Controlled Impedance Design Guide

How To Control Your Controlled Impedance

High-speed designs are more commonplace and the impact on the performance is becoming greater and greater. As a PCB designer, you need to know what nets require controlled impedance, how to avoid common mistakes when designing, what to specify in the fabrication drawing, how to design controlled impedance traces, how to get a stack-up from your manufacturer, as well as make sure they can meet your requirements.


This design guide empowers designers: the purpose is to get you on the advanced side of controlled impedance.


See What’s Inside

5 Chapters
36 Pages
10,000+ Downloads



1. Overview

    1.1 What is controlled impedance?
    1.2 When and why do you need controlled impedance?
    1.3 What affects impedance
    1.4 Specifying a controlled dielectric board instead of controlled impedance

2. Controlled impedance for manufacturing

    2.1 Defining cores and prepregs
    2.2 The PCB stack-up design
    2.3 Common mistakes to avoid in the stack-up
           2.3.1 Prepregs
          2.3.2 Impedance trace / space
          2.3.3 How to calculate the average effective dielectric constant
          2.3.4 High-speed materials
    2.4 Why manufacturers change your trace width and spacing
    2.5 Stack-up examples for 4, 6 and 8-layer boards

3. How to design a board with controlled impedance

    3.1 Determining which signals require controlled impedance
    3.2 Annotate the schematic with impedance requirements
    3.3 Common mistakes to avoid when designing
           3.3.1 Routing differential pairs
           3.3.2 Placing components, vias, and coupling capacitors
           3.3.3 Length matching
           3.3.4 Reference layers for return path of controlled impedance signals
    3.4 How to document controlled impedance requirements in the design files

4. Sierra’s capabilities

    4.1 How Sierra checks for controlled impedance
          4.1.1 Controlled dielectric
          4.1.2 Impedance control using TDR coupons
          4.1.3 Cross-section
    4.2 Sierra’s free Impedance Calculator

5. Sierra Circuits

    5.1 About us
    5.2 Talk with our experts

About Us

Sierra Circuits has been faithfully serving PCB designers and engineers since 1986, and has worked with over 20,000 customers since then. We specialize in PCB design, manufacturing and assembly and High-Density Interconnect technology. From PCB layout and design to assembly and manufacturing, Sierra Circuits handles all aspects of PCB production. We provide our customers with unprecedented quality, reliability, and a single point of support.



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