Defining Board Regions and Bending Lines

A Board Region is the term used to describe a user-defined area of the board that can have a unique layer stack assigned to it. When a new board is created it defaults to having a single board region, the outline of this follows the board shape. If the board design requires multiple layer stacks, then the designer can split the single default board region into multiple regions, and assign a unique layer stack to each of those regions. In the image below the board shape has been divided into three distinct board regions: the upper circle, the center strip, and the lower circle, these 3 regions have been created by placing the two horizontal dashed blue Split Lines.

The interesting board shape of the Bluetooth Sentinel design example. Note the shape has been divided into three distinct board regions, created by the two horizontal dashed blue Split Lines.

Splitting the Board into Regions

Defining a new board region or editing an existing region is done by switching the PCB editor to Board Planning Mode (View » Board Planning Mode, or press the 1 shortcut). You split the original, single board region into two regions by placing a Split Line.

Placing a Split Line

To place a Split Line:

1. Select View » Board Planning Mode (or press the 1 shortcut) to enter Board Planning Mode.
2. Select Design » Define Split Line to enter Split Line placement mode.
3. Click within the board shape to begin the Split Line definition process. One end of the line will attach to the closest point on the board shape outline to where you clicked, the other end of the line will attach to the cursor.
4. Position the cursor in the required location then click once to place the second end. 
5. You remain in Split Line placement mode, ready to place another Split Line if required. If not, right-click or press Esc to exit Split Line placement mode.

A board is split into distinct regions by placing a Split Line, which runs from one edge of the board shape to another edge.

The board has been split into 5 distinct regions by placing 4 Split Lines. Note that bending lines have also been placed .

Moving a Split Line

To move a Split Line:

1. Select View » Board Planning Mode or press the 1 shortcut to enter Board Planning Mode.
2. To relocate the end of a line, click, hold and drag it to the required location around the perimeter of the board shape. The cursor will be constrained to the current snap grid.

Removing a Split Line

To delete a Split Line:

1. Select View » Board Planning Mode or press the 1 shortcut to enter Board Planning Mode.
2. Click and hold by one of its end points, then press the Delete key. Alternatively, click, hold and move an endpoint to a point around the board shape that results in the split turning red (signifying an invalid split), then release.

Editing the Board Region Name and Assigning a Layer Stack

When a new board is created it will have a single region, and this region will be assigned the default layer stack, named Board layer stack. When the board shape is split into multiple regions, each new region is also assigned this default main layer stack. Each board region is also given a default name, with the original region named Default Layer Stack Region, and subsequent regions named using the format Layer Stack Region n. The task now is to give each region a more meaningful name, and also assign the required layer stack to that region.

To rename a region and assign a layer stack:

1. Select View » Board Planning Mode or press the 1 shortcut to enter Board Planning Mode.
2. Double click on on the board region to open the Board Region dialog.
3. Edit the Name as required.
4. Assign the Layer Stack by selecting the required stack from the Layer stack list.
5. Click OK to accept the settings and close the dialog.

Double-click on a region to define the region's name and assign a layer stack.

Placing and Positioning a Bending Line

To define how a flex board should bend, you place one or more Bending Lines. The Bending Line defines where on the surface of the flex region that the bend is to take place. The Bending Line also defines the angle and radius of the bend, and the width of the strip of board surface that is being bent. Bending Lines are placed and edited with the PCB editor in Board Planning Mode (View » Board Planning Mode, or press the 1 shortcut).

Placing a Bending Line

To place a Bending Line:

1. Select View » Board Planning Mode or press the 1 shortcut to enter Board Planning Mode.
2. Select the Design » Define Bending Line command.
3. Click inside the board region where the Bending Line is to be placed, one end of the line will attach to the edge of the region closest to the click location, the other end will attach to the cursor.
4. Position the second end in the required location then click once to place it.
5. You remain in Bending Line placement mode, ready to place another Bending Line if required. If not, right-click or press Esc to exit Bending Line placement mode.

