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

Woven glass is incorporated into printed-circuit-board (PCB) materials to provide structural strength. It aids the mechanical stability of a laminate, but what does it do to its electrical behavior? One of the classic concerns regarding woven glass reinforced laminate PCBs is that the “glass weave effect” can have negative impact on the electrical performance of high-speed or high-frequency circuits fabricated on these laminates. In this blog post, we examine some of the factors affecting the glass weave effect phenomenon.

Depending on the particular resin system of a woven-glass laminate, the dielectric constant (Dk) of the material can vary by location, in extremely small and periodic ways. These small areas with different Dk values can be due to the glass weave pattern, where the woven-glass fabric has areas of glass bundles and areas that are openings between the glass bundles (see the figure). The Dk of the glass bundles is typically about 6, while the Dk of the laminate in open areas between the bundles is much lower, typically around 3. The variation in Dk value has been a concern for circuit designers working with woven-glass laminates, since the impedance of high-speed / high-frequency transmission lines is highly dependent upon Dk.

As an example of how the glass weave effect can have an impact on a microstrip transmission-line circuit, consider a laminate with top and bottom copper layers (signal conductor and ground plane for microstrip) with a Dk of 3.0 in the z-axis (thickness) at 10 GHz. Dk variation in the circuit material typically will affect performance more at higher frequencies, such as millimeter-wave frequencies (30 GHz and above). At 77 GHz, for example, the one-quarter wavelength of signals propagating through the circuit is about 0.024 in., which would make the one-eighth wavelength about 0.012 in. In theory, when an electromagnetic (EM) wave encounters any kind of Dk change in its propagating medium that is larger than one-quarter wavelength of the frequency of interest, propagation will be disrupted and resonances can occur.

Practical experience has shown that even anomalies as small as one-eighth wavelength can cause wave propagation issues. Circuit laminates with openings in the glass or glass bundles that are one-eighth wavelength or larger at a frequency or frequencies of interest could suffer performance irregularities because of the distribution of glass bundles (and corresponding variations in Dk). Given the various styles of glass used to reinforce different circuit laminates, it is not unusual for several of these glass types to have window openings that are one-eighth wavelength or larger at 77 GHz (0.012 in.).

As multiple plies of woven glass are stacked to form a laminate, it is less likely for glass bundles and openings to align. As a result, it is less likely for discrete Dk variations due to the location of glass bundles and window openings. Therefore, the impact of the glass weave effect at millimeter-wave frequencies is decreased for woven-glass circuit materials using two or more layers of glass fabric.

Greater concern regarding the glass weave effect is for high-speed and high-frequency circuits using a laminate with a single layer of woven-glass fabric. Using a microstrip circuit as an example, fabricated on a laminate with one glass weave layer, one concern has to do with the randomness of the glass weave effect when using woven-glass circuit materials and trying to achieve repeatable performance in high-volume production. Variations due to the glass weave effect can result in circuit-to-circuit performance variations. The random location of the woven-glass pattern as it relates to the circuit pattern can result in microstrip impedance variations that cause shifts in the phase angles of propagating high-frequency waves, resulting in degradation of any phase-sensitive signal characteristics, such as phase-based modulation.

While a laminate using multiple layers of a woven-glass fabric may help mitigate the glass-weave effect for high-speed and high-frequency circuits, multiple coupled or differential conductors on a single-layer circuit can expose additional problems with the glass weave effect. The degradation in conductor phase characteristics noted earlier can also impact coupled circuits or differential lines. Because such circuits have well-defined relationships between or among the conductors, each conductor requires the same wave propagation medium. If each conductor in a coupled pair has a different medium, they will not couple as expected. In pairs of differential lines, the phase angles will vary if the Dk values of the wave propagation medium varies between the pairs of lines. The end result is a slowing of the propagation of one signal wave versus the other, resulting in skew. Particularly in high-speed digital circuits, skew caused by the glass weave effect can significantly degrade performance due to changes in signal timing.

