Power electronics is changing rapidly. New packaging technologies are facing a rise in chip temperatures as seen in such applications as EVs / HEVs. Electronics increasingly need longer lifetimes to function in harsh conditions, such as wind turbines. Power electronics based on SiC components need to handle faster switching in the face of higher temperatures. While beneficial, the challenge is that these changes produce considerable stress on power systems and, consequently, result in reliability problems.

Traditional power module designs were primarily based on Al2O3 or AlN ceramics. But the need for higher performance is leading designers to choose more advanced substrates. substrates with Si3N4 ceramics use the excellent bending strength, high fracture toughness, and good thermal conductivity of Si3N4 to build substrates that can handle a variety of today’s challenges.

In the following video, the Power Electronics Solutions team at Rogers takes a look at how to make the right substrate choices to support demanding applications.

VIDEO: 3 Steps to Select the Right DBC / AMB Ceramic Substrate for Your Application

In this video, Olivier Mathieu, Product Innovation Manager, discusses how to use the latest substrates in power electronics designs. He walks us through: (a) How to select the right ceramic thickness and its influence on basic isolation voltage, (b) How to select the right ceramic grade and its influence on heat removal, and (c) How to select the right copper thickness and its influence on functional isolation, ampacity, and heat removal.

Watch the video, Selecting the Right DBC / AMB Ceramic Substrate.

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The end of summer is right around the corner in the Northern Hemisphere with the Autumnal Equinox on September 22nd. Happy Spring Equinox to all of you in the Southern Hemisphere 🙂

Did you know that equinoxes are not daylong events? They actually occur at the exact moment the Sun crosses the celestial equator, the imaginary line in the sky above the Earth’s Equator. At that instant, the Earth’s rotational axis is not tilted with respect to the Sun. In 2017, the Sun crosses the celestial equator from north to south on September 22nd at 20:02 UTC. Parts of Australia, New Zealand, and Russian will experience it on September 23rd due to time differences.

In the meantime, Rogers Corp. has had a busy summer. The Rogers Germany team won the Bosch Preferred Supplier of the Year Award. Congrats!

Rogers Elastomeric Material Solutions/Asia held their Preferred Partners Conference in July in Phuket, Thailand. About 140 people from 52 companies were in attendance. The conference theme of “Winning Partnerships” aptly describes the collaborative relationship between Rogers and its customers — partnering and working together to secure business.

Of course, there were also a few BBQs along the way, with happy, smiling Rogers employees around the world.

Evergem, Belgium

Rogers, Connecticut, USA

Eschenbach, Germany, Interns


 

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

Printed circuits for high-speed and high-frequency applications rely on fine-featured transmission lines for signal transmission. Three of the most commonly used transmission-line technologies for these applications are microstrip, stripline, and grounded coplanar-waveguide (GCPW) transmission lines. Ideally, the loss through these transmission lines is minimal, and this requires an electrical impedance that is consistent and without interruptions, and with a value most appropriate for the types of signals to be transferred through the circuit. Variations from the nominal impedance of a circuit can result in increased insertion loss, increased return loss, higher radiated energy, degraded signal integrity (SI), and degraded rise time. A number of factors can affect the impedance of a PCB, including the physical and electrical characteristics of the circuit and circuit material, but by reviewing and better understanding these variables, their effects can be minimized.

Several different types of impedance are associated with high-speed, high-frequency PCB transmission lines, including wave impedance, input impedance, characteristic impedance, and frequency-dependent impedance. For RF/microwave circuits, for example, a characteristic impedance of 50 Ω is typically used for low-loss performance. The characteristic impedance, Z0, of a circuit can be defined as the ratio of voltage to current for a wave propagating in one direction without interference from any other wave in the circuit. In mathematical terms, it is simply:

Z0 = V(x)/I(x)

where V(x) is voltage and I(x) is current. To include the effects of inductance (L) and capacitance (C) as required for high-frequency/high-speed circuits, the characteristic impedance for microstrip can be determined by the square root of inductance divided by capacitance:

Z0 = (L/C)0.5

where C is a function of the product of the circuit substrate dielectric constant (Dk) and the area between the signal plane and the ground plane divided by the substrate thickness, or C = (Dk area)/thickness. For thicker substrates, the capacitance decreases and the impedance increases. The lower capacitance is less supportive of the flow of electrons needed for current flow. For thinner substrates or substrates with higher Dk, the capacitance increases and the impedance decreases in support of greater current flow. A wider conductor will increase the area and achieve the same effect.

