Connect the Dots: The Split Planes Challenge

PCBs don't explode every day, but if your design calls for more than one voltage on a power plane layer, spontaneous combustion is just one of the many problems this tricky challenge for PCB designers can cause.

It may seem counterintuitive, but when a PCB fails spectacularly, the cost is less because it’s both immediate and easier to measure. If you make a small crater the first time you turn on the first production device, you lose an entire lot of boards and the time spent on designing and prototyping. When less noticeable or intermittent issues occur, they can eventually cost far more depending on how long they remain undiscovered.

The severity of the PCB failure seems to have an inverse relationship to the amount of effort required to fix it. When there’s smoke coming out of your PCB, it’s relatively easy to find out why. Digital glitches and signal anomalies are more subtle issues that can take many hours of tedious detective work to solve.

Split planes are enclosed regions on an internal plane layer, and problems with them can be among the most difficult design flaws to ferret out. The further a board makes it through the development cycle without someone noticing, the more it costs. Production delays and resources directed at solving the problem can be quite costly, but the worst-case scenario involves malfunctioning boards making it out into the field. Those events create warranty claims, product recalls, damaged reputations, and lost jobs.

Here we will explain why managing split planes can be so challenging and examine some best practices for avoiding this common issue.

Why Does This Happen?
There often exists a gap between what a design tool allows the designer to do with split planes and how difficult it can be to recognize issues with the design.

Your PCB design tool will offer the ability to assign voltage amounts to the entire plane, but that can lead to problems if your design assigns multiple voltages to the same plane. Problems are avoided if you divide the plane into separate, electrically isolated areas using a split plane.

Just because different voltage amounts are “isolated” doesn’t mean you’re out of the woods. When more than one voltage is assigned to a power plane layer, your CAM tool does not check whether the voltage of your via matches the section of the board it’s going into. If you have a 12V via going into a 3V section of the board, it will fail.

Mixing digital and analog signals can also create headaches. An analog ground is noisy, and it fluctuates, while digital grounds are quieter and steadier. Connecting digital and analog planes together probably won’t result in a board failure that trips the smoke detector, but there will be performance anomalies from the noisy analog ground interfering with signals on digital pins.

If you are relying on manual oversight to discover such issues before production, it is easy to lose track of individual connections—especially on a complex board design with hundreds of vias.

How Do You Best Manage Mixed-Signal Output?
When you need to assign one or more power nets to a layer on a simpler design, applying plane splits that segregate areas containing each voltage is a simple and efficient way to distribute power.

Warning! This method relies on the human eye to ensure accuracy and gets risky for more complex board designs.

We think a better method is to use polygon area fills to make connections. With polygon area fills, when you name every net connection on each layer, they become visible. Vias of different nets will not connect. The enhanced visibility makes it so your CAM tool can perform error checking on your separate area fills and automatically recognize mismatched voltages.

How Do You Prevent Mixed-Signal Problems?
Digital and analog signals don’t play well together. Here are some actions you can take to prevent problems with mixed-signal output.

  • Keep the power ground and control ground separate for each power supply stage.
  • To keep your digital and analog grounds separate, build in a small impedance path. This will limit power circuit interference and help protect your control signals. 
  • Partition your PCB with separate digital and analog areas.
    • Make sure digital and analog components are assigned to their respective areas
    • Never route digital signals through analog territory and vice versa
    • Straddle analog-to-digital converters along the border of the two territories
    • Use a single, solid ground plane
    • If you must route a signal trace from one area to the other, place it entirely over the PCB’s ground plane
    • Pay attention to routing. For example, you want your analog grounds crossed only by analog lines. This will reduce capacitive coupling on a large ground plane with lines routed above and under it.

A Designer’s Best Friends: Vigilance and Awareness 
Designing with voltage top of mind is vital, as is knowing what the design tool’s error checker will and will not catch regarding connections to split planes. This is how you avoid burning boards and doing costly rework. If you build your designs such that you can rely on automated error checking, we believe that is the best method for dealing with complex power plane schemes.

This column originally appeared in the August 2021 issue of Design007 Magazine.

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2021

Connect the Dots: The Split Planes Challenge

08-11-2021

Losing track of voltage in your PCB design can lead to explosive problems. Your CAM tool will not manage split planes for you.

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Connect the Dots: The Board Thickness Challenge

07-21-2021

Size constraints, functional requirements, and environmental factors can make selecting PCB thickness difficult. Here we will examine best practices for choosing board thickness that results in quality, highly functional PCBs.

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Connect the Dots: There is No ‘Final’ Frontier for PCB Design

06-10-2021

Our ongoing mission: To explore more manufacturable designs, to seek out higher-quality boards and enhanced functionality, to boldly design PCBs that no one has designed before.

