Managing PCB Materials: Dielectric Constant (Dk)

On September 11, 2018, in Uncategorized, by sharilee

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

Choosing a high frequency circuit board material often requires weighing several factors, including cost and performance. A key starting point in sorting through printed circuit board (PCB) materials is usually the dielectric constant, or Dk, one of the essential characteristics of a laminate material and one that is subject to many comparisons among different suppliers of PCB materials.

ROG_DkApp_finalThe dielectric constant of a laminate refers to a measure of the capacitance or energy between a pair of conductors in the vicinity of the laminate compared to that pair of conductors in a vacuum. The value for a vacuum is 1.0, with all other materials having a value somewhat higher than that. A laminate with higher values of Dk can store more energy than materials with lower Dk values. But at higher Dk values, electromagnetic energy will flow at a slower rate through the conductors (lower frequency).

Several earlier blog posts addressed different approaches available to measure the Dk of PCB materials. These methods involve different test fixtures and circuit configurations, such as the clamped stripline resonator test method and the full sheet resonance (FSR) test. Unfortunately, depending upon the laminate being measured and the frequency, these methods can reveal very different values of Dk for the same material under test.

For that reason, Rogers Corp. has developed alternative sets of dielectric-constant values, Design Dk values, to represent the company’s laminates during the design and engineering stages. These are Dk values that can be used reliably and accurately within commercial computer-aided-engineering (CAE) software tools. The Design Dk values are measured by yet other measurement techniques, the differential phase length method. The approach is based on fabricating two microstrip circuits of significantly different length on the same laminate and in close proximity, identical in every way except for length. The test method measures the transmission characteristics of a quasi-transverse-electromagnetic (quasi-TEM) wave propagation and its phase response for a pair of microstrip transmission line circuits. By comparing the expected phase of the lines for a given frequency with the measured results, it can be possible to calculate the Dk for the laminate. In this approach, a large difference in length, such as 1:3, is recommended to simplify the measurements; the shorter circuit will limit the low-frequency accuracy.

But rather than just take Rogers’ word for it, it is also possible to apply the differential phase length method to a laminate of choice to determine its Dk firsthand. For those interested, Rogers Corp. now offers free downloadable software, Rogers’ Microstrip Dk Calculator Software, to determine PCB Dk values. The software works with the aid of associated test equipment, such as a microwave vector network analyzer (VNA). A high-quality test fixture should be used with the same signal launch for both circuits under test. The software can gather data from the measurements and produce a plot of Dk versus frequency, of particular value to designers of broadband circuits wishing to know the dielectric constant of the laminate beyond a certain operating frequency range. The range of frequencies across which this method can test depends on the lengths of the circuits, the return loss between the test fixture and the analyzer, and a number of different network analyzer parameters. The accuracy of the measurements depends on these different parameters and the length ratio between the two transmission lines. In addition to the software, an operator’s manual for performing the measurements can also be downloaded for free. The user’s manual provides details about the test method and why it tends to provide reliable results for Dk values.

These Design Dk values are generated for all of Rogers’ commercial laminates, based on this measurement method. The Rogers Microstrip Dk Calculator Software is available online for free download from the Rogers Technology Support Hub, which also includes technical papers and videos and several calculators, including the latest version of the MWI Microwave Impedance and loss calculator, MWI-2017. This free downloadable software tool features an improved grounded coplanar model and added capability to display the Design DK for any of Rogers’ products in the calculator when using the microstrip model.

Visitors to the Rogers Technology Support Hub can also download a copy of the ROG Converter software, a web-based application designed for a tablet or smartphone. It can provide simple conversions of dimensions from metric to English units and back, for temperature, for copper thickness, for CTE, and for thermal coefficient of dielectric constant (TCDk). Recently added conversions include for return loss: as VSWR, mismatch loss, and reflection coefficient. Based on Rogers’ materials, it can also help when planning multilayer material stack-ups.

Do you have a design or fabrication question? Log in to the Rogers Technology Support Hub and “Ask an Engineer” today.

