This post authored by John Coonrod originally appeared on the ROG Blog hosted by Microwave Journal.

Transmission lines are akin to electronic roadways, routing signals along different paths of a printed circuit board (PCB). At RF/microwave frequencies, circuit designers often create PCBs based on three popular planar transmission line approaches: microstrip, stripline, or coplanar waveguide (CPW). Each uses circuit-board materials in a different way, with different results in terms of insertion-loss performance. By getting a grasp on the insertion-loss mechanisms for these different transmission-line formats, circuit designers can better match the mechanical and electrical characteristics of their circuit substrates to their intended applications and transmission lines when choosing PCB materials.

Achieving low loss in an RF/microwave circuit is more critical for some applications than for others, and many excellent low-loss commercial PCB materials such as RO4350B™ laminates from Rogers Corporation are available to help optimize a circuit’s loss performance. But the choice of transmission line for a design can also impact the insertion-loss performance of that circuit. The insertion loss of a PCB’s transmission lines is actually the sum of a number of contributing losses, such as losses attributed to the conductors, to the dielectric material, and due to radiation from the PCB. Microwave transmission lines can also suffer leakage losses, although these tend to be associated more with semiconductors than with PCB materials.

Conductor losses are related to the type of metal (and possible finish on the conductor metal) in the PCB’s conductor layer as well as the operating frequency. Signal propagation at higher frequencies tends to use less of the conductor’s metal as the frequencies increase, with signal “skin depth” becoming very shallow at the highest operating frequencies and only the outer surface of the conductor used for signal propagation at the highest frequencies.

An ideal electrical conductor would exhibit minimal resistance and high conductivity for signals of interest. Of course, real conductors do exhibit loss and have imperfections, including surface roughness, which can contribute significantly to a conductor loss. At RF/microwave frequencies, a rough conductor surface represents a longer propagation path than a smoother conductor surface, with higher loss. A PCB’s dielectric loss is related to the material properties of the circuit substrate, in particular its dissipation factor (Df). Selecting circuit materials with low Df can help minimize this component of transmission-line insertion loss.

Radiation loss is due to energy passed by a PCB’s transmission lines into the surrounding environment. This insertion-loss component can be affected by a number of factors, including the choice of transmission-line topology, the PCB’s dielectric constant, the operating frequency, even the circuit-board thickness. It tends to decrease with thinner PCB materials and for circuit materials with higher dielectric constants. Radiation losses are most noticeable at junctions in a circuit, including impedance transitions and signal launch areas, such as the transition from a transmission line to a coaxial connector’s center pin. Of the three popular RF/microwave transmission-line formats, microstrip is particularly susceptible to radiation loss.

Each of the transmission-line technologies suffers some insertion loss, no matter how good the PCB material. Understanding how loss occurs for the different transmission-line approaches can help guide a circuit designer when choosing a PCB material for a given loss budget. As mentioned, microstrip can suffer more from radiation loss than stripline or CPW, requiring additional shielding for some microstrip circuits. But microstrip is the most popular of the three transmission-line formats, since it is the simplest and least expensive to fabricate. It is basically a metal conductor on the top of a dielectric layer with a metal ground plane on the bottom of the dielectric layer. Factors that can influence performance include the type and weight of the metal for the conductor and ground plane, the width of the conductor lines, the relative permittivity or dielectric constant of the dielectric material, and the thickness of the dielectric layer.

In contrast, stripline transmission lines are sandwiched between top and bottom dielectric layers, which in turn have metal ground planes on the top and bottom of the dielectric materials. Plated through holes (PTHs) are machined through the metal and dielectric layers to electrically connect the top and bottom ground planes. Stripline presents difficulties in adding discrete circuit elements and active devices, which require viaholes to connect components on the outside of the circuit to the internal circuitry and transmission lines. This is in contrast to the simplicity of top-mounting components on a microstrip board. CPW circuits offer the simplicity of top-mounting components, since these circuits are formed with top-layer conductors surrounded by a top-layer ground plane, and with an additional bottom-layer ground plane separated by a dielectric layer. As with stripline, the top and bottom ground planes are electrically linked by PTHs machined through the substrate material. The additional ground planes help improve electrical performance but also add size, complexity, and cost to the stripline and CPW circuits compared to microstrip circuits, which are among the tradeoffs that circuit designers must weigh when choosing a transmission-line format for a particular circuit application.