This relationship for impedance, relating inductance and capacitance, is lossless, with no frequency dependence. To account for the numerous inductances and capacitances of complex circuits, such as differential circuits, a more comprehensive relationship can be used. This relationship is frequency dependent and does include conductor loss and dielectric loss:

Z0 = [(R + jωL)/(G + jωC)]0.5

where

ω = 2πf is the angular frequency;
G is related to dielectric loss; and
R is related to conductor loss.

Inductance and capacitance have opposite effects on a circuit’s impedance. An increase in inductance can cause an increase in impedance, while an increase in capacitance can result in a decrease in impedance. For example, in a 50-Ω system in which impedance variations may reach 45 Ω at one time and 55 Ω at another, the decrease in impedance may be due to an increase in capacitance while the rise in impedance may be the result of an increase in inductance.

The physical characteristics of transmission lines can affect capacitance and impedance, which in turn impact circuit impedance. As conductors are made narrower, the inductance increases and the impedance increases. As conductors are made wider, the capacitance increases and the impedance decreases.

Sudden changes in impedance or differences in impedance are problematic for maintaining high performance in high-speed/high-frequency circuits. Such changes can occur at any transmission-line junction, such as between a coaxial connector and the feed point of a PCB. The change in impedance can cause reflections of RF/microwave signals or high-speed digital signals back to the signal source. This results in less energy delivered to the load as well as with the reflected energy interfering with the propagation of forward energy from the source to the load.

Tracking Transmission Lines

For high-speed/high-frequency circuits, an ideal signal path maintains the same impedance throughout, such as a 50-Ω characteristic impedance, with minimal losses in energy along the path. Most of these signal paths use microstrip, stripline, or GCPW, which may be integrated into complex multilayer circuits. Closed-form equations are available to determine the impedances of these circuit structures, although field-solving techniques typically provide more accurate results.

A closed-form equation to determine the impedance for microstrip, for example, is:

Z0 = [87/(Dk +1.41)0.5 ]{ln[5.98H/(0.8W + T)]}

where

H is the thickness of the dielectric substrate;
W is the width of the transmission line; and
T is the thickness of the transmission-line copper layer.

To ease the calculations, the MWI-2017 impedance-modeling software is available to download for free from the Rogers Corp. Technology Support Hub.

The calculations for finding the impedance of stripline transmission lines are similar to those for microstrip:

Z0 = [60/(Dk)0.5]{ln [1.9B/(0.8W + T)]}

where

B is the thickness of the dielectric substrate from ground plane to ground plane;
T is the thickness of the stripline conductor; and
W is the width of the stripline conductor.

GCPW is a somewhat more complex than microstrip or stripline, with correspondingly more complex closed-form equations for predicting impedance. But again, the free MWI-2017 software provides a quick and straightforward way to perform the calculations based on proven closed-form equations.

Delving into Differences

The physical characteristics of high-speed/high-frequency circuits play significant roles in determining PCB impedance, since differences in substrate thickness, copper conductor thickness, and conductor width lead to differences in impedance in such circuits. To explore the effects of differences in these parameters, various microstrip test circuits were fabricated using a 20-mil-thick substrate with 2-mil-thick copper and 43-mil-wide conductor (50.07 Ω characteristic impedance) as a baseline. One of the other substrates had a slightly lower dielectric constant (Dk), one had a 1-mil-thick copper conductor, one had an 18-mil-thick substrate, and one had a 42-mil-wide conductor, to explore what the changes in physical parameters would do to the impedance in each case. The thinner substrate exhibited significantly lower impedance, the use of a circuit material with lower Dk resulted in a minimal difference in impedance, the thinner copper conductor provided only slightly lower impedance, and the narrower conductor also led to only slightly lower impedance.

