Examining the Intricacies of Rapid PCB Construction
In the realm of high-speed PCB design, Agilent Technologies has released a comprehensive guide that delves into the intricacies of designing boards for faster data transfer rates. The guide, titled "High-Speed PCB Design Guide," spans 8 chapters, 115 pages, and takes approximately 150 minutes to read.
The guide covers a wide range of topics, including explanations of signal integrity issues, understanding transmission lines and controlled impedance, the selection process of high-speed PCB materials, and high-speed layout guidelines. Agilent Technologies also offers a case study on high-speed video boards and a webinar by Jim Choate, the USB technology product manager, about compliance testing for USB 3.1 devices.
One of the key issues addressed in the guide is signal loss, particularly in USB 3.0. Signal losses for copper traces running on FR-4 materials can be significant at USB 3.0 SuperSpeed signaling rates. To mitigate these losses, the guide suggests keeping traces short, routing on outer layers, using lower DF and DK rated laminates, and routing at a 45-degree angle to the material weave direction.
However, the guide does not discuss the potential for future generations of semiconductor devices to be faster than their predecessors. It also does not mention any specific high-performance materials or their prices.
As the USB standard has evolved, so has the need for materials with lower dielectric loss. The latest USB chip sets are now facing limitations due to the properties of FR-4 PCB laminates. In such cases, repeaters would be necessary if USB signal rates are pushed beyond 10 Gb/s, and their architecture would likely be much different for USB chip sets.
For high-speed electronics requiring low dielectric loss beyond what FR-4 can offer, PTFE-based laminates and their composites are considered the best choice. PTFE laminates offer much lower dielectric loss and better high-frequency performance compared to FR-4. They also have higher thermal stability and excellent dimensional stability under thermal stress.
Jim Choate, with a background in computer motherboard design and validation at Intel during the 1990s and as the USB Implementers' Forum (USB-IF) compliance committee chairman, contends that there is enough margin to push USB signal rates beyond 10 Gb/s without abandoning FR-4 for PC motherboards. However, he believes that using a material other than FR-4 for a PC motherboard would be a deal-breaker.
The total allowable loss in the USB channel end-to-end is -20 dB at the maximum signaling rate, according to the USB organization's model. Choate's contention is a testament to the ongoing advancements in high-speed PCB design, as the industry continues to push the boundaries of what is possible with existing materials.
References: [1] Agilent Technologies [2] PCB Web [3] Pulsonics [4] Tempo Automation [5] Altium
- In the thorough high-speed PCB Design Guide by Agilent Technologies, topics such as controlled impedance in transmission lines, data-and-cloud-computing technologies, and signal integrity issues are meticulously explained.
- As the USB standard continues to advance, the requirement for materials with lower dielectric loss, such as PTFE-based laminates, becomes increasingly significant for managing signal loss in high-speed electronic devices.
