Working with a Board Shape Object on a PCB in Altium NEXUS

Parent page: PCB Objects

The Board Shape defines the shape of the finished board.

Summary

The board shape, also referred to as the board outline, is a closed polygon that defines the boundary, or extents, of the board. As well as providing a visual guideline of the extents of the space available for the placement and routing of the design, the board shape is also used by the internal power planes as the reference for the power plane edge pullback and the edge for splitting power planes.

Availability

The board shape is available only in the PCB editor. When a new PCB file is created, it opens with a default board shape.

There are a number of ways this shape can be altered. The commands available depend on the current View mode:

• Board Planning Mode - when viewing the board in planning mode, the following commands are available from the main Design menu:
  • Redefine Board Shape - use this command to interactively draw a new shape.
  • Edit Board Shape - use this command to interactively modify the shape of the board by moving vertices or sliding the edges of the shape.
  • Modify Board Shape - use this command to interactively modify by the board by adding new vertices.
  • Move Board Shape - use this command to move the location of the board shape within the workspace.
  • Move Board - use this command to move the board and all objects placed on it within the workspace.
• 2D Layout Mode - when viewing the board in 2D, the following commands are available from the Design » Board Shape sub-menu:
  • Define from selected objects - select a set of line and/or arc primitives that define a closed shape then use this command to redefine the board shape to match this shape.
  • Create Primitives From Board Shape - use this command when the board shape exists but there are currently no objects along the boundary.
  • Define Board Cutout - use this command to define a region that will result in a hole being cut through the board when the board is fabricated.
• 3D Layout Mode - when viewing the board in 3D, the following command is available from the Design » Board Shape sub-menu:
  • Define from 3D body - use this command to define the board shape by selecting the desired surface of a 3D model.

Interactively Redefining the Board Shape

Main article: Defining the Board Shape

After launching the Redefine Board Shape command (in Board Planning Mode), the cursor will change to a crosshair and you will enter the standard polygonal object placement mode. Board shape definition is made by performing the following sequence of actions:

1. Position the cursor and click to anchor the starting vertex for the board shape.
2. Move the cursor ready to place the second vertex. The default behavior is to place 2 edges with each click, with a user-defined corner shape between them. Refer to the Placement Modes section below for more details on changing corner modes.
3. Continue to move the mouse and click to place further vertices.
4. After placing the final vertex, right-click or press Esc to close and complete the definition of the board shape. There is no need to manually close the board shape as the software will automatically complete the shape by connecting the start point to the final point placed.

Placement Modes

When redefining the board shape there are five available corner modes, four of which also have corner direction sub-modes. During redefinition:

• Press Shift+Spacebar to cycle through the five available corner modes: 45 degree, 45 degree with arc, 90 degree, 90 degree with arc, and Any Angle.
• Press Spacebar to toggle between the two corner direction sub-modes.
• When in either of the arc corner modes, hold the  key to shrink or the key to grow the arc. Hold the Shift key as you press to accelerate arc resizing.
• Press the 1 shortcut key to toggle between placing two edges per click, or one edge per click. In the second mode, the dashed edge is referred to as the look-ahead segment (as shown in the last image in the set below).
• Press the Backspace key to remove the last vertex.

Press Shift+Spacebar to cycle through the five available corner modes, press the 1 shortcut to toggle placement between two edges or one edge.

Graphically Editing the Board Shape

Edit Board Shape

After launching the Edit Board Shape command (in Board Planning Mode), the existing board shape will turn green. The outer shape is defined by a series of edges: where each edge is represented by an end vertex, shown as a solid white square; and a center vertex, shown as a hollow white square. Each end vertex represents the location where two edges meet.

Editing handles for an example board shape after entering edit mode.

• Click and drag A to move the applicable end vertex.
• Click and drag B to move the applicable center vertex, effectively creating a new end vertex and splitting the original edge into two.
• Click anywhere along an edge away from editing handles then drag to slide that edge.
• Ctrl+click anywhere along an edge away from editing handles to insert a new end vertex.
• Click and hold on an end vertex then press Delete to remove that vertex.
• Exit editing mode by clicking anywhere in the workspace (on or away from the board shape).

Modify Board Shape

The Modify Board Shape command allows you to easily change the shape of the board. The command is accessed in Board Planning Mode and is run by selecting Design » Modify Board Shape. Once the command is launched, the cursor becomes a crosshair. Each time you click, a new vertex is added. The Shift+Spacebar keys can be used to change corner shapes.

Modifying the board shape.

Graphically Moving the Board Shape

After launching the Move Board Shape command (in Board Planning Mode), the existing board shape will turn green and an outline copy of the shape will be attached to the cursor. Move the shape to the desired new location within the workspace and click or press Enter to effect placement.

An outline copy of the board shape attaches to the cursor, while the original shape can be used as a reference.

