At the heart of most modern electronic devices are one or more printed circuit boards. These boards can be large or small, and have almost any shape imaginable. They can be simple constructs with only a few components on one side, or complex multi-layer high density designs. They can be made out of hardened laminated materials, or they may be flexible in order to thread their way through the contours of the devices they control. But no matter what they look like or how they are built, they will all have one thing in common. They will all be created from a schematic.
The heart of the electronic device may be the PCB that controls it, but the heart of the PCB is the schematic that is used to create it. In order to have the best PCB layout, it is essential to first start with a well-designed schematic. It is common knowledge that a schematic documents the functionality of the PCB with symbols and lines that represent the connectivity of the electrical components. There is a lot more to a schematic than just those symbols and lines though. The schematic must also communicate the intent of the design by depicting the circuitry in the correct order, and include all the details needed to accurately create the PCB.
To create, or capture, a schematic that will do the job that it is required of it takes a unique set of skills in itself. As with writing a book you need to first understand the story that you are telling, and then you need to lay that story out with all the details organized in a way that the reader can easily follow. The same principle applies to capturing a schematic, and there are specific techniques that can help you to create the schematic you need to best tell its story. Here are some of those techniques that can help you to capture an effective PCB schematic design.
Be Prepared for PCB Schematic Design Before You Start Throwing Parts on the Screen
It is human nature to want to charge into things, and this holds true especially for those of us that are designing circuitry. The problem is that by throwing symbols and nets on the screen without being prepared for what we are doing will usually result is greater difficulties later on. We may have to change or update parts, or we may end up reorganizing nets and text to squeeze additional data in. To be prepared for the schematic that you are about to create, consider these points:
Understand the Scope of the Task: Make sure that you know what it is that you are designing before you jump into it. Yes, your PCB design will go through a lot of changes while you are working on it, but having a clear understanding of what is required first can save yourself a lot of headaches later on. This also includes understanding any applicable company and/or industry standards, plus who the contract manufacturer is that is going to build the finished printed circuit board.
Research the Components to be Used: There are different sources for schematic symbols, and if you are pulling them from a corporate library you need to make sure that they are current and up-to-date. If your system is updated by current vendor information, or you are pulling parts directly from the vendor, you will have better assurance that the parts are correct. Work with your procurement department, and make sure to engage the services of your contract manufacturer early. A good CM will have the relationships with part vendors you need in order to help you with component management.
Know the Tools: Having a good understanding of how to use the tools will save you time and make you more productive. Specific functions like copy and paste may seem obvious, but if you are unfamiliar with features like these you aren’t likely going to try to use them. This can lead to frustration as you manually do tasks that are already automated, whereas working fluidly with the tools will actually help stimulate your creativity.
Schematics are more than just documentation, they intelligently link their component and connectivity data together with other tools including layout and simulators. For all of this functionality to work correctly, the component and net information must be current and accurate. By being prepared first before you start designing, you will help yourself to create a good schematic that will serve as a solid foundation for your entire design.
A properly prepared schematic will lead to the design of a PCB like this
Good Schematic Capture Practices for Readable Schematics
In addition to their intelligent component and connectivity capabilities, schematics must also be easily read and understood by those using them. They will be used by layout engineers, component engineers, manufacturing personnel, test technicians, and field repair specialists. As such they need to clearly communicate what their circuitry is doing. Here are some key points in creating a schematic that will be useful to everyone:
Parts Placement: Components should be placed as neatly and organized as possible. Rows of parts such as resistors should be aligned with each other with enough space for nets and text. A haphazard approach to component placement on a schematic can make it more difficult for people further on down the line to quickly locate a specific part that they are looking for.
Signal Paths: Components should be placed according to their signal paths. The path should start at the driver pin, go through the circuit in a logical flow, and finally finish at the termination. Not only does this make your schematic more orderly in appearance, but it will reduce the clutter giving you more room for other circuitry and make the circuit more understandable for the layout team to work with.
Give Yourself Room to Grow: Although your schematic may possibly be reduced in size, it is far more likely that it will grow as new functionality and enhancements are added. For this reason it is a good idea to give yourself room to add additional circuitry as needed. If for nothing else you likely will have changes and corrections while you design, and the additional room makes moving parts and nets around a lot easier.
