Placement Rule Types

As well as defining a room by clicking the Define button in the design rule, rooms can also be created/edited using the various commands available from the Design » Rooms sub-menu. Note that a room created using one of these commands adds a new Room Definition design rule.

• When placing a room in the design using commands from the Design » Rooms sub-menu, the room can either be placed empty and the components associated at a later stage, or the room can be placed around components in the design, automatically associating them to the room. The scope (or query) for the room definition rule depends on whether all components are part of an existing component class or not. If they are, then this component class will be used. If not, a new component class is created, with these components as its members. It is therefore possible to have multiple rooms, each with a scope that targets a particular component class, and have one or more mutual component members between those classes.

• Use the Create room from selected components-based commands (Design » Rooms sub-menu) to automatically generate a Rectangular, Orthogonal or Non-Orthogonal shaped room, whose members are the selected components. The room will be sized accordingly, in order to fit all components in the selection, as defined by the limits of their bounding rectangles.

• Automatically re-wrap an existing room around a set of selected components, using one of the Wrap commands in the sub-menu.

• One technique to exactly positioning a room in the workspace is to place suitable Vertical, Horizontal, or Point (Snap) Guides, and enable snapping to Guides in the Properties panel. Learn more about Guides and configuring the Cursor-Snap System.

If rooms are being placed in the design to hold a group of components, those components can be grouped together by creating a component class (Design » Classes) and that class assigned to the room by setting the scope (Full Query) of the rule to InComponentClass('YourClassName').

• To move a class of components into their assigned room, run the Tools » Component Placement » Arrange Within Room command and follow the prompts on the Status bar.

• A component can be scoped by multiple Room Definition rules. In this case, all rules are obeyed. Rule contentions are not possible.

The shape of a room can be edited:

Graphically – to edit a polygonal room or perform polygonal-type edits on a rectangular room, use the Design » Rooms » Edit Polygonal Room Vertices command (or right-click on the room and run the command from the Room Actions sub-menu). Standard polygonal object editing techniques are used, learn more about editing polygonal shaped objects.

Numerically – select the room, then edit the vertices in the Properties panel.

Click, hold and drag to move a room. If components have been assigned to a room they move when the room is moved. Any nets associated to an object within the room will remain connected and the connection lines follow the object when the room is moved. Any routed track connected to the object that is outside the room will not be moved. To move a room without moving the components, temporarily disable the associated Room Definition rule. 

Learn more about modifying and moving a room.

 As well as being a design rule in its own right to contain or exclude components, a room can also be used to define the scope of another rule, such as Clearance, Height, Routing Width, Solder Mask Expansion, Power Plane Connections, and so on (), controlling the behavior of the design objects within that room (). As the room is to be used as an object rather than a rule, you can disable the rule, or set the query (rule scope) to False. The following two queries can be used when using a room object in another rules' scope definition:

• TouchesRoom(RoomName) - use to find objects that are completely or partially within the room.

• WithinRoom(RoomName) - use to find objects that are completely within the room.

Two modes for specifying vertical clearance are available:

• Infinite – clearance checking is performed using a value representing infinity. This means that any components placed above or below will be in violation. An example of use would be a board that has an adjustment mechanism that must remain accessible. Using this rule on that component will cause a violation against any components that protrude into the area above or below the component.

• Specified – clearance checking is performed using the exact shape defined by the component 3D bodies or component footprint properties. When using 3D bodies, it is possible to have an acceptable overhang between one component over another, provided they are not in violation. With this mode enabled, the Minimum Vertical Clearance constraint becomes available.

The value for the minimum permissible clearance, in the vertical sense, between components placed in the design. Enter a negative value to disable clearance checking for the components targeted by this rule. If a component includes a 3D model, it is the clearance above the model. If there is no 3D model, it is the clearance above the component's Height property (). 

Enable this option to show lines between the points of greatest violation between components. The failure distance is displayed at the line, which can be useful in determining the distance required to move an object to resolve the violation.

• Enabled – all components that do not include a 3D Body are excluded from being clearance checked by this rule.

• Disabled – for components that do not include a 3D body, the component's DRC bounding box defines its area in the X-Y plane, and the component Height attribute is used for clearance checking in the vertical (Z) direction.

