PCB Board Layout | How To Make Printed Circuit Board Layout

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What Is PCB Layout?

PCB layout is the process of designing the physical placement of components on a printed circuit board (PCB). It involves arranging electronic components, creating paths for electrical signals, and ensuring proper connections between them. The goal is to optimize space while ensuring signal integrity and functionality.

Imagine a world without mobile phones, computers, or cars. Without PCBs, electronic components couldn’t be organized or connected effectively. Most devices rely on proper PCB layouts to function. Creating a PCB layout is like crafting artwork, requiring time and precision. While it may seem difficult at first, with practice and starting with simple designs, anyone can master PCB layout. This guide will help you understand the basics and guide you through the process.

Optimizing Component Placement and Signal Routing in PCB Layout

Effective PCB layout depends on strategic component placement and careful signal routing. Components should be arranged to minimize signal paths and interference, ensuring efficient use of space. Grouping related components allows easier connections and improves circuit performance.

Signal routing involves creating short, direct paths to reduce noise and ensure power and ground planes are correctly linked. By optimizing both placement and routing, the PCB layout becomes more reliable and functional, improving overall circuit performance.

What are the Elements of a PCB Layout?

The key elements of a PCB layout include schematic diagram, managing high-frequency signals, and proper signal routing using ground and power planes. Component placement is crucial for functionality and manufacturability, while maintaining appropriate spacing prevents short circuits. Effective thermal management, using techniques like heat sinks, ensures reliable performance. These factors together ensure a functional and manufacturable PCB design.

The Schematics 

A schematic is a diagram of components, circuits, and connections laid out in a way that's easy to follow. When designing PCB layouts, it's always necessary to begin with schematics. Schematics help with constructing and understanding the system of circuits.

High-Frequency Signals

PCBs supporting high-frequency signals demand special requirements. Many of the interfaces used today operate at more than 50 MHz, meaning that some knowledge on how to avoid issues with high-speed signals is essential. At high frequencies, PCB layouts are all about understanding the physics of electron flow.

With technology continuing to advance at unprecedented speeds, the frequency of signals has become blazing fast. Therefore, the need to understand signal propagation is a big necessity. Also, there's a need to close the gap between analog and digital designs.

The Routing of Signal and Placement of Components

When it comes to signal routing and the placement of components, all you need to know is the direction in which the signal and currents will flow on your PCB. You need to keep your digital signals as far away from the analog signals as possible. Analog circuits tend to be sensitive to digital signals, which can introduce noise on the analog side.

PCB Layout Design Rules

Whether designing a low-speed or high-speed PCB, you should follow these rules to develop an efficient PCB layout.

• Determine the PCB layout rules with the fab house before designing to avoid re-routing and component shifting later.
• Fine-tune component placement
• Place SMDs on the same board side to reduce assembly costs (to have one pass down)
• Avoid or minimize crossing nets (try to rotate the components to eliminate net intersections)

PCB layout design using CAD software

• Place ground planes and power traces on the outer layers to sandwich the signal lines.
• Group analog and digital components into different parts of the board to prevent electrical interference
• Separate high-power components that dissipate lots of heat from the rest
• Round out your design using the electrical and design rules check to ensure you've met the established constraints

Step by step PCB Layout Design Process

Before designing the PCB layout, you should understand the system's electrical parameters, which include the following.

• Voltages
• Maximum operating current
• Capacitance limitations
• Signal types
• Shielding considerations
• Impedance characteristics
• Component and connector types and location
• Net wire schematic and listing

Once you understand these circuit parameters, proceed to schematic creation.

PCB Layout Design Step 1: Schematic Creation

A schematic diagram represents the system's elements using graphic and abstract symbols. Therefore, schematic creation involves creating the circuit's logical equivalent. The diagram contains component symbols connected to create your electronic product's circuit.

A PCB schematic

The schematic creation process involves these steps.

Symbol Creation

Create the symbols by inserting them into the CAD software's design editor or workspace. Pick these symbols from the software's library, then number the connection points for the input and output pins.

These points represent the connection pins on the physical component and give the symbol its electrical properties.

Remember to assign each component a unique reference designator, and it should include the following.

• Value
• Category
• Product manufacturer
• Part number
• Supplier

Lastly, assign each component a footprint, which gives an idea of the physical component's size. Include its height, area, and silkscreen information in this footprint data.