Net Connectivity: As with component placement, a neat and orderly flow of the nets will make everyone’s work a lot easier. Buses should be drawn together as much as possible. Especially for the layout team, seeing the flow of the signal paths and how busses are grouped together will help them with their floor-planning of the PCB layout.
Don’t Neglect the Details: When all of the components are placed and routed together in your schematic, you still aren’t done. The reference designators need to be moved and rotated so that they are readable. The same goes for net and bus names, which should be aligned in the same direction of their wires for readability. Title blocks need to be filled out with board names and numbers as well as dates and other company information. Lastly, don’t forget specific notes or design details that will help those who use the schematic for layout, manufacturing, and repair.
There is a lot to do in order to create a fully functional schematic that is useful to all, and fortunately there is plenty of information on how to be better prepared for all aspects of PCB schematic design. You can see what it takes to become a design engineer and what the future is for schematic capture and PCB layout. You can find out more about what it takes to convert a PCB layout from a schematic as well as the PCB layout design steps that you will be going through. You can even find some helpful PCB layout tips.
A closeup of a 3D PCB layout
More About PCB Schematic Design and PCB Layout
There is a lot of good information available on schematic capture and PCB layout if you want to find out more. Here are some resources that can help you get started:
The Basic Steps in How to Become a Design Engineer
There are a lot of growing industries such as communications and aerospace that will need new PCB designs to stay ahead of the technology curve. To keep up with this demand, PCB design tool companies are expecting increasing demands for their design software. This all means that the world needs more and more PCB design engineers to meet these demands. Here is some information on what it means to be a PCB design engineer and what you can expect will be required of you.
Here is more information on how to become a design engineer.
The History and Future of Schematic Capture and PCB Layout
From schematics drawn with pencil and paper to the ease of capturing schematics in today’s PCB design tools, here is some historical perspective on the design process. With the advancements in today’s PCB design systems, engineers can now focus more attention on the job of design instead of manipulating the tools. The question now is, what new technologies and design challenges will come next?
If you would like additional information on schematic capture and PCB layout, read about it here.
How to Convert PCB Layout Starts with a Good Schematic
The goal of the schematic is to drive the successful layout of the printed circuit board, and provide the documentation needed for its manufacturing, test, and repair. To ensure that your schematic will cover all of the bases, you need to focus on the details of your schematic. Not only does this mean how you organize the schematic data on the sheet, but also the specific data that you are including.
You can read more about converting a schematic to PCB layout here.
A typical schematic sheet from OrCAD Capture
PCB Layout Design Steps to Consider When Capturing a Schematic
Creating a good PCB layout requires that you have the necessary information and data captured in the schematic. With so much of the layout information being transferred from the schematic, your schematic needs to have complete information in. Not only does this include items such as component symbols and their corresponding PCB footprints, but it also includes physical data for the board such as the layer stackup and the number and locations of items such as mounting holes.
Additional information on basic PCB layout steps can be found here.
PCB Layout Tips: The Importance of a Good Schematic
When it comes to schematic capture and PCB design, there are a lot of requirements that you will have to fulfil. As a new designer one of the best ways to get the help you need is to be mentored by someone who has a lot of experience in the field. Another great source of information is to find design tips written by others that can answer a lot of your questions.
For some good insider information on PCB design, check out these PCB layout tips here.
The Goal of Schematic Capture: A Precision PCB Layout
It is an amazing experience to hold in your hand the manufactured printed circuit board that resulted from the schematic that you captured. The time you spent preparing for this career and studying engineering will pay great dividends in the PCBs that you will create. The key to your success will be your persistence in making sure that all of the details have been taken care of in your design.
With the right PCB Design tools, you can be creating designs such as this
Another important part of schematic capture in the creation of precision PCB designs is in the PCB design tools that you are using. The PCB design systems from Cadence have the features and functionality to make sure that all of the key elements discussed here are completed accurately. With its advanced capabilities, OrCAD PCB Designer is the PCB design tool that you need for success on every schematic that you create.
If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.
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