The Golden Rule of PCB Design
Time:2023-04-23
Views:1063
Despite the increasing integration of semiconductors and the availability of on-chip systems for many applications, as well as the increasing ease of access to powerful and out of the box development boards, many electronic product applications still require the use of custom PCBs. In one-time development, even a regular PCB can play a very important role. PCB is the physical platform for design and the most flexible component used for electronic system design of original components. This article will introduce several golden rules for PCB design, most of which have remained unchanged since the birth of commercial PCB design 25 years ago and are widely applicable to various PCB design projects. They have great guiding effects on both young electronic design engineers and more mature circuit board manufacturers.
The following content of this article introduces the ten most effective design principles that electronic design engineers should remember and practice when using design software for PCB layout design and commercial manufacturing. Engineers do not need to follow these rules in chronological order or relative importance, as they can greatly change product design by following them all.
Rule 1: Choose the correct grid - Set and always use the grid spacing that matches the most components. Although multiple grids may seem effective, if engineers can think more in the early stages of PCB layout design, they can avoid difficulties in spacing settings and maximize the application of circuit boards. Due to the use of multiple packaging sizes for many devices, engineers should use products that are most conducive to their own design. In addition, polygons are crucial for copper plating on circuit boards, and multi grid circuit boards generally generate polygon filling deviation when copper plating is applied. Although not as standard as based on a single grid, it can provide a lifespan that exceeds the required lifespan of the circuit board.
Rule 2: Maintain the shortest and most direct path. This may sound simple and ordinary, but it should be kept in mind at every stage, even if it means changing the circuit board layout to optimize wiring length. This is particularly applicable to analog and high-speed digital circuits where system performance is always partially limited by impedance and parasitic effects.
Rule 3: Use the power layer to manage the distribution of power and ground wires as much as possible. Copper coating on the power layer is a faster and simpler option for most PCB design software. By connecting a large number of wires together, it is ensured to provide the highest efficiency and minimum impedance or voltage drop current, while also providing sufficient grounding return path. If possible, multiple power supply lines can also be run in the same area of the circuit board to confirm whether the grounding layer covers most of the layers of a PCB, which is beneficial for the interaction between lines running on adjacent layers.
Rule 4: Group relevant components together with the required test points. For example, placing the discrete components required for the OpAmp operational amplifier closer to the device allows the bypass capacitor and resistor to collaborate with it on the same ground, thereby helping to optimize the wiring length mentioned in Rule 2, and also making testing and fault detection easier.
Rule 5: Repeat the required circuit board multiple times on another larger circuit board for PCB assembly. Choosing the size that is most suitable for the equipment used by the manufacturer can help reduce prototype design and manufacturing costs. Firstly, layout the circuit board 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 high or low component values but similar performance. By integrating within a smaller range of standard values, the bill of materials can be simplified and costs may be reduced. If you have a series of PCB products based on preferred device values, it is also more advantageous for you to make correct inventory management decisions in the longer term.
Rule 7: Perform Design Rule Check (DRC) as much as possible. Although running DRC function on PCB software only takes a short time, in more complex design environments, as long as you always perform checks during the design process, you can save a lot of time, which is a good habit worth maintaining. Every wiring decision is crucial, and by executing DRC, you can always be reminded of the most important wiring.
Rule 8: Flexible use of screen printing. Screen printing can be used to annotate various useful information for future use by circuit board manufacturers, service or testing engineers, installation personnel, or equipment debugging personnel. Not only should clear functional and test point labels be labeled, but also the direction of components and connectors should be indicated as much as possible, even if these annotations are printed on the lower surface of the components used on the circuit board (after assembly). Fully applying screen printing technology on the upper and lower surfaces of circuit boards can reduce repetitive work and streamline the production process.
Rule 9: decoupling capacitor must be selected. Do not attempt to optimize your design by avoiding decoupling power lines and based on the limit values in the component data sheet. Capacitors are cheap and durable, so you can spend as much time as possible assembling them, while following Rule 6 and using a standard value range to keep inventory tidy.
Rule 10: Generate PCB manufacturing parameters and verify them before submitting to production. Although most circuit board manufacturers are happy to download and verify directly for you, it is best to first output the Gerber file and use a free reader to check if it is as expected to avoid misunderstandings. By personally verifying, you may even discover some careless errors and thus avoid losses caused by completing production according to the wrong parameters.
Due to the increasingly widespread sharing of circuit design and the increasing reliance of internal teams on reference designs, basic rules similar to the above will still be a characteristic of printed circuit board design, and we believe this is crucial for PCB design. By clarifying these basic rules, developers can be very flexible in enhancing the value of their products and maximizing profits from the circuit boards they manufacture. Even beginners in circuit board design can accelerate the learning process and enhance confidence by keeping these basic rules in mind.
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