How does the choice of PCB material impact the insertion loss of one of these high-frequency circuits? The loss characteristics of a microstrip circuit, for example, will change for different thicknesses of the same PCB material. A free personal computer (PC) software tool, MWI-2010, available for download from the Technology Support Hub on the Rogers Corp. web site, can show the influence of a circuit material on transmission-line loss. MWI-2010 contains models of different circuit board materials, permitting designers to explore the impact of different material parameters on performance.

The software was used to analyze the impact of substrate thickness on microstrip transmission-line loss, modeling simple 50-Ω microstrip transmission-line circuits on three different thicknesses (6.6, 10, and 20 mils) of RO4350B circuit material. The material has a process dielectric constant of 3.48 at 10 GHz and low dielectric loss, with Df of 0.0037 at 10 GHz. For microstrip transmission lines, the software shows that the insertion loss is the least for the thickest circuit board, with conductor and dielectric losses that were relatively low and similar in value. The thinnest circuit board had the highest insertion loss, with conductor loss the dominant of the three loss components. Conductor loss can be somewhat diminished by choosing a PCB material with smooth conductor metal, such as RO4000® LoPro™ circuit material from Rogers Corp. The dielectric loss changed little with the three thicknesses of RO4350B laminate, indicating it is an electrically stable PCB substrate.

When loss is critical for a circuit, a low-loss circuit material can help achieve design goals by minimizing dielectric losses. And conductor and radiation losses can be controlled through choice of transmission-line technology, although that choice will also depend on a number of other factors, such as required circuit size, complexity, and cost.

Do you have a design or fabrication question? John Coonrod and Joe Davis are available to help. Log in to the Rogers Technology Support Hub and “Ask an Engineer” today.

This post authored by John Coonrod originally appeared on the ROG Blog hosted by Microwave Journal. You can view Bandpass Filters, Part 1 here.

Bandpass filters make many of our modern electronic systems possible, from dependable cellular telephones to secretive military surveillance and radar systems. The last blog – Part 1 of this two-part series on bandpass filters – highlighted the versatility of one circuit material from Rogers Corporation, RT/duroid® 6010.2LM laminate, for fabricating RF/microwave bandpass filters. But not all circuit materials are the same and there may be some advantages to designing bandpass filters on other materials, such as Rogers RO4000® family of printed-circuit-board (PCB) materials. This blog will examine different grades of these and other circuit materials and the impact they have on the design and fabrication of high-frequency bandpass filters, especially compared to filters formed on filled-PTFE-based circuit materials.

The first installment of this two-part blog on bandpass filters described different bandpass filter responses, including Chebyshev, Bessel, and Butterworth filters, and reviewed a number of the performance parameters for comparing bandpass filters, such as center frequency, passband, passband insertion loss, and stopband responses. As was noted in that first part, the choice of PCB material for a bandpass filter usually starts with the material’s dielectric constant (Dk). Materials with higher values of Dk, such as 10.2, have long been favored for RF/microwave filters because of the relationship of the Dk value to the size of the filter. Quite simply, higher Dk values result in shorter wavelengths and higher frequencies, enabling filter designers to occupy less PCB area for a given filter structure.