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Connect the Dots: A Closer Look at Surface Finish

05-17-2021

The final surface finish of a PCB is an important consideration. This coating between your components and the bare board is applied to ensure solderability and protect any exposed copper circuitry. Selecting the right type of surface finish can be daunting, and for good reasons.

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Connect the Dots: The Power Behind the (PCB) Throne—Power Supply Design Tips

04-13-2021

Delivering the required power to each component on a PCB can be a complex challenge. Designers have to manage converting AC to DC while also delivering the correct voltage and current to each component. A well-designed PCB results when the designer takes power supply seriously—paying close attention to the effects that power delivery can have on surrounding components, such as through heat management or signal interference.

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Connect the Dots: IoT is Changing How We Design PCBs

03-11-2021

Demand growth is fueled by business as well as consumers, with pandemic-accelerated healthcare and industrial machinery applications leading the way. IoT devices of every stripe will continue to improve and add functionality while also becoming smaller, lighter, and faster.

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Connect the Dots: The Case for Expansive Parts Libraries

02-10-2021

PCBs are the foundation of every electronic device, the home for the components that make up your assembly. Those integrated circuits, connectors, headers and passives are what makes it function. How it needs to function determines whether standard components alone can make it work.

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Connect the Dots: Design Tips to Avoid Part Fit Problems

01-19-2021

“Will my parts fit on the board?” That seems like it should be a rhetorical question that needs no answer but reality tells us, as you transition from the design stage to manufacturing, issues with parts fit are one of the most frequent causes of delays and cost overruns. Bob Tise and Matt Stevenson share six tips for ensuring parts will fit on your board.

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2020

This Month in Design007 Magazine: Connect the Dots—Is 2020 Really Coming to an End?

12-09-2020

As we approach the end of 2020, we are able to look back on one of the most challenging years that I have ever experienced. Throughout these trying times, Bob Tise and Matt Stevenson were consistent in their desire to share knowledge with everyone. Matt shares a synopsis of the topics they shared from the perspective of a PCB manufacturer.

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Connect the Dots: The New Recipe for Customer Service Success

11-11-2020

How are you holding up these days during the pandemic? Each of us is dealing with life struggles and changes differently. With this in mind, Matt Stevenson asks Al Secchi, global customer support and sales manager, what he has learned professionally from the pandemic and how to serve customers.

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Connect the Dots: Unraveling the Mysterious BGA Routing Mess

10-19-2020

A ball-grid-array (BGA) device can be a daunting component to route, especially in fine-pitch arrays featuring solder ball counts in the hundreds and pitch values as tight as 0.5 millimeters. Bob Tise and Matt Stevenson describe how you can take the mystery out of BGA routing and create a PCB design that can handle all those pesky narrow spaces.

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Connect the Dots: How to Know If a CAD Tool Is Right for You

09-21-2020

The tool that defines PCB designers is our CAD software, and many discover quickly that not all CAD tools are created equally. Bob Tise and Matt Stevenson answer the question, "How can designers find the right CAD tools to fit their particular methodology and needs?"

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Connect the Dots: The Nuts and Bolts of Electrical Testing

08-12-2020

In this column, Bob Tise and Matt Stevenson explore the world of electrical testing. They examine a variety of testing methods, what options to look for in a PCB manufacturer, and how to ensure that you're getting the best value out of the electrical test options available to you.

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Connect the Dots: Reassessing the Risk of Offshore PCB Manufacturing

07-15-2020

Offshore board production has long been considered an effective way to reduce the cost of producing electronic devices here at home, but those savings often demand a higher tolerance for delivery issues and come with lowered expectations for quality. Bob Tise and Matt Stevenson explain.

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Connect the Dots: The Power of Forward Thinking

06-06-2020

Innovation comes in many forms and from more places these days. Bob Tise and Matt Stevenson discuss how innovative electronic devices all contain PCBs, and share pro design tips for bringing new products to the market.

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Connect the Dots: Picking a Prototyping Strategy

05-29-2020

No matter how simple or complicated your electronic project, PCB prototyping is part of its journey from concept to reality. This process of turning the design into something physical can teach you a lot about what needs to be tweaked and improved before your PCB is ready for full production. Bob Tise and Matt Stevenson explain how before you can prototype, you have to design.

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Connect the Dots: Increased Focus on Health and Wellness Transforms the PCB Industry

04-04-2020

Our increased focus on health and wellness drives technology advancement for personal devices and those used in the delivery of healthcare. Bob Tise and Matt Stevenson explain how this trend also drives both PCB production innovation and a long-overdue update of the employer/employee relationship.

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Connect the Dots: The Seven-year Etch

03-16-2020

PCB etching seems like a simple task on the surface, but quite a few things can go wrong during this process. Adhering to best practice and continuous improvement is a must to help avoid issues with your finished board. Bob Tise and Matt Stevenson share their design tips for a better etching process.