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This post (originally by Dave Sherman) appeared on the PORON Cushioning Blog. Updated 08/21/2018

A Foam is a Foam is a Foam, Right?

In a word (or three), not so much. Our customers are often surprised to learn that all PORON® Comfort materials are open cell polyurethane foams, especially when what they’re used to seeing are closed cell EVA foams or closed cell polyurethane foams.

Open cell foam has many benefits and properties not present in closed cell foams. One of the biggest is that it offers the best resistance to compression set (C-Set) or, for the non-foam aficionados out there, resistance to break down after multiple uses. Essentially, this means that the foam is very durable and won’t break down or lose its cushioning properties after multiple uses. In the footwear world that equates to a consistent fit, form, and functional level, and maintains the look and feel of the shoe as it was designed.

Closed Cell Foams vs. Open Cell Foams

Here’s something else to consider…

Closed Cell Foam:

Closed cell foams, or EVA foams, are comprised of complete bubbles of air. The bubbles of air are trapped in the foam with cell walls all around that prevent air from escaping. Bunched together like soap bubbles in a bubble bath, the air pockets are crucial to the function of the foam. When the foam is compressed, so is the air inside the bubbles, which allows the foam to spring back when pressure is removed. For this reason, they are often used in shoe insoles and sports padding where resistance and protection are key.

Evidence of this property can be demonstrated with a tennis ball. Tennis balls are known to be bouncy due to the air trapped inside the ball. But once a tennis ball has been used repeatedly the air begins to leak out, causing the ball to lose its springy resistance.

tennis ball - closed cell foam

Applying this analogy to closed cell foams, this is the point at which the foam begins to go flat or “take a set” (remember that whole C-Set thing?). That’s why insoles or padding made solely from closed cell foam become less comfortable over time or are less protective on the next hit.

Open Cell Foam:

Open cell foams have their plusses and minuses as well. PORON Comfort materials are comprised of open cells connected by portals which allow air to flow between them.

This means these materials are not dependent upon air bubbles for their properties, but instead on the properties of the materials in their cell walls. Because of this, they react to pressure in a manner similar to that of a spring, returning to an original position after each compression without fail due to air moving freely through the cells. An open cell structure also allows for moisture vapor transmission, helping with breathability and maintaining the environment of the shoe.

spring - close cell foam

Available in an array of proprietary formulations, PORON Comfort open cell materials are engineered to provide specific functionality, providing the right level of support and breathability to the end user throughout the day and over the life of the shoe.

So Which One is Right for Your Application?

There are advantages and disadvantages to each type of foam that should be considered when deciding which one to use. Closed cell foams can be very light, as their cell walls can be very thin, but are usually stiff because of the incompressibility of the air inside them. They can also be better than open cell materials at resisting liquid penetration.

Open cell foams, in addition to being resistant to taking a set, are softer and easier to compress. Their cells also allow for breathability and a better Compression Force Deflective (CFD) or, in other words, a measure of their firmness or load-bearing capacity.

Occasionally the right foam solution is actually a combination of closed cell and open cell materials. Capitalizing on the best of both worlds, some designs layer a closed cell foam and open cell foam, allowing the more flexible open cell layer (such as PORON Comfort) to conform to the shape set into the closed cell material (an EVA for example).

Refer to the table below for a summary of the advantages of each type of foam:

Foam Properties Open Cell Closed Cell Property Measurement
Compression Force Deflective (CFD) Softness/Conformability
Compression Set Resistance Life of Properties
Anti-Microbial  ✓* Integral Coating
Breathability MVTR-Yes/No
Water Absorption % Uptake After Some Time
Washability Cycles at Setting
Shaping
Flexibility

*Optional additional protection available

Be mindful of these differences as they relate to your application and design.  If your application requires lighter weight and washability, opt for a closed cell foam. However, if longevity and reliability are critical to your application, choose PORON Comfort materials as your solution.

 

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Selected quotes from our recent earnings call. Read the corporate financials news release: Rogers Corporation Reports Second Quarter 2018 Results.

