Free Trials

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

Altium Online Store

Buy any Altium Products with few clicks or send us your quote to contact our sales


Download the latest in PCB design and EDA software

  • Altium Designer

    Complete Environment for Schematic + Layout

  • CircuitStudio

    Entry Level, Professional PCB Design Tool

  • CircuitMaker

    Community Based PCB Design Tool


    Agile PCB Design For Teams

  • Altium 365

    Connecting PCB Design to the Manufacturing Floor

  • Altium Concord Pro

    Complete Solution for Library Management

  • Octopart

    Extensive, Easy-to-Use Component Database

  • PDN Analyzer

    Natural and Effortless Power Distribution Network Analysis

  • See All Extensions
  • Live Courses

    Learn best practices with instructional training available worldwide

  • On-Demand Courses

    Gain comprehensive knowledge without leaving your home or office

  • 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


    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

    Altium Online Store

    Buy any Altium Products with few clicks or send us your quote to contact our sales


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

    • 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

    Pin Swapping and Gate Swapping in Your PCB Layout to Clean Up Your Rat Nest

    Altium Designer
    |  March 20, 2018

    Clean up the rat nest in your PCB design

    I recently moved into a new apartment, and it was time to unpack all of my electronics. When I reached into the box to pull out my audio cords, power cords, and extension cords, everything was a tangled, helpless mess. If I had taken more time to pack them properly, they probably would not have become tangled. If you are routing traces between an FPGA and external logic ICs on your PCB, your design might look like my mess of cords on moving day.

    No matter how much planning goes into your PCB designs, you may find yourself in the position of your pin swap during trace routing. Moving between schematic and layout leaves room for ambiguity, and it is up to the to route traces such that crossover is minimized. If you find that your design is a rat’s nest, it can be cleaned up by doing a pin swap in your PCB.

    Pin swapping may not be so important in simpler designs with a low number of components. But in devices that have components with high pin density, like FPGAs or microcontrollers, routing your signals can quickly become a complicated mess of crisscrossing connections in your PCB layout.

    FPGA Pin Swapping

    The trend towards system-on-a-chip devices has increased the use of FPGAs. Using FPGA technology allows designers to implement nearly any logic-based functionality in their device. Rather than designing a system with hundreds or even thousands of logic ICs, FPGAs provide the same design freedom in a single IC. The challenge to integrating an FPGA on your PCB successfully is in routing your power, ground, configuration, clock, and user I/O signals properly.

    Connecting the right traces to an FPGA on a PCB can be a difficult task. On the FPGA side, the pins are assigned to the hardware description language signals that form the logic implemented in the FPGA. The pins have to be connected to the proper net that will connect it to other components on the PCB. Current devices can have over 1500 pins, and performing a pin swap manually can be time-consuming and is prone to mistakes.

    Integrated circuit pin layout
    A 169-pin integrated circuit

    Certain FPGA pins cannot be swapped without also swapping other components on the circuit board. For example, ground and I/O pins, power and I/O pins, or power and ground pins should not be swapped with each other. If you do make these swaps in your layout, redesigns will be required on other of the circuit board. Thankfully, a good piece of design software with built-in rules checks can prevent this mistake.

    I/O pins within a group, however, can be swapped with each other, and this may help clean up your PCB design. Be careful before you start swapping I/O pins willy-nilly. Some pins may be part of a differential pair, and these should only be swapped with another differential pair. While some pins have the capability to be bidirectional, they may be configured as solely input or output on the schematic. Input pins should not be swapped with output pins and vice versa.

    Gate Swapping

    As FPGAs and other components may be required to interface with an external logic IC, gate swapping may also be necessary to clean up your PCB design. Gate swapping can involve rearranging trace routing to different pins on the IC, or even swapping the IC out for one with a different pin layout. Both strategies can help minimize crossover and clean up your signal traces.

    Gate swapping can only be performed in chips that have interchangeable devices in a single package. Two good examples are the 74xx00 quad-NAND package and the CD4000 three input NAND package. These chips have multiple identical devices in a single package, so you can move your traces to a different gate without affecting your overall design.

    Exchanging one IC for a different IC is another beast. A different IC may have a different pin layout that allows you to detangle your traces. If you must swap ICs, the electrical input and output levels should be compatible with both IC packages. For example, changing out your IC may result in a new fan-out value and swapping may not be possible if too many gates are driven downstream. It is also important to swap ICs within the same logic family (TTL or CMOS).

    Swapping logic ICs without sacrificing performance requires a comprehensive component with predefined electrical characteristics and pin layout. Be careful when accommodating a pin swap by using a different IC. You will need to pay attention to issues like fan-in and fan-out, propagation delay, and power and ground pin placement in your new IC. A different propagation delay will be especially important in high speed devices.

    Logic ICs in DIP packaging
    Logic ICs in DIP packaging. Editorial Credit: Panuwat Phothikamol /

    In low power devices, a pin swap on logic ICs can reduce power dissipation by lowering the capacitive loads on your logic gates. The pins should be swapped so that the trace carrying the highest frequency signal is connected to the pin with the lowest capacitive load. This is especially important when working with asymmetric logic gates.

    If you are interested in simplifying pin swapping and routing, Altium Designer®  can help you streamline your PCB layout. The ActiveRoute® tool can help you efficiently arrange your traces and can reduce crossover with automated pin swapping. To learn more, talk to an Altium Designer expert.

    About Author

    About Author

    PCB Design Tools for Electronics Design and DFM. Information for EDA Leaders.

    most recent articles

    Back to Home