Working with Custom Pad Shapes in Altium NEXUS
The standard pad object can:
- Be set to a number of different shapes, including round, rectangular, rounded rectangular, and octagonal.
- Be sized differently in the X and Y directions, extending the range of shapes that can be created.
- Be customized to change the shape for each layer of the board.
- Have a round or slotted hole, which can be offset from the pad center.
However, there is a huge variety of pad shapes needed for component footprints, and standard pads are not always enough. To create a different shape from those listed above, you must create a custom pad shape.
An example of a footprint with custom shape pads.
Strategies for Creating Custom Shape Pads
Custom pad shapes can be created by converting placed Region objects or a closed outline, or directly, by selecting the new Custom Shape entry from the Shape drop-down in the Pad mode of the Properties panel.
Converting Regions
To create a custom shape pad by converting regions:
- Place one or more overlapping regions defining the custom pad shape in the design space. The regions can be defined on any layer.
- Place a pad so its center is located within the area of the region(s) that define the custom shape. The center of the pad will define the origin of the custom pad shape to be created. The layer on which the pad is placed will define the layer of the custom shape pad.
- Select the pad and the region(s).
- Right-click on the selection and select the Pad Actions » Add Selected Region to Custom Pad command from the context menu or select the Tools » Convert » Add Selected Region to Custom Pad command from the main menus.
The pad of the custom shape will be created on the layer on which the original pad has been placed.
A custom pad shape can be created by converting selected region(s).
Converting an Outline
In some cases (e.g., if the pad shape should be defined according to a component datasheet or using imported data), it can be more convenient to define a custom shape by creating a closed outline. To create a custom shape pad by converting an outline:
- Define a closed outline of the shape using lines and arcs. The outline can be defined on any layer.
- Place a pad so its center is located within the area of the outline that defines the custom shape. The center of the pad will define the origin of the custom pad shape to be created. The layer on which the pad is placed will define the layer of the custom shape pad.
- Select the pad and the outline.
- Right-click on the selection and select the Pad Actions » Create Custom Pad from Selected Outline command from the context menu or select the Tools » Convert » Create Custom Pad from Selected Outline command from the main menus.
The pad of the custom shape will be created on the layer on which the original pad has been placed. Note that the outline objects will remain – you can reuse or remove them.
A custom pad shape can be created by converting a closed outline.
Directly from Pad Properties
A pad of a standard shape (round, rectangle, octagon, etc.,) can be converted to a custom shape pad directly from its properties. To do this:
- Place a standard shape pad in the design space.
- In the properties of the selected pad, select Custom Shape from the Shape drop-down in the Pad Stack region.
- Click the Edit Shape button in the Properties panel and then drag the desired vertices to the required location using the standard polygonal-shaped object editing techniques (to finish editing, click outside the pad area). Alternatively, select the Outline Vertices to open a grid table in which you can configure the coordinates of the custom shape vertices.
Set the pad shape as custom and make the required changes through the Pad mode of the Properties panel.
A custom shape pad can have a calculated Solder and/or Paste Mask, which can either be a user-specified amount or controlled by the rule system. This is achieved by enabling the appropriate Mask Expansion settings in the pad's Properties panel. When the mask opening requirements are not simply an expansion or contraction of the copper shape, it will not be possible to use a calculated mask. In this case, place suitable design objects on the required Mask layer. Keep in mind that the Solder Mask is defined in the negative, that is, the placed objects define openings in the Solder Mask layer.
A PCB component that has the solder mask opening defined by a manually placed Fill object placed on the Top Solder mask layer.
Editing a Custom Shape Pad
To edit the shape of a custom pad, you can use techniques similar to those when creating a new custom pad shape from scratch.
Select region object(s) or an outline placed and the existing custom shape pad in the design space and select the Add Selected Region to Custom Pad or Create Custom Pad from Selected Outline command. You will be prompted to select a required action: replacing the existing custom pad shape or merging the new shape with the existing one.
Alternatively, use the outline vertices grid in the pad properties or the Edit Shape button to edit the pad shape interactively similar to when defining a custom shape for a pad just converted from a standard shape pad (see above).
The Modify Custom Pad shape command from a custom shape pad's right-click Pad Actions menu is also available. Once the command is launched, the cursor becomes a crosshair. Each time you click, a new vertex is added to the existing pad shape. You can extend the original border outside of the existing shape and/or come back inside the original border to essentially 'remove' an existing area. Use Shift+Spacebar to change placement modes and the Spacebar to switch end cornering modes.
You can also explode a custom shape pad to a region and a standard shape pad by selecting it and choosing the Pad Actions » Explode Custom Pad to Free Primitives command from the pad's right-click menu or the Tools » Convert » Explode Custom Pad to Free Primitives command from the main menus.
Thermal Relief Support
When a custom shape pad is placed in a PCB document, thermal relief conductors connecting the pad with a surrounding polygon are placed so they intersect the pad origin. The number of conductors (2 or 4) and their rotation angle (45 or 90 degrees), as well as the width of conductors and the air gap between the pad and polygon, are defined by the applicable Polygon Connect Style design rule.
This behavior can be overridden by enabling the Thermal Relief option in pad properties and clicking the ellipsis button. When the Conductors by Pad Edges option is disabled in the Edit Polygon Connect Style dialog that opens, the thermal reliefs for this pad are placed as described above. When the option is enabled, the thermal relief conductors are placed from the center of each side of the custom pad shape region.
Examples of custom shape pad connections to their surrounding polygons when the Conductors by Pad Edges option is enabled and disabled for these pads are shown in the image below.
Query Keywords
To simplify the process of selecting custom shape pads, scoping design rules, etc., the following query keywords are available:
| Custom Shape Pad Type Query | Returns |
|---|---|
| IsCustomShapePad | All pad objects of a custom shape. |
| IsCustomPadShapeOnLayer | All pad objects of a custom shape on the specified layer, e.g., IsCustomPadShapeOnLayer('Top Layer') |
You can also use the PadShape_AllLayers, PadShape_TopLayer, PadShape_BottomLayer, and PadShape_MidLayer<n> keywords with the 'Custom Shape' string to get pads of custom shape on a specific layer. For example, the PadShape_TopLayer = 'Custom Shape' query returns pad objects with a custom shape on the top layer.
Custom Shape Pads in Outputs
Pads of custom shapes will be exported as pads of the Custom DCode Shape to Gerber and ODB++ outputs. Custom pad shapes are output in these formats as true contours with arcs.
