Defining a Bending Zone for Your PCB in Altium Designer

Created: December 15, 2022 | Updated: December 15, 2022

Parent page: Designing a Rigid-Flex PCB

There are two rigid-flex design modes available in Altium's PCB design software. The original, or standard mode, referred to as Rigid-Flex, supports simple rigid-flex designs. If your design has more complex rigid-flex requirements, such as overlapping flex regions, then you need the Advanced Rigid-Flex mode (also known as rigid-flex 2.0). The mode is chosen in Tools menu in the Layer Stack Manager.

The fundamental difference between the modes is that in the original mode, the board shape is split into separate board regions by placing a Split Line, and that Split Line remains as an object defining where one board region ends and another begins. In the Advanced mode each board region is placed separately, or if a larger region is Sliced it becomes two separate region objects. In the Advanced mode, the edges of adjacent board regions define where those two regions meet, not the presence of a Split Line. Because of this difference, there is no Split Line object when the board is in the Advanced Rigid-Flex mode.

Learn more about Designing a Rigid-Flex PCB

Working with Bending Lines

Bend Lines are defined and edited in Board Planning Mode (View menu).

The View menu has three PCB editor working modes with easy-to-remember shortcuts, allowing you to quickly switch between:

  • Board Planning Mode (1)
  • 2D Layout Mode (2)
  • 3D Layout Mode (3)

The default behavior when switching between 2D and 3D view modes is to retain separate zoom and orientation settings for each view mode. If you want to see the same location and orientation of the board as you switch, press Ctrl+Alt+2 or Ctrl+Alt+3, instead of 2 or 3.

Defining Bending Lines (Standard Rigid-Flex Mode)

You've just opened a PCB and are wondering if it is using the standard rigid-flex mode or the advanced rigid-flex mode?

You could open the Layer Stack Manager to check. Alternatively, switch to Board Planning Mode (1 shortcut) and have a look at the Active Bar:

Standard Rigid-Flex mode
Advanced Rigid-Flex mode

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 as well as 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).

A Bending Line can only be placed on a region that is configured as a Flex region in the Layer Stack Manager.


A Bending Line is placed over the flexible region and configured so the board can fold 180 degrees. This video demonstrates placing a Bending Line in Standard Rigid-Flex mode.

Placing a Bending Line (Standard Rigid-Flex Mode)

To place a Bending Line:

  1. Select View » Board Planning Mode or press the 1 shortcut to enter Board Planning Mode.
  2. On the Mutli-layer tab, 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.

The PCB panel in Layer Stack Regions mode displays Bending Lines data. Double-click on an entry to open the Bending Line dialog. 

Three Bending Lines have been placed on this flex board region. The width of the orange strip is the Affected area width.
Three Bending Lines have been placed on this flex board region. The width of the orange strip is the Affected area width.

When a board region is set to use a Flex layer stack, a Bending Line is automatically added vertically down its geometric center. Remove or reposition and configure this Bending Line as required.

Moving a Bending Line (Standard Rigid-Flex Mode)

To modify the location of an existing Bending Line:

  1. Select View » Board Planning Mode (or press the 1 shortcut) to enter Board Planning Mode.
  2. Click once to select the Board Region the contains the Bending Line. The handles for all bending lines within that region will be displayed.
  3. To relocate the end of a line, click, hold and drag the node to the required location on the perimeter of the board region outline. The cursor will be constrained to the current snap grid and/or existing design objects.
  4. The bend location will be redefined by the Bending Line's new position.

Select and drag a Bending Line end node to change bend's positioning on the board.
Select and drag a Bending Line end node to change bend's positioning on the board.

Precisely Locating a Bending Line (Standard Rigid-Flex Mode)

When a Bending Line is moved, the handle 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 handle 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 handle being snapped to a line on Mechanical 2; note that this layer is the active layer.
The number 1 refers to a Bending Line handle 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 that 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 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 that were snapped to the construction lines on Mechanical 2.The board in Board Planing Mode showing the diagonal Bending Lines that were snapped to the construction lines on Mechanical 2.

Removing a Bending Line (Standard Rigid-Flex Mode)

To remove a Bending Line:

  1. Select View » Board Planning Mode (or press the 1 shortcut) to enter Board Planning Mode.
  2. Click and hold one of its end points then press the Delete key. Alternatively, select and delete a bending line entry in the PCB panel Bending Lines region.

When a board region is set to use a Flex layer stack, a Bending Line is automatically added, vertically down its geometric center. Remove, or reposition and configure this Bending Line as required.

Configuring the Bending Line Properties (Standard Rigid-Flex Mode)

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 design space or they can be edited via the PCB panel when it is set to Layer Stack Regions mode. To display the panel, click the Panels button at the bottom-right of Altium Designer, then select PCB from the menu. In the panel, select Layer Stack Regions in the drop-down at the top of the panel. In this mode, the panel shows:

  • The available board layer stacks in the Layer Stacks region.
  • The Regions assigned to those stacks in the Stackup Regions region.
  • The Bending Lines defined in the selected Region in the Bending Lines region.

