Fresh PCB Concepts: PCBs for Harsh and Extreme Environments, Part 2

Ryan_Miller_v1.jpgIn the first column of this series, I talked about applications and challenges that PCBs face in harsh and extreme environments. This time, I'll dive deeper into PCB design considerations. Designing a PCB for a non-demanding environment can be a daunting task. There are many issues to consider, especially as you make certain decisions. But when I think about some of the challenges unique to extreme environments, I am amazed at the robust technology that is available. There are also negative effects of altitude, vibration, shock, and heat that plague the electronics systems that we rely on every day.

One challenge many PCB designers must resolve is the effects of air density that occur with a change in altitude. Without going into too much detail—I am a PCB engineer, not an atmospheric scientist—the density of the atmosphere becomes lighter as altitude increases. There is a region in the atmosphere between the lower atmosphere and the vacuum of space where electricity can arc at lower voltages. The breakdown voltage of the air in a thinner atmosphere is smaller. This allows electricity to arc across conductors at lower voltages than at sea level.

To make matters worse, charge builds up quicker at a point than it does on a rounder surface. The charges that build up can potentially act as arc points. There are some things we can do to mitigate this challenge. First, consult IPC-2221, Section 6, the part of the design specification that calculates how much electrical clearance your design will need.

Another way we can add mitigation to keep arcing at bay is to round out the corners in the design. Eliminate the 90° inside- and outside-corners on plane pours, surface mount pads, and the bends of traces. Engineers also can look at connection pins. Since these areas of the board are often associated with different voltage levels, there is more of a risk for arcing at these places as well. Sometimes we have unused pins on the connector that allow even greater clearance if we use every other pin.

Shock and Vibration Events
Some environments subject PCBs to extreme shock and vibration events. Extreme shock events subject PCBs to a high amplitude of movement force for a short time, whereas extreme vibration events subject PCBs to longer periods of movement with less amplitude. The movement force causes the board to oscillate about the center of mass. In turn, the oscillations stress the PCB materials and connection points. The materials will be stressed at the point where the pre-preg bonds with the copper. The hole barrels are internal connection points that could possibly crack, causing intermittent operation.

There are many small things we can do to mitigate shock and vibration. The key is to find the minimum amount of mass to add to the system while maintaining mechanical stability. Along with staking and potting compounds, what follows are some PCB design considerations.

First, we can design more mounting holes into the board, which means more mounting points to the chassis and more stability. This also will allow for more dampening devices to be mounted into the system.

Another aspect of the PCB is the stackup. In class, my favorite assignment was designing a board and stackup for a satellite application. For boards that will be subject to extreme shock or vibration events, it is critical to ensure the pre-preg has enough resin content to withstand these types of events. The pre-preg resin is the glue that holds the board together. During shock and vibration events, the PCB may flex and cause stress on the connection points. To mitigate as much stress as possible, we should consider using pre-pregs with over 50% resin content. Moreover, adding more than two sheets is another way to add bonding strength. This should be considered because signal integrity requirements do not always allow for changing dielectrics easily. What if you do not have a signal integrity requirement? If three sheets of pre-preg are good, then four sheets are better, right? Maybe. At a certain point, too much pre-preg will be detrimental to the layer-to-layer registration.

I would try to stay with three sheets at most, unless your PCB vendor says otherwise. If you are after more thickness but cannot add any more pre-preg, consider using unclad cores in the stackup. Unlike the pre-preg, an unclad core is already cured, so it does not add any resin to the press cycle. Layer-to-layer registration is not sacrificed.

Finally, there are the internal connection points. As the PCB oscillates, the hole barrels are also oscillating, stressing the plating in the holes. As the plating is stressed, it can crack. Some PCBs may work again after they are brought up to operating temperature, and some may experience catastrophic failure. Either way, it is not always possible to retrieve these PCBs in the field. Adding extra plating to the holes is just one more consideration to having a robust PCB. It will not work for every application.

