How to Start with Cadence Allegro to Create a Board Outline for PCB Layout

While growing up, I really enjoyed building model planes, cars, and ships. When first opening the box of a new model, there was such a feeling of joy looking at all of those little tiny plastic pieces. There was also a feeling of apprehension as I wondered how in the world I would ever be able to fit all of those little tiny plastic pieces together into just one model.

I have found some of these same emotions stirring within me when working with a new PCB CAD system for the first time. Just looking at all of the functionality in the menus is exciting, until I realized that I don’t know where to start. Simply trying to open a new design can be a challenge if you’ve never worked with this system before.

Cadence Allegro is flat out one of the best PCB layout tool systems that you can use today. It carries within it enough power and flexibility to handle anything that you will ever design. To support this level of technology however requires a lot of input from the designer, and there are a lot of different features and options in the user interface to learn how to use. That’s where we are going to help, by giving you a simple introduction on how to start with Cadence Allegro. So let’s take the lid off of this box, and start exploring the wonders within Allegro version 17.4.

How to Start with Cadence Allegro and Understanding Its File Structure

Cadence Allegro uses plenty of different file types in the design of a printed circuit board, and it will create many as well. We won’t get into all of the file types within the Cadence design system, but here are a few that you may see when you open an Allegro design directory:

• .dsn: The schematic database file.

• .opj: The schematic project file.

• .olb: The schematic library file.

• .pad: A padstack file.

• .dra: A drawing file used to create symbols, such as footprint packages for layout.

• .psm: The binary equivalent of a drawing file, and represents the footprint package’s physical shape in layout.

• .brd: This is the main board file for PCB layout.

Each of these files can be named as you want, with the file type being designated by the dot extension. One of the nice things about Cadence is that you can open the tools by simply clicking on the appropriate file. For instance, to open the PCB editor, you simply would click on <board_name>.brd, and Cadence will pop open a menu allowing you to choose which version of the tools that you want to use. These choices could include Allegro Sigrity SI, Allegro Sigrity PI, Allegro Physical Viewer Plus, Allegro Venture PCB Designer Suite, or whatever tools you have licensed in your system.

For our purposes though, we are going to access the design tools through the desktop icon. Clicking on the “PCB Editor 17.4” icon brings up the same product choice menu, and we will select Allegro Venture PCB Designer Suite from the list. Remember, your list will probably show different tools to work with. To save you time when working on a large project, the PCB Editoropens up to the last design that was worked on. You also can navigate to a different design to open, or as we are going to do, open up a new design.

Creating a New Design in Cadence Allegro

The Design Start Page in Cadence Allegro PCB Designer

By clicking on the “Start Page” tab, you will bring up the design start options where you can select the design you want to work on. In our case we clicked on “New” under “Start Design,” which brought up the “New Drawing” dialog box. As you can see in the picture above, we browsed to the directory that we wanted to store our design, gave the name “Example” to the design, and selected as the drawing type, “Board (wizard).” Although we could have chosen the board option without the wizard, this will allow us to quickly create a very simple board outline example.

As you can see in the picture below, the board wizard takes us through the creation process of a board outline very easily. Although the parameters that we are going to enter can all be done manually, the wizard simplifies the process and combines it all into one menu. By clicking the “Next” button, the wizard takes us into the “Import Data” step. Since we aren’t going to import any board data, we will leave all of these optional steps set to “No,” and continue to click “Next” until we get to the Parameters section.

The Board Wizard in Cadence Allegro PCB Designer

Creating a Board Outline Using the Wizard

In the Parameters section of the board wizard we will set our units to Inch, our drawing size to “B,” and our drawing origin to the lower left corner. In the next screen we will set our grid spacing to “0.025,” our etch layer count to “6,” and generate default artwork films. As we click “Next” again, we are forwarded into the “Custom Data” category. Here you can name your inner layers if you desire, and in our case we will set Layer 2 and Layer 5 to be “Power planes” by clicking on their layer types. We will also enable the “Generate negative layers for Power planes” option if not already enabled, and click next again to set up spacing constraints for the board.

We’ll set our minimum line width as well as our minimum line to line, line to pad, and pad to pad spacing all to 0.006 inches for simplicity. For the “Default via padstack,” click the browser button to bring up the “Board Wizard Padstack Browser,” scroll down and select “Via.” As we continue to the next screen by clicking “Next” again, we will select “Rectangular board” to define the board outline. In the next screen we will set up the board outline as you see in the picture below, and once that is done, the PCB Editor will prompt us to confirm that we want a board file created in our directory. Click “Yes,” and then save your design if you wish to create a new Example.brd file.

Setting up the board parameters in Allegro PCB Designer’s board creation wizard

Now that you have a simple board outline created, you will discover that there are many other board parameters and features that you can edit and adjust. Go ahead and take some time to explore Allegro PCB Designer’s user interface and see all of the different design parameters that you have control over.

The Allegro PCB design tools from Cadence have many useful features and functions within them such as the board creation wizard that you’ve just seen. Beyond that you will find powerful functionality for place and route to complete your most challenging PCB designs. Allegro PCB Designer has the capabilities that you need as a designer today to create the leading edge PCB designs of tomorrow. Should you be looking to truly master your skills with Allegro, consider taking certifications to be a Cadence designer. 

If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.