-
- News
- Books
Featured Books
- design007 Magazine
Latest Issues
Current IssueCreating a Culture of Collaboration
PCB designers could learn quite a bit from NASA and the private companies that develop spacecraft: Every one of these vehicles is a testament to the value of collaboration among disparate stakeholders. Without a collaborative culture, the rocket might never get off the ground.
Breaking High-speed Material Constraints
Do you need specialty materials for your high-speed designs? Maybe not. Improvements in resins mean designers of high-speed boards can sometimes use traditional laminate systems. Learn more in this issue.
Level Up Your Design Skills
This month, our contributors discuss the PCB design classes available at IPC APEX EXPO 2024. As they explain, these courses cover everything from the basics of design through avoiding over-constraining high-speed boards, and so much more!
- Articles
- Columns
Search Console
- Links
- Events
||| MENU - design007 Magazine
Estimated reading time: 1 minute
Beyond Design: Material Selection for Digital Design
In a previous column, Material Selection for SERDES Design, I pointed out that materials used for the fabrication of the multilayer PCB absorb high frequencies and reduce edge rates and that loss, in the transmission lines, is a major cause of signal integrity issues. But we are not all designing cutting-edge boards, and sometimes we tend to over-specify requirements that can lead to inflated production costs.
In this column, I will look at what types of materials are commonly used for digital design, and how to select an adequate material to minimize costs. Of course, selecting the best possible material will not hurt, but it may blow out the costs.
Figure 1: Simulated signal propagating through a curved waveguide.
Signals propagate in a vacuum or air at approximately the speed of light. But, as the electromagnetic energy is enveloped in a dielectric material, sandwiched between planes in the PCB medium, it slows down. Figure 1 illustrates a signal propagating through a curved waveguide. This is representative of a typical stripline configuration of a PCB. What needs to be understood is that the signal traces on a PCB simply guide the signal wave, as the electromagnetic energy propagates in the surrounding dielectric material. It is the dielectric material that determines the velocity (v) of propagation of the electromagnetic energy:
Keep in mind that c is the speed of light (in free space) and Er is the dielectric constant of the material (FR-4 is ~4.0). By contrast, the Er of air is 1. Therefore, the velocity of propagation in FR-4 is about half the speed of light or 6 inches per ns. The important concept is that it is the electromagnetic energy that propagates down the transmission line--not electron flow. Electrons flow at about 0.4 inches per second, a snail’s pace by comparison.Read the full column here.Editor's Note: This column originally appeared in the August 2014 issue of The PCB Design Magazine.
More Columns from Beyond Design
Beyond Design: Dielectric Material Selection GuideBeyond Design: The Art of Presenting PCB Design Courses
Beyond Design: Embedded Capacitance Material
Beyond Design: Return Path Optimization
Beyond Design: Just a Matter of Time
Beyond Design: Design Success with IPC Standards
Beyond Design: Integrating AI Into PCB Design Flow
Beyond Design: Standing Waves in Multilayer PCB Plane Cavities