Free Trials

Download a free trial to find out which Altium software best suits your needs

How to Buy

Contact your local sales office to get started on improving your design environment

Downloads

Download the latest in PCB design and EDA software

  • PCB DESIGN SOFTWARE
  • Altium Designer

    Complete Environment for Schematic + Layout

  • CircuitStudio

    Entry Level, Professional PCB Design Tool

  • CircuitMaker

    Community Based PCB Design Tool

  • NEXUS

    Agile PCB Design For Teams

  • CLOUD PLATFORM
  • Altium 365

    Connecting PCB Design to the Manufacturing Floor

  • COMPONENT MANAGEMENT
  • Altium Concord Pro

    Complete Solution for Library Management

  • Octopart

    Extensive, Easy-to-Use Component Database

  • PRODUCT EXTENSIONS
  • PDN Analyzer

    Natural and Effortless Power Distribution Network Analysis

  • See All Extensions
  • EMBEDDED
  • TASKING

    World-Renowned Technology for Embedded Systems Development

  • TRAININGS
  • Live Courses

    Learn best practices with instructional training available worldwide

  • On-Demand Courses

    Gain comprehensive knowledge without leaving your home or office

  • ONLINE VIEWER
  • Altium 365 Viewer

    View & Share electronic designs in your browser

  • Altium Designer 20

    The most powerful, modern and easy-to-use PCB design tool for professional use

    ALTIUMLIVE

    Annual PCB Design Summit

    • Forum

      Where Altium users and enthusiasts can interact with each other

    • Blog

      Our blog about things that interest us and hopefully you too

    • Ideas

      Submit ideas and vote for new features you want in Altium tools

    • Bug Crunch

      Help make the software better by submitting bugs and voting on what's important

    • Wall

      A stream of events on AltiumLive you follow by participating in or subscribing to

    • Beta Program

      Information about participating in our Beta program and getting early access to Altium tools

    All Resources

    Explore the latest content from blog posts to social media and technical white papers gathered together for your convenience

    Downloads

    Take a look at what download options are available to best suit your needs

    How to Buy

    Contact your local sales office to get started improving your design environment

    • Documentation

      The documentation area is where you can find extensive, versioned information about our software online, for free.

    • Training & Events

      View the schedule and register for training events all around the world and online

    • Design Content

      Browse our vast library of free design content including components, templates and reference designs

    • Webinars

      Attend a live webinar online or get instant access to our on demand series of webinars

    • Support

      Get your questions answered with our variety of direct support and self-service options

    • Technical Papers

      Stay up to date with the latest technology and industry trends with our complete collection of technical white papers.

    • Video Library

      Quick and to-the-point video tutorials to get you started with Altium Designer

    PCB Trace and Pad Clearance: Low vs. High Voltage

    Zachariah Peterson
    |  April 28, 2020
    PCB Trace and Pad Clearance: Low vs. High Voltage

    High voltage/high current designs carry safety requirements which need to be met by designers. Similarly, high speed designs need to have suppressed crosstalk in order to ensure signal integrity. The key design aspects that relate to both areas are your PCB trace clearance and pad clearance values. These design choices are critical for balancing safety, noise suppression, and manufacturability.

    The IPC 2221 standards provide guidance for preventing ESD between conductors, but not all boards will need to meet this standard. Depending on the voltage and frequency of your signals (or edge rate for digital signals), you may need a different value for your PCB trace clearance. Here’s how to balance these two aspects of your PCB layout while also ensuring manufacturability.

    Low Voltage (<15 V)

    Under the IPC 2221 standards, the minimum PCB trace clearance (really, the clearance between any two conductors) is 0.1 mm for general purpose devices, or 4 mils. For power conversion devices, this minimum spacing is 0.13 mm, or 5.1 mils. These boards could hardly be considered “high voltage” and the conductor spacing in these boards starts to border on the HDI regime.

