Demonstrations for Multi-Layer Designs: Best Uses for Each Layer
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In your career as a PCB designer, you will design a lot of different printed circuit boards to accommodate various design technologies that you’ll be confronted with. To that end, you will use a plethora of circuit boards with all kinds of different sizes, shapes, and layer counts. How you decide to configure your PCB layers and what you put on each layer will, of course, be dictated by what you’re designing. Stripline and microstrip routing will require certain layer stackup configurations but other details like signal integrity, power, and thermal requirements will factor in as well.
The important thing now is to understand how to best to use your PCB design tools so you can create exactly what you need for each layer when setting up your multi-layer designs. We’re using Altium Designer to create our circuit board designs, and its versatility gives us lots of flexibility when setting up designs. Here are some key points that you should know when setting up your own multi-layer designs.
Once you create the board outline shape that you need for your design, you are ready to configure the layers that you’ll be working with. To display the layers in a PCB design, Altium Designer provides you with a “View Configuration” panel. You can open this panel by clicking the “Panels” button, going to the “View > Panels > View Configuration” pulldown menu, or by simply hitting a lowercase “L” shortcut keystroke. The panel will look similar to the picture below.
The Layers & Colors tab in the View Configuration panel in Altium Designer
The View Configuration panel has two tabs on it: “Layers & Colors” and “View Options.” You can see these tabs in the picture above, and as you can see, there’s a lot there. Even though this board is a simple two-layer design, the layers tab is very deep, so much so that we’ve chopped it in half to show you all of the content side by side. With this panel, you have the ability to toggle ‘on’ or ‘off’ the visibility of “Signal Layers,” “Component Layers,” “Mechanical Layers,” and “Other Layers.” You can also control layer sets and the active layer as well as configure the system colors.
In the picture below, you can see the “View Options” tab of the view configuration panel. Here you have additional control over general settings and object visibility. You will find all of these controls useful as we begin to create different layers that will be needed for our PCB design.
The View Options tab of the View Configuration panel
To add layers to the design, you will want to open up the “Layer Stack Manager” by going to the “Design” pulldown menu. Our simple two-layer design doesn’t have much set up for its board layers, as you can see in the picture below. However, Altium Designer offers us lots of tools in the layer stack manager to make changes with, as you are about to see.
The Layer Stack Manager in Altium Designer
The first thing you’ll notice is that across the top left of the layer stack manager, you have buttons to save, load, or configure the layers from a list of preset board layer stacks. To the right of those buttons are more controls to change the units of measurement as well as copy and paste data. Below that is the main window of the layer stack manager where you can add, edit, or delete board layer information.
The main window is separated into columns for the layer name, type of layer, material of the layer, and much more. Each layer has its own row and as you can see, there are rows for metal, dielectric, and solder mask layers. Each row and column form individual cells in the format of a spreadsheet and many of these cells, such as the layer name, can be edited by clicking in the cell and inputting a new value. Some of the cells, like Material, have dropdown menus to select options from when you click in them.
By right-clicking in the main window, you will have a small menu that allows you to add or delete layers. The same commands are also available in buttons below the main window. You also have controls to move layers around in the stack as needed. In the picture below, we have modified the layer stack manager to add some internal signal layers and corresponding dielectric layers along with thickness data for each.
The Layer Stack Manager modified for a 4 layer board
Your PCB designs may also need power and ground plane layers. There are two different ways to do this in Altium Designer. You can either create a copper pour on a signal layer or create a dedicated internal plane layer in the layer stack. To pour copper on a signal layer, use the “Polygon Pour” command in the “Place” pulldown menu. This same command can also be found in the main session right mouse button menu, or the taskbar. Once the polygon pour is created you can then associate it with the desired net and change the parameters as needed, as shown in the picture below.
A Polygon Pour in Altium Designer
Altium Designer gives you a lot of control over poured copper. You can name the pours, specify the fill mode, and remove isolated copper. You can also modify pours, split them, or combine them to name a few of the polygon pour editing functions available to you.
The other way of working with power and ground planes requires you to create an internal power plane in the layer stack manager. Again, you will add a new layer in the stack manager, but this time, you will add an “Internal Plane” layer instead of a signal layer. Internal plane layers also give you the option of specifying the amount of copper that you want to pull back from the board edge. Once we add our new plane layers, we move them around in the stack manager, adjust their thicknesses, and make other changes, as displayed in the image below.
The Layer Stack Manager modified for a 6 layer board
Another method that Altium Designer gives you for working with layers in your PCB design is through the design rules and router setups. By going to the “Design > Rules” pulldown menu, you can open the “PCB Rules and Constraints Editor,” as demonstrated in the picture below.
Design Rules setups in Altium Designer
On the left side of the rules editor dialog box, you can see various settings for routing like width, topology, priority, and others. We have selected “Routing Layers” in the picture above to show you how you can enable or disable which layers are permitted for routing.
You can also control the preferred direction of routing for each layer when using the auto routers in Altium Designer. Go to the “Route > Auto Route > Setup” pulldown menu to open the “Routing Strategies” dialog box. Click on the “Edit Layer Directions” button to open the layer’s directions dialog. As you can see below, you can use the drop-down menus to choose which direction you want the routers to use on any of the layers within your design.
Routing direction setups
Depending on your application layer, your PCB can have a vast array of functions. Utilizing layers properly in multi-layer designs can become an immense selling point for yourself as a designer and as an engineer. Thankfully, strong PCB design software can make multi-layer PCB, cross-layer design, ground plane, and any circuit design space you need to work with easy.
By understanding how to work with layer configurations, you will be ready to meet any design challenges that come your way. Whether it’s a simple two-layer design or a complicated flex design, Altium Designer is a comprehensive PCB design software that offers layer configuration capabilities and the design power you need in order to get the job done.
Would you like to learn more about how Altium can help you design a DFM-compliant PCB? Talk to an expert at Altium.