Circuit materials with a Dk of 10.2 are typically based on polytetrafluoroethylene (PTFE), which provides excellent electrical characteristics but tends to be more expensive than other circuit materials. As pointed out in the first part of this blog, circuit materials based on PTFE with some form of filler are also susceptible to moisture absorption, which can result in shifts in their Dk values in high-humidity environments. As that earlier blog suggested, a lower-cost material such as RT/duroid 6010.2LM laminate, which is a composite of PTFE and ceramic materials, can also provide the high Dk value without the concern for moisture absorption.

But are there benefits to designing and fabricating bandpass filters on materials with lower values of Dk? Rogers RO4000 circuit materials are widely favored by amplifier designers for their mechanical and electrical stability, but they are also excellent starting points for bandpass filters. The materials are based on reinforced hydrocarbon/ceramic laminates, not PTFE. RO4360™ laminates, for example, have a Dk value of 6.15 in the z-axis at 10 GHz, held to an impressive tolerance of ±0.15. The material is based on a ceramic-filled, thermoset-resin system reinforced by glass fiber for excellent mechanical stability. These lead-free-process-capable laminates exhibit dissipation factor (loss) of 0.0030 at 2.5 GHz and 0.0038 at 10 GHz, both in the material’s z-axis.

In terms of bandpass filter size, the lower Dk value of 6.15 for RO4360 laminates  compared to a Dk of 10 or higher for filled PTFE circuit materials translates into somewhat larger filter structures, with wider conductor widths. The higher loss of RO4360 laminates compared to filled-PTFE-based materials typically means somewhat higher passband insertion loss, but the differences in loss between filters formed on the two materials may not be so significant when factoring in RO4360 laminate’s wider conductors. RO4360 laminates offer lower material costs than filled-PTFE-based substrates, and circuits are easier and lower in cost to fabricate compared to filled PTFE. RO4360 laminates provide improved mechanical stability and consistency compared to filled-PTFE-based materials, especially in environments with high humidity. Essentially, the tradeoffs between the two materials involve cost versus the levels of performance required for a particular application, as well as the somewhat smaller size possible for high-frequency bandpass filters fabricated on materials with higher Dk values.

Larger filter dimensions may not always be a design goal but at times can be a benefit, especially for applications that involve higher power levels. When designing and fabricating filters on higher-Dk materials, transmission-line conductor widths must be reduced compared to lower-Dk circuit materials to maintain the typical 50-Ω impedance of higher-frequency designs. But those thinner conductor widths, along with the circuit material’s thermal properties such as its thermal conductivity, will serve as a limit for a filter’s power-handling capabilities on that particular material. Also, the thinner conductor widths can result in penalties in terms of production yields.

RO4360 circuit materials provide better thermal conductivity than many substrates based on filled PTFE, although with somewhat higher loss that can in part offset the enhanced thermal conductivity. RO4360 laminates provide typical thermal conductivity of 0.8 W/m/K, enabling it to dissipate heat produced by circuits handling high power levels. In addition, RO4360 laminates have coefficients of thermal expansion (CTE) of 16.6 and 14.6 ppm/°C, respectively, in the x and y directions, very closely matched to copper in support of good circuit reliability at higher power levels.

For some small sacrifice in passband insertion-loss performance compared to filled-PTFE-based materials, RO4360 circuit materials can deliver RF/microwave filters without complicated production processes. The thermoset material can be handled in much the same way as low-cost, epoxy-based FR-4 circuit materials, and even readily combined with these lower-cost materials as part of a multilayer circuit structure. Often, a circuit design is “segmented” by material type in a multilayer design, with higher-frequency circuits, such as RF/microwave bandpass filters, fabricated on materials such as RO4360 laminates and less-critical circuits, such as power supplies, formed on lower-cost circuit materials such as FR-4.

Compatibility in processing the different materials not only simplifies production, but also ensures reliability of the plated through holes (PTHs) used to electrically connect the different circuit layers in a multilayer circuit construction. The reliability of those PTHs in multilayer circuits with RO4360 laminates is also aided by the materials excellent CTE in the z-axis (30 PPM/ºC), also closely matched to that of copper to minimize stress of connections and circuitry across a range of operating temperatures.