• Enabled – instead of the actual 3D model being used for clearance checking, the component boundary is used. The component boundary is defined by the DRC bounding box. Note that if the shape defined on the courtyard layer is a closed shape created from tracks/arcs, whose end vertices are coincident (exactly touching), the centerline of those tracks is used to define the bounding box. Since it is the track centerlines that are checked, this feature allows courtyard outlines to be overlapped when the Minimum Horizontal Clearance = zero ().

• Disabled – the 3D model is used for clearance checking. If the component does not include any 3D Body objects, the DRC bounding box is used. If the component includes a 3D Body, then the exact shape of the contained 3D model is used for clearance checking without regard to objects on any other layer. Exact shape detection applies to all 3D shapes, including imported 3D models, as well as extruded, cylindrical and spherical 3D Body objects. 

The area that the component occupies on the fabricated board is defined by the component footprint. The component that is mounted on that footprint can be modeled using 3D Body objects. As well as modelling the component shape out of one or more 3D body objects, a 3D Body object can be used as a container into which a generic MCAD format model is imported.

• Learn more about creating a PCB footprint.

• Learn more about working with 3D bodies. 

How DRC views the component – the DRC Bounding Box 

Each component is made up from a collection of track, arc and pad objects placed on various layers. The basic approach the software uses to interpret this set of objects as a component is determined by an advanced option called PCB.ComponentSelectioni.

• The fundamental difference between the selection modes is: choosing to use the combination of the objects on multiple layers (by graphic mode), or choosing to use the objects on a specific layer, (by layer mode).

• In the default by graphic mode, the component selection area is defined by the combined geometries present on the Courtyard (Layer Type, not the Layer Name) + the Silkscreen + 3D Body objects + Copper layers (including soldermask expansions). 

• In the by layer mode, the first layer that contains geometries is used, with the layers being searched in the following order: Courtyard (Layer Type); 3D Body; Silkscreen + Copper Layers; Copper Layers (including soldermask expansions). 

• The mode is chosen by setting the value of the PCB.ComponentSelection Advanced Setting. Learn more about the component selection area and the available selection modes.

In terms of how the DRC system views the components:

• The DRC system obeys the PCB.ComponentSelection choice of using either multiple layers (by graphic mode), or a single layer (by layer mode).

• In the by graphic mode, the DRC system extends the view of each component beyond what the selection system uses by defining a DRC bounding box, which include the contents of all component layer pairs and all mechanical layers (not just those listed above that are used for component selection).

• Note that if all of component objects are within the outline defined on the Courtyard layer then that exact outline is used, not the DRC bounding box. When the outline on the Courtyard layer is being used the outline follows the centerline of the objects, allowing curved component shapes to be defined ().

• If components scoped by a Component Clearance design rule have the component boundary defined by a closed shape on the Courtyard Layer Type and the rule's Minimum Horizontal Clearance value is set to 0, there will be no violations of this rule when component courtyard outlines exactly overlap (). Learn more about Mechanical Layers and the Courtyard Layer Type.

The Component Clearance rule checks for clearance violations between bond wires and other (non bond wire) objects in the 3D space (). For more information about wire bonding, refer to the Wire Bonding page.

The layers permitted to be used when placing components. The following layer options are available:

• Top Layer - allow component placement on the top layer.

• Bottom Layer - allow component placement on the bottom layer.

The rule acts as a test when performing a Batch DRC, ensuring that targeted components have been placed on a permitted layer. To give an example of how this rule could be used to detect if a bottom-side component was suitable to pass through a wave solder bath:

• The schematic components include a parameter, for example SupportsWaveSolder, which gets the value set to Yes or No during schematic capture.

• A Permitted Layers rule is added during PCB design with the following settings:

Full Query: CompParameterValue('SupportsWaveSolder') <> 'Yes'

Permitted Layers: the Top Layer constraint is enabled, with the Bottom Layer constraint disabled.

This rule then checks that components that do not include the parameter SupportsWaveSolder = Yes are mounted on the Top Layer. If they are not, they are flagged as being in violation during Batch DRC. The advantage of this approach is that it detects both components that have the parameter/value SupportsWaveSolder = No, as well as components that do not include the SupportsWaveSolder parameter.

• Minimum – the value for the minimum permissible component height.

• Preferred – the value for the preferred component height.

• Maximum – the value for the maximum permissible component height.

The height of a component is defined by:

• If the component includes a 3D body, the overall height of that 3D body object is used.

• If the component does not include a 3D body, the component's Height property is used.