Changes in Dk due to the glass-weave effect can be moderated by fabricating a laminate with a filled resin system rather than an unfilled resin system. The filler typically has a different Dk value than the resin or the glass, and it fills the open spaces between the glass. The use of a filler results in a material with less-drastic changes in Dk in the small isolated areas between the glass bundles, with an effective averaging of the Dk values with the combinations of glass fabric, resin, and filler.

Another method is the use of spread/flat glass fabric along with minimizing the relative glass content in the laminate with respect to the filler and resin. This combination provides the mechanical benefits of glass reinforcement while minimizing the Dk variation along the signal propagation path.

Of course, one way to overcome the glass weave effect altogether in a circuit laminate is to do without the woven glass. An example of such a material is RO3003™ laminate from Rogers Corp., with no woven glass fabric. It has become quite popular as a laminate solution for high-volume millimeter-wave circuits. RO3003 laminates are ceramic-filled PTFE composite materials with dielectric constant of 3.00. The dielectric constant is maintained within ± 0.04 across the circuit board and from lot-to-lot of circuit material. Such Dk consistency is vital for the small wavelengths of millimeter-wave circuits, but also for coupled lines as well as differential pairs in high-speed digital circuits. It is the type of Dk consistency that is difficult to achieve with woven-glass circuit materials, due to the glass weave effect.

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Over the years, battery technology has been slow to change. Li-Ion has dominated thus far because a lithium anode has a high energy density and is lightweight. Recent research demonstrates that new developments are showing promising results.

Fade, Capacity, and Size

As most mobile phone users know, batteries fade as they age. This “capacity fade” means the amount of charge a battery can supply diminishes with use. Researchers at the U.S. Department of Energy’s Argonne National Laboratory have identified the mechanism behind the scenes of fade in Lithium-ion batteries.

Other energy storage issues include capacity and size of the battery package. Researchers at Stanford have created an innovative mathematical model that will help develop new materials for storing electricity.

The high costs and technical challenges of battery storage have taken great leaps toward mainstream use, expanding exponentially along with renewable technologies. Further development and expansion of renewable energy infrastructure promises significant gains with the advent of grid-connected electrochemical battery systems. These systems will also provide a more flexible and reliable grid.

Hybrids & Electric Vehicles

A recent breakthrough in rechargeable zinc-based batteries may be able to store as much energy as lithium-ion batteries. Zinc-based devices could also end up being safer, cheaper, smaller, and lighter. Applications include microhybrids, electric vehicles, electric bicycles, and eventually, smartphones and power grid storage.

Pininfarina, designer of exotic cars from Ferrari, Maserati, and Alfa-Romero, has several new projects in the works with Hybrid Kinetic Group, a clean-energy auto company. The new vehicle designs feature high energy, high density “super batteries” that can recover energy. Micro-turbine generator range extenders recover almost 30% of the total energy stored and can extend the EV’s range to 1000 kilometers in one charge. The motors have a long lifespan, too, up to 50,000 hours of operation or 50 million kilometers.

A new, fast-charging, solid-state battery technology for EVs has been developed by John Goodenough, inventor of the lithium-ion battery. The new technology uses a glass electrode instead of a liquid one, sodium instead of lithium, and provides three times the energy density of Li-ion batteries.

Chemists at the U.S. Naval Research Laboratory (NRL) have announced a new safe, rechargeable battery technology that could end up in electric vehicles, bikes, or ships. Lithium-ion batteries are a problem because of the liquid inside them. If the battery or device gets too hot. in the form it usually takes inside alkaline batteries, zinc doesn’t cooperate with recharging. It’s prone to forming dendrites—tiny, problematic spikes. The NRL scientists reconstituted the zinc into another form, which makes the alkaline battery rechargeable without risking dendrite formation.

Power Electronics

In battery technology, semiconductors serve critical functions: boosting performance, reducing power losses, and optimizing thermal management.

Rogers’ ROLINX® busbars act as power distribution “highways.” These laminated busbars provide a customized power liaison for connecting battery cells or interconnecting between battery packs. The busbars can integrate both power and signal lines, including, for example, temperature measurement.

In IGBT and MOSFET power modules, substrates provide connections and cool components. curamik® ceramic substrates are able 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.