Thermal Management
Last is thermal management. For a non-demanding application PCB, passive cooling such as convection will be an adequate thermal management solution. Other PCBs may be connected to the chassis for heat transfer, and some may be cooled by other devices. PCBs that operate in extreme environments cannot always be cooled by these methods. We can design the PCB to have active cooling solutions.

An easy way to add heat mitigation is to increase the copper thickness of the PCB. Simply stated, thicker copper dissipates heat better. As a word of caution, make sure the electrical space in the PCB data will support manufacturing the PCB with thicker copper. Your PCB vendor will know how much space you will need for sure. They are always a good source for this type of information.

If simply increasing the thickness of the copper does not alleviate the thermal management issues, there is the option to add copper coin technology to the PCB. This technology is like building a discreet heat sink into the PCB. It is positioned directly under the component so that it is in contact with it. In some cases, the coin can be electrically connected to the component.

The advantage is greater heat transfer, rather than simply increasing the copper thickness. A disadvantage, however, is the number of copper coins that can be placed on one panel. This amount will vary from manufacturer to manufacturer, but be sure to consider that every time a coin is inserted into a PCB, a weak spot is created in the PCB material. Too many weak spots can cause warpage and unintended consequences. Consider an environment with shock and vibration events with many coins in one design.

Instead of designing the PCB with too many copper coins, consider metal core construction. Metal cores can be pressed into the stackup or pressed onto a layer to provide the ultimate in heat sinking ability. When planning for metal cores, dielectric thicknesses should be carefully considered. We want to use the thinnest dielectric possible between the component layer and the metal core, because thinner dielectrics have less heat resistance. (This advice goes directly against the recommendation I made for designing stackup to resist shock and vibration events. As the PCB gets more complex, we must consider each moving part of the “machine” in relation to other parts.)

Extreme environments subject PCBs to many new hazards that we must consider. Other challenges will amplify in magnitude. It is difficult to learn everything we can do to mitigate the effects extreme environments on our PCBs. Hopefully, adding a little here and there will help you design a more robust PCB.

The best advice I can provide is to always work with your PCB supplier as early as possible in the design phase. They know the design considerations and manufacturing capabilities to help design the PCB in the most efficient and sustainable way.

Ryan Miller is a field applications engineer at NCAB Group. 



Fresh PCB Concepts: PCBs for Harsh and Extreme Environments, Part 2


Designing a PCB for a non-demanding environment can be a daunting task. There are many issues to consider, especially as you make certain decisions. But when I think about some of the challenges unique to extreme environments, I am amazed at the robust technology that is available. There are also negative effects of altitude, vibration, shock, and heat that plague the electronics systems that we rely on every day.

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Fresh PCB Concepts: PCBs for Harsh and Extreme Environments, Part 1


At the end of 2022, NCAB's Ryan Miller completed IPC’s six-week IPC training certification, PCB Design for Military, Aerospace and Other Extreme Environments. This in-depth course provided me with the knowledge and tools to provide support to customers who are designing within these harsh and/or extreme environments. Whether it is for applications such as aerospace, military, or industrial, harsh environments can expose the PCB to extreme temperature, humidity, vibration, shock, and other conditions that can affect its performance and reliability.

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Fresh PCB Concepts: Designing Controlled Impedance PCBs


Imagine that you are getting ready to work on a new PCB when the electronics engineer you work with suddenly gives you a controlled impedance requirement for the board. This will be your first experience designing a PCB with controlled impedance traces. Where do you begin? I encourage you to seek out IPC-2141, Design Guide for High-Speed Controlled Impedance Circuit Boards, to help answer that question; in addition, this introduction may also help. Controlled impedance traces are necessary on some PCBs for high-speed signal transmission. The goal with controlled impedance traces is to design the proper propagation delay into the trace.