Symbol Connection

The next step is to interconnect these components to form the electrical circuit. Any pair of intersecting wires with an electrical connection should have a junction dot. But intersecting electrical lines that don't have an electrical connection should not have this dot.

A schematic diagram with the electrical symbols connected (note the junction dots)

Netlist Generation

A netlist contains information about the component name, the pad it connects to, and the connection numbers in serial order.

Contact pads on a PCB

Netlist Checking

Do a net-by-net verification of the schematic diagram to check and ensure the nets have the correct connections.

BOM Generation

CAD software can generate a bill of materials from the schematic diagram. This document lists all the materials required to manufacture your PCB.

PCB Layout Design Step 2: Pre-Layout

This step involves designing the PCB stack-up. But first, you have to verify the BOM and check whether all the components are active (not obsolete).

BOM Validation

The BOM lists all the components needed to assemble the circuit board, and you have to verify if the following parameters are correct.

• Part numbers (manufacturing and vendor)
• Component quantity

Also, check if the designators and schematics match and whether the BOM has marked DNI (Do Not Install) components.

Stack-Up Design

It is vital to design the board's stack-up with the help of your PCB manufacturer or using stack-up tools. The former is better.

You'll have to input these variables if you use stack-up planner tools.

• PCB material (should match the environmental conditions and frequency requirements)
• Number of layers (separate signal and power/ground layers)
• Required impedance (ohm value and whether it is single-ended or differential)
• Copper layer thickness

Working with your PCB manufacturer is easier because they'll help you create an accurate stack-up.

PCB Layout Design Step 3: PCB Layout

Here comes the fascinating part. We'll begin the layout stage by setting the stack-up.

Set Up the Stack-Up

Go to the layer stackup manager tool in your CAD software. It should create a single-layer stack-up by default.

PCB layers

You can add or import the stack-up design you created earlier with the help of the fab house, then edit the stack-up order. If designing a flexible PCB, ensure you have the flex option enabled.

Set the Design Rules

Design rules are instruction sets that the layout tool uses to design the board. They fall into these three categories.

• Physical/Manufacturing Rules: Defines parameters like via-hole size, trace width, and differential pairs
• Electrical Rules: Deals with factors like frequency, insulation, and impedance
• Routing/Spacing Rules: Details the spacing between high-voltage power tracks, acute angle avoidance, clearances, and the like

Draw the Outline

The board outline is a closed contour of the PCB shape. You can draw it manually by moving board vertices, from a 3D body by importing a blank board into a 3D body object, or from selected objects on a mechanical layer.

Component Placement

Once you draw the board's shape, place the components on it and group them into different parts. For instance, you can divide the board into these regions.

• Analog circuits
• Digital circuits
• Power circuits
• Low-frequency circuits
• Connectors

A circuit board layout after component placement

After making these divisions, place the fixed-location parts, such as connectors, followed by primary components like CPUs and memory chips.

The last step is to place the auxiliary components that support the primary ones. They include resistors, decoupling capacitors, oscillators, etc.

Here are some placement guidelines to help you in this step.

• Position high-speed ICs near connectors
• Allow test point access
• Distribute heat sources to eliminate hotspots
• Consider the requirements for rework

Thermal Management

Thermal management is critical to ensuring high-power and other devices operate efficiently. Use these design techniques to manage heat effectively.

Temperature distribution in a circuit board

• Position the hot parts to have more surface area contact with heat sinks
• Ensure maximum airflow access through heat sinks and vents
• Include thermal pads
• Place thermal vias under the pads of hot devices
• Design thick copper planes to evacuate the heat
• Add internal thermal layers linked by thermal vias

Route the Nets

Routing involves laying the copper traces, and you can route single nets, differential pairs, or group components to route recurring circuits quickly. The best practice is to lay them orthogonally and avoid 90° turns.

Conductor tracing in a multi-layer PCB

Begin with the power vias and decoupling capacitors when routing the nets, then go to the critical lines like high-speed and impedance traces. Complete the process by routing the non-critical transmission lines, then connect the ground and power planes.

Remember, the critical lines should have short paths, so give them a higher priority.

Do a Design Rule Check

Compare the layout's logical and physical integrity with the enabled design rules, then verify the design using DFx simulations in these areas.

