PCB Design Principles for Beginners

The Most Important PCB Design Principles

Ground Separation

When working on a mixed-signal design, it’s crucial to keep both analog and digital ground planes apart. Analog components ought to be grouped together on top of a dedicated ground plane. The same applies to their digital counterpart. Both ground planes must only be connected at a single point to prevent ground loops.

EMI Mitigation

Every PCB can potentially suffer from EMI or become a source of interference. As a designer, you’ll need to be cautious when working on a PCB layout. Some best practices include:

  • Increasing clearance between high-frequency traces and low-frequency or analog traces.

  • Minimizing the return path of high-speed signals and ensuring they are not crossing over a split-plane. A smaller current loop reduces the strength of EMI radiation.

  • High-speed differential signals should be routed beside each other and be equal in length, otherwise, it would negate the noise-suppression nature of differential pairs.

  • Avoiding the use of vias on high-speed traces, as they might contribute to EMI emission.

PDN Stability

A circuit on a PCB is only as good as its power delivery network. This means you’ll need to ensure that the voltage regulator module is capable of supplying the maximum current required by the load.

Besides that, the supply voltage needs to be stable and free from electrical interference from noisy components. Include a low-pass filter at the regulator’s output to help suppress high-frequency noise and add a bypass capacitor close to components like microcontrollers to prevent unwanted disruptions.

Thermal Management

With components and PCBs getting smaller, thermal management is an area that demands a designer’s attention. The use of thermal vias, heatsinks, and the placement of temperature-sensitive components are crucial to ensure thermal reliability.

Design Manufacturability

If you want to avoid issues at the assembly stage, you’ll want to ensure that the PCB is designed for manufacturability. Ensure that the component pad size is correct and fiducial markers and tooling strips are present for surface-mount designs.

SOURCE :- https://resources.orcad.com/design-reliability/2021-pcb-design-principles-for-beginners

PCB Design Layout Guidelines

Rule 1: Choose the right grid-set and always use the grid spacing that matches the most components.

Although the multi-grid seems to be effective, if engineers can think more in the early stage of PCB layout design, they can avoid the problems encountered in the interval setting and maximize the application of the circuit board. Because many devices use multiple package sizes, engineers should use the product that is most conducive to their own design. In addition, polygon is very important for circuit board copper. Multi-grid circuit boards generally produce polygonal filling deviation when polygonal copper is applied. Although it is not as standard as based on a single grid, it can provide more than the required circuit board life.

Rule 2: Keep the path shortest and most direct.

This sounds simple and common, but it should be kept in mind at every stage, even if it means to change the circuit board layout to optimize the wiring length.

Rule 3: Use the power layer as much as possible to manage the distribution of power lines and ground lines.

The power layer copper is a faster and simpler choice for most PCB design software. By connecting a large number of wires in common, it is possible to ensure that the current with the highest efficiency and minimum impedance or voltage drop is provided, while providing sufficient ground return paths.

Rule 4: Group related components together with the required test points.

Rule 5: Copy the required circuit board on another larger circuit board multiple times for PCB imposition.

Choosing the size that is most suitable for the equipment used by the manufacturer will help reduce the cost of prototyping and manufacturing. First carry out the circuit board layout on the panel, contact the circuit board manufacturer to obtain their preferred size specifications for each panel, then modify your design specifications, and try to repeat your design multiple times within these panel sizes.

Rule 6: Integrate component values.

As a designer, you will choose discrete components with higher or lower component values ??but the same performance. By integrating within a smaller standard value range, the bill of materials can be simplified and costs can be reduced. If you have a series of PCB products based on the value of the preferred component, it will be more conducive to you to make the correct inventory management decision from a longer-term perspective.

Rule 7: Perform design rule checks (DRC) as much as possible.

Although it only takes a short time to run the DRC function on the PCB software, in a more complex design environment, as long as you always perform checks during the design process, you can save a lot of time. This is a good habit worth keeping.

Rule 8: Use screen printing flexibly.

Screen printing can be used to mark various useful information for future use by circuit board manufacturers, service or test engineers, installers, or equipment debuggers. Not only mark clear function and test point labels, but also mark the direction of components and connectors as much as possible, even if these comments are printed on the lower surface of the components used on the circuit board (after the circuit board is assembled). The full application of screen printing technology on the upper and lower surfaces of the circuit board can reduce repetitive work and streamline the production process.

Rule 9: Decoupling capacitors must be selected.

Don't try to optimize your design by avoiding decoupling the power lines and based on the limit values ??in the component data sheet. Capacitors are inexpensive and durable. You can spend as much time as possible to assemble the capacitors. At the same time, follow Rule 6 and use the standard value range to keep your inventory tidy.

Rule 10: Generate PCB manufacturing parameters and verify them before submitting for production.

Although most circuit board manufacturers are happy to download it directly and verify it for you, you'd better output the Gerber file yourself and check whether it is the same as expected with a free viewer to avoid misunderstandings. Through personal verification, you may even find some negligent errors, and therefore avoid losses caused by completing production according to the wrong parameters.