PCB News - Ten Principles of PCB Layout Design

Although the current level of semiconductor integration is getting higher and higher, many applications also have system-on-chips available at any time, and many powerful and out-of-the-box development boards are becoming more and more easily available, but the application of electronic products in many use cases Still need to use custom PCB. In one-time development, even an ordinary PCB board can play a very important role. PCB is the physical platform for design and the most flexible part for electronic system design of original components. This article will introduce several golden rules of PCB design. Most of these rules have not changed since the birth of commercial PCB design25 years ago, and they are widely applicable to various PCB design projects, whether for young electronic design engineers or more mature ones. Circuit board manufacturers have a great guiding role.

The following content of this article introduces the ten most effective design rules that electronic design engineers should keep in mind and practice when using design software for PCB layout design and commercial manufacturing. Engineers do not need to execute these rules in order of chronology or relative importance. They only need to follow all of them to greatly change the product design.

Rule 1: 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 rugged. 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 2: 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 3: 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 can maximize the application of the PCB board. Because many devices use multiple package sizes, engineers should use the product that is most conducive to their own design. In addition, polygons are very important for circuit board copper. Multi-grid circuit boards generally have polygonal filling deviations 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 4: Group related components together with the required test points.

For example: placing the discrete components required by OpAmp operational amplifiers closer to the device so that bypass capacitors and resistors can cooperate with them in the same place, thereby helping to optimize the wiring length mentioned in the second rule, while also enabling testing and fault detection It becomes more convenient.

Rule 5: 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 changing the circuit board layout to optimize the wiring length. This is especially applicable to analog and high-speed digital circuits whose system performance is always partially limited by impedance and parasitic effects.

Rule 6: 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 the smallest impedance or voltage drop is provided, and at the same time, an adequate ground return path is provided. If possible, you can also run multiple power supply lines in the same area of the circuit board to confirm whether the ground layer covers most of a certain layer of the PCB, which is conducive to the interaction between the running lines on adjacent layers.

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. Every wiring decision is critical, and you can be reminded of the most important wiring at any time by implementing DRC.

Rule 8: Copy the required circuit board multiple times on another larger circuit board 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 9: 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, it is best for you to output the Gerber file first and use a free viewer to check whether it is as expected 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.

Rule 10: 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). 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.

As circuit design sharing becomes more and more widespread, and internal teams rely more and more on reference designs, basic rules similar to the above will still be a feature of printed circuit board design. We believe this is very important for PCB design. With these basic rules clarified, developers can increase the value of their products very flexibly and get the most benefit from the circuit boards they manufacture. Even a novice circuit board designer can speed up the learning process and increase confidence as long as these basic rules are kept in mind.