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PCB Layout Design Process and Guidelines

Over 25% of the Gerber files we receive have various types of problems such as ambiguous or missing information, conflicting design rules, and conflicting data specifications. We recommend that you use our PCB design guidelines as a checklist to ensure that your design is correct and, if possible, work with your PCB supplier as early as possible in the pre-design phase.

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The development of a PCB layout is analogous to the completion of a work of art. To create something really one of a kind, it might take engineers days, weeks, or even months to design these patterns. On the other hand, you don’t need to be an engineer to design an accurate PCB layout; you can do it yourself.

This article was written specifically for you in case you have no idea how to get started. It covers the fundamentals of PCB layout, the design process, and many variables to consider while designing a PCB layout.

Beginning the process of constructing a PCB layout may first appear to be intimidating; however, if you start with simple designs and give yourself plenty of time to practice, you will quickly learn that you will soon become an expert.

Fundamentals of PCB Design

What is PCB Layout?

A PCB layout is the arrangement of various components on a printed circuit board (PCB). It is a crucial step in the design of electronic circuits, as it determines how the components will be physically connected and how they will interact with one another.

In a PCB layout, components such as resistors, capacitors, transistors, and integrated circuits are placed on the PCB in a specific pattern to create the desired circuit. The layout also includes the routing of the traces, which are the conductive pathways that connect the components and allow electricity to flow through the circuit.

The layout of a PCB is typically created using CAD software, which allows the designer to position the components on the PCB, specify the connections between them, and automatically generate the routing for the traces. The resulting layout is then used to create a physical PCB through a process called PCB fabrication.

PCB Layout Design: The Schematic

Essential Elements of a PCB Layout

Component:The circuit components, such as integrated circuits (ICs), resistors, capacitors, connectors, and other electronic devices, are placed on the PCB layout. Each component has specific electrical and mechanical requirements that need to be considered during placement.

Traces: Traces, also known as tracks or conductive pathways, are copper lines that connect the components on the PCB layout. Traces carry electrical signals and power between different parts of the circuit. They are routed to provide proper signal integrity, minimize interference, and ensure electrical connectivity.

Pads and Via Holes: Pads are metalized areas on the PCB where components are soldered or surface-mounted. They provide electrical connections between the components and the PCB traces. Via holes are plated holes that connect different layers of the PCB, allowing traces to pass through.

Copper Layers: PCBs consist of multiple copper layers. These layers are typically sandwiched between insulating layers of the PCB substrate material. The copper layers provide the conductive pathways for the traces, power planes, and ground planes within the PCB.

Power and Ground Planes: Power planes are large areas of copper on the PCB dedicated to carrying power supply voltages. Ground planes are similarly large copper areas that provide a low-impedance return path for current flow. These planes help distribute power and maintain signal integrity, reducing noise and voltage drops.

Designators and Annotations: Designators, such as reference designators and part numbers, are labels associated with each component on the PCB. Annotations may include additional notes, comments, or specifications to aid in the understanding and assembly of the PCB.

Keep-Out Zones: Keep-out zones are designated areas on the PCB layout where components, traces, or other elements should not be placed. These zones ensure proper clearance for mechanical considerations, prevent electrical interference, and maintain safety standards.

PCB Layout vs PCB Design

PCB Layout and PCB Design are closely related terms but refer to slightly different aspects of the overall process of creating a printed circuit board (PCB).

PCB Layout refers to the physical arrangement and placement of electronic components, traces, and other elements on a PCB. It involves determining the optimal location and orientation of components, designing the routing paths for electrical connections (traces), and considering factors such as signal integrity, thermal management, and manufacturability. PCB Layout is primarily concerned with the spatial arrangement and interconnection of components on the board.

On the other hand, PCB Design encompasses a broader scope that includes both the PCB Layout and the schematic design. PCB Design involves creating a schematic diagram, which is a graphical representation of the circuit functionality and interconnections, and then translating that schematic into a physical layout on the PCB. It encompasses the entire process of designing the circuit, planning its layout, and preparing the PCB files for manufacturing.

EDA Tools for PCB Design

Electronic Design Automation or EDA is the group of software tools used for the design and testing of printed circuit boards. EDA tools are used to generate the physical layout of an electronic device through the specifications of placing of each component on the board. The preciseness of the designs, verification of errors and meeting manufacturing standards can be done through the use of EDA tools. The five most important EDA tools for designing a PCB are as follows:

  1. Altium Designer: Altium Designer is a comprehensive PCB design software that offers schematic capture, PCB layout, 3D modeling, signal integrity analysis, and manufacturing outputs. It provides an integrated environment for designing complex PCBs with a user-friendly interface.
  2. Cadence Allegro: Cadence Allegro is a powerful EDA tool suite that includes schematic entry, PCB layout, signal integrity analysis, power integrity analysis, and manufacturing preparation features. It offers advanced capabilities for high-speed and high-density designs.
  3. Mentor Graphics PADS: PADS by Mentor Graphics is a popular PCB design software that provides schematic capture, layout design, constraint management, signal and power integrity analysis, and manufacturing outputs. It offers an intuitive interface suitable for both beginners and experienced designers.
  4. KiCad: KiCad is an open-source EDA tool suite that offers schematic capture, PCB layout, 3D modeling, and extensive component libraries. It is widely used for hobbyist projects and small-scale PCB designs and provides a cost-effective option for PCB design.
  5. Autodesk Eagle: Autodesk Eagle is a popular PCB design tool known for its ease of use and accessibility. It provides schematic capture, PCB layout, 3D modeling, and extensive component libraries. It is widely used by hobbyists, makers, and small-scale design projects.