This year, Rogers Hungary chose to support an organization that serves a noble purpose and contributes to making the world a better place. Út a Mosolyért Alapítvány (The Smile Foundation) in Dunakeszi, Hungary, facilitates the curing of sick children. Our donation contributes to the foundation’s purchase of an intensive care bed, which will increase the survival rate of children taken to hospital.

József Sinkó Plant Manager represented Rogers Corp. at the donation ceremony. He said, “We are proud that through our business activities we can save the lives of children.”

About Út a Mosolyért Alapítvány

The foundation is focused on the education, employment, and health rehabilitation of disabled children and young adults in Hungary. The foundation provides programs that support equal opportunity and and help the disabled develop their skills and abilities so they can earn own livelihoods and improve their living conditions.

 

Selected quotes from our recent earnings call. Read the corporate financials news release: Rogers Corporation Reports First Quarter 2017 Results

In Q1 2017, Rogers achieved all time record quarterly net sales and earnings. Our sales were $204 million, an increase of 27% over Q1 2016. Results were driven by organic sales with solid growth in each of our business units, as well as exceptional performance in our recently acquired businesses. This is confirmation that we have implemented a winning strategy and our solid execution is taking Rogers to a new level of performance.

Bruce Hoechner, CEO, on Innovation Leadership

We are confident that our technology portfolio, marketing initiatives, and new product pipeline are well aligned with the growth drivers of Advanced Connectivity and Advanced Mobility where our solutions are proven, innovation is valued, and the growth outlook is compelling.

Bruce Hoechner, CEO, on Growth Drivers

As a market-driven organization, we are focused on select markets that are far outpacing global GDP growth, for example, Advanced Driver Assistance Systems (ADAS) and the Internet of Things. We are well positioned to take full advantage of these significant opportunities as the markets grow.

Rogers’ innovation expertise is enabling us to develop a new product platform to meet the most challenging segment of the Wired Internet infrastructure market. Our extremely low loss material is in various stages of customer qualification at key network infrastructure OEMs. Customer testing and feedback indicate that our material enables a performance level previously thought unachievable on copper clad laminate systems.

Our operational excellence initiatives are helping us improve profitability in four key areas: footprint rationalization, process improvement, optimizing cost structure, and back office utilization. We have refined our growth strategy by business unit to enable ACS, EMS, and PES to capitalize on their individual market opportunities and capabilities to accelerate growth.

Bruce Hoechner, CEO, on Rogers’ Business Units

Advanced Connectivity Solutions (ACS) achieved all time record revenue growth in Q1 2017, driven by continued strong demand in ADAS, as well as in aerospace and defense. Rogers has achieved several substantial 4.5G design wins as telecom equipment OEMs and telecom service providers move to the next level of system performance. We are very encouraged by the acceleration in the development of the 5G technologies. Other promising opportunities include automotive OEMs that are offering more models with ADAS features and fast tracking their plans to introduce cars with autonomous capabilities, both of which utilize Rogers Technologies. Overall, we continue to broaden the ACS portfolio of wireless infrastructure, wired infrastructure, advanced mobility, and aerospace and defense solutions to meet unsolved needs in the market.

In Elastomeric Material Solutions (EMS), demand across all of our product lines contributed to organic growth in the portable electronics, general industrial, automotive, and mass transit segments. Significant contributions from our acquired DeWAL and DSP businesses helped EMS achieve all time record quarterly net sales. As we look ahead, we expect to see continued penetration in the back pad solution for portable electronics, as well as in high performance gasketing for automotive applications.

Power Electronics Solutions (PES) net sales during the quarter increased due to broad based demand in many key markets, including renewable energy, hybrid electric vehicles, variable frequency motor drives, rail, and laser diode cooling products. Government mandates and consumer demand continue to drive adoption of eMobility applications, particularly in electric and hybrid electric vehicles. We expect to see continued growth, particularly in clean energy applications such as variable frequency drives, renewable energy, and advanced mobility.

Q1 2017 Earnings Call Full Transcript 

Q1 2017 Financials Press Release

Q1 2017 Earnings Call Slides

 

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.

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.

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