Three Bending Lines (yellow, dashed) have been placed on this flex board region. The width of the yellow strip is the Affected area width.

Moving a Bending Line

To modify the location of an existing Bending Line:

1. Click once to select the Board Region the contains the Bending Line.
2. Click and hold on the Bending Line vertex, move it to the new location, then release the mouse button.

Precisely Locating a Bending Line

When a Bending Line is moved, the vertex will snap to locations on the current Snap Grid. As it is moved, it can also be snapped to existing design objects, such as lines on a mechanical layer. The image below shows a Bending Line vertex being positioned on the end of a line on layer Mechanical 2 (highlighted by the number 1). Note that the mechanical layer must be the active design layer for the snap behavior to work.

The number 1 refers to a Bending Line vertex being snapped to a line on Mechanical 2, note that this layer is the active layer.

To show the above process in more detail, the images below show the construction lines that have been placed on Mechanical 2 in 2D Layout Mode, which accurately define upper and lower reference points that can be used to place a 45 degree Bending Line.

The board in 2D Layout Mode, showing the construction lines to help accurately place the diagonal Bending Lines.

The board in Board Planing Mode showing the diagonal Bending Lines, which were snapped to the construction lines on Mechanical 2.

Removing a Bending Line

To delete a Bending Line, click and hold by one of its end points, then press the Delete key.

Configuring the Bending Line Properties

Board regions, Split Lines and Bending Lines are examined and edited in Board Planning Mode (press 1). Bending Lines can be edited interactively in the workspace, or they can be edited via the PCB panel when it is set to Layer Stack Regions mode. To display the panel, click the PCB button down the bottom right of the workspace and select PCB from the menu, then in the panel select Layer Stack Regions in the drop down list at the top of the panel.

To edit the properties of a Bending Line in the PCB panel:

1. Bending Lines can be edited in either 2D Layout Mode (press 2), or Board Planning Mode (press 1).
2. Enable the Select checkbox at the top of the panel.
3. Select the required region in the Stackup Regions section of the panel.
4. All Bending Lines within the selected region will be listed in the Bending Lines section of the panel, double click on a Bending Line in the panel to open the Bending Line dialog, as shown in the image below.
5. In the Bending Line dialog, edit two of the first three properties, for example the Radius and the Bending Angle. The third property will be calculated automatically (more on this below). Note that each Bending Line's Affected area width is displayed in dark yellow.
6. In the Bending Line dialog, set the Fold Index as required, this defines the sequence that the bends are folded when the Fold State slider or View » Fold/Unfold command the is used. The slider is in the panel, just below the Bending Lines section, use it to fold the board up in 3D mode.

Double-click to edit a Bending Line via the PCB panel, and configure its properties in the Bending Line dialog. Note the yellowish stripe, this shows the width of the surface that will bend for the specified angle and radius.

3D Display of a Rigid-Flex Board

Main article: Presenting a Rigid-Flex Design in 3D

Altium Designer includes powerful 3 dimensional display capabilities, you can switch to the 3D Layout Mode at any time by pressing the 3 shortcut (press 2 to return to 2D Layout Mode, or 1 to return to Board Planning Mode). This mode is ideal to examine the various board areas, including the flexible areas. In 3D mode the board defaults to display in its flattened state, that is no Bending Line settings are applied.

To apply all Bending Line settings and display the board folded:

1. Slide the Fold State slider in the Layer Stack Region mode of the PCB panel from the left to the right, or
2. Select View » Fold/Unfold (or press the 5 shortcut).

Notes on using the Fold State feature:

• One board region must have the 3D Locked checkbox enabled in the Board Region dialog to define the physical ground reference for the 3D display mode (where Z = 0). If this is not done, bends will not be applied when you move the Fold State slider.
• If the order that the bends are applied is important, set the Fold Index (Sequence values) in the Bending Line dialog so that the bends are applied one after the other. Sequence values that are the same, are applied at the same time during folding.

A rigid-flex board shown in: 3D unfolded, 3D folded, and 2D.