When entering Board Planning Mode, the PCB panel will automatically be configured to Layer Stack Regions mode.

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 box at the top of the panel.
  3. Select the Board Region that contains the Bending Line in the Stackup Regions area in the PCB panel.
  4. Select the Bending Line from the list in the panel's Bending Lines region. The bending line will be highlighted (selected) on the board if the PCB panel's Select option is enabled. A Bending Line entry can also be deleted from the Bending Lines region.
  5. Double-click on the Bending Line entry in the Bending Lines region to open the Bending Line dialog as shown in the image below.

  6. In the Bending Line dialog, edit two of the first three properties, for example the Radius (the distance away from the bend surface that the bending center-point is located) and the Bending Angle (the angle that the surface of the flex region is to bend). The third property - Affected area width (the width of surface area that will be bent for the given Radius and Bending Angle) - will be calculated automatically (more on this below). Note that each Bending Line's Affected area width is displayed as an orange shaded region.
  7. In the Bending Line dialog, set the Fold Index as required to define the sequence that the bends are folded when the Fold State slider in the PCB panel or View » Fold/Unfold command is used, which are used to fold the board in 3D mode. The bend with the lowest value is applied first, through to the highest value.

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, the Affected area width for each defined Bending Line will not be displayed.

The Bending Line dialog can also be accessed by pressing Tab while placing or moving a Bending Line handle, or by double-clicking on a Bending Line handle.

Summary of Defining Bends (Standard Rigid-Flex Mode)

A bending Line is a linear object that is placed across a region to define the location, radius and angle of the bend that is to be applied to that flex region of the board.

Defining a Bending Line:

  • Bending Lines are placed in Board Planning Mode (1 shortcut).
  • To place a Bending Line, run the Design » Define Bending Line command.
  • Place the Bending Line across the flexible board Region. It is not necessary to precisely touch each edge of the region with the start and end of the Bending Line, the software will automatically extend it (if too short) or reduce it (if too long). At least one end of the Bending Line must touch or pass over the edge of the Region.
  • To edit the properties of a Bending Line, click anywhere within the region to display the verticies for all Bending Lines within that region, then:
    • Double-click on the vertex of a Bending Line to open the Bending Line dialog, or
    • Display the PCB panel and set it to Layer Stack Regions mode, where you can examine and edit the Regions and Bending Lines.
    • Set the Bending Angle and the bend Radius and as required.
    • Bends are folded in the order of their Fold Index, use this feature when the folding order is important to check.
  • To move a Bending Line, click and drag on each vertex.
  • A Bending Line can be removed by clicking and holding on one of the vertices, then pressing Delete on the keyboard.
  • Bending Lines cannot be applied to the edge of a board cutout. If your board requires this, switch to Rigid-Flex Advanced mode.

Defining Bending Lines (Advanced Rigid-Flex Mode)

You've just opened a PCB and are wondering if it is using the standard rigid-flex mode or the advanced rigid-flex mode?

You could open the Layer Stack Manager to check. Alternatively, switch to Board Planning Mode (1 shortcut) and have a look at the Active Bar:

Standard Rigid-Flex mode
Advanced Rigid-Flex mode

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 bending is to take place. The Bending Line also defines the angle and radius of the bend. The width of the strip of board surface that is being bent is displayed in orange, this width is calculated from the bend angle and radius (learn more about the bending line properties). Bending Lines are placed and edited with the PCB editor in Board Planning Mode (View » Board Planning Mode, or press the 1 shortcut).


A Bending Line is placed over the flexible region and configured so the board can fold 180 degrees. This video demonstrates placing a Bending Line in Advanced Rigid-Flex mode.

Placing a Bending Line (Advanced Rigid-Flex Mode)

To place a Bending Line:

  1. Select View » Board Planning Mode or press the 1 shortcut to enter Board Planning Mode.
  2. Select the Place » Define Bending Line command, or click the  button on the Active Bar.
  3. A Bending Line is placed over the required Board Region, it does not attach to it (Bending Lines are associated with one or more Board Regions by the Stack Regions property). Click near the edge of the Board Region to define the Bending Line start location.
  4. Move the cursor to the required end location and click to place the Bending Line. Note that at least one end of the Bending Line must touch or cross the boundary of the Board Region that it applies to.
  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.

The properties of a selected Bending Line can be edited in the Properties panel. Because the Bending Line is on top of a region, you might find that when you click on the Bending Line the region underneath it selects instead. Without moving the cursor, click a second time to select the Bending Line instead of the Board Region.

The properties of the selected Bending Line are displayed in the Properties panel.
The properties of the selected Bending Line are displayed in the Properties panel.

