Unveiling the Secrets of Rapid PCB Engineering
========================================================================
In the ever-evolving world of electronics, the quest for faster and more efficient components continues unabated. One such area that has garnered significant attention is the use of advanced PCB laminates in high-speed electronics.
Jim Choate, the former USB Implementers' Forum (USB-IF) compliance committee chairman and current USB technology product manager at Agilent Technologies, recently presented a webinar on compliance testing for USB 3.1 devices. His insights shed light on the challenges faced by the latest USB chip sets due to the properties of the conventional PCB material, FR-4.
FR-4, a widely used and cost-effective material, has served as the backbone of PCB manufacturing for decades. However, its dielectric properties limit its use in very high-speed applications. To address this issue, designers are increasingly adopting advanced laminates that offer superior electrical performance.
Key among these materials are PTFE (Teflon)-based laminates and ceramic-filled laminates. PTFE laminates, with their low dielectric constant and dissipation factor, result in significantly reduced signal attenuation, making them ideal for high-frequency circuits. On the other hand, ceramic-filled laminates combine relatively low dielectric constants with enhanced thermal conductivity, addressing both signal integrity and thermal dissipation needs in compact, high-power devices.
For instance, PTFE laminates offer a dielectric constant (Dk) of 2.5 – 3.5 and a dissipation factor (Df) of less than 0.005, compared to standard FR-4's Dk of 3.8 – 4.7 and Df of 0.015 – 0.03. This results in lower signal loss and better high-frequency performance, critical for applications like 5G, Wi-Fi 6/7, and high-speed networking.
Microchip, a company that manufactures chip sets to implement USB 3.0, suggests ways to mitigate losses, including using lower-loss materials like FR408HR, FR408HRIS, N4000-13SI, and Rogers. Another way to reduce signal loss is to route SuperSpeed (SS) traces on outer layers rather than inner layers.
The total allowable loss in the USB channel end-to-end is -20 dB at the maximum signaling rate, according to the model by the USB organization. If the loss exceeds a 7-dB budget in the USB channel, active repeaters would be required.
To help designers navigate the complexities of high-speed PCB design, a High-Speed PCB Design Guide has been developed. The comprehensive guide, spanning 115 pages and a 150-minute read, covers explanations of signal integrity issues, understanding transmission lines and controlled impedance, the selection process of high-speed PCB materials, and high-speed layout guidelines.
Despite the advantages of advanced laminates, Jim Choate contends that there is enough margin to push USB signal rates beyond 10 Gb/s without abandoning FR-4 for PC motherboards. However, he acknowledges that the architectural approaches for USB chip sets might be very different.
As the development of electronics has been paced by advances in semiconductor manufacturing, the transition to PCB laminates with better dielectric properties than FR-4 is anticipated to progress electronics further. The question remains: would 30% lower loss at 10 GHz be worth it to you?
References: [1] High-Speed PCB Design Guide [2] Advanced PCB Laminates for High-Speed Applications [3] The Impact of PCB Materials on High-Speed Signal Integrity
In the realm of high-speed electronics, the adoption of advanced PCB laminates like PTFE and ceramic-filled laminates, which offer superior electrical performance over traditional FR-4, is being driven by science and technology. This shift towards data-and-cloud-computing-centric devices is pushing the boundaries of PCB material capabilities, with the use of these advanced laminates playing a crucial role in addressing signal integrity and thermal dissipation needs in cutting-edge applications such as 5G, Wi-Fi 6/7, and high-speed networking.
