PCB Design Fundamentals
Early circuit board designs relied on through-hole structures, followed by surface mount technology (SMT). For decades, designs were drawn by hand, making manufacturing slow and costly. The introduction of computers revolutionized the entire design process, accelerating production and improving product consistency and functionality. Today, manufacturers use simulation software for PCB design to model, analyze, and validate their designs at every stage of development. Challenges in PCB design include size constraints, thermal factors, electromigration, mechanical integration, and power efficiency. These complexities require designers to collaborate with experts from different fields to ensure that electrical, mechanical, and thermal engineering issues are addressed throughout the process. Below is a summary by the Geyuan Electronics team of the fundamentals of modern high-precision printed circuit board design.
PCB basics
Before starting a PCB project, you need to understand what a PCB is and how it works. A PCB uses copper wires to connect components. These copper wires act like conductors. PCBs are typically made of non-conductive materials such as fiberglass and have layers of conductive copper foil. Different types of substrates are used for PCBs; some are single-sided, meaning the copper wires are only on one side. Others are double-sided or multi-layered, such as a 6-layer printed circuit board. More layers mean more space for complex circuits and better signal integrity. You should choose the type based on your project requirements, taking into account factors such as the PCB stack-up configuration and interlayer dielectric thickness.
Generally, every printed circuit board (PCB) has several key components. These include the substrate (bottom layer), copper layers, solder mask, and silkscreen layers. The solder mask protects the copper layers from damage. Silkscreen printing displays labels and part numbers. In more complex designs, such as 6-layer PCBs, you’ll find multiple signal layers, power planes for better power distribution, and ground planes for noise reduction. These reference planes play a crucial role in maintaining signal integrity and reducing power supply noise. Designing a PCB also involves placing components in the correct locations. Good component placement helps reduce interference and improve performance. You also need to plan how you connect components via traces, considering trace widths and wiring density. Clear connections help circuits function better, especially when handling high-speed signals and differential pairs.
What are the key elements of understanding the PCB design workflow?
To design a PCB layout that meets mass production requirements in terms of both quality and layout, it’s best to take some time to familiarize yourself with the standard workflow. Regardless of the type of PCB you’re designing, understanding the fundamental design standards and processes is crucial to ultimately creating a mass-producible design. The typical PCB design workflow follows these steps:
- Select core components that are in stock and can be sourced from major distributors.
- Create and review schematic diagrams according to project requirements.
- Create a blank PCB, build the layer stack and create design rules.
- Import component data from the schematic into the new PCB layout.
- Place components and review the placement to ensure it meets engineering requirements.
- Wiring traces and connections between components
- Clean up the PCB layout and perform final design review
- Prepare design outputs and send them for manufacturing.
- After gaining a high level of understanding of the design process, please read the following link to learn how the PCB design workflow unfolds and the standard set of tasks that each designer must perform to complete a new circuit board.
Specific tasks in the PCB design process
Printed Circuit Boards (PCBs) are among the most familiar things to electronic engineers. PCBs help engineers connect various electronic components and chips to form a stable and reliable circuit structure. PCB design is a major subject at any stage of an electronic engineer’s career. While PCB manufacturing technology and related technologies are constantly advancing, with new devices, packages, and materials emerging, PCB design, production, and testing technologies are also changing accordingly. However, regardless of how these technologies change, they cannot escape the basic design principles of PCBs. We have summarized the basic steps of PCB design as follows.
Schematic creation
Designers use computer-aided design (ECAD) software to create 2D blueprints of PCBs to determine PCB components, component layouts, and their connections.
Material selection
Designers select materials for the circuit board based on the final assembly requirements. Material choices include FR-4, polyimide laminates, composite epoxy resins (CEM), and liquid crystal polymers.
Design review
Before production, simulation software is used to test and verify the performance of the circuit board under various conditions. These tests ensure that the component layout meets all requirements.
Schematic Design
This is the starting point for PCB fabrication. Based on the functional requirements of electronic products, engineers use professional circuit design software (such as Altium Designer, Cadence Allegro, etc.) to draw circuit schematics. The schematics clearly show the electrical connections between various electronic components, including the selection and layout of components such as resistors, capacitors, chips, and inductors, ensuring that the circuit can achieve the expected functions, such as signal amplification, filtering, and data processing.
PCB layout design
After completing the schematic design, the layout phase begins. Designers need to place the components from the schematic onto the PCB board rationally, considering numerous factors. On one hand, they must follow the signal flow of the circuit to minimize signal transmission paths and interference; for example, separating high-frequency and low-frequency circuits to avoid mutual interference. On the other hand, they must consider the physical dimensions, mounting methods, and heat dissipation requirements of the components; sufficient space must be reserved for high-power components to prevent overheating and damage. The rationality of the layout directly affects the PCB’s performance, manufacturability, and the difficulty of later debugging.
Cabling design
Routing is a crucial step in PCB design. Based on the layout, engineers plan the connection lines between various components on the PCB board. Routing must follow certain rules. For example, the trace width should be set appropriately according to the current; generally, high-current traces have wider trace widths to reduce resistance and prevent overheating. The trace spacing must meet electrical safety requirements to prevent short circuits, especially in high-voltage areas where trace spacing must be strictly controlled. Furthermore, for high-speed signal lines, special routing techniques, such as serpentine traces, are used to match signal delays, ensure signal integrity, and reduce signal attenuation and reflection.