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Fresh PCB Concepts: Copper Coin for Dissipating Heat


Are you trying to fit more high-power parts on your board, but can’t find the proper heat management technique? With more high-power components there is a need for increased thermal management. When you’ve tried everything else and are still having trouble keeping your parts within proper operating temperature, copper coin is one of the best ways to dissipate heat throughout your board. Nicholas Marks writes this month's installment.

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Fresh PCB Concepts: How Large Does That Pad Really Need to Be?


Annular ring is the amount of copper left and surrounding the hole after processing. This measurement is taken from the edge of the hole to the edge of the land at the thinnest part. To ensure a robust design, we must design efficient annular ring for PCB interconnections. From Ryan Miller's experience, annular ring design is a misunderstood aspect of printed circuit board (PCB) design. Not because it is complex; it is a dry subject with a few moving parts.

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Fresh PCB Concepts: Part 5—How to Handle Possible Moisture During Shipping, Handling, and Storage


This is the fifth part in a series titled “What Damage Does the Assembly Process do to a PCB?” In part four of this series, I discussed the effect moisture has on the printed circuit board at soldering temperatures. I explained the material properties of FR-4 laminate and how they are hygroscopic. We also covered an acceptable practice known as dry baking used to force moisture from the product just prior to being exposed to soldering temperatures. I thought it appropriate expand further on part four in this column.

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Fresh PCB Concepts: Sustainability in PCB Design


In order to meet the increasing demand for smaller, more powerful, and complex electronics, PCB designers are under pressure to create boards that are not only reliable but also sustainable. This can be a challenge, as many of the design choices that maximize performance can be less environmentally friendly. However, with a little extra effort, it is possible to create circuits that are both high-performing and sustainable. In this column, I will explore some of the key factors to consider when designing sustainable PCBs.

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Fresh PCB Concepts: The Right Board for the Flex Job


We like to say we like the board that is best fit for the job, but what does the right board for your job specifically look like? In this article we will go over the benefits and design types of flexible PCBs. So, what is a flex PCB? A flex board is defined as a bendable board with one or more conductive layers. There are different types of flex boards to fit any situation you may have. IPC defines them in five types, all are different constructions. To put it shortly these constructions are as follows, One layer of flex, double sided, multilayer flex, multilayer rigid-flex, and double or multilayer flex without electrically connected layers.

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Fresh PCB Concepts: What Damage Does the Assembly Process Have on a PCB? Part 4


In Part 3 of this series, I discussed how phenolic cured laminates can be mechanically weaker than their dicey cured laminate counterparts. I pointed out some of the material properties listed on material data sheets that explain and support this point. Whereas the phenolic systems are better at thermal management, the dicey systems are better under mechanical stress. There is no right or wrong here. The systems just perform differently under different circumstances. Understanding the differences and how they relate to the applied assembly process are important to ensure success. For this post I would like to discuss the effect moisture has on the printed circuit board.

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Fresh PCB Concepts: Does the Assembly Process Damage a PCB? (Part 3—Phenolic Epoxy Systems)


In part 2 of this series, I explained how the T260 and T288 material datasheet values could be used as an indicator of how durable a laminate system (FR-4) shall be when exposed to heat. The higher the temperature applied, the less time it takes to delaminate the FR-4. Traditional dicey cured epoxy systems do not stand up to lead-free assembly temperatures as well as one would think. The phenolic cured epoxy systems are much better suited and able to withstand the higher temperatures applied with lead-free assembly temperatures for longer periods of time.

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Fresh PCB Concepts: Recommendations for Track Welding and Open Circuit Repair


Track welding is what some factories may opt for if they find an open circuit. The technique is to attach/stick/weld a thin piece of copper across the broken track. Sounds okay, right? But how reliable is the repair? And how does IPC cover this subject? Well, IPC doesn’t have too much to add on this subject other than mentioning that the customer and supplier should agree whether repairs are acceptable or not. Therefore, if the customer does not advise it is not acceptable, then it is acceptable by default. In my experience, the issue is rarely discussed between the supplier and customer.

