Breakouts are used to create predefined ‘potential’ track patterns for use where space around pads is restricted on a Footprint. Typically these patterns would be used where routing is very dense on a surface mounted device, and where ’ human’ intervention is the most sensible option. The breakout patterns are more suited to designs where automatic routing will take place. They often give the router more solutions to what may appear a ‘fixed’ option. For instance on a surface mounted QFP where all the pads are on one side of the design, by using breakouts and breakout vias, the pins then become accessible to all layers through the via at the end of the breakout.
Breakouts are generated and stored in the Footprint definition and can be used on SMD and through-hole pads. This means that on any component using a footprint with breakouts you can convert them to track paths and vias within the PCB design.
The Process of using Breakouts
The ‘flow’ for using breakouts is as follows:
- Create the breakout pattern in the PCB Footprint interactively, or using the Footprint Wizard, and save this to the library.
- In the PCB design the breakout paths will be displayed as part of the component.
- To use the breakout path for a track, either:
- Start a track from the breakout path, which will be a legal starting point. The breakout will automatically become a track when as soon as it is picked.
- Edit a track/connection and end the track on the breakout path, which will be a legal finishing point. The breakout will automatically become a track as soon as it is picked.
- Select the breakout, component pad or whole component and, from the right mouse menu, select Hide Breakout or Show Breakout to toggle the display of the breakouts.
- Select the breakout, component pad or component and, from the right mouse menu, select Convert Breakout To Track to create tracks and vias directly from the breakouts.
- Use the Autorouter with the Use Component Breakout Paths switch enabled to create tracks from breakouts.
Breakouts in the Footprint
The Footprint editor has the ability to create breakout patterns, with or without breakout vias. The method for creating breakouts is the same as if adding a track to the Component in a PCB design.
The advantage of creating the breakouts within the footprint is that it only has to be done once. Whenever the footprint is used it then automatically has these potential track paths. Each Footprint instance for a component can have the breakouts switched on or off, and they can automatically be converted to tracks in the PCB design.
Creating Breakouts
You have two main design features for creating breakouts. Use Insert Breakout from the Insert menu to create the path from the pad and End On Breakout Via to finish on a via.
On the Options dialog there is an Edit Breakout tab containing user preferences for interactive adding and editing of the breakout patterns. You can set the Double Click Operation to Finish On Via to easily finish the breakouts on a via.
Breakouts use the Track Style and Via Pad Style from the Technology file. They are created on the normal electrical layers but once the component is added to the PCB design these layers act as the ‘default’ layer for the converted track.
Default values for breakouts are taken from the Design Settings Breakout Defaults tab. The Breakout section defines the Minimum and Nominal breakout segment widths (track style) and the default via size (pad style). The Track section defines the default layers to be used. The breakout via always uses the through hole layer span, but any vias created from it in the PCB design will use the “best fit” via span for the tracks attached to it.
When editing a footprint, you can generate a default breakout pattern on all surface mount pads using the Create Breakout Pattern command.
Breakout Properties
In a PCB design a breakout pattern on a component can be interactively converted to track by attaching a track to its end. There is also a method of automatically converting these breakout paths to tracks either using the Convert Breakouts To Tracks operation on a component, pad or entire net, or by using the Use Component Breakout Paths switch in the autorouter. Both these operations normally convert breakouts patterns to tracks and vias if the component pad they are attached to is on a net. There are two switches in the Properties on a breakout in a footprint that control this:-
- Automatically convert to Track (when pad is on a net) can be turned off to stop the breakout from ever “automatically” being converted to a track.
- Convert to Track on unconnected pads can be switched on to allow breakouts attached to pads that are not on a net in the PCB design to “automatically” be converted to tracks. You would not normally have this option on as redundant tracks attached to unconnected pads would just form an obstacle to normal routing, but sometimes a small breakout pattern is required on all pads, for thermal balancing for example.
Saving Breakouts
Once a footprint contains a breakout it is saved to the library in the normal way. If a breakout pattern needs to be changed, the footprint can be edited and saved, then reloaded into a PCB design in the usual way. You cannot edit breakouts directly in the PCB design.
Footprint Generator
From the Pads page of the PCB Footprint Wizard, you are now able to generate a single segment breakout on each pad of a BGA.
The X Offset and Y Offset allow you to set the direction of the breakout. The value entered in these boxes can be positive or negative numbers depending on the direction required. You can also specify the Track Width and Style required for the breakout as well as the Via Style if you wish to end on a via.
