PCB Layout Design: An Extensive Guide for Beginners

Introduction:

PCB layout provides an extensive design showing the location of electronic components, such as resistor, capacitor, and integrated circuit (IC). It is a complex arrangement that maintains the operations of an electronic device. PCB layout design requires a deep understanding of electronic components, circuit theories, and design principles.

Creating a PCB layout requires careful design and implementation. The first step is to generate a schematic diagram that is a symbolic representation of the circuit. The objective of this diagram is to show the connections of all the components in a circuit. The schematic acts as the guide for the PCB layout that is a physical view of the circuit. After the completion of the schematic, it needs to be converted into a PCB layout. PCB layout is related to the position of components, routing the interconnections and complying the design according to the industry standards and guidelines.

The main content of printed circuit design is the layout design. PCB layout design is complicated and rigorous and it needs high consideration of some important factors, such as component location, signal reliability, thermal management, and electromagnetic interference. In this article, we will discuss PCB layout design techniques and rules, advantages of CAD tools for layout design and challenges of layout design in detail.

 

Figure 1: PCB Layout Design

PCB Layout Design:

• Schematic Capture: Specialized software, known as Schematic Capture, is used to create an electronic schematic diagram of a circuit. It displays the logical connections and operations between the components. Schematic capture helps to visualize the design of the circuit and ensures that the connections between components are correct.

• Component Placement: Component Placement is the technique that is used to locate the electronic components on the PCB. The purpose of component placement is to generate an effective circuit board that will meet the electrical and mechanical issues of the PCB layout design. Some of the essential considerations for component placement are adjustment, signal flow, thermal management, mechanical issues, assembly process and electrical performance.

• Routing: Routing is related to the connection of electronic components on the PCB.  Some of the important considerations for routing in PCB layout design are improvement of the space and width of traces, enhancing signal integrity, minimization of voltage drop and noise, topology of the circuit, component placement and maintaining the design rules. 

 

Figure 2: Routing of electronic components on PCB

• <h3>Ground Plane: < /h3>A ground plane is a large copper plane on a PCB layout and a part of the design. The size, shape and placement of the ground plane can be improved according to the electrical and mechanical requirements of the circuit design. Some of the advantages of a ground plane are in the followings:

1. Ground plane can create a low-impedance path.

2. It can be used as a shield in EMI reduction.

3. Signal integrity can be improved by reducing the interference.

4. Routing of signals can be simplified.

5. Ground plane reduces the dissipation of heat.

• Power Supply: Power Supply is an important component of PCB layout design. It can provide the required amount of voltage and current to the components.

• Design Rule Check: Design Rule Check or DRC is used in PCB layout according to the well-defined design rules. PCB uses DRC to recognize and solve the problems before manufacturing. DRC minimizes the risk of errors and enhances the overall quality of the final product.

• Generation of Output Files: PCB layout software provides the output files that are used by the manufacturer to create the PCB. Gerber Files, NC Drill Files, Bill of Materials, Assembly Drawings, and 3D Models are some of the output files generated in the PCB layout design process.

• Fabrication: Fabrication is a process of creating the actual PCB from the design file. Some of the important steps in the fabrication process are imaging, etching, drilling, plating, and testing. After the fabrication and testing of the PCB, it becomes prepared for assembly so that the components can be mounted and soldered onto the board.

Principles of PCB Component Layout:

Some of the principles of the PCB component layout have been mentioned below:  

• Components should be evenly distributed and packed on the board. They need to be located on the surface of the board. The board around the edge is supposed to leave some space. Components located on the edge of the printed circuit board are required to be greater than 3 mm away from the edge of the PCB.

• Components are required to be placed on one side of the PCB, and each component of the lead pin should have a different pad.

• The layout of the components should not be crossed up and down. It is important to keep a minimum distance between the two nearest components. If there is a high potential difference between the nearest components, a minimum distance should be kept for safety. The safety voltage for the gap is usually 200 V/mm.

• The lead of components need to be within 5 mm of the board for the stability against vibration.

• The axis of the component direction is chosen according to the location of installation in the PCB.
  
  
  

Figure 3: Component layout direction

PCB Layout Software:

PCB layout software is an important tool to design including the location of components and routing of traces. It can verify design rules, simulate circuit performance, and create files for manufacturing.

• Advantages of PCB Layout Software:

1. Component Placement: PCB layout software has the capacity to generate and maintain a library of components. The library integrates the physical dimensions, pin architectures, and other specifications of each component. This software can place the components on the PCB layout automatically for accurate alignment and spacing.

