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In multilayer PCB designs, copper areas have many uses and are critical to the performance of a design. As a designer, you have a fair idea of how and where to create copper areas in your designs. These copper areas are created as shape objects in the PCB design, and any change in the design, for example, moving components or adjusting routing, affects shapes. Of course, you cannot avoid moving design objects or adjusting routes in the process of PCB design, inevitably leading to shape-related issues. To resolve these issues, you might need to regenerate the shapes or change the net assignments of the shapes. Validating shapes and fixing shape DRCs are essential to get the design ready on time for manufacture.
To address issues related to shapes, Allegro® PCB Editor offers an easy-to-use set of commands and features. You can use these shape commands and features for creating, editing, voiding, and setting up shape parameters. This post introduces the shape commands available within Allegro layout editors.
Copper areas or shapes can be added to both conductor and plane layers. To create copper areas in your design, use either the Shape menu or the toolbar icons.
You can add a shape to any design layer by doing the following steps:
1. Choose Shape – Rectangular from the main menu.
The options required to draw a rectangular copper shape are displayed in the Options pane.
2. Specify the active class and subclass in the Options pane.
3. Select the shape type.
Allegro layout editors support two basic shape types.
Dynamic copper is preferred in a concurrent design environment because it is voided in real-time. Dynamic copper is mostly used for conductor layers.
Static copper is the conventional shape type and remains unchanged until voided manually.
4. Assign a net to the shape.
5. Draw a rectangular copper area or shape in the design canvas.
Do the following to see shape voiding when you route inside a shape. Assume you are routing a different net in the shape.
1. Choose Route – Connect.
2. Specify the routing options in the Options pane.
3. Select a design element, such as a pin, and start routing.
4. Extend the route inside the shape.
5. To add a via, right-click and choose Add via.
6. Right-click and choose Done.
You do not see any voiding because you have not enabled shape checks.
7. Choose Display – Status and in the Shapes section set Dynamic Fill to Smooth.
By default, Dynamic Fill is set to Disabled so that performance is not compromised when you have multiple ground and power planes in your design.
8. Click Update to Smooth to update the copper pour and close the Status dialog box.
You can now see the clearance around the routing and the via inside the shape.
Since you have added a dynamic shape and the update shape option is enabled, you can see the changes in real-time on the canvas as soon as you start routing inside the shape.
ECO (Engineering Change Order) may cause shapes to be out-of-date in a design; for example, the shape might not be filled or voided correctly or an incorrect net might be associated with the shape. To resolve these shape issues, regenerate or merge the shapes or change their shape settings. You can adjust the shape settings either for a specific shape instance or for all the shapes in a design.
You can modify a copper shape to change the assigned net by doing the following steps:
1. Choose Shape – Select Shape.
2. Select the shape in the design canvas.
3. Assign a net to the selected shape.
Use the Global Dynamic Shape Parameters window to make global changes for shapes. Global changes impact all shapes in a design. Choose Shape – Global Dynamic Shape Param to open the window.
The different tabs of the Global Dynamic Shape Parameters window are designed for specific purposes. The following table describes the tabs.
Specifies the dynamic fill type and Xhatch style.
Specifies shape voiding on different layers, artwork format, and trim control angle. Always set the artwork format that matches your manufacturer's requirements.
Specifies the distance between shape and surrounding design objects, such as a line or a via, to prevent shorting. You can also specify oversize values.
Thermal relief controls
Specifies how the connections are made for pins and vias.
Use the Dynamic Shape Instance Parameters window to modify a shape instance. Select the shape and choose Parameters from the right-click menu to open the window.
As an example, you can modify the clearance around a via or the connection type of a shape.
Another way to change shape settings is by modifying shape properties. For example, to have additional clearance around a via inside a shape, do the following:
1. Select a via and choose Properties from the Edit menu.
2. In the Edit Property window, look for dynamic shape properties prefixed with DYN.
3. Choose Dyn_Clearance_Oversize and increase its value.
Additional clearance is added around the via as shown in the following image.
You can also change the importance or priority of a shape using the Shape Priority command. For example, adding a shape on top of another shape results in shape overlapping. When shapes overlap, the shape on top has lesser copper than the overlapped shape. To make the top shape more 'important', that is, have more copper, select the top shape and choose Shape Priority from the pop-up menu.
To learn in detail about this flow, watch How to Create and Modify a Copper Area from within the Allegro PCB Editor - v17.4-2019 training byte on the Cadence Support portal. Click the training byte link now or visit Cadence Support and search for this training byte under Video Library.
If you find the post useful and want to delve deeper into copper shapes, enroll in the following online training course for lab instructions and a downloadable design: Allegro PCB Editor Basic Techniques v17.4-2019QIR2 (Online) You can become Cadence Certified once you complete the course.
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