Copper conductor surface roughness is yet another PCB parameter, although it is not always considered when analyzing different circuit variables for impedance. Smoother copper conductor surfaces exhibit lower conductor losses than copper conductors with rougher surfaces, but how do they affect impedance? For one thing, rougher copper surfaces will slow the velocity of a wave propagating through the circuit. The slower wave is perceived by the circuit as a higher effective Dk, even if the Dk of the circuit material itself has not changed.

As is apparent, a number of variables can affect the impedance of high-speed/high-frequency circuits, including substrate thickness, copper thickness, conductor width, and Dk. A number of additional factors can influence PCB impedance. For example, absorbed moisture can decrease the impedance of microstrip lines since water has a high Dk. Circuit substrate materials with high moisture absorption will suffer these effects on impedance, especially in conditions of high relative humidity (RH). This post is based on a presentation that will be given by the author, John Coonrod, at the PCB West Conference & Exhibition on September 13, 2017. The presentation will provide additional information on the variables that affect PCB impedance.

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As we celebrate our 185th year, we honor our history and look ahead to a promising future. We are proud to be listed on the prestigious New York Stock Exchange, where we rang the closing bell to commemorate the anniversary of our founding.

“The NYSE congratulates Rogers Corporation on its 185th Anniversary of Founding. We’re honored that Rogers, which is among our oldest listed companies, celebrated this milestone by ringing the NYSE Closing Bell.”       

Photo Credit: NYSE

Since 1832, Rogers has anticipated and adapted to the changing world around us. From our earliest days, we have been on the forefront of groundbreaking technology. Our passion to be ahead of vital market trends still drives us today.

Watch Investor Day webinar archive

As a market-driven innovator, Rogers’ leverages our technology expertise, deep understanding of our markets and extraordinary customer relationships to envision and enable the future. For leading technology and manufacturing companies, we are the engineered materials solutions partner trusted for reliability, innovation and collaborative support that enable their products to power, protect and connect our world.

Our global team of 3,100 employees propels us forward with their talent, dedication and commitment to an ethical culture. At Rogers, we are proud of our history, committed to the present and planning for an exciting future. It was a thrill to ring the closing bell at the New York Stock Exchange for the fifth time in our history in recognition of our 185th year.

 

 

You think the pace of technology innovation is fast now, wait til you see what’s going to happen with 5G wireless. 5G will drive an Internet of Things (IoT) ecosystem of intelligent, fully connected sensors and devices, capable of improving economies small and large, and further blurring geographical borders.

According to the 2017 Cisco Mobile Visual Networking Index (VNI), 5G networks will be able to support advanced applications such as remote surgery, immersive experiences through virtual and augmented reality, autonomous cars, and so on.” All are game changers in their industries.

By 2021, it is predicted there may be as many as 25 billion 5G-capable devices and connections globally. The first few years of IoT deployment will run mostly on LTE networks using NarrowBand IoT (NB-IoT) and LTE M. But 5G growth is expected to be fast.

The Cisco VNI report states, “While 4G was the network that made smartphones prolific as a personal infotainment device, 5G is going to be network of the IoT. 5G will be capable of offering a new high bandwidth benchmark of 1 Gbps or higher and sub 1 ms latency. Operationally, 5G’s support for dynamic resource allocation and application prioritization will accommodate a variety of M2M devices, including those that require very low bandwidth.”

Today’s cellular networks operate in the 700 MHz to 2.6 GHz bands. Mobile service providers have introduced 4.5G and 4.9G technology to improve speeds immediately. 5G fixed wireless access will follow shortly; Verizon has been running trials in 11 cities. 5G mobile technology will follow shortly; AT&T estimates as soon as late 2018.