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Fresh PCB Concepts: High-tech PCBs from Design to Volume Production


Today I will talk about producing high-tech PCBs from design to volume production, since it is within this area that customers often do not reach their initial targets regarding time, cost and performance.

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Fresh PCB Concepts: HDI PCBs for New Kids in the Industry


I have been working with NCAB Group for three years now. When I began I had no experience with PCBs and since have learned so much working with our customers’ PCB designs. I would like to share the basic fundamentals and design features of my favorite type of PCB, high-density interconnect, or HDI.

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Fresh PCB Concepts: Holy Cow, What a Lead Time


It's summertime and we are adapting to our second COVID summer. However, things are most definitely a bit different these days. Recently I got an order, just like every day. The designer had spent the last three weeks completing the design and got it approved for order placement. The next step in the flow is when the purchaser spends a few days to get prices right, and then the order can be placed.

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Fresh PCB Concepts: Does the Assembly Process Damage a PCB? (Part 2—Time to Delamination)


In part 1 of this series published back in April, I commented upon the effect the assembly process has upon a printed circuit board. There is another gauge that can be used to help a designer or contract manufacturer understand this point and that is the time to delamination test. These are referred to as either the T260 or T288 tests.

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Fresh PCB Concepts: Auditing a Factory—When Everyone Wins in the PCB Supply Chain


One of the most important activities when it comes to maintaining the best quality of PCBs is to constantly be evaluating partner factories. An important tool for securing this is auditing those factories on a consistent basis. When the factory develops and the bar gets pushed a little higher each time, we’re in a situation where we all benefit.

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Fresh PCB Concepts: HDI Microvia Features in Illustrations


Ruben Contreras explains microvias and discusses aspect ratios with microvias. This is important to know when designing an HDI PCB because the different types vary in complexity. And the more complex, the more this affects the cost.

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Fresh PCB Concepts: Don't Forget AABUS


The most important thing is to know a standard and how to use it. Here is all you need to know about AABUS, what it means, how to handle it, and basically a list of issues that needs AABUS.

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Fresh PCB Concepts: Does the Assembly Process Damage a PCB? (Part 1—Soldering)


Every time a printed circuit board is exposed to soldering temperatures it is damaged. This is the case not only for lead-free soldering applications but also for eutectic soldering consisting of tin-lead.

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Fresh PCB Concepts: How 5G is Influencing PCB Technology Trends


We have all heard about the Internet of Things (IoT) and artificial intelligence (AI). In combination with the increased data transfer rates available through 5G, they can open up a whole new level of connectivity and communication between devices and things.

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Fresh PCB Concepts: Finding and Qualifying a Long-Term Partner


Finding the right factories is not an easy task. Anyone can take customers’ files and send them to whichever factory is available. But what guarantees does the customer have that the factory used is reliable in producing the design? Ruben Contreras details how to find and qualify a long-term partner.

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Fresh PCB Concepts: 4 Characteristics to Consider When Selecting PCB Base Materials


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Fresh PCB Concepts: Advantages of Application-Engineered PCBs


When working with your PCB supplier, do you have a dedicated engineering resource to help with the design of your PCB before fabrication? How about a resource that has experience and knowledge about the different applications for PCBs? Jeffrey Beauchamp explains how this is one of the most important and valuable factors when producing high-reliability PCBs, as well as what—or who—this resource could be.

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Fresh PCB Concepts: How Do You Calculate Finished Copper?


How do you calculate finished copper on a PCB? This may sound simple, but Ruben Contreras has seen copper thickness called out either on the drawing or the specification, which can lead to additional EQs and, in some cases, additional costs. In this column, he explains the unintentional results that can come from misunderstanding what was requested.

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Fresh PCB Concepts: Pros and Cons of the 6 Most Common Surface Finishes


There are only two different types of surface finishes for PCBs: organic and metal. Harry Kennedy describes the pros and cons of the six most common finishes on the market.

