Design the PCB stackup layers to eliminate impedance buildup and shunt RF energy to chassis. Mitigate RF energy with a floorplan that discourages unwanted impedances and unnecessary materials such as excessive copper weight thickness.
When unwanted impedance builds onto nets greater than that of air, RF energy takes the path of least resistance and emits into free space.įinetune signal characteristics per layer during route Incorporate Layers that Avoid Discontinuities and Loops ICs and interfaces with other materials cause mismatches that build unwanted impedance also leading to generation of RF currents. Whether it’s a single standard PCB thickness board, multiple boards, multilayer PCB, or a design where your primary concerns are the PCB traces, holes, and pads involved, impedance can always be an issue. Loops give opportunity for switching currents to produce RF energy into the air. Impedance builds as inductance on windings of inductors and on the leads of discretes such as resistors. RF currents develop when unwanted impedances build within the Printed Circuit Board during design. The root cause of noise in a PCB is development of RF energy across unwanted impedances throughout the PCB stackup. Design PCB Layers to Minimize Unwanted RF Energy Development Ground fill between traces on outer layers with plenty of ground stitches provide return paths and mitigate creation of loop currents. Further routing techniques incorporate aspect ratio for chassis ties with ground stitches between each. Less sensitive traces at low risk for coupling through air are best routed microstrip on the outer layers of the Printed Circuit Board. High-speed traces are best routed stripline to take maximum advantage of both shielding and of flux cancellation on the inner layers with adjacent ground planes. Intentional routing continues best practice layer stackup design for signal integrity. Minimizing spacing between conductive layers increases flux cancellation. Including a ground plane next to each signal plane enhances flux cancellation and removes noise. Signal planes should always have a ground plane adjacent in the PCB stackup. Maximum capacitive decoupling in the power distribution network is achieved by placing power planes directly adjacent to ground planes in the layer stackup (see figure above). The PCB layer stackup may be designed to incorporate features useful to maintaining signal integrity. Noise presents itself as reflections, ringing, or crosstalk. RF energy gets into the power distribution network or emits into free space as noise. Common-mode currents are the primary source of RF energy. RF currents are generated through unwanted impedances built in the material giving opportunity to generate common-mode currents. Signal integrity occurs when RF current generation is avoided with careful organization of the layers.
When considering how to determine PCB layers stackup, the best practices is to prioritize signal integrity. Use inner layers with adjacent ground planes for clocks Professional PCB design tool with proficient PCB layer stackup management.