Rubout Area for your PCB in KiCad

By Christian Torres

Background

What is a Rubout area?

Some electrical components will contain an antenna for wireless communication. These antennas can be affected by electromagnetic interference that are near the antenna. A “Rubout area” (also known as a “Keepout area”) prevents traces and components from being placed in a specific location. These can protect the antenna from any interference.

A rubout area can be used for other electrical components but in this case, we will use to it prevent interference of the BLE module. In this case, the antenna (see step 1 image) will have a rubout area to avoid any interference with signals.

Further Information

On the data sheet for the CY8CKIT-042-BLE-A Bluetooth® Low Energy (BLE) Pioneer Kit Guide, section 5.2.4 gives more detail in regards to the antenna on the module. Infineon also has provided an Antenna Design Guide for further details on Antenna & RF Design. Section 12 gives the design guidelines for antennas (see below).

Steps

For this tutorial we will be adding a rubout area for the CY8CKIT-143A PSoC® 4 BLE 256KB Module to prevent interference to the BLE antenna.

This tutorial is performed with the ground planes already placed. If you have not placed your ground planes yet, please follow this tutorial. You can add a rubout area before the ground planes, however it will be easier to place and see if you already have the ground planes made.

  1. Locate the antenna of your component.

  1. Locate the antenna on your PCB footprint design. Remember to follow the orientation that you made for the component.

It is important to know where to place the antenna is to be able place the rubout area in the correct location.

  1. Once your component are placed and traces are routed, place your component as close to a corner or edge as possible. This may vary based on your project design. By utilizing an edge or corner, you will limit the antenna from being near other components and maximize space. Should you place the antenna in the middle of your PCB, you will have a larger rubout area that will take up more space on your board and limit your placement of components.

Please note: The PCB design in the image below is an example made for the purpose of this demonstration. Do not copy it. Your PCB design should either be your individual subsystem or team design.

  1. Find and select “Add Rule Area” This can be done through the Place tab at the top of the KiCad program, or the sidebar shortcut.

  1. Select the point where you would like the rubout area to be. In this case we will select at the corner of the area. Then you will open the Rule Area Properties.

    Check all the boxes under basic rules. Uncheck all boxes below Area Name. You do not need to name the area, but you can if you would like. Be sure to select both layers.

  1. Enclose the area to which the rubout area will be. In this case we will enclose the area where the antenna will lie.

  1. Select the area that you outlined to be a rubout area.

  1. Now you will fill in the rub out area. This can be done by going to “edit” at the top of the KiCad program. Then you will select “Fill All Zones” You may also use the keyboard shortcut by pressing the letter “B” on your keyboard.

  1. You should now see an empty area which you outlined. Check to make sure this will apply to both the top and bottom planes of your schematic.

  1. Congratulations you have now created a rubout area for your PCB. You should also now notice you are not able to run any trace or place any components inside that area. You are now free continue with the rest of your PCB design.

    You should now be able to see the rubout area in your PCB design. You can also verify it in the 3D model viewer (see image below). To view this select “View” on the top row then select “3D Viewer”.

    You are also able to apply the rubout area before you place your ground planes. In this case, you will place ground plane last instead of first. See this tutorial for setting up your ground planes if you need help.

Things to check in case of mistakes:

  1. Make sure your rubout area applies to both the top and ground plane.

  2. Make sure you checked all the boxes in the basic rules section.

  3. Make sure the orientation of your antenna is near or close to an edge or corner as possible.

  4. Make sure that your rubout area does not affect any necessary traces or pads. The antenna is close to the module headers, be sure that you did not accidently affect a pin.

  5. Make sure that your rubout area does cover the antenna location.