These are just a few examples of the EDA tools available for PCB design. The selection of the tool depends on factors such as the complexity of the design, required features, budget, and personal preference. It’s advisable to evaluate the specific needs of the PCB project and explore the features, licensing options, and support provided by different EDA tool vendors before making a choice.

Process of PCB Layout Design

From the time you realize you need a PCB until the moment you ship the completed product, PCB layout design is an integral part of the printed circuit board manufacturing process. There are 5 stages involved in the fundamental PCB layout design process.

PCB Layout Design Flow
PCB Layout Design Flow

Stage 1: Initial Concept

Initial concept, which comes after confirming that a PCB or a PCB service is required, is to settle on a definitive concept for the board. During this first step, the functions that the PCB will have and execute, its characteristics, its interface with other circuits, its placement in the final product, and its approximate dimensions will all be defined. In addition to this, you should think about the temperature range that the board will function in approximately, as well as any other environmental considerations.

Stage 2: Schematic Design

The following step is drawing the circuit diagram or schematic based on the final concept that was chosen. This diagram contains all the information required for the electrical components of the board to work correctly. Included in this diagram are particulars such as the names of the components, their values, their ratings, and the manufacturer part numbers.

You will generate the bill of materials concurrently with the creation of the schematic you will be using. This bill of materials (BOM) provides details on all the components that must be included on your PCB. Always make sure that these two papers have the most recent information.

PCB schematics design

Stage 3: Component Placement

The last stage PCB Layout design is called component placement, and it involves deciding where on the board you will put each individual part. In many cases, you might have to go through numerous iterations of tweaking the location of components. Correct orientation and suitable location selection are key considerations in this stage.

PCB Component Placement

Stage 4: Routing and Testing

Next, determine the routing and the routing priority for the circuit. After you have finished the design, you should put it through a battery of testing to confirm that it satisfies all your requirements. If it does, then the design process is finished. If this is not the case, you will be forced to restart the phases during which you are required to make corrections.

Stage 5: DRC / DFM

Design Rule Check (DRC) is an important stage in the PCB design process to fill up manufacturing and performance requirements.
– Trace width and clearance: It includes the validation of the trace widths and clearances to meet the manufacturer’s requirements.
– Component spacing: One of the main objectives of DRC is to ensure accurate spacing between components is an important criterion of DRC.
– Silkscreen and solder mask clearance: For flexibility and adjustment, DRC is applied for checking the silkscreen and solder mask layers.

Design for Manufacturability (DFM) check is aimed at ensuring that the PCB design can be efficiently and accurately manufactured. This process is critical for lowering the risk of production difficulties, cutting expenses, and then create a better product at the lowest price. The DFM check includes many critical aspects and processes:

– Verify placement: This stage ensures that components are laid out on the PCB layout in a way that allows for efficient assembly while minimizing mistakes. It’s also vital to check the pad size of components and the space between them.
– Check vias: ensure robust connections and withstand the manufacturing process.
– Avoid acid traps: When routing PCB traces, sharp angles should be avoided since they can cause serious complications when cleaning etching chemicals off the board, resulting in a loss in trace thickness. Making ensuring that the angles between the tracks are always less than 90 degrees prevents traces from delaminating off the board during PCB fabrication.

Below is a table showcasing common violations of Design for Manufacturability (DFM) principles and their contributing factors:

IssueFactors
Inappropriate trace width and spacing
  • Failure to consider manufacturing process tolerances
  • Improper material selection
  • Inadequate rule checks
Unreasonable component placement
  • Dimensional tolerances
  • Poor layout planning
  • Design tool limitations
Incorrect hole sizes
  • Failure to consider manufacturing tolerances
  • Incorrect hole specifications
  • Inadequate rule checks
Impedance control issues
  • Failure to consider manufacturing tolerances
  • Material characteristics
  • Wiring rules
Solder pad design problems
  • Inadequate rule checks
  • Inappropriate solder pad dimensional tolerances
  • Improper material selection
Improper material selection
  • Insufficient understanding of material properties and manufacturing requirements
  • Material selection constraints
Manufacturing process limitations
  • Insufficient knowledge of manufacturing processes and techniques by design personnel
  • Lack of collaboration with manufacturers
Electromagnetic compatibility issues
  • Improper grounding design
  • Inadequate consideration of layout ground wires and power planes

Design Considerations for PCB Layout

When it comes to the layout and design of PCBs, there are a lot of things to considerate. Certain factors should be considered throughout the entirety of the procedure, while others are relevant just to certain phases. The following are seven important considerations to keep in mind:

PCB Board and Number of Layer

The restrictions that are related with the bare board should be the very first ones that you investigate. The dimensions of the board as well as its contours are examples of these fundamental limitations.