  • It is not critical to exactly start or finish the Bending Line on the edge of the Board Region, the software will automatically extend or shrink the Bending Line so that it is defined from one edge of the region to the other edge.
  • Ensure that the correct Board Region is enabled in the Stack Regions section of the Properties panel.

Moving a Bending Line (Advanced Rigid-Flex Mode)

To modify the location of an existing Bending Line:

  1. Select View » Board Planning Mode (or press the 1 shortcut) to enter Board Planning Mode.
  2. Click and hold on the vertex at either end of the Bending Line, then drag that vertex to the required location and release the mouse button. The cursor will be constrained to the current cursor snap settings, press Ctrl+E to change the settings as you work.
  3. The bend location will be redefined by the Bending Line's new position.

Select and drag a Bending Line vertex to change the Bending Line's position on the board - the cursor will be constrained by the current cursor snap settings.
Select and drag a Bending Line vertex to change the Bending Line's position on the board - the cursor will be constrained by the current cursor snap settings.

Precisely Locating a Bending Line (Advanced Rigid-Flex Mode)

When the handle of a Bending Line is moved the handle will snap in accordance with the current snap settings. Press Ctrl+E during movement to pop up the snap setting interactive control panel, as shown in the image below. Press Esc after changing settings to apply the settings and close the panel.

As well as snapping to the snap grid and workspace guides, the Bending Line can also be snapped to existing design objects, such as lines on a mechanical layer. The image below shows a Bending Line handle being positioned on the end vertex of a line on a Mechanical layer. Note that the current Hotspot Snap setting applies (shown on the Status bar) during movement, if the mechanical layer is not the active design layer Hotspot Snap must be configured to All Layers for this snap behavior to work. Press the Shift+E shortcut to cycle the Hotspot Snap setting through the available modes, as you work.

The handle of a Bending Line is being snapped to the vertex of a track placed on a mechanical layer.
The handle of a Bending Line is being snapped to the vertex of a track placed on a mechanical layer.

Removing a Bending Line (Advanced Rigid-Flex Mode)

To remove a Bending Line:

  1. Select View » Board Planning Mode (or press the 1 shortcut) to enter Board Planning Mode.
  2. Click and hold on one of its vertices to select the Bending Line, then press the Delete key.

Configuring the Bending Line Properties (Advanced Rigid-Flex Mode)

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

  1. Switch to Board Planning Mode (press 1).
  2. Click anywhere within the orange band of the Bending Line to select it.
  3. The Bending Line can be edited in the Properties panel.

Properties

  • Name - the user-definable name of this Bending Line. Naming each Bending Line can help distinguish their function in the design.
  • (X/Y) the X and Y location coordinates of the reference vertex of the Bending Line. Edit to change the X or Y position of the Bending Line. Values can be entered in either metric or imperial; include the units when entering a value whose units are not the current default.
The  icon to the right of this region must be displayed as  (unlocked) in order to access the location fields. Toggle the lock/unlock icon to change its lock status.

Stack Regions

List of all Board Regions that are underneath the selected Bending Line.

  • Used - enable the checkbox to apply the Bending Line to the named Board Region.
  • Name - the name of the Board Region to which this Bending Line can be applied.

Bend Line

  • Start (X/Y) - the X and Y location coordinates of the first Bending Line vertex. Edit to change the X or Y position of that Bending Line vertex.
  • Angle - the angle that the Bending Line is oriented in the design space.
  • Length - the distance between the Start and End vertices.
  • End (X/Y) - the X and Y location coordinates of the second Bending Line vertex. Edit to change the X or Y position of that Bending Line vertex.
  • Fold Index - value is used to determine the order that the bends are applied when the rigid-flex board is folded in 3D Layout Mode. The bend with the lowest Fold Index value is applied first, through to the highest Fold Index value.

Bend Zone

  • Radius - orthogonal distance from the Board Region surface to a point in space that the bending occurs around.

Bend Angle

  • Default - the angle of the applied bend. Enter a negative value to apply the bend in the other direction.

From the bend angle and the radius, the software calculates the area of the Board Region that will bend. This is displayed as the orange area that extends out from each side of the Bending Line.

The defined bends can be applied when the board is displayed in 3D mode, press the 5 shortcut to fold the board. The rigid Board Region that has the 3D Locked checkbox enabled is the physical ground reference for the 3D display mode (where Z = 0). If the board does not fold as expected, check that the correct rigid region has the 3D Locked checkbox enabled. Note that it is not necessary to uncheck the option in one Board Region before enabling it in another.

The Properties of a Bending Line

Bending Lines have the following inter-related properties:

  • Bend Angle (a) - the angle the surface of the Flex region is to bend.
  • Radius (r) - the distance away from the bend surface that the bending center-point is located.
  • Width (w) - the width of surface area that will be bent for the given Radius and Bend Angle.

The relationship between the Bend Angle, Radius and width can be expressed as:

  • w = a/360 * 2*Pi*r
  • or in words, width = Fraction of the circumference being bent * Circumference

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