How to Design a Printed Circuit Board: Board Layout using EAGLEBitahwa Bindu
This is part 2 of our tutorial: How to Design a Printed Circuit Board using EAGLE.
In part 1 we learnt how in any electronic design, the Printed Circuit Board or PCB is one of the most crucial parts with its quality affecting the overall quality of all these devices. Sooner or later you will have to take those hand built on breadboard designs to a more robust and elegant Printed Circuit Board. In this series, we are teaching you exactly that. In part 1 we started with the Schematic Design using EAGLE.
To learn more, please read first:
If you prefer to watch a video, please watch the video below, it will take you through all the steps from Schematic design to soldering your and testing your board.
In this tutorial we’ll cover the steps in EAGLE how to convert your Schematic Design to a Board layout which is one step closer to become a PCB.
Creating a Board from the Schematic
The schematic designed in the tutorial: How to Design a Printed Circuit Board: Schematic Design using EAGLE will be used in this tutorial, we will convert it into a board in this tutorial.
To switch form schematic editor to the board layout, just click on the tool: Generate/Switch to Board command (on the top toolbar, or under the File menu). For the first time you will get a warning stating that the board does not exist and asking to create it from schematic, Click Yes.
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All of the parts from the schematic should be there stacked on top of each other with yellow wires connecting them called airwires, your job is now to move them to the blank board and arrange them the way they should be on your board.
Moving the Parts
Use the MOVE tool — — to move the parts to the blank board. While you’re moving parts, you can might need to ROTATE — — them so that you can place them properly according to your design by either right-clicking or changing the angle in the drop-down box near the top.
While moving a part, notice how the airwires move with them, try your best to limit the criss-crossing airwires as much as you can as this will make routing much easier. While you’re relocating parts, hit the RATSNEST button — — to get the airwires to recalculate.
It’s always good to start placing the bigger components, place the connectors close to board edges, and if possible components performing the same functions could be placed next to each other like for example the buttons (Up, Down, Left, Right and Select) of this shield will be grouped together, decoupling capacitors for example should be very close to the IC.
Always remember as well, placing the components very close to each other will make your board small and cheap but the routing will be very difficult.
The image below shows all the components placed on the board.
A PCB is composed with different materials layered one material over another. A double-sided PCB will have a thick middle part of the board, an insulating substrate (usually FR4). On either side of that is a thin layer of copper (the top is the top layer and the bottom layer), where our electrical signals pass through. To insulate and protect the copper layers, we cover them with a thin layer of lacquer-like soldermask, which is what gives the PCB color (green, red, blue, etc.). Finally, to top it all off, we add a layer of ink-like silkscreen, which can add some text and even logos to the PCB. A multi-layer PCB will have more copper layers in the middle of the board.
There are many layers in EAGLE as well, the figure below shows the layers used in this tutorial, we are designing a double-sided PCB. To turn any layer off or on, click the “Layer Settings…” button — — and then click a layer’s number to select or de-select it. Before you start routing, make sure the top and bottom layers (aside from tStop and bStop) are visible.
Adding Text Information and Adjusting the Dimension of the Board
We can now add some Text information on the Board like the Title and labels on the connectors on the Silk screen layer of the board.
Click on the Text Tool — — and enter your text, in this example: “LCD Keypad Shield”, click OK then select the layer like the tPlace layer. You could also add some few mounting holes from the library if your board needs mounting holes.
Now we can resize the board to cover only our components using the MOVE tool — — just click and move/drag to resize. The remaining thing now is to route all the airwires to generate the copper traces for the board.
Routing the Board
Routing is the process of turning all the airwires (yellow wires) connecting our components together as per our circuit diagram into copper traces. As we are designing a double sided PCB, we are going to put the copper traces on the top and bottom layers of the board.
We are going to make sure that the width of the traces are big enough to support the current going through them (the power traces are usually thicker than the signals traces). we must also make sure not to overlap two different signals.
We can either route our board manually or using the Autorouter (will attempt to route automatically the board, if there are few airwires left, you can route them manually).
To route manually, use the ROUTE tool– — (not the WIRE tool!). After selecting the tool, there are a few options to consider on the toolbar above