In contrast to filled-PTFE-based materials, which require special processing measures, RO4360 laminates are compatible with standard PCB processing methods, as used with FR-4 materials. They boast a high glass transition temperature (Tg) of greater than +280ºC as assurance of handling high process temperatures. In addition to electrical and mechanical characteristics that make them attractive for fabricating RF/microwave bandpass filters, they are environmental friendly and RoHS compliant. For those bandpass-filter applications that can afford slightly higher passband loss and slightly larger circuit dimensions (than some filled-PTFE materials), RO4360 circuit materials offer a high-performance alternative that can cut both material and processing costs.

Do you have a design or fabrication question? John Coonrod and Joe Davis are available to help. Log in to the Rogers Technology Support Hub and “Ask an Engineer” today.

This post authored by John Coonrod originally appeared on the ROG Blog hosted by Microwave Journal.

Resonant circuits are critical for the generation and selection of desired RF/microwave frequencies. For any transmission line, including stripline, microstrip, or waveguide, a suitable length can be used as a resonator, with dimensions for the resonant structure that correspond to the desired wavelength. When that resonant structure is in the form of a cavity, it is simply called a cavity resonator. High-frequency cavity resonators, for example, serve as excellent starting points for RF/microwave oscillators capable of generating low-noise signals and for filters used to select signals at specific frequencies. For example, cavity resonators can be embedded within a multilayer circuit substrate, to achieve a high-quality resonance without a larger metal cavity or tuning screw. Excellent performance is available from such multilayer cavity resonators, given available high-frequency circuit laminates and the pre-impregnated glass fabric (prepreg) materials.

About Cavity Resonators

Cavity resonators are essentially hollow conductors or sections of a printed-circuit board (PCB) which can support electromagnetic (EM) energy at a specific frequency or group of frequencies. An EM wave entering the cavity that is resonant within the cavity will bounce back and forth within the cavity with extremely low loss. As more EM waves enter at that resonant frequency, they reinforce and strengthen the amplitude of the existing resonating EM waves.

The resonant frequency or frequencies of a cavity depend on several factors, including the dimensions of the cavity, the materials that form the cavity, and how energy is launched and/or extracted from the cavity. A resonant cavity is sometimes referred to as a form of in-circuit waveguide, short-circuited at both ends of the waveguide structure so that EM energy builds within the cavity at a designed frequency or band of frequencies. The size of a cavity resonator, for example, is a function of the desired resonant frequency and the characteristics of the PCB materials used for the resonator. PCB materials with higher dielectric constants will support smaller cavity resonators for a given frequency than circuit substrate materials with lower dielectric constants.

Creating a cavity resonator in a PCB

While there are many ways to create a cavity resonator in a PCB, most methods rely on either building up materials around an empty area on the PCB, or removing materials from a PCB structure to form an empty area, such as by means of laser ablation. In forming a window-type resonant cavity in a multilayer circuit assembly, the different layers that create the circuit assembly also form the walls of the resonant cavity. Such circuit-material layers often include a high-performance circuit material, such as RT/duroid® 5880, RO4003C™ LoPro™, or RO4350B™ LoPro laminates, and a compatible prepreg material, such as RO4450F™ prepreg, to bond the circuit layers together.

In the window-type approach to forming cavity resonators, windows are punched into some of the circuit layers used to assemble a multilayer circuit. As the laminate and bonding or prepreg layers are assembled, the layers forming the windows will create the walls of the soon-to-be resonant cavity. The size of this cavity, of course, determines the ultimate frequency or frequencies of the resonant cavity, so manufacturing efforts are usually focused on keeping the dimensions of the resonant cavity tightly controlled.

