Rapid PCB Manufacturing Lessons from Rick Hartley's Tutorial
In the world of electronics, the importance of high-quality circuit boards cannot be overstated. From the classroom to the workshop, experts are stressing the significance of controlled impedance in the design of high-speed PCBs.
On February 22, the Sierra team attended a two-day workshop called PCB2DAY in San Diego, where Rick Hartley, a former Senior Principal Engineer at L-3 Avionics Systems, presented a class on the topic. Hartley, known for his global travels to share PCB knowledge with designers and engineers, covered various aspects of controlled impedance design in his session.
High-speed signal traces behave like transmission lines with characteristic impedance. If this impedance is not controlled and uniform along the trace, mismatches cause reflections that distort the transmitted signal, leading to data errors or malfunction at the receiver end. By implementing controlled impedance, signal reflections are reduced, preserving waveform shape and timing. This, in turn, ensures improved data reliability, as distortion is prevented, enabling faster and more reliable data transmission.
Controlled impedance also plays a crucial role in maintaining signal timing, particularly at frequencies above 100 MHz and in applications like DDR memory, HDMI, and Gigabit Ethernet. Variations in impedance create delays and jitter, which can be detrimental to the performance of these high-speed systems. With uniform impedance, consistent signal timing is maintained, thereby enhancing the overall system's efficiency.
In addition to its impact on signal integrity, controlled impedance also influences electromagnetic interference (EMI). By maintaining consistent impedance and signal integrity, the PCB emits less unwanted electromagnetic noise. Discontinuities can cause reflections that also increase radiation of EMI. Furthermore, controlled impedance traces with well-defined return paths (usually ground planes) reduce loop inductance and radiated EMI.
Material selection is also vital in controlled impedance design. The dielectric constant and stability of PCB laminates directly affect impedance consistency and overall signal behavior. Choosing materials with stable electrical properties ensures predictable impedance, reducing signal distortion and EMI problems.
Rick Hartley, during his class, emphasized the importance of not cutting cost and corners to maintain high quality. He believes that designing a circuit board in a certain way can solve some problems and provided detailed examples during the class. Tom Burek, a PCB Designer at Ametek, found the class helpful in learning how to make and put together a good quality circuit board, while Kazuhiro Yokoi, Open Innovation Manager at Fujifilm, found it great and useful for avoiding design difficulties.
For those interested in delving deeper into the subject, Sierra offers a Controlled Impedance Design Guide. This comprehensive guide covers topics such as understanding why controlled impedance is necessary, stack-up design guidelines, how to design for impedance, and common mistakes to avoid. The guide consists of 6 chapters, 56 pages, and is a 60-minute read.
In summary, controlled impedance in high-speed PCB design is essential to preserve signal integrity by minimizing reflections and timing skew, reduce electromagnetic interference by ensuring clean signal paths and proper return currents, and enable reliable operation of high-frequency digital and RF systems. Failing to implement controlled impedance typically results in degraded signal quality, increased noise, and potential system failures, especially as operating frequencies reach multi-gigahertz levels.
Controlled impedance technology is integral to the design of high-speed printed circuit boards (PCBs), as it helps reduce signal reflections, preserve waveform shape and timing, and thereby enhance data reliability. In addition, controlled impedance plays a critical role in maintaining signal timing, reducing electromagnetic interference, and ensuring efficient performance of high-speed systems.