In Q2 2018, Rogers delivered revenues of $215 million, compared to $201.4 million in Q2 2017.

Bruce Hoechner, CEO, on Growth Drivers

There continues to be a strong demand that is projected in our key growth drivers of advanced connectivity and advanced mobility. Opportunities for growth in markets such as 5G, EV/HEV, and ADAS are driving our capacity expansion plans. It is a key imperative for Rogers to maintain its market leadership position by ensuring capacity is ready when our customers need it.

In advanced mobility, we are very encouraged by the continued adoption of our silicon nitride materials as automakers continue their race to introduce more EV and HEV models. This shift in the industry bodes well for the PES business, where our ceramic substrates offer high thermal connectivity and reliability. These features are essential for the smaller, more energy-efficient wide-bandgap semiconductors found in EV and HEV applications.

In the area of advanced connectivity, we continue to see signs that the transition to 5G is imminent, with testing and early deployments on the rise in China. For Rogers, 5G represents a much larger opportunity than past generations of wireless infrastructure due to the complexity of the systems and the greater material content they require. ACS holds a solid leadership position in this market, offering differentiated products that meet customer needs for very high frequencies, thermal management and high performance that minimizes crosstalk.

We look forward to capitalizing the large opportunities ahead.

Bruce Hoechner, CEO, on Rogers’ Business Units

Advanced Connectivity Solutions (ACS) achieved second quarter net sales of $76 million, a slight increased over Q2 2017, and sequential growth of 4% over Q1 2018. Revenues were largely driven by applications in aerospace and defense and tenant for 4.5G and 5G wireless structure and ADAS, partially offset by lower demand in portable electronics and wireless 4G LTE power amp applications. The latest independent market analysis indicates 2019 5G base station deployments at roughly 100,000 units, with some experts indicating more. ACS has significant design wins in this space, where base stations require 2x to 4x of Rogers’ content than that of the 4G LTE base stations.

Elastomeric Material Solutions (EMS) net sales of $79 million were relatively flat compared to Q2 2017. Higher demand in portable electronics, consumer, automotive and mass transit applications was offset by lower demand for clean room automation equipment used in OLED display manufacturing. In the second half of the year, we expect continued improvement in the general industrial segment. Additionally, we continue to drive operational synergies across our acquired businesses, including DeWAL, DSP and, more recently, Griswold.

Power Electronics Solutions (PES) delivered another great quarter with net sales of $54 million, a 12% increase over Q2 2018, excluding the impact of currency. Net sales increased due to broad-based demand across markets, including particular strength and electric and hybrid electric vehicles, renewable energy, mass transit and variable frequency drives. We expect the strength we’ve seen in the first half of the year to continue into the third and fourth quarters, driven by exceptionally strong demand for EV/HEV and x-by-wire applications.

Q2 2018 Earnings Call Transcript

Q2 2018 Financial Press Release

Q2 2018 Earnings Call Slides

Q2 2018 Earnings Call

 

This entry first appeared on Rogers Corporation’s internal “Leadership Blog.” Our CEO, Bruce Hoechner, and his senior leadership team write weekly posts for Rogers’ intranet, generating many likes and comments from colleagues around the globe.

 This blog was written by Gustavo Araujo, Rogers’ Vice President of Global Supply Chain, and has been edited for external publication.

I believe that one of the most valuable programs we have at Rogers is the Thank You Awards. What I like the most about the program is that it offers a way for our employees to demonstrate their gratitude to one another for efforts that go above and beyond their day-to-day activities. It is fascinating to see the great things our employees are doing every day and, even better, seeing that their colleagues are paying attention and thanking them for their dedication. Every day I read two or three Thank You Award stories and I really enjoy them.

Express Your Gratitude- VP of Supply Chain Gustavo Araujo

This is what prompted me to write this week’s blog. The importance of gratitude not only in our workplace but in our homes, in schools, in stores, in everyday situations.

Why should anyone thank you for just doing your job? And why should you ever thank your coworkers for doing what they’re paid to do?