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2019

Connect the Dots: A Penny for Your Thoughts on Copper

11-19-2019

You're probably thinking: “Bob can’t possibly write an entire article dedicated to the use of copper in PCBs.” To that, Bob says, “Hold my beer.”

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Connect the Dots: Build Quality Into Your Boards and Processes

11-06-2019

To the procurement clerk, a PCB may seem like it is just a line item on a bill of materials (BOM) or parts list during the production of an electronic device. At Sunstone, we know differently. The PCB is the building block for all of the components and parts in your electrical project.

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Connect the Dots: A Proactive Approach to Controlled Impedance

10-09-2019

You can save time, money, and effort if you are aware of the impedance math when you sit down to design your board. Gain this awareness by using a good impedance calculator, and you can build the right tolerances into your design. Impedance testing becomes a double-check of your work instead of the tool you rely on to tell you if your documentation is correct. Documenting impedance requirements properly is more onerous than most people realize. Though it seems simple, PCB documentation is a details game that often leaves knowledge gaps for your manufacturer.

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Connect the Dots: Managing Global Supply Chain Uncertainty

09-03-2019

We are well into the second year of tariff-centric trade policy, and one thing appears certain—uncertainty is here to stay. Though most of the media focus has been on cars and steel or consumer prices and corporate profits, the enduring challenge for both the electronics and PCB industries has been maintaining reliable global supply chains.

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Connect the Dots: Five Best Practices to Ensure Manufacturability

08-01-2019

When you send your design for manufacturing, your partner does not know what type of device the board will be part of nor the conditions in which it will have to perform. It’s common for harsh environments or exposure to mess up a board’s performance. If you call out materials that will not tolerate the end-product’s operating environment, bad things can happen—such as a smoking board, for example. Be sure your board can tolerate thermal stress or solder joints risk breaking and damaging components.

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Connect the Dots: The Future of PCB Manufacturing Doesn't Belong to Robots, but to the Users

07-09-2019

Is the world ready for the consequences of rapid automation? Will the use of robots displace entire categories of workers? Can artificial intelligence really “think”? How will manufacturing, including PCB manufacturing, be affected by all of these smart robots? These questions actually come from a pamphlet published in 1955: "The Age of Automation: Its Effects on Human Welfare."

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Connect the Dots: Accurate Gerber Files Are Mission-Critical for Smooth PCB Manufacturing

05-30-2019

Gerber files can reveal design issues ahead of the quote process and ensure your manufacturer has everything needed to produce your boards correctly. After consulting with Engineering Support Specialist Eric Haugen, we explored some best practices for making sure that Gerber files are accurate.

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Connect the Dots: Preparing for Tomorrow’s Technology Today

05-16-2019

At a recent Sunstone Circuits planning summit, Matt Stevenson, VP of sales and marketing, and Bob Tise had a wide-ranging discussion about emerging technologies and how they will impact PCB manufacturing. The following is an abridged transcript of this conversation.

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Connect the Dots: MakeHarvard 2019: Bigger and Better!

04-09-2019

Sunstone Circuits was eager to return to MakeHarvard as a sponsor and creator of a competition category this year, also serving as both mentors and competition judges. If you were there, you saw us—we were hard to miss in our bright orange vests. As mentors, we were out and about helping students and answering questions.

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Connect the Dots: Exploding PCBs: Don’t Lose Track of Voltage in Your Design

04-01-2019

Managing split planes? Your CAM tool will not do it for you. We see this almost every day—not exploding PCBs, which pretty rare—but rather problems created by having more than one voltage on a power plane layer. From where we sit, this is one of the more insidious and costly challenges facing PCB designers.

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2018

Connect the Dots: Six Tips to Ensure Parts Fit on Your Board

12-12-2018

One of the most frustrating mismatches with alternative through-hole parts occurs when the land pattern matches, but the pin size is off. If hole sizes are too tight, pins may not fit through the holes, or if they do go into the holes, they may not solder well. Solder will need to flow through the gap between the pin and the hole barrel. If there is not enough space to allow enough solder mass to flow through the hole, the circuit board will absorb heat from the molten solder and cause the solder to solidify partway up the hole. This is called a cold solder joint and can result in a premature failure of your circuit.

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Connect the Dots: New Landing Design to Reduce Thermal Pad Failure

11-16-2018

You’ve finally finished your design. All the traces are correct and the IC landings are to the manufacturer’s specifications. A short run of test boards performs perfectly. For best results, you select a reputable domestic board house for production and a quality assembly shop to do the soldering. When the finished boards arrive, everything looks great. You’re in high spirits and congratulate yourself on a job well done. Then the reports start coming in.

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