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.

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

Congratulations to our Advanced Connectivity Solutions team on their 100th ROG Blog post. For six years they have been providing technical advice about PCB design for RF/microwave applications. Here’s to 100 more posts!

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Predicting the future is never easy. Similarly, knowing which types of circuit materials will be needed for the next decade’s RF/microwave applications can be difficult to predict, but the past can provide invaluable guidance. With this being the 100th installment in this series, the previous six years of ROG Blogs provide a bit of a map for the high-frequency road ahead and what might be needed in terms of electrical and mechanical characteristics for what are expected to be large-volume applications in this industry, including in radar-based automotive electronics systems, Fifth Generation (5G) wireless communications systems, and Internet of Things (IoT) sensors almost everywhere.

This first six years of the ROG Blog offered guidance on the use of many different types of circuit materials from Rogers Corp., for everything from high-frequency analog circuits to high-speed digital circuits. It explored the effects of circuit material characteristics on the performance of different types of high-frequency transmission lines, including microstrip, stripline, and various types of coplanar waveguide (CPW) transmission lines. And it has examined how the choice of printed-circuit-board (PCB) material impacts the performance of many different types of components, such as low-noise amplifiers, power amplifiers, delay lines, filters, and resonators.

In the next few years, this industry is expected to face new challenges in circuit design, with the high-volume growth of automotive electronics systems, 5G wireless, IoT, even with the steady growth of existing wireless applications such as WiFi and WLAN.

For many high-frequency circuit designers, wireless communications systems such as Third Generation (3G), Fourth Generation (4G), and Long Term Evolution (LTE) have represented rapid growth areas. But even without a standard in place, excitement is growing for the coming of 5G wireless communications systems and the type of services they will provide in the years to come, including fast wireless data with almost zero latency. Transferring high-speed digital signals will be an important part of any future communications network and the ROG Blog from January 22, 2015, “Selecting PCB Materials For High-Speed Digital Circuits,” detailed how RO4003™ circuit materials provided the proper mix of characteristics for speeds to 25 GB/s and beyond.

Higher-frequency (millimeter-wave) signals are expected to play important roles in 5G next-generation communications systems, and the ROG Blog has already provided several installments on choosing materials for millimeter-wave circuits, such as “Making The Most of Millimeter-Wave Circuits” and “Matching Materials To Millimeter-Wave Circuits.” Since millimeter-wave frequency bands are planned for high-data-rate backhaul links throughout 5G networks, the need for circuit materials capable of reliable, low-loss performance at 50 through 70 GHz should continue to grow, prompting more ROG Blogs on this topic.

The expected boost in the number of wireless signals in use during the next decade should also focus circuit designers’ attention on the material characteristics needed for low-PIM performance. An earlier ROG Blog, “Perusing PCBs For Low PIM Levels,” explained the role of circuit materials in the design of PCB antennas and how circuit material characteristics should be chosen to minimize PIM. That blog presented Rogers’ RO4725JXR™ and RO4730JXR™ circuit laminates as non-PTFE, halogen-free circuit materials with the characteristics needed to minimize PIM. With the growing number of wireless signals to be generated during the coming decade, in high-volume applications such as 5G and IoT, the importance of minimizing PIM only increases and certainly should be a recurring topic of this ROG Blog series.

The first six years of the ROG Blog series provided circuit specifiers with key insights on different aspects of circuit materials, such as material parameters important for impedance matching, for dissipating heat, and for minimizing losses. ROG Blogs have explored such things as the importance of circuit laminate finish, in “Finish Makes a Difference in Broadband PCB Loss,” and the reason for using a high-dielectric-constant (Dk) circuit material, in “Harness High-Dk Circuit Materials.” The next 100 ROG Blogs hope to provide guidance on the best use of these high-frequency materials, as starting points for what appears to be many high-frequency, high-speed circuits in the decade to come.

ROG 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.

We are pleased to announce that Rogers Corporation has signed a definitive agreement to acquire Arlon, LLC, currently owned by Handy & Harman Ltd. (NASDAQ: HNH), for $157 million, subject to closing and post-closing adjustments. The transaction, which is subject to regulatory clearances, is expected to close in the first half of 2015. Rogers intends to finance the transaction through a combination of cash and borrowings under an existing bank credit facility.