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Fresh PCB Concepts: 7 Options for Via Treatment


In some cases, it's acceptable to have via holes that are completely exposed in a PCB design. But there are many others where the hole should either be covered and/or tented, or in most cases, plugged. Jeffrey Beauchamp shares seven different via hole protection types based on IPC-4761.

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Fresh PCB Concepts: Why Design and Produce PCBs Beyond Industry Specification?


While questions may be an annoyance, especially when you finally have a board designed and are ready to have it built for a product, Ruben Contreras explains the importance of asking these questions and requiring specifications.

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Fresh PCB Concepts: Can Better Guidelines on Cosmetic Failures ‘Save’ Functioning PCBs?


Every year, fully functional PCBs are scrapped due to cosmetic “failures” that are not approved. Is this right, or do we need to make an even more precise set of rules on how to handle this? Jan Pedersen shares his thoughts on the issue.

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Fresh PCB Concepts: What You Should Know About Your Board’s Solder Mask


It’s a weird time we’re all in, and for most designers, work has slowed down or even stopped. While work might have slowed, now is a good time to review some of your past PCB projects to see if you can improve functionality and reduce field failures. Harry Kennedy explains how one of the simplest ways to do that is to start from the top: solder mask.

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Fresh PCB Concepts: Designing a PCB for Telecom Applications


Jeff Beauchamp and Harry Kennedy discuss PCBs for telecommunication applications, including key factors to consider, such as design and material considerations. They also recommend involving your PCB supplier at the time of design to help ensure manufacturability at the lowest possible cost.

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Fresh PCB Concepts: The Current Material Situation


We have all heard about the component crisis in the circuit board industry, and maybe you heard about the CCL shortage, but how many are aware of the bare board material shortage? Ruben Contreras explains the current material situation and tips to address this issue.

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Fresh PCB Concepts: Getting It Right From the Start


When faced with critical time-to-market situations, it is all too easy to say, “It doesn’t matter because this is just the prototype; we can fix this later.” However, if the design is perfected from the beginning, cost savings can be applied, and manufacturability can be ensured. Perhaps most importantly, the design can be adapted with reliability in mind, leaving a seamless transition from prototype to production. How do we get it right from the start?

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Fresh PCB Concepts: Why Material Selection Matters


When you’re designing a PCB, it’s standard to call out FR-4 material, but you could be holding yourself back or even exposing your board to risk by not knowing more about PCB materials. Let’s take a small look into why. What Is FR-4, exactly? Harry Kennedy of NCAB explains.

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Fresh PCB Concepts: Qualities of Medically Applied PCBs


In this inaugural column from NCAB Group, Alifiya Arastu discusses details of PCBs used in medical applications, highlighting some of the differences in terms of demands and how the design must be handled.

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Fresh PBC Concepts: What Is Reliability Without Traceability?


High reliability and compliance are hot topics at conferences all over the world. If you are a supplier to industries like defense, automotive, medical, and aerospace/space, high-reliability and regulatory compliance are strict demands for electronic device manufacturers. This column discusses how high-reliability demands enforce the need for traceability, and at what level the traceability should be.

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Fresh PCB Concepts: My Flexible Story—Flex Circuit Development Through the Decades


Senior Technical Advisor Jan Pedersen is celebrating 26 years at Elmatica. In this column, he shares his thoughts from his long experience in this exciting industry, and talks about those things that have changed a lot in the past few decades, and the others that haven't.

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Fresh PCB Concepts: Technology’s Future Comes Together—A Great Slogan for Us All!


“Technology’s Future Comes Together” was the theme of this year's IPC APEX EXPO, which is quite suitable during these changing times. I guess we all need to come together, especially the automotive industry.

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Fresh PCB Concepts: PCB Standards for Medical Device Applications—A Hard Nut to Crack!


With digitalization, AI, and IoT, the traceability and transparency to how a PCB is produced will be even more important. We must rule out the PCBs that follow the standards to the ones that do not. The day will come when you or someone you know might need a medical device, and you want to make sure it does its job correctly.

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