Heidi Barnes, Senior Application Engineer and Power Integrity Product Owner

Heidi Barnes is an anomaly in the PCB design world—a long-time, senior-level woman, and hardware engineer, whose career has been steeped in a wide variety of experiences with numerous technologies. Within the industry, she is widely recognized for her knowledge and expertise. Heidi holds five patents, was awarded the NASA Silver Snoopy for her work on hydrogen fire and gas detection, she is the author of over 20 papers on signal integrity and power activity, and she is an active member in developing the new IEEE P370 Standard involving interconnect S-parameter quality after fixture removal. In 2017, she was the recipient of the DesignCon Engineer of the Year award.

Heidi is well known for her signal integrity and power integrity experience and expertise in the design-to-test product development cycle. With the growing emphasis on getting the PDN design right for today’s ever-increasing high-frequency products, her insight is particularly relevant and beneficial. In this article, we'll look at Heidi’s current role within Keysight and her experience prior to joining the company; the technologies, products, and services provided by Keysight; the challenges that product developers make when factoring the test process into their PCB designs; future trends and challenges and some of the changes the company has made in terms of customer interaction and support as a result of the on-going COVID-19 pandemic.

About Keysight

Keysight is legendary in the world of electronics, with roots in test and measurement. Bill Hewlett and Dave Packard founded the original company. Over the years, the company’s name has changed from HP to Agilent, and now to Keysight, but the leadership in electronic measurements and simulations remains the same. Keysight is bringing a new focus to the company with integrated solutions for industry applications. The integration of simulation and measurement data, as seen in Keysight’s PathWave technology, provides valuable management of a product’s full life cycle from design, through hardware test, and production. 

As noted above, the company is based in Santa Rosa, California; it has 15 R & D sites worldwide; 32,000 customers in more than 100 countries; and a global total of approximately 13,000 diverse employees. Keysight Technologies, Inc. (NYSE: KEYS) is a leading technology company that helps enterprises, service providers, and governments accelerate innovation to connect and secure the world. Keysight’s solutions optimize networks and bring electronic products to market faster and at a lower cost with offerings from design simulation, prototype validation, manufacturing test, optimization in networks, and cloud environments. Customers span the worldwide communications ecosystem, aerospace and defense, automotive, energy, semiconductor, and general electronics end markets. Keysight generated revenues of $4.3B in the fiscal year 2019. Complete company information for Keysight is available here.

About Heidi Barnes

Heidi currently serves as a Senior Application Engineer and Power Integrity Product Owner for High-Speed Digital applications in the Design Engineering Software Group of Keysight Technologies. Heidi joined Keysight eight years ago and oversees Keysight’s EDA PI tools. She focuses on the application of electromagnetic, transient, and channel simulators to solve signal and power integrity challenges. Before Keysight, she had seven years’ experience in signal integrity for ATE test fixtures for Verigy; eight years’ experience in RF/Microwave microcircuit packaging for Agilent Technologies; 10 years with NASA in the aerospace industry, and one year with Arco Solar in the solar cell industry. Heidi holds a bachelor’s degree in electrical engineering from the California Institute of Technology in Pasadena, California. Market Sector Sales and Solutions Offered When it comes to the breakdown of the technologies that benefit from Keysight’s PathWave product, Heidi notes, “It’s electronics. They all need to use power; it is the foundation for everything.” When it comes to the geographical breakdown of those sales, she states, “I can only speak to Power Integrity EDA tools, which is seeing growth in all regions. The sale of PI EDA tools is driven by advancing technology needs and the ability to educate design engineers on the benefit of the simulation even for power delivery. Robert Ferenec has a popular YouTube blog on electronics, and he showed how non-intuitive, simple DC IR drop can be and what the benefits of simulation are.” Note: The link to this video can be found here. 

As noted above, Keysight’s high-speed digital signal integrity and power integrity offerings center around PathWave ADS, its flagship product. “This tool brings together schematic capture with layout and data display analysis to enable users to access multiple simulators for pre-and post-layout simulations,” she continues. “This capability together with Keysight’s strength in electrical component models and leadership in electronic measurement technology makes for an ideal combination to enable simulation to measurement correlation.”

Interfacing Between Design and Test

As noted in several of my other articles as well as others throughout the rest of the industry, testing is like any other measurement process; you go through the process thoroughly and ultimately to ensure that your final product will work as specified. Borrowing from the world of carpentry where the axiom is “measure twice, cut once,” if the measurement process is not done properly before committing a product to hardware, no amount of “fixing” will make the product correct.

In terms of PCB product development, the distance between the design and test process is often represented by a cognitive leap that can be significant in terms of understanding what’s needed and why it is necessary. Heidi explains, “Accurate simulation models are critical for reducing design spins and enhancing the troubleshooting efforts to find robust design solutions. The primary issue is that high-speed digital signaling is very broadband, often covering DC to GHz microwave frequencies. This dynamic load is challenging for power integrity since all power supplies are limited in bandwidth and typically can only deliver power up to kHz frequencies. Anything faster must be delivered by decoupling capacitors and on-package/die capacitance.”