Design Rule Check (DRC)
After completing the PCB layout and routing, a rigorous DRC (Design for Control) process must be performed. DRC software comprehensively checks the design documents based on pre-defined industry standards and manufacturing process requirements, including whether parameters such as trace width, trace spacing, via size, and pad size comply with regulations. If any non-compliance is found, such as traces that are too narrow and may cause open circuits during production, the software will promptly prompt the designer to make modifications, ensuring that the design can be successfully translated into the actual product.
Don’t forget that your ultimate goal in designing a PCB is production.
Even after all components in the layout have been routed and finalized, your work is not yet complete. As a designer, you need to create manufacturing files based on the PCB layout. PCB design software includes tools that automatically create these output files. Even after the output is ready, you should still check these files to ensure that no settings in the output file exporter have been incorrectly applied, so take some time to review everything before sending it to the manufacturer.
Finally, once you have completed all the design work, the next step is the manufacturing phase. You will need to have your design drawings reviewed by an experienced manufacturer to ensure they meet their mass production capabilities. If everything passes the final DFM review, your circuit board will enter the production and assembly phase.
Final determination and manufacturing of printed circuit boards
Once the PCB design is complete, it’s time to prepare for PCB production. First, export the design files. These files, known as Gerber files, tell the factory how to manufacture the circuit board, including details such as drill hole dimensions and board thickness. Most software has a built-in export tool.
Make sure to include all necessary files. These files typically include the top copper layer, bottom copper layer, solder mask, silkscreen layer, and drill file. For multilayer boards (such as a 6-layer PCB), you will also need to include files for the inner layers and power layers. Some tools will create a compressed file containing all of this information.
Secondly, choose a PCB manufacturer. Many online services accept Gerber files and offer fast delivery. You simply upload the file, select the board size, thickness, and color, and then place an order. For complex designs, discuss with the manufacturer their ability to control impedance and layer coupling.
Upon receiving the circuit boards, inspect them for defects. Ensure all components appear correct, including outer layers and any special functions such as differential pairs. Then, you can solder the components. Solder slowly and carefully. Use a multimeter to check connections if necessary, paying particular attention to power and ground connections. Now your printed circuit board is complete. You can test it and use it in your projects.
The relationship between PCB design and manufacturing
Once you’ve designed your desired PCB layout, any design you intend to produce as a physical product should be mass-producible. ECAD software will allow you to implement virtually any imaginable design functionality within the PCB layout. However, your design decisions need to be manufacturable within standard processes, so designers need to be familiar with the manufacturability limitations of PCBs.
This means every PCB designer should take the time to learn the fundamentals of PCB manufacturing to ensure their designs are fully manufacturable. This involves a set of important practices that should be included in the design process: Design for Manufacturability (DFM). Take the time to understand some basic design mistakes that can derail manufacturing and cause your boards to be returned for redesign before production.
Therefore, the process of manufacturing a PCB is very complex. It begins with a conceptual product and ends with the actual PCB assembly. First, a schematic diagram is created to outline the circuit connections. Then, the PCB designer lays out the circuitry to enhance characteristics while adhering to design constraints. This entire process is crucial to ensuring the effectiveness and reliability of the PCB. Every stage, from design to assembly, plays a role in creating a recessed printed circuit board that conforms to specified standards.
PCB design techniques
Different settings are required at different stages of the design process. In the layout stage, a large grid can be used for component placement. For large components such as ICs and non-positioning connectors, a grid precision of 50-100 mil can be used, while for small passive components such as resistors, capacitors, and inductors, a grid precision of 25 mil can be used. Larger grid precision is beneficial for component alignment and layout aesthetics. In high-speed routing, we generally use millimeters (mm) as the unit, but mils are more commonly used. Furthermore, in high-speed PCB design, the continuity of controllable impedance boards and line impedance is a crucial issue. A common approach is to ensure that adjacent layers of signal lines have a complete GND plane or power plane.
Choose Geyuan Electronics as your partner for your next PCB project
At Geyuan Electronics, we understand the crucial role PCBs play in your projects. Therefore, we offer end-to-end solutions from PCB manufacturing and assembly to testing and custom enclosures to meet the needs of industries such as telecommunications, medical devices, automotive, and consumer electronics. With sophisticated engineering and a commitment to quality, we are dedicated to helping you turn your concepts into reality. Contact us today to learn how we can power your next great idea with reliable, high-performance PCBs.
Summarize
Understanding PCB manufacturing processes is crucial for ensuring the high quality and functionality of electronic components. From initial design and material selection to complex processes such as etching, electroplating, and testing, each step plays a vital role in the performance and reliability of the final product. By using the right design software, understanding the detailed steps involved in manufacturing, and gaining a deep understanding of testing and quality control, you can better solve problems and optimize manufacturing processes. This comprehensive knowledge also helps in selecting the best PCB assembly manufacturers, understanding customization options, and effectively managing costs. Ultimately, a deep understanding of PCB manufacturing processes leads to more reliable products and more efficient production.
Because PCB design is a highly meticulous task, it requires extreme care and patience, fully considering all factors, including manufacturing, assembly, and ease of maintenance. Furthermore, developing good design habits will lead to more rational designs, higher efficiency, easier production, and better performance. Good designs, when applied to everyday products, will give consumers greater confidence and trust.