How to Lay Out a PCB Using Eagle

Learning automated ways of laying out a PCB is important to create relevance for your knowledge in the present, fast-paced world. In a string of board designing tools that have become popular amongst users, one name that is most common is Eagle. This software guides on various points, such as, dimensions of the board, the arrangement of parts and the connection of copper traces. Here is the stepwise procedure to create a PCB layout using Eagle.

  1. Bringing schematic on board

Eagle schematic tool is used to create a schematic diagram to start with. This is followed by bringing schematic on board. To complete this process, ‘Generate/Switch to Board’ command is used. This command is available in File menu and prompts the opening of a new editor. All parts that were introduced in schematic diagram are brought to this editor and are stacked one above the other, preparing them to place and route as per conceived design.

  1. Composing the PCB

A typical 2 layer PCB looks something like this:

PCB service providers use Eagle to create layers which are overlapped systematically to produce the design. In this tool, you will be given around 16 layer names to select or deselect, depending upon the requirement laid out in the schematic diagram:

  1. Top and bottom layer of copper

  2. Through-hole pads

  3. Vias

  4. Unrouted airwires

  5. Outline of the board

  6. Silkscreens – top and bottom

  7. Origins – top and bottom

  8. Top and bottom stopmasks (solder masks)

  9. Non-conducting holes

  10. Top documentation layer

According to design, you can turn on or off any layer. Overlapping objects are also to be dealt with while creating a layout. Since Eagle is two-dimensional, overlapping objects that are to be picked up are not understood clearly. Eagle solves this problem by giving us options from the list of overlapping objects

Till now, all these points are confined to preparing for laying out the PCB. The actual layout process involves:

  1. Arranging the board

When the schematic is transferred onto the board, it requires a lot of arranging the components. The gold wires, also known as airwires, connect between the pins and represent the connections made on the schematic. Arranging the parts is done to minimize the area covered by PCB dimension outline. The aim is to reduce the size of PCB as small as possible so that cost can be controlled.

  1. Understanding the grid

Eagle offers the ease of understanding the grid better. It helps adjust the granularity of the grid by using icon – . Once the grid is defined, all parts, traces and other objects are made to snap on to the Size box. There is an Alt key available which can be pressed to access the alternately possible grid.

  1. Moving the parts

The parts are moved with the help of icon – . The options of rotate, or change angle etc are provided in Eagle to enable better fitting of the parts on to the board. The parts should be moved so that these are not overlapped, airwires are not frequently crossed, and those placement considerations, which are crucial for faster signal movement and better performance, are taken into account, and finally, the placement should be loose enough to make the routing smooth.

  1. Dimension layer adjustment

In this step, you will require using icons – (delete) and (wire) tool quite often. When the existing lines are removed, delete function helps and wire is needed to draw a new outline, if required doing it from scratch. It is preceded by setting the layers to 20 dimensions. Refrain from intersecting the dimension layer with any hole, as it will disrupt the connection completely.

  1. Routing the board using a route tool

The above is the bar of options that you come across on Eagle while creating copper traces. You can decide whether you want to start with layer 1 (topmost) or layer 16 (Bottom most). In routing, we are basically converting all gold airwires into copper traces which are further classified as top and bottom. Before starting the routing process, using the options above, you can choose various parameters, the bend style to continue with after selection of layer. Normally, 45o is the bend angle chosen. You can also choose the width of the copper trace which should preferably be 0.001” to 0.007” wide.

Actual process

You start the process by picking a pin and left click on it and drag the line till the termination point of airwire. Good connection starts glowing and a red or blue line defines the trace. The resulting trace is completed by left-clicking the top of the pin.

  1. Placement of vias

Vias are the tiny copper filled holes that are used amidst the trace route to mark its path when the trace goes from one side of the board to another. Placing a via in the middle of the route is done by left-clicking the black ether to define the trace down between pins. You can continue routing till the end by clicking the middle mouse button to swap the sides, while on the way to your destination.

  1. Completing the routing

The routing process is completed with route clearance and ripping up the route wherever required. EAGLE is provided with RIP-UP tool wherever it is required to delete the trace or redo it.

  1. Quality testing

Once you have finished the routing process, you need to eliminate errors after checking for them critically. The route checking is done by verifying the board with the schematic diagram to ensure that all traces mapped on the latter are there on the final PCB layout. Design rule check is also done for quality testing. If nothing is missed, EAGLE will display the message, “Ratsnest – Nothing to do!”

Finally, the touchers and silkscreen are added and quality testing is again done. All satisfactory results are stored in soft files called Gerber files.

To conclude, EAGLE is a reliable way to lay out a PCB board. It not only helps build PCB smoothly, but also enables documenting of work so that it can be used and improvised by the future users.

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