• Signal integrity
• Power integrity
• Thermal profile
• Electromagnetic interference
• Electromagnetic compatibility
• Ability to withstand mechanical stresses and vibrations

Use the feedback from these simulations to finetune the layout's design. For instance, you can:

• Reroute signal lines affected by noise
• Adjust the component placement to reduce coupling
• Increase thermal vias or the copper plane thickness for faster cooling

A vector image of a PCB layout with contact pads, transition holes, and copper traces

Complete the Manufacturing/Fabrication Notes

These notes are vital to the manufacturer because they contain this data.

• PCB class
• IPC standard
• Number of layers and their impedance details
• Board thickness
• Silkscreen color
• Solder mask color
• Stack-up details
• Cut-out details
• Drill chart (including drill sizes) for via and hole drilling
• Design version number
• Date

PCB Layout Design Step 4: Generate the PCB Manufacturing Files

Generate these production files using the CAD software to send to the fab house.

• Gerber files
• NC (Numerical Control) Drill file
• Pick-and-place file (X-Y rotation and coordinates of each component)
• IPC 356 netlist file
• ODB++ file
• Schematic PDF file
• Layout PDF file
• Assembly drawing PDF files

A PCB layout's Gerber file

PCB Design and Layout Tips

Be Clear about Producer Demands

Before you can begin placing components, you need to consult your producer first. It’s important to be clear about their demands, such as the number of layers they can handle. Other requirements may include things such as minimum trace widths and trace spacing.

Manage the Spacing of Originals in the Layout

When electricity passes through the copper traces, it will generate heat. This heat needs to be managed so that it doesn’t increase past a safe threshold. You can control this heat by managing the width of the marks and ensuring adequate space between them, a process called PCB line spacing.

Line spacing can be challenging when dealing with a high-density interconnect PCB. The good news is that most PCB design software is designed based on the important parameters that need to be observed in specific situations.

Avoid Using a 90-degree Angles

In PCB design, your most important goal is to incorporate all the components needed in your PCB. To do this, you need to determine spacing and the angle that your lines will take.

Most designers use either a 90-degree or a 45-degree angle. However, there is often disagreement about whether a 90-degree angle works better than a 45-degree one.

Autodesk.com suggests that you should avoid using 90-degree trace angles. This is because “When you have a bunch of traces that have a sharp, right-angle turn on your board, the outside corner of that 90-degree angle has the likelihood of being etched narrower than your standard trace width.”

Instead of using 90-degree angles, rather use 45-degree tracing aspects because they prevent short circuits.

Always Create a Ground Plane

It’s always important to have a common ground terminal in the circuit schematics. It is essential for a PCB layout as it provides traces with the same reference point for measuring voltages. Problems arise when you utilize traces rather than ground planes to route to the ground.

The software, hardware, and IP provider Cadence.com identifies the three crucial roles played by the ground plane in PCB design:

• Voltage return: Most, if not all, of the components in the PCB, connect to a power net, and the ground net provides a pathway for the returning voltage.
• Signal return: Provides a pathway for returning signals so that they do not generate too much interference.
• Noise and interference reduction: A ground plane’s huge conducting area helps lower disturbance because it has a lower impedance than when traces are used to route the ground net.

Avoid Overlapping

In mixed-signal PCB layouts, one of the challenges is overlapping planes. A mixed-signal PCB layout has digital circuits and analog circuits on one board. If not properly managed, this overlapping could introduce the problem of interference between the digital and analog signals.

Radiofrequency mixer printed circuit board

Therefore, at all costs, you will need to ensure that you avoid issues with overlapping when it comes to PCB layouts. You should “always leave room between components at all times.”

Pay Attention to Electromagnetic Interference

PCB designers often struggle with issues related to electromagnetic interference (EMI).

The three types of EMI:

• Conducted Coupling: This happens if the noise from the energy source is conducted on all circuits.
• Electric field coupling: This is a situation where energy is coupled from one circuit to the other via an electric field, usually when the source circuit impedance is high.
• Magnetic field coupling: Is the coupling energized or driven by the current; it’s equivalent to the source’s flow.