2. Routing of Traces: PCB layout software can route traces automatically between components according to the schematic diagram following design rules like minimum trace width and clearance. This software emphasizes spaces of probable interference or violation of design rules to make required changes.

3. Performance of the circuit: PCB layout software integrates simulation tools to predict the performance of the circuit. Simulation tools are used to find out the flow of current, propagation of signals and generation of heat. Simulation helps to recognize the possible errors before the PCB is manufactured. This software produces the files to be applied for manufacturing the PCB. The Gerber files specify the layout of the traces and components, and the drill files show the positions of holes for through-hole components and vias.

• CAD and Simulation Tools for PCB Layout: CAD and simulation tools are very useful to make a high-quality and reliable PCB. Skills and expertise required to make an efficient PCB can be developed through the deep understanding of the key concepts and challenges of CAD tools. 

1. CAD Tools: Computer-aided design (CAD) tools are special software for PCB layout that provides higher capacities for designing and simulating PCBs.  Accurate regulation over components and trace location as well as simulation characteristics for circuit behavior analysis can be performed through the application of CAD tools. CAD tool features include 3D PCB modeling for advanced visualization and assistance for mechanical design. CAD tools provide complicated routing characteristics, complex trace designs and multi-layer routing to improve signal reliability and performance.  These tools produce complete manufacturing files that include Gerber files, drill files, and assembly drawings with accurate direction for PCB production.

2. Simulation Tools:The purpose of advanced simulations is to optimize performance and reliability of PCB through the assessment of circuit characteristics under various conditions, such as temperature, voltage, and frequency variations. Simulation tools play a crucial role in the PCB design process to predict the performance of the circuits and recognize possible errors before manufacturing. These tools can simulate various factors of the circuit, such as signal integrity, power distribution, and thermal performance.

•  Advantages of using CAD software for PCB Design: Most PCB designers apply advanced computer-aided design (CAD) software systems to create their PCB. Using this software can help solve many of the layout errors. Some of the advantages of using these software systems include:

1. Design Process: CAD software can drag and drop components in a design and generate the traces. This technique can boost up  the efficiency and preciseness of the design method.

2. Design Validation: The design needs to be  tested using a CAD system for tolerances, adaptability, component placement and other factors before sending the design to the manufacturing stage.

3. Manufacturing File Generation: Gerber files and other file formats can be generated for sending to the manufacturer. Generating these files directly from the design software can improve their accuracy.

4. Documentation: CAD software systems can be used to create and save detailed documentation regarding component use, errors, design, version control and more.

5. Higher Efficiency and Minimized Cost: Integration of CAD tools into operations can improve the efficiency and accuracy of the design process that will minimize overall costs.

Figure 4: PCB Layout with routing traces.

Challenges of PCB layout:

Designing a PCB layout can be complex and challenging due to some issues. Some of the key challenges have been discussed below:

• Signal Reliability: High-speed signals can be prone to deterioration due to some issues, such as reflection, crosstalk, and signal degradation. Some important matters, such as routing of traces, application of termination techniques, choice of appropriate elements, should be considered for the maintenance of signal integrity for the PCB layout.

• Component Placement:  The location of components on the PCB layout has a major effect for the execution and reliability of the circuit. During the placing of components, some important factors, such as signal integrity, thermal management, and electromagnetic interference should be considered.

• Electromagnetic Interference (EMI): EMI can generate unexpected noise and signal deterioration in a PCB. Careful routing traces, using shielding methods and proper grounding should be done to minimize EMI for better layout design.

• Thermal Interference: Heating and temperature sensitive components need to be analyzed and identified for the design of PCB layout.

• Assembly: Some important factors, such as trace width, via size, and component tolerance, need to be considered to ensure that the PCB can be assembled without errors. A successful PCB design is required to be manufactured with efficiency and cost-effectiveness.

• Design Rule Check (DRC): PCB design is required to follow the established design rules that are very important for reliable performance and preventing manufacturing errors.  DRC tools have to be used to verify any violation of design rules before the PCB is manufactured.

• Cooperation: PCB design heavily relied on good collaboration among electrical, mechanical and manufacturing engineers. To ensure the proper design and potential errors of PCB design, effective cooperation and communication are very essential.

Conclusion:

The first step for designing a PCB is to create a logical layout of electronic components on a certain board area. It is important to create a reasonable layout of the components and their connections on the PCB in order to make the whole machine work in a stable and reliable way. The layout design is not about making connections of components through printed lines based on circuit principles. Various interferences may happen if the layout is not reasonable. The quality and functionality of manufactured PCB is highly controlled by the quality of the PCB layout design.