RogersCorporation logoBruce Hoechner, President and Chief Executive Officer of Rogers said, “This transaction is truly a unique strategic fit for both Rogers and Arlon. We are energized by the opportunity to serve our customers with our complementary capabilities and technologies in circuit materials and engineered silicones and to enhance value for our shareholders. We look forward to closing this acquisition as another significant milestone in Rogers’ growth as a premier global engineered materials solutions company.”

arlon_logoArlon: A Strong, Strategic Fit

The proposed acquisition of Arlon is consistent with Rogers’ strategy as it adds complementary solutions to its Printed Circuit Materials and High Performance Foams business segments and expands Rogers’ capabilities to serve a broader range of markets and application areas.

Arlon’s circuit materials product family positions Rogers for additional growth in the rapidly expanding telecommunications infrastructure sector, as well as in the automotive, aerospace and defense sectors. Arlon produces its circuit materials in Bear, Delaware; Rancho Cucamonga, California; and Suzhou, China.

The engineered silicones product family of Arlon will further diversify the Company’s solutions and market opportunities in sealing and insulation applications. Arlon will bring new capabilities in precision-calendered silicones, silicone-coated fabrics and specialty extruded silicone tapes. Used primarily for electrical insulation, these materials serve a wide range of high reliability applications across many market segments, including aviation, rail, power generation, semiconductor, foodservice, medical and general industrial. This product family is primarily manufactured in Bear, Delaware.

Revenue and operating income for the Arlon segment of Handy & Harman Ltd. were $100.4 million and $16.7 million, respectively, for the trailing twelve months ended September 30, 2014 (compiled based on amounts reported by Handy & Harman Ltd. in Forms 10-K and 10-Q filed with the Securities and Exchange Commission).

Press Release: Rogers Corporation Signs Definitive Agreement to Acquire Arlon, LLC

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Screen shot 2014-08-08 at 1.33.54 PMNow you can access Rogers’ PCB materials resources with the ROG Mobile App. Quick and easy access to calculators, literature, technical papers. You can even request samples on your smartphone or tablet

  • The app has tools and technical information to assist you with Rogers printed circuit board materials.
  • The Microwave Impedance Calculator assists with microwave circuit design in predicting the impedance of a circuit made with Rogers High Frequency circuit materials and also provides capabilities for predicting transmission line losses.
  • The ROG Calculators assist RF engineers with thermal and mechanical simulations for microwave PCB designs.
  • Data sheets and fabrication guides can be downloaded and material samples can be ordered.

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The Advanced Circuit Materials Division has announced RO4360G2™, next generation PCB laminates with improved thermal reliability for higher UL maximum operating temperatures (MOT’s).

In 2010, Rogers Corporation introduced its groundbreaking product, RO4360™ laminate, the first high Dk RF thermoset laminate. We have now launched the next generation, RO4360G2 laminate, with improved thermal reliability that will help fabricators achieve higher UL MOT’s.

With a tailored high Dk of 6.15 @ 10 GHz, this material allows next generation power amplifier designers to meet size and cost reduction targets. Specifically, the laminate’s higher Dk allows for a significant reduction in finished circuit board size (20-30%). RO4360G2 laminates process similar to FR-4, are automated assembly compatible, and offer the same reliability and repeatability that customers have come to expect from Rogers RO4350B™ material.

RO4360G2 laminates are UL 94V-0 flame rated (pending) and fully lead-free process capable. They possess excellent thermal conductivity of .81 W/m/K for improved reliability, a low Z-axis CTE for reliable plated through holes, and drill performance as good as or better than RO4350B laminates.

Typical applications for RO4360G2 laminates are power amplifiers, LNAs, RF components (combiners/splitters), patch antennas, and as a replacement material for designs previously employing LTCC (low temperature, co-fired ceramic). RO4360G2 laminates are the material solution designers working on 4G and next generation defense/aerospace platforms have been looking for!

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