Issue link: https://resources.pcb.cadence.com/i/1534337
4. Power Plane 1: f Provides a low-impedance path for power distribution. f Paired with ground planes to create decoupling capacitance, improving power integrity and reducing noise. 5. Ground Layer 2: f This acts as a reference layer for signals on the bottom of the PCB and for the power plane below it f Stronger capacitive coupling between this layer and the power plane below. 6. Internal Signal Layer 2: f Convenient for routing high-speed signals to manage EMI and shield from outside EMI. 7. Power Layer 2: f Great coupling between this layer and Ground Layer 2, as opposed to Ground Layer 1 f Placed here avoids introducing EMI effects from signal propagation, say from Layer 1 through this Layer. 8. Bottom Layer (Signal or Power): f May be used for additional signal routing or as an additional power/ground plane, depending on design requirements. f Typically reserved for less critical signals if used for routing. Material Selection Considerations Material choice is a crucial part of stackup design, especially for high-speed PCBs, as it affects signal speed, impedance, and loss characteristics. Here are the main considerations for selecting PCB materials: 1. Dielectric Constant ('Er' or 'Dk'): f A lower dielectric constant (Er) reduces signal delay, which is beneficial in high-speed designs. f Materials with stable Er over the board's operating frequency range ensure predictable signal behavior, such as certain high-performance laminates (e.g., Rogers, Isola). 2. Loss Tangent (Df): f The loss tangent measures how much signal energy is lost as heat. Lower Df values are preferable for high-speed designs to minimize signal loss. f Common materials with low Df include high-frequency laminates like FR-408 and Megtron 6. 3. Thermal Stability: f High-speed PCBs can generate significant heat, so materials must have good thermal stability to prevent warping or dielectric breakdown. f Look for materials with high glass transition temperature (Tg) and thermal conductivity, ensuring the board performs reliably under operating conditions. 4. Cost Considerations: f High-performance materials can be more expensive, so it's essential to balance performance needs with cost constraints. f A good compromise is using an FR4 core for most layers while adding specialized low-loss materials for the high-speed signal layers. 15 www.cadence.com OrCAD X High-Speed Digital Design Guide