Impedance and PCB Etching: Utilizing Altium Designer for Your Board Needs
Today’s high-speed PCB designs require that the design engineer take charge of how the circuit board will be built. There was a time where PCB construction specifics were handled by manufacturing engineers in another department, or even in another company. How the board was built up didn’t have an important effect on the signal performance, and the purpose of the design team was to simply create electrical circuitry that performed the function that it was designed for.
Over the years though, that model of PCB design has changed. As signal speeds increased, board designs began to run into associated problems such as reflection and crosstalk. This forced design teams to pay more attention to their layer stackups and board houses had to refine their manufacturing techniques to match. Later on as signal speeds continued to increase, PCB designers began to contend with additional issues such as interplane capacitance calculations. With even higher speeds care was needed in choosing the laminates and prepreg used in PCB manufacturing to counter the effects of skew due to the glass weave used in those materials.
For the PCB design engineer today, there is a lot that needs to be considered when creating a PCB design. PCB manufacturing materials and the configuration of the board layer stackup will have a major effect on your impedance and PCB etching. Fortunately, there are PCB design tools like Altium Designer® that can help you calculate your board configuration so that you get the best high-speed design results.
Using the Power of Altium Designer to Create Your PCB Layer Stackup
Starting in Altium Designer version 19, the layer stack manager has gone through some important enhancements including enhanced profiles, via displays, materials, and a 3D visualizer to name a few. The first thing that you will notice is that the layer stack manager now opens up as a document giving you the ability to leave the layer stack manager open while you work on the board in another document. While in the layer stack manager document, the context-sensitive “Tools” pulldown menu will adjust to give you different options, and you also have new right mouse menu options as well as pop-up menus within the layer stack manager. You can see some of the new enhanced options below.
The enhanced layer stack manager in Altium 19
Going to the “Tools” pulldown menu gives you the option to open up the Altium Material. Here you can select from a wide range of materials and processes to add to your layer stack manager. You can also add custom materials and processes as well. In the image below you can see a list of the core dielectric materials that the materials comes stocked with for you to choose from.
Selecting PCB fabrication materials is easy with the materials in Altium 19
Another major enhancement to Altium is the ability to design printed electronics. The layer stack manager now gives you the ability to set up your design for printed electronics as well as setting up for rigid/flex designs. You can in the picture below that this option is available to you from the “Tools” pulldown menu.
Among the options in the layer stack manager is being able to set up for printed electronics
The changes made to the layer stack manager now give you more control over the materials that you set up for your board layer stackup. In the layer stack manager, you can specify those materials and their width to get the precise layer configuration that you need. You can also configure and save different layer stacks as well as defining sub-layer stacks within your current design for different areas of the board.
From the Impedance Calculator to the Design Rules; PCB Design Tools that Work With You
Altium has had their impedance calculator built into the tools for a long time now. Like the layer stack manager though, it too has gone through a lot of enhancements. By clicking on the “Impedance” tab at the bottom of the layer stack document, you will open the impedance calculator. From here you have the option to create multiple impedance profiles for single or differential pairs in either microstrip or stripline configurations. By clicking on the specific layers on the right side of the window, you can see the impedance configuration on the left in the properties panel as shown below.
Then enhanced impedance calculator in Altium 19
In addition to setting up impedance values, having the layer stack manager open at the same time gives you the added advantage of being able to view the results of your configuration. If the results aren’t what you want, you can easily change your values until you achieve the layer stack configuration that is best suited for your design.
As in past version of Altium, the values you set in the layer stack manager with the impedance calculator are automatically forwarded into the design rules. Make sure to set your design rules to use the impedance profile that you saved in the calculator as you can see in the picture below. Once set, the design rules will now conform to the values of the impedance profile that you created working with the layer stack manager.
The design rules are able to automagically import the values from the impedance calculator
High-Speed Design Tools for Controlled Impedance and PCB Etching Routing
With the design rules prepped with the data forwarded from the impedance calculations, you are now ready to set up your design rules. Altium has a full set of standard rules governing trace widths and clearances, as well as routing topologies, vias, power planes, and many other similar rules. On top of that, you also have specific high-speed design rules for lengths, matched lengths, stub lengths, and many others high-speed specific categories. Altium also gives you the ability to set up and manage multiple nets combined into a single signal path. This gives you the ability to control the entire signal path, from the driver to the termination, instead of all the individual nets separately.
Altium comes equipped with a utility called “xSignals®” to create and manage these signal paths. A signal path can be created in by either using a creation wizard or by manually working within the utility. This gives you the ability to either create the entire signal path manually or by pre-selecting components or pins and creating the signal path from those elements. Below is an example of the menu when working with selected components.
One of the set up menus in Altium 19
In the picture below you can see where we have created a signal path that starts at the driver pin on the left and goes through a resistor. On the other side of the resistor, the signal path continues on until eventually reaching its destination pin on the lower right of the picture. Using gives us the ability to report and work with the two individual nets as one complete signal path. The menu will report net names, segment lengths, total signal path length and much more.
Routing a signal path using the tools in Altium
There are a lot of factors to consider when deciding how to best configure your board’s construction for high-speed design. Fortunately, you have many powerful PCB design software tools built into Altium that will assist you in many ways as you design your board. The enhanced layer stack manager with its improved impedance calculator along with the utility, are just a few of the resources that Altium will put into your hands.
To find out more about all of the advantages that Altium will give you when you tackle your next high-speed design, talk to an expert at Altium.