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Even the simplest board needs design detail beyond the tracks and pads that implement the circuit. It might be the board dimensions or the fabrication detail, it might be the component courtyards, or it might be the 3D component models.
In Altium Designer, this type of additional information is detailed on Mechanical Layers. These layers can be included in printouts or in fabrication outputs, as required.
Mechanical layers are added, edited and removed in the View Configuration panel. Their display state is also configured in the panel. Use the button at the bottom-right of the workspace then select View Configuration or press the L shortcut key to display the panel.
There are several layer types that can be specified when adding a mechanical layer. Right-click in the Mechanical Layers region of the View Configuration panel then select the Add Component Layer Pair command or the Add Mechanical Layer command from the context menu. In the Edit Layer dialog that opens, use the Layer Type drop-down to select the required layer type. Available layer types are defined below.
.Designatorspecial string. This layer pair can then be included in assembly drawings that require the component designator to be displayed. Learn more about special strings.
.Commentspecial string. This layer pair can then be included in assembly drawings that require the component value to be displayed. Learn more about special strings.
In some situations, the extra detail included on a mechanical layer is only needed once, for example, assembly notes that detail the component load order and important assembly instructions. In this situation, a standard mechanical layer is added, named, and where possible, has its Layer Type assigned (more on this below).
If the extra detail is required for a component, for example, component courtyard outlines, there needs to be two mechanical layers assigned: one layer holding the courtyard detail when the component is placed on the top side of the board; the other mechanical layer holding that same courtyard detail if the component is flipped to the bottom side of the board.
In this situation, a pair of mechanical layers are added as a Component Layer Pair. When mechanical layers are added as a Component Layer Pair, they are displayed in the Component Layer Pairs section of the View Configuration panel, as shown below.
A common approach to managing mechanical layer usage is to assign a dedicated layer number for each required mechanical layer function. This approach requires all designers to adhere to the same layer assignment and numbering scheme. It can also create difficulties when components are obtained from other sources that do not follow the same assignment and numbering scheme. If a different scheme has been used, the design objects must be moved from their current mechanical layer to the mechanical layer assigned for that function.
This issue is resolved with the introduction of the Layer Type property. When a component is placed from a library into the PCB editor, or copied from one library to another, or created by the IPC Footprint Wizard, existing Layer Type assignments are automatically matched, regardless of the mechanical layer number(s) assigned to those Layer Types. The objects are relocated on the correct layer(s) according to their Layer Type. If the software is unable to match by Layer Type, it will fall back to matching by Layer Number.
For both individual mechanical layers and Component Layer Pairs, you can select a Layer Type from a pre-defined list of types. The images below show the list of available Layer Types. You can access the dialogs shown below by right-clicking on an individual layer, then selecting the Edit Layer or Add Component Layer command from the menu.
When a Layer Type is assigned, the layer automatically has its Layer Name property changed to be the same as the Layer Type. This can be overridden, if needed, by typing in a user-defined name. When a layer has a user-defined name and a Layer Type assigned, both are displayed with the Layer Type shown in brackets, as shown below for the Layer Pair
If an individual mechanical layer or a Component Layer Pair has a Layer Type assigned, the mechanical layer number is no longer displayed, reflecting that the software will manage and map the layer by type instead of number.
There is one exception to the naming behavior just described when a Layer Type is assigned - a user-defined name is not permitted when the Layer Type is set to Route Tool Path. The reason for this is that older versions of the software use the name of the Route Tool Path layer to identify the layer that contains the route information (also referred to as rout information). Fixing the naming of this layer ensures that the design will continue to function correctly in an older version.
The Route Tool Path layer type is used to indicate the layer that contains the mechanical routing information. A typical approach to using this layer is to place tracks and arcs around the outer edge of the board shape to define the machining path and width. Solid sections are left to hold the board within the panel, then a series of small holes are placed across each solid section to create perforations (often referred to as mouse-bites), allowing the board to be snapped out of the panel once the assembly process is complete.
When the board is displayed in 3D mode, objects detected on the Route Tool Path layer are displayed as a routed slot in the board, as shown below.
Use the Line/Arc Primitives from Board Shape dialog to trace the outside of the board shape with tracks and arcs. Enable the Route Tool Outline option in the dialog to have the objects placed outside the board shape rather than centered along its edge. Some designers prefer to add the fabrication information when they use the Embedded Board Array feature to create an assembly panel, rather than including this detail in the actual board file.
Where possible, it is recommended to edit the source library and assign Layer Types. When a component footprint is placed (or copied) from a library, mechanical layers and Component Layer Pairs of those Layer Types are automatically created in the target board (or library) if they do not exist. If those Layer Types already exist in the target board (or library), the layer contents are automatically mapped to the correct layer.
Mechanical layers are used for a broad variety of tasks, detailing information used during board design, fabrication, assembly, and product documentation. To support all of these requirements, mechanical layers can be excluded or included in all forms of layer-based output generation, including printing and output file generation.
Any of the layers that are present in the design can be included in the specification of a PCB Printout, including mechanical layers. Printouts are configured by adding the required layers and setting their order in the PCB Printouts dialog.
► Learn more about Configuring PCB Printouts
All fabrication-type outputs, such as Gerber and ODB++, allow mechanical layers to be included as an output Layer to Plot or to be added as detail to every layer being plotted. The output is generated when the configured output generator is run by using an ODB output generator in an OutputJob Configuration file (*.OutJob).
► Learn More about Outputs
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