping the Homeless

Adopt a FamilyFor over five years, Rogers’ Lettie Schultz has organized the company’s “Adopt a Family” donations program for the Killingly Family Resource Center in Connecticut. The center provides support for homeless families, families living in shelters, and local families in need.

This is a family affair for everyone involved. Each year, Lettie’s grandchildren help her shop, create tags, and distribute the gifts. Tags are also given to all our Connecticut facilities, including R&D and manufacturing.  “We collect the gifts in one area,” Lettie explains, “and our helpful guys in IT take them to the Family Resource Center.”

The resource center has commented about Roger’s generosity. The gifts intended for one family are sometimes shared with other families. This allows more families to participate, spreading the holiday spirit throughout the region.

Redesigning Sports Grounds

The Rogers Germany team was victorious in a charity soccer game to support a redesign of the sports ground at HPZ Irchenrieth, a therapy-based day center primarily for people with mental health disabilities.  The game provided exciting entertainment. In the end, Anette Enders (HR Manager) and Johannes Beierl (Industrial Training Manager) handed over a donation of 1.000 EUR for the redesign of the sports field. Daisy Brenner, Chairwoman of HPZ was very thankful and confirmed that the money would be in good hands.

A big thank you to our soccer team from Rogers Germany: Daniel Küfner, Benjamin Reiter, Andreas Farnbauer, Johannes Wiesend, Thomas Kohl, Andre Brunner, Michael Pfleger, Marco Wöhrl, Johannes Bauer, Tobias Weber, Michael Melchner, Fabian Gradl, Raphael Hösl, and Alexander Schäffler.

Top 10 Employee Caring Enterprise

Suzhou Cares PosterRogers Technologies (Suzhou) Co., Ltd was awarded “Top 10 Employee Caring Enterprise” by the General Labor Union of Suzhou Industrial Park. Suzhou delivers their corporate caring culture from a number of angles, including their “Journey Towards Care” program, which focuses on employees’ happiness, learning, and growth, as well as their efforts to spread care to the community.

Caring for our Teachers

Rogers’ Chandler, Arizona building is undergoing renovations.  Employees have pitched in to clear out the building. Large recycle bins hauled away massive amounts of “stuff”—including outdated books and files with paperwork—some with notes for the inventions and processes that have led to our current success.  It’s awe inspiring to know Rogers has been a part of so many game-changing innovations for over 180 years.

After an employee “rummage sale,” we had an opportunity to recycle unused office furniture and supplies.  Habitat for Humanity took some items and suggested we donate the rest to Treasures 4 Teachers (T4T).

Barbara Blalock began T4T in 2004, collecting donations for a YMCA preschool and storing them in her garage.  As more donations poured in from the community, her vision of supporting educators grew into a community resource warehouse.

Teachers join T4T for $35/year and are given unlimited access to shopping for low or no cost. Teachers might spend as much as $1,000 a year out of their own pocket for school supplies, so T4T offers these items at no cost or at a nominal fee to help sustain our educators.

The Fight Against Cancer

Former Rogers Belgium colleague, Arsène Demaret, and his team “De Gulden Sporen” (the Golden Spurs) from Brussels, took part in the Levensloop (Run for life), a unique concept in the fight against cancer.

The Levensloop brings together communities to watch the 24-hour relay and enjoy festive events for all ages.  “Levensloop” is all about solidarity and fundraising for the fight against cancer. The event:

  • Celebrates people who survived cancer or are still fighting the disease,
  • Commemorate people who died from cancer, and
  • Invites participants to stand up and fight as a community against cancer.

levensloop big picture

 

This post authored by John Coonrod, Technical Marketing Manager, and team originally appeared on the ROG Blog hosted by Microwave Journal. 

Recipes are often refined with time, in hopes of improving the results. Such is the case with RF/microwave circuit laminates, created from carefully blended mixtures of materials, with the goal of achieving the best possible results in electrical and mechanical performance. Over the years, many different formulations have been applied to create high-frequency circuit materials. The efforts have led to a variety of current circuit laminate choices for a wide range of high-frequency applications and performance requirements.

The high-frequency material perhaps most familiar to users of circuit laminates is polytetrafluoroethylene, more commonly known as PTFE. It is a synthetic thermoplastic fluoropolymer formed of carbon and fluorine. It has a high molecular weight and low coefficient of friction, the main reason it is often used to create “non-stick” surfaces. With a dielectric constant (Dk) of 2.1, PTFE has excellent dielectric properties at microwave frequencies.

PTFE has been a “building-block” material for microwave circuit laminates for some time. It is combined with other materials to modify its electrical and mechanical properties to the requirements of high-frequency circuit designers. For example, PTFE-based circuit materials are typically reinforced with woven glass for improved mechanical stability. The woven-glass reinforcement will raise the material’s Dk value and also decrease material expansion as a function of temperature, better matching the coefficient of thermal expansion (CTE) of the circuit material to that of its copper conductors. PTFE-based laminates also use ceramic fillers to achieve higher Dk values and to fine-tune other material properties, such as CTE.

At one time, the choice of circuit laminates for high-frequency, thin-film circuits came down to almost an “either/or” decision for circuit designers: fabricate it on lower-cost FR-4 circuit material or on higher-performance (and higher-cost) PTFE-based laminates (or alumina ceramic substrates, in the case of high-frequency thick-film circuits). FR-4 really refers to a family of circuit materials based on woven-glass-reinforced flame-retardant epoxy. The material is popular for its low cost and ease of circuit fabrication, but suffers degraded electrical performance at higher frequencies, typically above about 500 MHz, and many circuit designers had learned their own “cutoff frequency point” below which they could use FR-4 and above which required a PTFE-based circuit laminate.

