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Connecting Multiple Nets Using Copper Ties
You can tie two or more nets together while maintaining the ability to route them separately and preserving the netlist integrity through the use of a special polygon upgraded to a copper tie. For example, you may want to connect a number of ground nets to create a common ground. This is done in one of two ways: by placing a copper tie on top of routed nets that you want tied together or by routing the nets into an existing copper tie.
To create a copper tie:
1. Place a polygon on a signal layer. Give the polygon a unique shape to identify it as a copper tie.
2. Select the polygon and then right-click and choose Properties from the shortcut menu. The Polygon Properties dialog appears.
3. Click on the Tie tab.
4. Check the Copper Tie check box.
5. In the TieNet field, type a name for the copper tie.
6. Designate which nets should be connected to the Copper Tie, by transferring them from the Existing Nets list (which shows all the nets in the design) to the Tied To list. (Remember that there must be at least two nets in the Tied To list.
7. Click OK.
If you select each of the nets in turn that you have just assigned to the copper tie and look at their attributes, you will see that they each have an attribute labelled TieNet, with the value of whatever name you gave for the copper tie.
It is possible to place multiple entry points for the same copper tie within the design. This allows you to tie multiple nets together, but the nets can be routed differently and the netlist integrity remains unchanged. To do this, place multiple polygons on a signal layer and make sure the entry in the TieNet field is the same in each case.
The characteristics of a copper tie that distinguish them from ordinary polygons are:
n A copper tie must connect two or more nets.
n The TieNet value of the copper tie and the TieNet value of the connected nets must be the same.
n A copper tie behaves as free copper in all parts of the system with a few exceptions as noted below.
The conditions listed below can occur when a copper tie is placed under a certain set of circumstances:
n When a copper tie is placed over a copper pour in a net, the copper pour, when repoured, will back away from the copper tie.
n A copper tie pasted from one design to another adapts to the conditions existing in the receiving design. For instance, a copper tie named CT1 in design 1 is connected to nets A and B. The copper tie CT1 is copied into design 2 which has nets C and D. Copper tie CT1, in design 2, is now connected to nets C and D.
n Polygons are considered copper voids when placed on a plane layer. Therefore, a Copper Tie cannot connect split plane regions.
n You cannot use a copper tie to connect the unrouted nodes of a net since a copper tie is not considered real copper. Design Rules checking considers those nodes to be unrouted. Reconnect does not regard the copper ties as free copper.
n See Copper Ties and DRC to learn how DRC treats copper ties.
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