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

    Creative Design with Buried Vias in Your Next HDI PCB

    Altium Designer
    |  February 11, 2019

    HDI PCB with vias on the surface layer

    Once I learned how to use different types of vias on my PCBs, I found that my routing strategies greatly improved, and I was able to reduce my overall board size. Judicious use of the right vias lets you place connections only between the layers you absolutely need for your board to function, instead of making connections that aren’t necessary.

    As newer devices pack more functionality (and more components) onto a single board, vias are indispensable for routing connections between layers in your board. By choosing the right type of via, you’ll be able to save space on your surface layers, allowing you to pack more functionality into your board.

    Buried Vias in Your HDI PCB

    So, what is a buried via anyways? A buried via is like a blind via that runs between two of the inner layers in a multilayer PCB. Both of these types of vias connect between two or more layers. In a multilayer board, blind vias only connect an outer layer to one or more of the inner layers of the board, whereas buried vias only connect between inner layers. Buried vias come in the through-hole variety, or they can be be filled and used to connect between two adjacent layers.

    ELIC PCBs that require HDI design can use buried vias to connect between individual layers, rather than selectively spanning pairs of layers. In an ELIC PCB, blind and buried vias can be stacked in order to access every layer in the board. All vias in the stack must be filled with copper in order to create the required electrical contacts between layers and provide structural integrity to the via stack.

    There is another reason that stacked vias in an HDI PCB should be filled. Lateral manufacturing tolerances on the position of stacked vias in an HDI PCB need to be very tight. If tolerances are not tight enough, buried vias that are stacked on adjacent layers can be offset slightly. Filling these vias with copper ensures that the vias in the stack will form a reliable contact, even in the presence of some lateral offset.

    Stacked vias give designers a simple way to gain access to multiple layers when the vias diameter becomes very small and drilling becomes difficult. Smaller holes require slower drilling, especially when the vias have large aspect ratio. Drilling smaller via holes also increases costs as the increased stress on small drill bits causes them to break more often. Stacked blind and buried vias in an ELIC board are drilled and plated in the individual layers, rather than drilling and plating through an entire stack.

    Using buried vias can also help you reduce the number of layers required to route all of your traces and/or reduce the overall size of your board. Since these vias only run between inner layers, you’ll have more room to route traces on the surface layers. This is useful when fanning out a BGA. If you're using through-hole vias and your escape routing is taking up too much space, you can reach the inner layers with blind and buried vias and widen the breakout channels.

    Because buried vias do not take up space on the surface layers in a multilayer board, components can be placed directly over a buried via. Buried vias are really no different than conventional vias as long as designers obey the typical clearance rules in the buried layers.

    Vias used for fanout and escape routing from a BGA

    Vias used to fanout a BGA

    How Cost and Quality Standards Affect Design with Buried Vias

    It’s one matter to include vias in your multilayer design, but your manufacturer may have something important to say about your design choices. Many manufacturers do their best to ensure that their processes are compliant with industry standards, including ISO, IPC, and UL standards. Manufacturers will take steps to place limits on the number of lamination and thermal press steps used in a process, the sizes of annular rings in vias, and other design aspects.

    In HDI PCBs, laser drilling may be a better option for placing access between the inner layers. However, when the number of lamination and thermal press cycles is limited due to quality control standards, particularly UL standards, laser drilling between each layer may not be possible given the prescribed limits on the number of lamination cycles.

    In this case, you’ll have no choice but to drill through a layer stack and use a plated through-hole buried via to reach between the internal layers. The outer layers can then be accessed using blind and buried vias. As long as you’re creative with designing your stackup and defining drill pairs between layers, then you won’t exceed the acceptable number of lamination and thermal press cycle steps.

    Blind and buried vias also have a cost trade-off compared to through-hole vias. Blind and buried vias incur higher manufacturing costs per via as the board will require additional machining steps. However, they allow denser routing on the surface layers and can be used to reduce the layer count. This might offset the overall cost of the additional machining steps, depending on how creative you can get with your routing.

    Dense routing on a green PCB

    Utilize all your knowledge when working with buried vias

    If you want to include buried vias in your next HDI PCB, the CAD tools in Altium Designer 18.1 are just what you need. These features help you automate much of your routing process and make it easy to visualize your layout in 2D and 3D. The rules checking, simulation, and deliverable generation features help guide you throughout the design process.

    To learn more about Altium Designer and how it can make your design process more efficient, talk to an Altium expert today.

    About Author

    About Author

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

    most recent articles

    Back to Home