2.Footprint Assignment

Objective

In this section, you will use the Symbol Fields Table to link your logical schematic symbols to their physical hardware dimensions.

What are footprints?

Before assigning components, it is necessary to establish the difference between logical intent and physical reality.

The Schematic Symbol (The Idea): In the schematic editor, a resistor is a theoretical concept represented by a zigzag line. It tells the software how the electricity flows, but it contains zero physical information.
The Footprint (The Reality): The footprint dictates the physical, real-world dimensions of that component on the fiberglass board.

For example, a 330-ohm resistor can exist as a large through-hole component with long wire legs, or as a microscopic surface-mount rectangle. The software cannot guess which one you are holding. It requires the footprint to know exactly how far apart to drill the copper holes on the PCB. The footprint is the digital stencil of the physical object.

Getting to Know the Symbol Fields Table

Instead of assigning footprints one by one, the Symbol Fields Table provides a centralized spreadsheet of every component in your design. This is the most efficient way to assign values and physical footprints in bulk. Below, you will get an overview of how it works, then put it into practice with the circuit your building.

The Symbol Fields table

To open the Symbol Fields table, click the grid like button in the top toolbar and a window will pop up.

Reference Column: Displays the unique identifier assigned to each component (e.g., D1, J1, R1).
Value Column: Allows you to define the specific electrical value or name of the component.
Footprint Column: The field where you will assign the specific physical dimensions from the KiCad library to your logical symbol.
Apply, Save Schematic & Continue: The button located at the bottom right, which must be clicked to commit your spreadsheet changes back to the schematic canvas.

Exercise: Continue with your first schematic Blinking LED

Step 1. Open the Table

Navigate to the top toolbar and click the Symbol Fields Table icon (it resembles a small spreadsheet).

Step 2. Assign Values

Locate the row for your resistor (R1). Click into the Value column and change the text to 330 to match your physical circuit.

Step 3. Assign Footprints

Click inside the Footprint column for each component. A small library book icon will appear in the cell. Click this icon to browse the footprint library and assign the following precise dimensions:

Connector (J1): Connector_PinHeader_2.54mm:PinHeader_1x02_P2.54mm_Vertical
Resistor (R1): Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P10.16mm_Horizontal
LED (D1): LED_THT:LED_D5.0mm

A Note on Footprint Types: THT vs. SMD

When browsing the footprint libraries in the previous step, you likely noticed the suffixes _THT and _SMD. These denote the two primary methods for physically mounting components to a printed circuit board.

THT (Through-Hole Technology): These components have long metal wire legs (leads). To mount them, you insert the legs through holes drilled completely through the PCB and solder them on the opposite side. THT is ideal for manual soldering, physical durability, and directly matches the physical breadboarding components you are already familiar with.
SMD (Surface-Mount Device): These components do not have wire legs. Instead, they have small metal contacts that sit entirely flat on the surface of the PCB and are soldered directly to exposed copper pads. SMD components are significantly smaller and are the standard for modern, automated electronic manufacturing.

For this introductory layout, we exclusively selected THT footprints because they are the easiest to solder by hand and correspond directly to the components in your physical kit.

Step 4. Apply and Save

Click Apply, Save Schematic & Continue at the bottom of the window. Once the changes are applied, click OK to close the Symbol Fields Table.

This is how your table should look like once its all filled out.

Tip: Don't forget to periodically save your work as you go by selecting File > Save or Ctrl + S.

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