Since we spend most of our time at work, it’s a perfect place to practice gratitude! Human nature makes it easier to be grateful when we have good days. But I think we should practice being grateful even if we are having an “off” day. It can actually lift you to find something to be grateful for in the midst of difficulty.

I’d like to share an article that appeared in Forbes magazine written by Amy Morin, “Scientifically Proven Benefits of Gratitude that will Motivate You to Give Thanks Year-Round.”

  1. Gratitude opens the door to more relationships. Not only does saying “thank you” constitute good manners, but showing appreciation can help you win new friends, according to a 2014 study published in Emotion, the magazine of the American Psychiatric Association. The study found that thanking a new acquaintance makes them more likely to seek an ongoing relationship. So whether you thank a stranger for holding the door or send a thank-you note to that colleague who helped you with a project, acknowledging other people’s contributions can lead to new opportunities.
  1. Gratitude improves physical health. Grateful people experience fewer aches and pains and report feeling healthier than other people, according to a 2012 study published in Personality and Individual Differences. Not surprisingly, grateful people are also more likely to take care of their health. They exercise more often and are more likely to attend regular check-ups, which is likely to contribute to further longevity.
  1. Gratitude improves psychological health. Gratitude reduces a multitude of toxic emotions, from envy and resentment to frustration and regret. Robert Emmons, a leading gratitude researcher, has conducted multiple studies on the link between gratitude and well-being. His research confirms that gratitude effectively increases happiness and reduces depression.
  1. Gratitude enhances empathy and reduces aggression. Grateful people are more likely to behave in a pro-social manner, even when others behave less kindly, according to a 2012 study by the University of Kentucky. Study participants who ranked higher on gratitude scales were less likely to retaliate against others, even when given negative feedback. They experienced more sensitivity and empathy toward other people and a decreased desire to seek revenge.
  1. Grateful people sleep better. Writing in a gratitude journal improves sleep, according to a 2011 study published in Applied Psychology: Health and Well-Being. Spend just 15 minutes jotting down a few grateful sentiments before bed, and you may sleep better and longer.
  1. Gratitude improves self-esteem. A 2014 study published in the Journal of Applied Sport Psychology found that gratitude increased athletes’ self-esteem, an essential component to optimal performance. Other studies have shown that gratitude reduces social comparisons. Rather than becoming resentful toward people who have more money or better jobs—a major factor in reduced self-esteem—grateful people are able to appreciate other people’s accomplishments.
  1. Gratitude increases mental strength. For years, research has shown gratitude not only reduces stress, but it may also play a major role in overcoming trauma. A 2006 study published in Behavior Research and Therapy found that Vietnam War veterans with higher levels of gratitude experienced lower rates of post-traumatic stress disorder. A 2003 study published in the Journal of Personality and Social Psychology found that gratitude was a major contributor to resilience following the terrorist attacks on September 11. Recognizing all that you have to be thankful for —even during the worst times—fosters resilience.

So whether it’s through a Thank You Award or simply telling someone you appreciate them, let’s give gratitude a chance. Practice it and enjoy it.

Rogers Advanced Connectivity Solutions (ACS) has introduced an updated design program that is free to download called the MWI-2017 Microwave Impedance Calculator, a transmission line modeling tool for electronics engineers (setting up an account is required).

The MWI-2017 Microwave Impedance Calculator software doesn’t replace sophisticated suites of modeling tools, such as the Advanced Design System (ADS) from Agilent Technologies or Microwave Office from AWR. Nor can it challenge the prediction capabilities of a planar or 3D electromagnetic (EM) simulator such as HFSS from Ansys or the Sonnet suites from Sonnet Software. But what it does, it does well, which is to calculate key parameters for most common microwave transmission lines, including microstrip, stripline, and coplanar-waveguide transmission lines. The software is downloaded as an executable (.exe) file and runs on most Windows-based personal computers, including those with Windows XP, Windows 7 and Windows 10 operating systems. To speed and simplify the use of the software, Rogers also offers a 22-page operator’s manual in PDF file format.

