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


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

    World-Renowned Technology for Embedded Systems Development

  • 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


    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

    Flexible Circuit Designs with Large or Heavy Components

    Tara Dunn
    |  January 15, 2020

    One of the primary benefits of using a flexible circuit versus a rigid PCB board or wire and cable is the savings in weight and space. Flexible materials are thin, extremely light weight, and allow you to package in 3D, bending and folding to make necessary connections, allowing you to shrink the overall package size or fit additional electronics in a similarly-sized unit. As an example, a very typical two-layer construction for a flexible circuit is .010”, including coverlay and can often be even thinner than that. But what happens when you have a larger, heavier component that is going to be assembled to this flexible circuit? Connectors can often outweigh the flexible materials and require special attention during assembly and installation.

    Let me share a story. A two-layer flexible design required a large, heavy connector in the center of the flex and an FR4 stiffener was included for added support in that area, which is the recommended design practice. As it was being assembled, the engineer observed cracked traces and failures in this area. This was originally attributed to the FR4 not being thick enough to support the component. Because time was tight (isn’t it always?), a second FR4 stiffener was added to the other side of the flex as a short term fix to provide additional support before assembling the through-hole connector. This adjustment did not fully resolve the issue, but it did improve yield enough to be able to fulfill the prototype build.

    As this moved from prototype to pre-production volumes, the full design was reviewed for yield improvement opportunities. A few different things were done mechanically: the thickness of the FR4 stiffener was increased, and the thickness of the flexible materials was also increased to provide additional support. What was most interesting, is that it was also identified that in that component area, best design practices were not followed. The pads were not tear-dropped. The intersection of the trace and pad area is one of the highest stress areas of a flex design and it is always recommended to add the largest fillets possible to your flex designs. In this case, not only was the component putting stress on the pad to trace transition areas, those areas were already at high risk.

    What are some of the things to consider to successfully navigate the challenge of a heavy component needed on a thin flexible circuit? One of the first decisions that needs to be made is whether to use a flexible circuit with a stiffener or a rigid-flex construction. There can be confusion with regard to the terminology of a rigidized flex when compared to a rigid-flex. To be clear, a rigidized flex is a flexible circuit with an FR4 stiffener added to provide support to component areas. This stiffener is purely a mechanical support. A rigid-flex, on the other hand, will typically have circuitry on the rigid layers and use plated through-holes to electrically connect the rigid and flex layers.

    This decision should factor in the full scope of the flex and assembly, not just the larger heavier connector area. Often, with lower layer count flexible circuits, a flex design with added FR4 stiffener is a logical, lower cost alternative to a rigid-flex. But a rigid-flex construction should not be readily dismissed if there are multiple, higher density component areas, particularly on both sides of the board.

    Once the decision is made to move forward with a rigidized flex, there are several things to take into consideration with the design. First, what is the shape and thickness of the stiffener? Typically, FR4 stiffeners are created by taking rigid board laminate and etching the copper on both sides,  then drilling and routing the appropriate size and shape. Common FR4 stiffener thicknesses range from .003” (0.008mm) to 0.125” (3.18mm). The overall size of the stiffener should include a review of not only the size of the component being supported, but also how that stiffener might influence nearby bend and fold areas.

    Once the stiffener is designed, a decision needs to be made as to how the stiffener will be bonded to the flex circuit. Will bonding the stiffener to the flex with a pressure-sensitive adhesive be sufficient or will the application require a thermal set adhesive to used? PSA’s are typically a lower-cost option, not requiring an additional lamination cycle by the fabricator.

    We talk quite a bit about following good design practices for flexible circuit designs including tear dropping the pads, providing tie downs or rabbit ears for those pads, routing perpendicular to any bend and fold areas, keeping plated through-holes away from bending and folding areas, etc. As we saw from the example earlier, this is critical even if the area is going to be supported by a rigid stiffener. Bypassing these recommendations can prove to be a costly shortcut.

    One last recommendation when using a rigid stiffener to support a heavy component on a flexible material is to be sure to add an entry in the fabrication notes to have epoxy applied at the flex and rigid interface to help reduce the stress on the traces in that area.

    Don’t be nervous about using a larger, heavier component on a thin, lightweight flex circuit, just be sure to follow the best practices for design!

    Have more questions? Call an expert at Altium or continue reading about flex and rigid-flex PCB assembly in Altium Designer®.

    About Author

    About Author

    Tara is a recognized industry expert with more than 20 years of experience working with: PCB engineers, designers, fabricators, sourcing organizations, and printed circuit board users. Her expertise is in flex and rigid-flex, additive technology, and quick-turn projects. She is one of the industry's top resources to get up to speed quickly on a range of subjects through her technical reference site and contributes regularly to industry events as a speaker, writes a column in the magazine, and hosts Her business Omni PCB is known for its same day response and the ability to fulfill projects based on unique specifications: lead time, technology and volume.

    most recent articles

    Back to Home