FreePCB User Guide

 Version 1.2


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5. PCB Layout (continued)

5.11 Parts

5.111 The Anatomy of a Part

Every PCB will include one or more parts.  Each part contains the following elements:

Actually, when we use the term "part" during PCB layout, we are usually referring to the part's footprint, because this is what we are working with in the layout. The actual part is the electronic component which will be soldered to the footprint when the PCB is assembled.  

Footprints have the following elements:

Some typical footprints are shown below.

In the screenshot above, U1 is an IC in a 20-pin DIP package, with though-hole pins. It has been placed on the top (or component) side of the board, so the silk-screen elements of the footprint are on the top silk-screen layer. It has been selected for editing, so its selection rectangle is visible. Since the top copper layer is the active routing layer, its  top pads are shown in the color for the top copper layer.

U2 is an IC in a 20-pin surface-mount PLCC package, also on the top side of the board. Its pads are drawn in the color for the top copper layer. C10 is a surface-mount capacitor in a chip package. R12 is a surface-mount resistor in a different chip package, on the bottom (or solder) side of the PCB. Its pads are drawn in the color of the bottom copper layer and its silk-screen elements are drawn on the bottom silk-screen layer. Also, its reference text is drawn as a mirror-image, so that it will be readable from the bottom of the board.

5.112 The Partlist

In FreePCB, all of the parts in a project are contained in a data structure called the partlist, which is empty when the project is first created. Normally, parts are added to the partlist by importing a netlist file from a schematic editor. This will be covered in Section 5.14: Importing Netlist Files. You can view or edit the partlist by selecting Parts... from the Project menu, which pops up the View/Edit Part List dialog, as shown below.

Each part in the project is listed by reference designator, package and footprint. Individual parts can be selected from the list by clicking on them, or multiple parts can be selected by clicking with the Ctrl key held down. The partlist can be modified using the Add New Part, Edit Selection, and Delete Selection(s) buttons. These will be described in the following sections.

Important Note: You should be careful when modifying the partlist, for two reasons. 

5.113 Editing Parts

Parts can be added, deleted or modified from either the View/Edit Part List dialog (shown above) or the layout window, using the methods described below.

5.114 Moving or Resizing the Reference Designator

The reference designator for a part may be moved by selecting it and pressing F4 ("Move Ref Tex"). Then you can drag it to a new position. While dragging, it can be rotated 90 degrees clockwise by pressing F3 ("Rotate Ref Text"). 

You can change the size of the text string by selecting it and pressing F1 ("Set Size"). This pops up the dialog shown below. You can change the character height and the stroke width. If you select Use default for height, the stroke width will automatically be set to 1/10 of the height.

5.115 Making the Reference Designator Invisible

If you set the character height of the reference text to "0", the reference designator will become invisible. To make it visible again, select the part and right-click, then select Set Ref. Text Size from the context menu that pops up. Then set the character height to a non-zero value.


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