Pads and vias are an essential ingredient of a modern PCB design. As well as providing mounting points for components, pads, along with vias, allowing a net to traverse the different layers of a PCB as it travels from one component pin to another. Pads and vias come at a cost though; they consume valuable board space, they create impedance mismatches for high-speed signals, and they create holes in large copper areas defined by polygon pours.
To help reduce their impact on copper areas, Altium NEXUS includes an Unused Pad Shapes removal tool. The tool scans all pads or vias in the design and removes the pad shape from each layer for which the pad or via is not used (meaning it has no other objects touching it on that layer). Polygons that surround that pad or via then only need to create the specified clearance to the pad or via hole instead of to the edge of the unused pad shape. In some situations, such as under a BGA, this can recover a substantial amount of copper lost in polygons.
In addition, teardrops are often added to a routed PCB design to create stronger track-to-pad, track-to-via, and track-to-track connections. This is valuable when the design objects are very small and is particularly valuable for drilled pads and vias, because misalignment between the drill center and the pad/via center can result in the drill hole removing much of the copper connecting the track to the pad/via.
This tool is intended to be used once the routing is complete, before the fabrication files are generated. To remove unused pad shapes, select Tools » Remove Unused Pad Shapes from the menus, the Unused Pad Shapes dialog will open, as shown below.
Configure the dialog options as follows:
Preserve pads on start and end layers - a pad or via might not use the pad shape on the outer most layers that its structure exists on, these outer-layer pad shapes can be retained if required.
The Pad and Via objects with pad shapes removed by using the Unused Pad Shapes removal tool will not be reported as objects offending a Minimum Annular Ring design rule.
Teardrops are especially valuable in flex designs to help prevent a crack forming where the track meets the pad/via or when the drill hole is not in the center of the pad/via. Teardrops are created out of region objects, requiring only one region per teardrop, which can have either straight or curved edges. Teardrops can also be added to the junction of two tracks at both a T-junction and a neck-down junction.
Teardrops are added (or removed) by selecting Tools » Teardrops from the main menu. When the command is selected the Teardrops dialog will open.
Teardrops can be added and their properties defined as follows:
70%. Click the blue percentage values to change these as required.
100%. Click the blue percentage value to change this as required.
100%. Click the blue percentage values to change these as required.
For more information on the dialog settings, refer to the Teardrops dialog page.