In recent times, technological advancement has paved the way for new-age electronic devices. Designers are constantly working to improve the performance of electronic technologies. However, they also need to consider signal integrity while designing PCBs. This directly affects the performance and reliability of electronic components.
Signal Integrity plays a vital role in electronic devices, measuring the quality of electric signals. It involves maintaining the fidelity of signals from the transmitter to the receiver. Moreover, PCB hardware designers should ensure good signal integrity in a PCB design. To achieve this, designers should handle bottlenecks, such as delay, impedance matching, and crosstalk.
In addition, businesses face various signal integrity challenges while designing, such as reflection, noise, transmission line effect, etc. In this blog, we will delve deeper into how to manage PCB hardware.
Different Ways to Manage Signal Integrity in High-Speed PCB Design
PCB Stackup Design
The foundation of signal integrity lies in the PCB stackup design. A properly designed stackup, such as the arrangement of layers, impedance control, and material choice, significantly impacts signal quality.
- Layer Arrangement: While designing a PCB, one should carefully consider signal, power, and ground layers arrangement. Critical signals when routed in inner layers of the PCB should have Ground planes above and below. Critical VDDs should have a Ground plane adjacent for additional Decoupling. This ensures that PCB maintains signal integrity and also mitigates interference.
- Impedance Control: The function of the PCB is to transfer signal power from the driver to the receiver. Proper impedance matching is vital. In modern designs, designers targeting PCIe Gen 6 or DDR5 must maintain impedance tolerances within ±5% to avoid destructive reflections. Consistent impedance prevents reflections and ensures signal fidelity.
- Material Choice: Dielectric material plays a significant role in signal loss for high-speed interfaces. Designers now frequently opt for ultra-low-loss laminates like Rogers 4000 series or Panasonic Megtron 7, which offer a dissipation factor (Df) as low as 0.001 to minimize signal attenuation at frequencies above 10 GHz.
Routing Techniques
Routing is one of the key factors that is vital to manage signal integrity. Here are some routing techniques:
- Trace Length Matching: Equal trace length is vital for signal propagation without timing mismatch (skew). For high-speed interfaces like HBM3 (High Bandwidth Memory), length matching must be precise within 5 mils to ensure data arrives synchronously with the clock.
- Differential Pair Routing: In differential pair routing, careful symmetry is vital to control skew and minimize crosstalk. Designers should maintain a consistent gap between traces and avoid routing over splits in the reference plane, which can cause significant return path discontinuities.
- Controlled Impedance Routing: In high-speed PCB design, designers need to maintain controlled impedance to ensure signal integrity throughout the transmission path. With controlled impedance, they can ensure that the signal encounters consistent resistance and capacitance. This prevents signal degradation.
- Via Design: Via plays a crucial role in connecting different layers during routing. There are different types of Vias based on the layers it connects. Blind vias and Micro vias connect only the layers needed so the stub is minimized. Stubs in vias act as an antenna causing Signal degradation. Designers need to use the right type of vias for their design to mitigate Signal Integrity issues.
Figure: The 4-Level Hierarchy for mastering signal integrity in modern hardware.
Design for Manufacturability (DFM)
Design for manufacturability is crucial for converting theoretical aspects into practical ones. It ensures that the design adheres to manufacturing rules and regulations.
With this practice, a PCB supplier optimizes the design, reducing the likelihood of errors during manufacturing. This considers various things for maintaining signal integrity in the high-speed PCB. It consists of component placement, solderability, etc.
Moreover, this also helps to identify any signal integrity issues in the early manufacturing process. This incorporates test points, accessible traces, and other features.
Signal Integrity Testing
Signal integrity testing ensures that high-speed PCBs should undergo testing to adhere to industry standards. This also ensures the signal integrity of the PCB.
TDR ensures impedance matching and provides valuable insight into the signal integrity. This sends a signal through the transmission line and analyzes the reflected signals.
BER testing is another test for signal integrity that quantifies the performance of digital signals. This allows a PCB supplier to assess and improve signal integrity. In BER testing, one should send a known bit sequence and compare the received data to the transmitted signal. This facilitates the quantitative measure of signal quality.
Shifting Left With System Technology Co-Optimization for IC Packaging
The Bottom Line!
Signal integrity is essential for better and more advanced electronic devices. While designing a PCB design board, designers should be careful of multiple factors to manage signal integrity. However, maintaining signal integrity can be challenging. So, Tessolve incorporates various strategies while providing a PCB design board in the USA.
