PCB Technical - PCB design and commercial manufacturing rules

This article will introduce 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: Choose the right grid-set and always use the grid spacing that can match the most components. Although multi-grid seems to be effective, if engineers can think more in the early stage of PCB layout design, they can avoid problems encountered in spacing settings and maximize the use of circuit boards. Since 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 service life of the circuit board. .

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 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 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 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 4: Group related components and required test points together. For example: placing the discrete components required by OpAmp operational amplifiers closer to the device so that bypass capacitors and resistors can work 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: 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 the design specifications, and try to repeat the 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 checking (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, always performing checks during the design process can save a lot of time, which is a good habit worth keeping. Every wiring decision is critical, and the most important wiring can be prompted at any time by executing DRC.

Rule 8: Flexible use of screen printing. 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.

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 ten: Generate PCB manufacturing parameters and verify them before submitting for production. Although most circuit board manufacturers are happy to download and verify directly, it is best to output the Gerber file first and use a free viewer to check whether it is as expected to avoid misunderstandings. Through personal verification, some negligent errors may even be found, and thus avoiding losses caused by completing production according to the wrong parameters.