The check box to Convert to Track on unconnected Pads is to set a property on the created breakouts. See Breakout Properties section above for details of this property.
Breakouts in the Design
Once a footprint is used in component in a PCB design, the breakout is a self-contained item within the component. It moves and rotates with the component and can be hidden as required. At this point the breakout is not a track or via, but a potential pattern that can be converted to a final track path when required by connecting to a track, or by using one of the automatic convert functions. Until this conversion is performed the breakout pattern does not form a physical part of the PCB design. After converting to a track the breakout still exists, but is automatically hidden for future use if the track is subsequently removed.
To differentiate component breakouts from actual tracks and vias in a PCB design, they have their own colour slots in the Colours dialog. Under the Vias tab you have a Breakout Layer Span entry, and under the Track tab, you have a Comp. Breakouts column.
For breakouts to work, the pads to which they are attached must normally be on a net. This is usually the case after creating a PCB design from a schematic, but occasionally you may require a breakout to be converted to a track on an unconnected pad in the PCB design. This process introduces a single pin net into the design that would be ripped off by the Synchronise Designs option. To stop these nets from being removed, use the Allow PCB Only single pin nets switch in the General Design Settings dialog.
Interactively Using Breakouts
To interactively convert any breakout pattern to real tracks and vias use Insert Track to start or end a track on the breakout. The breakout pattern will be copied from its pad to the gridded point that you picked on it, converted to tracks and vias, and inserted between the pad and the interactive track you were adding. All vias will be changed to use the “best fit” via span calculated from its attached tracks.
As you are adding a track a finish marker will be displayed when the cursor is over a breakout that you are allowed to use to complete the track. If whilst adding a track no breakouts are currently displayed, use the Show Breakouts On Net option from the right mouse menu to show all the potential breakout paths on the net.
While editing a connection that is attached to a pad with a visible breakout, if a breakout is at the end of the connection you have picked, an initial track will be created from the breakout.
If a breakout is at the other end of the connection, the connection will be redrawn to end at the end of the breakout. Using the Complete As Track option from the right mouse menu in this situation will use the breakout path as part of its completed track.
Also, double click in select mode on a visible breakout in a PCB design will add a new track that uses the breakout path from the selected point back to its pad. You will then be in Insert Track mode to complete the track.
Automatic Breakout Operations
Several operations on breakouts exist, all available on the right mouse menu for selected items that contain breakouts, or component pads with breakouts.
- Selected individual breakout, or breakout via.
- Selected individual pad(s) on a component.
- Selected whole component(s).
- Nothing selected, operations act on the whole design.
The following operations are available on these selections:-
Hide and Show Breakout
Will allow the breakout to be hidden or shown on a component. If the breakout has already been converted to a track it would have been automatically hidden, but can still be shown even though it may now be redundant. If you need to see the breakout pattern, for confirmation purposes of its original direction for example, you can then select the pad and from the right mouse menu select Show Breakout.
Convert Breakout To Track
By “convert” we mean create a track path with vias following the breakout path and it’s vias, using the same layers and styles. After the track path is created the breakout is then hidden giving the impression of being “converted” into a track.
If the selected item is a breakout, it is always converted. If not, all selected pads that contain breakouts will have their breakouts converted only if they follow the rules explained in the Breakout Properties section of the Breakouts in the Footprint chapter above.
Remove Redundant Breakout Tracks
A redundant breakout track path is a track path that was converted from a breakout path, still follows the same path as the breakout and does not contain vias that are needed to reach a power plane layer. Use this option to remove these redundant track paths.
After this operation, or if a track is completely unrouted thus also removing the breakout path, the breakout can be ‘regenerated’ by right clicking on the pad and selecting Show Breakouts.
Breakouts in the Autorouter
The Autorouter now has a switch Use Component Breakout Paths. If checked, all breakouts marked as auto convertible (see above) on pads on the nets to be routed will be converted to locked tracks prior to routing. After routing, any of these “converted” tracks that were not used to route from, and therefore are are redundant, will be removed.
Plotting Breakouts
You cannot output breakouts directly through the CAM Plot option, they must be converted to tracks or vias.
Related Topics
Autorouter | Breakout Colour | Breakout Defaults | Breakout Properties | Edit Breakout | Editing Options | End On Breakout Via | General Design Settings | Insert Breakout | Create Breakout Pattern | PCB Footprint Wizard | Synchronise Designs | Via Colour