MWI Microwave Impedance Calculator

 

Using the Transmission-Line Modeling Tool

 The MWI-2017 program is based on closed-form equations derived from Poisson’s wave equations. The simple-to-use software can determine key parameters for a selected transmission-line type and laminate material, such as the conductor width and conductor metal thickness needed to achieve given impedance at a target frequency. The software’s intuitive graphical user interface (GUI) screen allows a user to select from a variety of different transmission-line types, including conventional microstrip, edge-coupled microstrip, conventional stripline, offset stripline, and conductor-backed coplanar-waveguide (CPCPW) transmission lines. The on-screen menus allow a user to select a transmission-line technology and a laminate material. Once a material, such as Rogers RO3003™ material, is selected, its pertinent characteristics are also shown on the screen, including relative dielectric constant (permittivity), dissipation factor (loss), thermal conductivity, and thermal coefficient of dielectric constant. Moving a mouse cursor over any material name reveals additional information about the material.

Enter Parameters such as Thickness, Operating Frequency and RF Power Level

With a material in place, the next step is to pick a standard dielectric thickness from a menu, or enter a custom thickness. A standard copper cladding thickness must also be selected from a menu, or a custom thickness entered manually. Copper conductor roughness is also accounted for, either selected from a menu as a standard value, or entered manually as a nonstandard value. Similarly, a standard value for copper conductivity can be used in a calculation, or a custom value entered, although any change in the value for copper conductivity will affect all metal layers in a multilayer circuit.

The MWI-2017 software allows an operator to enter parameters pertinent to a specific application, such as operating frequency and RF power level. Once a user has selected the desired transmission-line type, dielectric material, material thickness, conductor width, thickness of the conductive metal cladding, etc., a calculation will provide results in terms of such transmission-line parameters as conductor width and conductor spacing for a selected impedance. The software can generate insertion loss tables of data that can be used to create plots of loss versus frequency, and these plots can then be compared to actual measured results from a microwave vector network analyzer (VNA).

This exact procedure was performed to evaluate the accuracy of the MWI-2017 software for calculations of conventional microstrip parameters. MWI-2017 calculations performed for conventional microstrip transmission lines have proven to be extremely accurate since they include the effects of dispersion as well as copper roughness. For example, calculations performed on RO3003™ laminates have compared quite closely with actual measurements. These are ceramic-filled PTFE composite materials with a dielectric constant of 3.0 at 10 GHz and dissipation factor of 0.0010 at 10 GHz. In a comparison of MWI-2017 predictions versus measurements for a 5-mil-thick microstrip transmission line on RO3003 laminate with 1/2-oz. ED copper cladding, predicted and measured data matched almost exactly through 110 GHz.

Microstrip Insertion Loss Graph

The MWI-2017 software may not be able to match the accuracy of an EM simulator for a given prediction, but it is considerably faster, providing results almost instantaneously. It has been found to be most accurate for calculations on conventional microstrip and stripline, very accurate with edge-coupled microstrip and offset stripline transmission lines, and fairly accurate with conductor-backed coplanar-waveguide (CBCPW) transmission lines, although in the case of CBCPW transmission lines, vias must be properly placed to ensure accurate results.

Stripline insertion loss graph

Calculating the impedance of transmission lines is not trivial, since a number of factors can affect impedance. In microstrip, the width of the conductor and thickness of the dielectric substrate impact impedance. In CBCPW, not only the conductor width and dielectric thickness, but the spacing on the signal plane between the signal conductor and the adjacent ground planes will affect impedance. The MWI-2017 software is free, and provides results fairly quickly that are accurate and can be saved for use in other programs, including in word processors or in spreadsheets for creating x-y plots. In addition to calculating the impedance and loss of a transmission line, the MWI-2017 software provides information on a laminate’s effective dielectric constant, signal wavelength, skin depth, the electric length for a transmission line at a selected frequency, and propagation delay. It can even calculate the temperature rise above ambient temperature for a selected laminate based on an input RF power level.

For anyone needing a quick impedance calculation for designing a filter, coupler, or other high-frequency circuit, the MWI-2017 software provides usable results. And the price is right!

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