Using -1 as a Value in the Spacing Table
I'll share another constraint quirk that you might find useful. Have you ever created a wirebond cage? One of the flukes of
wirebonding is that the wire flies over the top of the board with nothing but air for dielectric. The rule for 1 mil wire is a 1 mil
gap. The inboard wire can fly right over the pad of the outboard wire shorting to the pad for the wire.
Figure 6. Connecting the die (Blue) to the board or substrate (Brown) with wirebonds can be done with a one mil air gap from wire to wire. Note
how the wires are on the etch layer so we can apply this one mil trace/space rule around the wirebond cage. An exception to the rule where
the wires to the outer row pass over the pads for the inner row. That's where the negative one value for via to line allows the wirebond. Once
that is done, the wire can be represented in an assembly detail. Then, the etch layer is available to finish the last segments to the inner row.
The rules then go back to normal by deactivating the constraint region around the wirebond cage.
First, create a region around the passivation openings (where the wirebond starts) and set the Etch to Pin spacing value to -1.
When the spacing rule equals negative one, the wire will cross over the pad with no design rule violation. The other air gaps
like the 1 mil wire-to-wire rule remain in effect. You would memorialize the wirebond solution with a fab detail.
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Controlling Air Gaps Using OrCAD X and Allegro X Tools