5G, when it arrives, is expected to handle far more traffic at much higher speeds than current cell network base stations. This requires new technologies, including millimeter waves (mmWaves), massive MIMO (multiple-input multiple-output), beamforming, and full duplex. Let’s take a look at a few of these key developments.

Millimeter Wave Spectrum

5G networks will be based on millimeter wave technology that can run in the underutilized portions of the 10-300 GHz band. Some cellular providers have begun to use mmWaves to send data between stationary points, such as base stations. Providers are considering the next step, using millimeter waves to connect mobile users to nearby base stations.

They are called mmWaves because the wavelength varies in length from 1 to 10 mm vs. the radio waves that serve today’s wireless devices, which measure tens of centimeters in length. Because these signals are shorter, there are hurdles to overcome. The higher frequencies carry more data, but are easily blocked by buildings and foliage, and sometimes even rain.

Sub-6 GHz Spectrum

Certain frequencies under Sub-6 GHz will be defined as 5G frequencies by 3GPP. That means these defined frequencies will be included in 5G standards and will apply to all countries.

A wide range of 5G trials are underway across the globe. China Mobile recently demonstrated the first 5G remote driving technology using a consumer car. They also completed a commercial Massive MIMO deployment that attained speeds of 2 Gbps.

In Massive MIMO, a high number of antennas, potentially hundreds, are incorporated into advanced chips that are smaller, deliver more processing power, and use less battery. The large number of antennas helps minimize signal loss and energy consumption, and can mitigate obstruction issues by steering signals in specific directions.

The Challenge of High Frequency Materials

Designers of these high frequency devices need to balance cost, weight, size, and radiation characteristics (such as gain, beamwidth, side-lobe levels, polarization). High frequency circuit materials deliver the performance needed by wireless base stations, satellite antennas, and network servers and storage.

PCB materials with dielectric constant (Dk) values of about 2.8 to 3.5 are preferred for sub-6 GHz and millimeter wave circuit applications. The consistency of the Dk across a circuit board can also be an important concern at these frequencies since variations in the Dk can introduce variations in the signal phase. Performance can also be affected by the composition of the PCB material.

Given this challenging set of requirements, what types of real-world materials are suitable for sub-6 GHz and millimeter-wave circuits?

The majority of initial 5G applications will be under 6 GHz, frequencies that are similar to those used in 3G and 4G materials. For such applications:

  • Rogers’ RO4350B laminates provide tight control of Dk and low loss. They are rigid thermoset materials that do not use PTFE, but can achieve excellent RF/microwave performance over time and even at elevated temperatures.
  • The RO4835 laminates are a high-performance material for high-frequency applications, but because it is not based on PTFE, it does not require special preparation (such as a sodium etch) to enable the formation of reliable plated through holes.

For microwave and millimeter wave applications:

  • The RO4730G3™ UL 94 V-0 antenna-grade laminates are designed to meet present and future performance requirements in active antenna arrays and small cells, in 4G base transceiver stations (BTS) and Internet of Things (IoT) applications, as well as emerging 5G wireless systems. These flame-retardant (per UL 94V-0), thermoset laminate materials are an extension of Rogers’ dependable RO4700™ circuit materials, which are a popular choice for base station antennas. RO4730G3 laminates provide the low dielectric constant (Dk) of 3.0 favored by antenna designers, held to a tolerance of ±0.05 when measured at 10 GHz.

Other new technologies are being created to enable the IoT networks that will deliver valuable insight obtained from massive amounts of data:

  • High temperature silicone materials serve as gaskets and seals, cushions, and thermal and acoustic insulation in demanding and remote environments.
  • Laminated multilayer busbars provide efficient and compact connections for propulsion, auxiliary, and other IGBT based converters in connected car and connected rail systems.

5G and sub-6 GHz networks will impact every aspect of our lives. Finding the right balance of material performance and cost is a challenge, especially technologies that is are still being defined.

 
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