She continues, “The PI engineer uses target impedance (Z) to ensure that at each frequency, the impedance times the di/dt current never exceeds the maximum power rail ripple specification. The problem gets more difficult as power rail voltages decrease and, for some applications, as the dynamic currents increase into hundreds of amps. Matching the power delivery impedance from supply to load for a flat impedance design is the ultimate goal for quiet power delivery. To achieve this flat impedance, the product developer must follow the current from the supply to the load and compensate any inductance in the path with a capacitor that has lower inductance and ESR to keep the impedance matched.”

In order to achieve the desired target impedance, Heidi notes, “If you design with a parameter, you should consider making it a test requirement. If target impedance is used as a production test requirement, it can help to identify any potential field failures due to changes in component manufacturers and tolerances. The simple transient step load tests are not enough to identify the potential for rogue voltage waves with multiple resonances excited at the same time.”

Challenges and Mistakes

In terms of signal integrity and power integrity challenges and the types of mistakes that are made relative to the design-to-test process, from the broader perspective, they are the same we find in the other aspects of the PCB design process: crosstalk and capacitance. The more complex today’s designs are, the higher the frequencies at which they operate makes accounting for these two dynamics a paramount concern.

In terms of common mistakes that designers make, Heidi points out that are three areas of concern:

• “In the PI world, it is probably the willingness of designers to just leverage a design from a data sheet and blindly accept models without verifying that they have the required fidelity for engineering a product. Just remember, it might have been a summer intern that wrote the datasheet that is being leveraged for a critical new product introduction.”
• “I hate seeing high-speed PCBs with fabrication documents that simply specify FR4 as the material to be used. It’s as if it doesn’t matter how the board is constructed, as long as the DC flying probe says that everything is connected. Without precise requirements for materials and construction, all bets are off for getting repeatable high-frequency performance.”

And the last element to which she refers:

• “Just because a measurement can’t be made at a desired location doesn’t mean that there should be no test points or connectors added.”

In terms of quality issues and how they are addressed, Heidi explains, “Signal integrity suffers more from PCB quality issues, but PI can also be impacted by material variations, especially for the high dielectric and very thin layers needed to add high frequency decoupling capacitance.”

She continues, “Panel to panel and across panel variations of material properties, etch tolerance, and via drills can all be monitored, if needed. Many designers forget that there are very simple techniques like running traces to the board edge to have a quick look at etching tolerances and layer to layer registration. My favorite choice is to have a test panel with the same PCB stackup that creates test structures for monitoring the critical design needs and then use this when changing manufacturers or checking on-going quality. Wildriver Technology specializes in designing test panels for high-frequency applications.”

Note: The same answers can be found by adding stacking stripes directly on the PCB. This practice involves adding strips of copper that are plotted along one edge of the PCB. These strips are positioned so when the PCB is cut from the panel, and the strips are visible to the naked eye. This ensures that all the layers are stacked in the correct order. And, since the strips are built directly into the board, there’s no need for an extra test coupon to accompany the board through the fabrication process.

Trends and Challenges

As with every other phase of the PCB design, fabrication, and assembly process, there are a variety of trends and challenges in the test process. Heidi notes, “People don’t understand what ground is. [The] ground is for potatoes and carrots. Electronic designs have return paths that are just as important as the power and signal nets. Also, there is a lack of detail in the fabrication documents. A fabricator will assume that they can use wider tolerances if these documents are not fully vetted before going to production.”

In terms of the types of challenges that will arise over the course of the next few years with the design to-test process, as with similar phases in the process, the increasing complexity and density of high-speed products will definitely play a role. As Heidi explains, “Parasitics are critical so, going forward with PI design, EM is going to be an imperative. SPICE doesn’t do the job.”

She continues, “PI engineers will also need to sharpen their skills to go between the time and frequency domains in order to analyze the behavior of power delivery.”

I asked Heidi if there will ever be a point in time when conventional EDA tools and practices will no longer be effective. She responded, “I look at it the other way. EDA tools are always advancing with the technologies. The need for design tools and simulation to ensure reliability and avoid field failures is more important than ever. This will be an on-going trend as society becomes more dependent on electronics as a basic need rather than a luxury.” In terms of current product innovations, Heidi, notes, “We are focusing on the practical use of EM simulators to improve the simulation-to-measurement correlation to avoid design respins. We are also working on merging the EM technology with full PI ecosystem simulations to include advanced power supply control loop models and dynamic load excitation.” This investment in PI simulation’s future is best demonstrated with Keysight’s collaboration with PI expert Steve Sandler of Picotest.com to deliver a series of YouTube videos on How to Design for Power Integrity. Note: The link for this PI video series can be found here.

The Impact of COVID-19

As with the vast number of other companies within the electronics sector, COVID-19 has influenced the way in which Keysight interacts with its customer base. Heidi explains, “Our customers are leaders in technology that virtually connect and secure the world, and as such, are critical for today’s pandemic response. For its part, Keysight accelerates their breakthroughs by providing leading-edge design, test, manufacture, and optimization solutions.”

She concludes, “In response to COVID-19, we launched Innovate Anywhere to help customers maintain productivity and minimize disruptions as they adapt to working from home. This program featured complimentary 90-day software licenses for several powerful PC-based designs and test products alongside resources and technical support to get customers up and running quickly and smoothly. In this way, Keysight helped the engineering community and IT professionals maintain critical services today to innovate for the future.” Note: To learn more about the company’s response to COVID-19, go to Keysight’s response.

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