Prepreg Materials

Ideally, prepreg materials used for bonding the multilayer structure have the flow characteristics required for a multilayer resonant cavity. For example, in a multilayer construction in which voids must be filled, such as in circuits with plated copper, prepregs with “high-flow” characteristics are desired. But when bonding of multilayers is needed, without flow into the resonant cavity formed by those multiple laminate layers, a “low-flow” prepreg is preferred, with a high glass transition temperature (Tg) for good reliability. Because the bonding materials in a multilayer circuit assembly will flow during lamination, designers must be wary of bonding materials that lack good flow control and might flow into the resonant window or cavity area, changing the dimensions of the resonant cavity (and its operating frequency or frequencies). An effective multilayer prepreg should exhibit low loss, good adhesion to commercial PCB laminates, stable dielectric constant with temperature and frequency, and the capability of supporting multiple or sequential laminations if needed.

Ideally, any prepreg in a multilayer circuit assembly with a resonant window should have not only low-flow characteristics, but predictable flow characteristics. The predictability allows for tight control of the circuit manufacturing process. In a circuit with a resonant cavity, a prepreg with predictable flow may alter the size of the cavity because of that flow, but it will be in a manner that can be predicted and even modeled in a commercial EM computer-aided-engineering (CAE) software program such as Ansoft HFSS. However, if the prepreg has low-flow characteristics without predictable flow, the final size of the resonant cavity will vary according to the flow characteristics, as will the resonant frequency or frequencies of the cavity.

As an example, RO4450F prepreg is a low-flow prepreg material with relatively well-controlled flow characteristics. It is compatible with RO4350B or RO4350B LoPro laminates and well suited for forming multilayer cavity resonators with consistent and predictable characteristics. In contrast, our 2929 Bondply is also a durable prepreg material, but with greater flow than RO4450F material. Although both are candidates for a multilayer cavity resonator design, the fabrication and lamination conditions will dictate which prepreg provides a greater level of consistency in a final production run.

RO4450F and the RO4400™ family of prepreg materials are based on the RO4000® core materials and readily compatible with those laminates in multilayer constructions, such as in cavity resonator designs. The prepregs feature a number of key attributes that contribute to reliable performance in multilayer constructions, including a high post-cure glass transition temperature (Tg) of greater than +280°C, an indication that the prepregs are capable of handling multiple lamination cycles. The RO4400 prepregs also support FR-4-like bonding process conditions (+177°C), enabling the use of standard lamination equipment.

Achieving Optimum Performance

Optimum performance from any multilayer cavity-resonator-based design, whether for generating or filtering signals, requires careful consideration of the type of feed structure used with the cavity resonator, especially at higher frequencies. A number of approaches provide good results through millimeter-wave frequencies, including slot and probe excitation techniques. Using a slot is fairly straightforward and requires very simple fabrication while probe excitation, which can be somewhat more demanding in terms of fabrication, can yield extremely wideband results. Some cavity-resonator filters, for example, have used feed approaches as simple as a microstrip line through a coupled slot in the ground plane. In the case of either slot or probe feed in a multilayer cavity-resonator construction, high-quality prepreg materials help ensure minimal loss and stable performance.

Do you have a design or fabrication question? John Coonrod and Joe Davis are available to help. Log in to the Rogers Technology Support Hub and “Ask an Engineer” today.

curamik® electronics, which is part of Rogers’ Power Electronics business, will be presenting at the eCarTech Conference in Munich on October 23-25,
2012.  This conference takes place during  the 4th International Fair for Electric- and Hybrid-Mobility for electric vehicles. curamik recently released a new silicon nitride (Si3N4) ceramic substrate that can significantly extend the life span of power electronic modules, and will be presenting this product at the conference.