While well-established and accepted for high-frequency circuits, PTFE is just one of a number of “ingredients” in currently available high-frequency circuit laminates, which also include thermoplastic materials such as polyphenyl ether (PPE), polyphenylene oxide (PPO) epoxy resin, and hydrocarbon-based materials with ceramic fillers. Some high-frequency and high-speed applications have encouraged the development of even more exotic circuit laminate formulations, such as liquid-crystalline-polymer (LCP) materials for flexible circuits and polyetheretherketone (PEEK) thermoplastic materials for extremely high operating temperatures (to about +200°C). In fact, for circuits at microwave frequencies, the number of circuit laminate options seems to grow with time, with newer material formulations promising improvements in the key characteristics that define circuit laminate performance for printed-circuit boards (PCBs), including Dk, dissipation factor (Df), coefficient of thermal expansion (CTE), thermal coefficient of dielectric constant (TCDk), thermal conductivity, moisture absorption, and long-term aging.

Comparing Compositions

How do these different high-frequency material compositions compare? First of all, it is important to note that not all PTFE-based circuit laminates are created equal. Early PTFE-based laminates were reinforced with woven glass to reduce the inherently high CTE of PTFE alone. Further improvements in performance were possible for PTFE-based circuit laminates by adding micro-fiber glass to the mixture in RT/duroid® 5880 circuit material from Rogers Corp. PTFE-based laminates were further improved by adding special ceramic materials as fillers, not only to modify the Dk but to alter certain properties of the material to make them easier to process when fabricating PCBs.

In the case of RT/duroid 6002 circuit board material from Rogers Corp., it is based on PTFE but without woven-glass reinforcement. By adding special ceramic filler, the Dk of the base PTFE material is raised to a value of 2.94 that is highly consistent (within ±0.04) through a sheet of RT/duroid 6002 and with low Df (0.0012) and CTE through the z-axis (thickness) closely matched to that of copper for reliable plated through holes. In fact, the process of adding ceramic filler to a base material such as PTFE allows “fine-tuning” of the material’s ultimate Dk value, so that PTFE-based circuit laminates can be formulated with many different Dk values.

Through experimentation, it was also found that ceramic filler could also be used to fine-tune the Dk values of circuit materials other than PTFE, such as the thermoset hydrocarbon resin materials that are the basis for the TMM® laminates from Rogers Corp. For example, through the addition of different amounts and types of ceramic filler, TMM laminates achieve Dk values ranging from 3 to 13. These resin-based materials are somewhat easier to process into PCBs than PTFE-based circuit laminates, although the absence of glass reinforcement does result in some other challenges for circuit fabrication. To overcome those challenges, a circuit laminate formulation based on ceramic-filled hydrocarbon resin, but with woven-glass reinforcement—RO4350B™ circuit material from Rogers Corp.—was created to provide improved CTE and temperature stability while also maintaining the ease of PCB processing associated with hydrocarbon (non-PTFE)-based circuit laminates.

More recent circuit material formulations have included thermoset hydrocarbon-based PPE and PPO circuit laminates, typically reinforced with woven glass for improved mechanical stability. As noted earlier, such materials can offer unique benefits, such as ease of circuit fabrication and improved long-term aging characteristics. However, they are also limited to lower Dk values and tend to exhibit more rapidly increasing dielectric loss (Df) with frequency than PTFE-based materials and ceramic-filled, hydrocarbon-based circuit laminates.

This sampling of different circuit material compositions hints at some of the differences among the material choices. For example, whether they are glass reinforced or not, special ceramic fillers which are used in PTFE-based circuit materials contribute to good CTE and TCDk performance levels; they also make possible a wide range of Dk values for PTFE-based circuit laminates, from about 3 to 10. Without ceramic filler, PTFE-based circuit materials achieve better loss characteristics (low Df), but with degraded CTE and TCDk compared to ceramic-filled PTFE-based materials. As a general trend, PTFE-based circuit laminates with higher Dk values will exhibit higher Df values and are more anisotropic with increased Dk.

Ceramic-filled, hydrocarbon-based circuit laminates fortified with woven glass typically have higher Df (greater loss) than PTFE-based materials, although they also offer typically better CTE, TCDk, and thermal conductivity than PTFE-based circuit laminates. PPE and PPO-based circuit laminates also have higher Df values than PTFE-based circuit materials, or about the same values as hydrocarbon-based circuit laminates when tested at about 10 GHz or less. For the special features of those PPE and PPO-based circuit materials, including excellent long-term aging characteristics, they suffer higher moisture absorption than the other types of high-frequency circuit laminates.

For high-frequency circuit designers, more choices in circuit laminate compositions are available than ever before, each with its own benefits and tradeoffs. The requirements of a particular application can usually help to speed up and simplify the choice.

Screen shot 2014-08-08 at 1.33.54 PMROG Mobile App

Download the ROG Mobile app to access Rogers’ calculators, including the popular Microwave Impedance simulation tool, literature, technical papers, and the ability to order samples of the company’s high performance printed circuit board materials.

Ask an Engineer

Do you have a design or fabrication question? Rogers Corporation’s experts are available to help. Log in to the Rogers Technology Support Hub and “Ask an Engineer” today.

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