You will need to make sure that there is sufficient space on the board for the circuit. The size of the final product, the functionality that the board must give, and several other criteria all contribute to the determination of how big the board ought to be. The size of electronic items and the circuit boards that they integrate may be expected to continue their downward trend. Make an educated guess about the dimensions of the board before beginning the design process. If you do not have sufficient room for all the functionality that is necessary with a design that is more basic, you may be obliged to employ a design that is either multilayer or high-density interconnect (HDI).

PCB Layout and Board Sizing
PCB Layout and Board Sizing
Multilayer PCB Design
Multilayer PCB Design

The typical PCB takes the form of a rectangle. This continues to be, by a significant margin, the most popular form for PCBs. However, it is possible to construct boards in a variety of alternative formats. PCB designers typically use this due of size restrictions or because the board will be used in goods with an irregular form.

Another essential aspect to consider is the number of layers that will be required, the number of which will be determined by the power levels and the intricacy of the design. It is in your best interest to determine how many you require early in the process of designing the plan. It’s possible that adding additional layers could drive up production expenses but doing so will let you incorporate more tracks. It’s possible that more complicated boards with more extensive capabilities will require this.

When making layer transitions for high-current routes, always be sure to use a minimum of two vias. The utilisation of numerous vias at layer transitions results in an increase in reliability, an improvement in thermal conductivity, and a reduction in both inductive and resistive losses.

Manufacturability and Installation

You should also think about the manufacturing procedures that you want to use to create the board that you want to make. The limitations and restrictions that come with various procedures vary from one another. On the circuit board, you will need to make use of reference holes or points that are compatible with the manufacturing process. Always check to see that the holes are free of any components.

Additionally, take in mind the technique of installing the board. It’s possible that certain strategies will need you to leave different parts of the board unexplored. Utilizing several types of technology, such as through-hole and surface mount components, might result in a rise in the price of your boards; nonetheless, this approach may be essential in some circumstances. Always be sure to check with your fabricator to ensure that they can build the sort of board you want by asking them directly. Some companies, for example, might not be able to build circuit boards with a flexible design or with a design that contains several layers.

Component Organization

By systematically arranging your components in a way that makes sense, you may cut down on the number of steps that are necessary for assembly, which will both increase your productivity and lower your expenses. Your goal should be to place all of your surface mount components on one side of the board and all of your through-hole components on the top side of the board.

If possible, avoid placing components on the solder side of the printed circuit board (PCB) that will sit behind plated through-hole components. When you are installing components, you should try to align those that are analogous to one another in the same direction. The process of soldering will become more effective because of this, and it will also assist to reduce the number of errors that occur.

Tracing Considerations

The best practises for PCB layout dictate that you always insert short, straight traces between components wherever it is practicable; nevertheless, it is conceivable that this will not always be viable in bigger boards. If the location of your components requires horizontal traces to be routed on one side of the board, you should always route the traces vertically on the other side of the board. This is one of the many key guidelines for the design of a 2-layer PCB board.

An Example of Multilayer PCB Design
An Example of Multilayer PCB Design

The more layers you have in your stack up, the more complicated the rules and principles for designing printed circuit boards and laying out PCBs will become. If you don’t partition each signal layer with a reference plane, your routing strategy will need alternating horizontal and vertical traces in alternating layers. You will need to adhere to PCB board design standards that are specific to your application if you are designing particularly complex boards for specialised uses. This is because many of the generally promoted best practises for PCB design may no longer apply in these cases.

Power, Ground and Signal Trace

After the components have been installed, the next step is to route the power, ground, and signal traces such that the path taken by the signals is uncluttered and free of interference. At this point in the process of laying up your document, it is important to bear in mind the following guidelines:

Power and ground are often located on separate internal levels, as this is the most common configuration. It’s possible that doing this on a board with two layers won’t be as straightforward, in which case you’ll want to put a huge ground plane on one of the layers, and then route signals and power traces on the other layer. Instead of attempting to route ground traces, you should make use of ground planes when working with circuit board stackups that have four layers or greater. It is advised that components that require direct connections to power utilised common rails for each supply if a power plane is not used; ensure that the traces are large enough (100 mils is adequate for 5 to 10 A); and do not daisy chain power lines from one component to the next.

PCB Layer Design - Power, Ground Considerations

There are certain guidelines that indicate the positioning of plane layers need to be symmetrical, although this is not a necessary requirement for production. It is possible that this will be necessary for large boards to lessen the likelihood of warping, but this will not be an issue for smaller boards. Before you worry about maintaining perfect symmetry in the PCB stack up, you need make sure that you have access to power and ground and that all traces have a strong return path coupling to the ground plane that is the closest to them.

Conclusion

PCB design is a complicated method that needs specialization in electronics, circuit design, signal integrity, and EDA software tools. PCB design is the full procedure of generating a PCB through assistance and integration between numerous fields, such as electrical, mechanical, software, system, test, and manufacturing. A well-designed PCB is essential for the achievement, accuracy, and manufacturability of electronic devices for modern technology.