Manfred Götz, Product Marketing Manager from curamik will be giving a presentation about this new ceramic substrate on Thursday, October 25th at 3:00 PM:

“How silicon substrate can increase the duration of power modules”

“In test cycles we have conducted so far, ranging from -55 °C to 150°C , curamik® silicon nitride substrates have shown more than a 10X improvement over substrates typically used in the Automotive segment, especially HEV/EV. From this data, we can expect to see a longer life span for modules using these substrates,” reports Manfred

 About curamik’s New Ceramic Substrate 

Until now, the reliability of copper-bonded ceramic substrates used in power modules has been limited by the lower flexural strength of the ceramic that can result in reduced thermal cycling resistance. For applications combining extreme thermal and mechanical stress, such as hybrid and electric vehicles (HEV/EV), the current commonly used ceramic substrates are not optimal. The significant difference in thermal expansion coefficients of the substrate (ceramics) and the conductor (copper) exert stress on the bonding zone during thermal cycling, threatening reliability. Rogers Corporation introduced a new silicon nitride ( Si3N4) ceramic substrate under its curamik® ceramic substrates brand. Due to the higher mechanical robustness of silicon nitride relative to other ceramics, the new curamik® substrate is intended to help designers achieve critical, long-life performance under the demanding operating environments and conditions of HEV/EV renewable energy applications and other high reliability applications.

With the growth of HEV/EV and renewable energy applications, designers have struggled to find new ways to ensure reliability of the electronics required to power these new, challenging technologies. With an increase in operating life span of potentially ten times or more relative to other ceramics used in power electronics, silicon nitride substrates provide the mechanical robustness critical to achieving the necessary reliability requirements. The life span of ceramic substrates is measured by the number of repetitions of thermal cycles the substrates can survive without delamination or other failure modes that compromise the function and safety of the circuit. This testing is typically done by cycling the samples from – 55° C to 125°C or 150°C.

Download the data sheet.

The entire event will cover these topics:

  • Electric Vehicles
  • Drive and Motor Technique
  • Energy Storage Technology
  • Engineering and subcontracting
  • Reparation and spare parts
  • Connected Car – sMove360°
  • MATERIALICA – Lightweight Design for New Mobility
  • Finance
  • eCarLiveDrive – Test Area

For More information:

curamik electronics GmbH
A division of Rogers
Am Stadtwald 2
92676 Eschenbach, Germany
phone: +49964592220
fax:+499645922222
e-mail: info@curamik.com
www.curamik.com

This post authored by John Coonrod originally appeared on the ROG Blog hosted by Microwave Journal.

Evolution in automotive electronic systems

Evolution of the electronic systems in automobiles and other vehicles is exciting to watch, and many technologies once associated with the military, such as radar systems, are becoming available to average drivers. For example, 24-GHz short-range-radar (SRR) systems are being offered more and more in car models around the world. But vehicle designers and manufacturers are also looking ahead to the greater resolution possible with 77- and 79-GHz automotive radar systems. And for that evolution in automotive electronic systems to truly take place, printed-circuit-board (PCB) materials are important building blocks that will enable the potentially much safer automobiles of the future.

Compared to 24-GHz automotive radars, systems at 77 and 79 GHz with their smaller wavelengths can operate with considerably smaller antennas. Because the Doppler shifts are more significant at millimeter-wave frequencies than at 24 GHz, these higher-frequency systems also more precisely determine distances and relative speeds between vehicles and other objects. The high resolution possible at 77 and 79 GHz also enables radar systems that can detect dangerous road-surface conditions, including the presence of ice.

Circuit Materials for Higher Frequency Automotive Radar Systems

Circuit materials for these higher-frequency automotive radar systems must meet a similar set of requirements as detailed in the previous Blog about 24-GHz automotive radar systems, but perhaps with even tighter tolerances for systems operating at 77 and 79 GHz. The consistency of relative dielectric constant (εr) across a circuit board, for example, is particularly critical at 77 GHz, where variations in dielectric constant (Dk) can translate into changes in the impedance of transmission lines, and changes in frequency. Such variations in frequency can result in wrong readings in an automotive radar system that can compromise the safety of the system. In general, variations in a circuit material’s Dk can cause variations in the impedance of a transmission line, which result in higher reflected energy, higher return loss, and higher insertion loss.