Defining the Shape from Selected Objects

The board shape can also be defined from selected objects (in 2D Layout Mode). Typically this will be a set of lines and/or arcs placed on the Keepout layer or a mechanical layer. Use the following sequence of steps:

1. All the objects on a layer can be selected using the Edit » Select » All on Layer command from the main menus.
2. Once all the objects are selected, run the Design » Board Shape » Define from selected objects command. The board shape will update to follow the path defined by the selected lines. A warning dialog will appear if the software is unable to follow the centerline of the selected objects.

This Board Shape has been defined from a set of selected lines and arcs placed on the Keepout layer.

Defining the Shape from a 3D Body

This feature is accessed by using the Design » Board Shape » Define from 3D body command from the main menus (when in 3D Layout Mode). Prior to launching this command, you must have already placed a 3D body in the workspace. To define a board shape from the 3D body:

1. After launching the command, click the 3D body to select it, the cursor will change to a crosshair, ready to select the desired surface.
2. Move the cursor around the model, when a surface is found, it is highlighted by the rest of the model being made somewhat transparent.
3. Click on a flat surface of the model - this surface will become the new board shape.

An example of redefining the board shape based on the selected surface of a 3D body.

Creating Primitives from the Board Shape

As well as defining the board shape from selected primitives, it also is possible to create primitives from the board shape. Use this command when the board shape exists but there are currently no objects along the boundary. Situations where this command can be useful include:

• When you want to modify the board shape (or board cutouts) by modifying track and arc primitives first.
• When you need a keepout boundary for the board or keepout boundaries for board cutouts. This is discussed in more detail below in the Important Design Considerations When Using Board Cutouts section.

Cutting a Hole in the Board Shape

A board cutout can be placed anywhere in the board shape. To place a cutout, switch to view the board in 2D Layout Mode then use the Design » Board Shape » Define Board Cutout command from the main menus. Note that the cutout is actually a Solid Region object configured to be a negative object. To learn more about placing this type of object, refer to the Region object.

A Board Cutout has been placed on the Board Shape.

Important Design Considerations When Using Board Cutouts

Keep the following points in mind when creating a board cutout.

Keeping the Polygon Back from the Edge of a Board Cutout

Polygons that overlay a solid region board cutout will pour as close to the edge of the cutout as allowed by the applicable Clearance design rule. A specific Clearance design rule can be created if required, which could, for example, be scoped to apply between IsBoardCutoutRegion and InPolygon.

Defining a Route Tool Path Around the Edge of the Board and Cutouts

A common approach used to cut the finished board from the fabrication panel is to mill or route the board out of the panel. Board cutouts can also be routed out. A Route Tool path is defined by placing Line and/or Arc objects on a mechanical layer. This can be done manually or automatically by the software.

To define a Route Tool path for the board and any board cutouts:

1. With the board in 2D Layout Mode, run the Design » Board Shape » Create Primitives From Board Shape command. The Line/Arc Primitives From Board Shape dialog will open.
2. Define a suitable Width for the objects that will define the Rout Tool path. Consult with your fabricator if you are unsure of this.
3. Select an available mechanical layer. This layer should be reserved for just the Rout Tool path definition.
4. Enable the Include Cutouts option if the board has cutouts in it.
5. Enable the Route Tool Outline option. When this option is enabled the line/arc objects are placed so their edge touches the edge of the board shape and the edge of the cutout.
6. Click OK to create the Route Tool objects on the chosen mechanical layer. 
7. The mechanical layer used must be set as the Route Tool layer. To do this, access the Properties panel (with no objects selected in the workspace) and select the required mechanical layer from the drop-down listing for the Route Tool Path field (part of the Other grouping of options).

The images below show the Route Tool path defined on a mechanical layer.

A Board Cutout shown on the left, with a Route Tool path defined in the image on the right.

Keepouts

As well as the board shape, you also should define a placement and routing boundary around the edge of the board. This can be created automatically from the board shape itself using the Design » Board Shape » Create Primitives From Board Shape command (in 2D Layout Mode). Alternatively, this can be done manually by placing objects on the keepout layer. Objects placed on this layer define a no-crossing-allowed boundary for components and routing. Typically you want objects such as components and routing to be a certain distance from the edge of the board; this distance can be controlled by setting the applicable routing and component placement design rules. You also can define other routing and component keepouts areas for mechanical objects such as screw heads or other mounting requirements.

A keepout boundary defined by placing standard line objects on the keepout layer.

You also can define layer-specific keepouts on any copper layer. To do this:

1. Click on the layer tab of the required layer.
2. Define the boundary or area of the keepout area by placing layer-specific keepout objects (Place » Keepout submenu). Layer specific keepouts are standard objects with the Keepout attribute enabled. They are displayed in the same color as the layer with a keepout colored edge. Note that layer-specific keepout objects are not included in Gerber or ODB++ output files.