# Problem Net ties are used when two nets need to be connected in a single point, but should otherwise be kept separate during routing. ## Star Routing Multiple components need to be connected to a single point without being cascaded, typically found in supply nets where multiple components share some of the larger decoupling capacitors. ## Decoupling Capacitor Matching For ICs with many individual power pins, each should get a separate capacitor to avoid high currents inside the IC, and often there is also a mapping between supply and return pins as well. ## Shunt Resistors and Remote Sensing For current measurement with a low-value resistor or voltage feedback the same pad needs to be connected to both the current carrying trace or zone, and to a sense network that needs to be kept separate in order to get accurate measurements. # Workarounds Currently, people are building footprints that contain two copper pads without a soldermask opening and a (graphical) copper trace to connect the pads without having to fit a component. This approach takes up space on the top or bottom, and since graphical copper now takes part in DRC, it also causes DRC errors. # Requirements ## Schematic Entry - Net Ties are shown in the schematic, as they are part of the documentation of the circuit. - No industry standard exists for how they should be shown, so we are somewhat free to invent our own - For the current/voltage sensing use case, several vendor application notes exist that render net ties as junctions that are placed as close as possible to the component where the measurement should be taken, with one of the traces joining at a 45 degree angle. - For the decoupling use case, it might make sense to add an editing mode where capacitors can be directly associated with pins, this will probably need some integration with pin/unit swapping, so it will not be part of the first implementation - Net Ties are "connected" for ERC purposes ## Netlist - Nets connected by a net tie are still represented as separate nets in the KiCad internal netlist. - Net Ties are represented as a special component that is connected to the nets normally. - For other netlist formats, we need to investigate use cases and possibly offer different options. ## Layout - Net Ties take one of three forms: standalone, coincident with via, or coincident with pad - Standalone Net Ties behave like pads, except their size is automatically set (largest minimum width of connected nets according to netclass), and they can exist on any copper layer. No copper needs to be generated here, the connected networks will already do that. - Net Ties that combine with vias or pads reuse these, but make sure that DRC does not flag a conflict. ## Zone Calculation ### Zone vs Trace  The Zone keeps distance from the trace as usual for the length of the trace, but the endcap that attaches to the net tie does not generate an exclusion zone. ### Zone vs Zone The Zones keep distance as usual, except for an area centered around the net tie.  ## DRC TBD