How RO4000 and RO3000 Materials match up

The benefits of our RO4000® PCB materials for 24-GHz automotive radar systems were highlighted in this blog post. For 77- and 79-GHz automotive radar applications, our RO3000® circuit materials bring their own favorable attributes for these millimeter-wave circuits. RO3003™ high-frequency laminate, for example, has been used to fabricate antennas in automotive adaptive cruise control (ACC) circuits at 77 GHz, where its tight Dk tolerance contributes to stable frequency operation even this high in the spectrum. RO3003 laminates exhibit a Dk of 3.00 at 10 GHz with Dk tolerance within ±0.04. Minimizing loss at these millimeter-wave frequencies is also important, due to limited available transmit and receive power at 77 and 79 GHz. Antenna-grade RO3003 laminates are characterized by a very low dissipation factor of 0.0013 at 10 GHz, indicating that dielectric losses will be low even at 77 and 79 GHz.

Any change in a circuit material’s Dk can affect performance

Because any change in a circuit material’s Dk can affect the performance of a millimeter-wave automotive radar system, another important material parameter to consider at these frequencies is the temperature coefficient of dielectric constant, or TCDk. This property describes how much the material’s dielectric constant will change with changes in temperature, when tested over a set range of temperatures in a short time period. And since a typical commercial vehicle may be subject to a wide range of operating temperatures, this is an important parameter for projecting the stability of a 77- or 79-GHz automotive system with changes in temperature. Some laminates, for example, can exhibit TCDk values in excess of +200 ppm/°C at certain temperatures and frequencies, resulting in large swings in the value of relative dielectric constant with temperature. The RO3003 material, which is engineered for higher-frequency antennas and other circuits, has a typical TCDk value of + 11 ppm/°C at 10 GHz and for temperatures from -50 to +150°C. This last part is important to note when comparing materials, since TCDk must be referenced to a range of test temperatures to be meaningful.

Maintaining mechanical stability

Since an automotive radar system must endure a wide range of operating conditions, mechanical stability with temperature is also important for maintaining reliability, especially in high-resolution 77- and 79-GHz systems. The RO3000 PCB materials such as RO3003 laminates are ceramic-filled polytetrafluoroethylene (PTFE) composites engineered for high electrical performance but also excellent mechanical stability over changing environmental conditions. The RO3003 laminates, for example, have a coefficient of thermal expansion (CTE) in the x and y plane of 17 ppm/°C that is closely matched to that of copper for excellent dimensional stability over a wide range of temperatures (-55 to +288°C). Through the material, in the z direction, the CTE is 24 ppm/°C to ensure high reliability of plated through holes (PTHs).

Good Thermal Conductivity

Another material parameter to consider for automotive millimeter-wave electronic applications, including 77- and 79-GHz radar systems, is good thermal conductivity. Although the power levels of higher-frequency circuits tend to be relatively low, any increase in the thermal conductivity of a PCB is to be recommended, since it will mean a reduction in the maximum temperature of a circuit board for a given amount of power handled by the PCB. Good thermal conductivity in the PCB material can also improve the thermal stability of the dielectric constant, since heat will be better distributed across the PCB material while minimizing any hot spots on the circuit board.

Although we have developed other PCB materials that can achieve the electrical performance levels required by 77- and 79-GHz automotive radar electronics, such as RT/duroid® 5880 laminate, the RO3000 materials combine outstanding electrical and mechanical characteristics with low cost, three key parameters needed to expand the emerging market for 77- and 79-GHz millimeter-wave automotive electronic systems. The RO3000 materials can also be processed using standard PCB methods developed for PTFE-based circuit materials, to minimize processing costs even at these high millimeter-wave frequencies.

Do you have a design or fabrication question? John Coonrod and Joe Davis are available to help. Log in to the Rogers Technology Support Hub and “Ask an Engineer” today.

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