Some common methods of dealing with EMI:

• Use a multi-layer board so that you can have more options for handling high-speed traces.
• Only use ground planes when required.
• Connect split ground planes to one point.
• Connect bypass of decoupling capacitors to the ground plane.
• Avoid bends that turn at sharp right angles.
• Ensure that high-speed signals are separate from low-speed signals and analog signals are separate from digital signals.
• Make return paths as short as possible.
• Route differential traces as close as you can.
• Be careful when using vias, and avoid the use of vias in differential traces.
• Separate analog and digital circuits.
• Isolate high-speed components.

Radio Frequency PCB Layout

Radio Frequency (RF) PCBs are an exciting and growing sector across the PCB industry. Autodesk.com speculates that the popularity of this type of design is being driven by the “proliferation of IoT sensors, wireless electronics, and smartphones.”

In the PCB industry, any board that operates at frequencies above 100MHz is deemed an RF PCB. The microwave PCB frequency is about 2GHz.

The RF PCB design is usually a 2-layer or 4-layer board. Component arrangement requirements will be more stringent with RF PCBs, so professional PCB layout design knowledge is needed.

Issues with PCB Design and Layout

When it comes to the design and manufacture of almost everything, having a functional layout is essential. Likewise, in PCB production, having a good structure in place brings about the desired results. However, there are a few issues that concern the PCB layouts.

Wrong Designing Tools

As you would expect in any situation, using the wrong tools will produce the wrong results. In some cases, PCB designers use the wrong tools because they don't know any better. However, there are situations where designers use the wrong tools because they believe that this will save them money.

If you select the cheapest tools because you want to save money, you could end up paying a lot more to remedy the situation. You can circumvent this challenge by ensuring that you do your homework to identify the best hardware and software for your PCB design project.

Lack of Preparation

Producing a PCB turnkey is not an easy process. Some of the basic PCB design and layout considerations include the shape and size of the PCB. Complex PCB layouts preparation problems are related to creating the best layout between traces, trace widths, and other factors that may affect board functionality.

Solving layout preparation problems is usually accomplished through employing sophisticated software. Using PCB layout services is another way of leveraging the experience of companies that have been in the field for many years.

PCB Layout Software

In any industry, software programs reduce the effort and time required to produce goods and services. Like in most industries, PCB design and layout have come to depend on programs that automate processes.

Some of the best PCB layout software in the market include:

Autodesk Eagle: Comes with a schematic editor for designing diagrams and also has a PCB layout editor.

KiCad: This is a cross-platform and open-source electronics automation suite. It includes a PCB editor for producing professional PCBs and a schematic editor for editing and creating schematic designs.

Fritzing: Has several features, including a schematic, a breadboard layout, and a PCB view.

DesignSpark PCB: Provides an easy-to-learn environment consisting of schematics capture and a PCB layout tool.

EasyEDA: Delivers a library designer, a PCB editor, and a project management tool.

UpVerter: Has similar features to EasyEDA and enables hardware engineers to create, share, and review PCBs and schematics.

ExpressPCB Plus: Is EDA software for designing and creating electronics circuitry.

TinyCAD: This is an open-source software project that supports custom and standard symbol libraries. It also supports PCB layout programs consisting of several formats.

Osmond PCB: This is the only MAC-based EDA tool that supports schematic capture and PCB layout design.

PCB Layout Services

Even though you could do your own PCB layout, using a PCB layout service could deliver several advantages. These layout services can be of great assistance, particularly if you are a beginner in this field.

PCB layout services are available for existing and new PCBs. Some advantages of using PCB layout services include:

Technical competency: Having access to an expert is a significant advantage when designing PCBs.

Streamlined process: With PCB layout services, errors can be detected and fixed early, allowing you to improve products before marketing.

Better quality: Layout services come with better quality because every service wants to be better than the competition.

Fast turnaround: With the services of a specialist, PCBs can be designed on time based on careful planning.

Cheap: Due to economies of scale, using PCB layout services could be cheaper than doing your own PCB designs.

Standard PCB Layout Designer Deliverables

Credible PCB designers meet a minimum set of deliverables, including:

• Bill of Materials list (BOM)
• Fabrication files
• PCB layer stack diagrams
• Complete schematics
• Full Gerber files
• Plenty of software
• 3D PDF files
• Route and drill files

Conclusion

PCB layouts are essential for proper board functionality. Suppose you are having a tough time undertaking your board layout. In that case, you can always look for assistance from a company that PCB prototyping under the best layout plans. Ensure that the company understands the importance of PCB layouts so that your boards will function as intended.