    At these voltages, you may be working with digital signals, low frequency analog signals, or simply DC at moderate current. With digital signals, the typical rule is to simply follow the “3W” rule, where the clearance between traces is triple the width of the trace. For a typical 50 Ohm controlled impedance microstrip, your trace width will be ~20 mils, thus the recommended trace spacing is 60 mils. You’re still well within IPC 2221 requirements with these traces, and your primary focus should be efficient routing and DFM. Even in the HDI regime, where you may need to route between fine-pitch pads in a BGA, you won’t need to worry about these voltage requirements as you’re generally working at 3.3 V or ~1 V.

    PCB trace clearance for thin conductors
    When your routing is this tight, you’re still well within PCB trace clearance requirements below 15 V. Instead, focus on signal integrity and DFM.

    High Voltage (>15 V)

    At high DC voltage, the primary concern in choosing a PCB trace clearance value is preventing ESD and dendritic growth between exposed conductors. With high AC voltage, or with a switching regulator that outputs high current, you now have to worry about crosstalk, as well as ESD and dendritic growth. Crosstalk suppression guidelines still over-specify the required voltage spacing between conductors until you get to very high voltages.

    To see how you might need to find a balance between IPC 2221 and crosstalk suppression, consider the following hypothetical situation. Suppose you have a controlled impedance microstrip (20 mil wide) near a high voltage AC line, or near traces running in/out of a high current DC regulator. If you follow the “3W” rule, the spacing between parallel microstrips and the nearby high voltage line should be 1.5 mm, or ~60 mils. This is more than enough to comply with IPC 2221 until the high voltage level reaches 180 V for power conversion devices, or 340 V for other high voltage products.

    At high voltage, the concern is not so much a digital edge rate as is the frequency of a high voltage AC line. Any oscillating signal can induce a crosstalk signal in a nearby trace if the traces are close together; this is a known noise problem with high-voltage DC regulators and their downstream signal lines. At high output current, such crosstalk can induce unintended switching in high-speed digital components. It’s best to opt for greater spacing between a high voltage AC line and nearby DC or digital lines.

    Summary

    In general, we can define PCB trace and pad clearance rules into three different regimes based on voltage. In the two lower rows, be sure to calculate the required spacing using the IPC 2221 standard when determining which regime to work in. Note that, in the aforementioned article, your spacing can be made smaller when your traces are coated or are placed on inner layers.

    .

    Be sure to understand the difference between creepage and clearance in your design. Aslo, be sure to check that your traces will be wide enough to carry sufficient current without becoming too hot. This can be checked using the IPC 2152 nomograph.

    Once you’ve figured out the best trace and pad clearances to use in your board, you need to encode these values as design rules in your ECAD software. The unified design engine in Altium Designer® allows you to define your required PCB trace and pad clearance values as design rules, and these design rules are instantly checked as you route your board. This makes Altium Designer the ideal application for low and high voltage design tasks, as well as for high speed and high frequency designs.

    Now, you can download a free trial of Altium Designer and learn more about the industry’s best layout, simulation, and production planning tools. Talk to an Altium expert today to learn more.

    About Author

    About Author

    Zachariah Peterson has an extensive technical background in academia and industry. He currently provides research, design, and marketing services to electronics companies. Prior to working in the PCB industry, he taught at Portland State University. He conducted his Physics M.S. research on chemisorptive gas sensors and his Applied Physics Ph.D. research on random laser theory and stability. His background in scientific research spans topics in nanoparticle lasers, electronic and optoelectronic semiconductor devices, environmental sensing and monitoring systems, and financial analytics. His work has been published in over a dozen peer-reviewed journals and conference proceedings, and he has written hundreds of technical blogs on PCB design for a number of companies. Zachariah currently works with other companies in the electronics industry providing design, research, and marketing services. He is a member of IEEE Photonics Society and the American Physical Society, and he currently serves on the INCITS Quantum Computing Technical Advisory Committee.

    most recent articles

    Back to Home