Geometry rules

Hint: The second rule mentions a size as well as a spacing.

A wide conductor is more prone to the etch and lithography effects that close a gap, so the rule deck keys the spacing to the width. Timing tools see the same thing from the other side: a non-default rule that widens a net must also widen its spacing. the open rule decks reference

Hint: Two layers are named. Ask which one has to be bigger, and why.

Layers are printed by separate masks that never align perfectly, so the upper layer must overhang enough that the contact is still covered when they shift. Too little enclosure gives a weak or open connection. This is the same rule family as via enclosure higher in the stack. the open rule decks reference

Hint: One is about the shape; the other is about the gap inside it.

A tiny island of metal may not print or may lift off, and a tiny hole may close up during etch. Minimum-area violations usually appear where a via lands on a short stub, which is why routers extend such stubs. the open rule decks reference

Hint: Ask how the end of a wire differs from its side.

A line end rounds and pulls back as it prints, so its position is less certain than a long edge. The rule keeps extra distance there, and it commonly applies only below a width threshold and within a distance window, which is why it has more parameters than plain spacing. the open rule decks reference

Hint: Ask whether the chip is slow or unbuildable.

Timing violations cost performance; geometric violations cost yield, and a foundry will not accept the design at all. This is why detailed routing iterates until the violation count is zero, and why a tapeout gate treats any remaining violation as blocking unless it is waived. the open rule decks reference

Hint: A single via can fail; ask what costs almost nothing to add.

Doubling raises yield. A via is one of the most failure-prone features in manufacturing, and a lone via in a signal path makes the whole net fail. Where the layout allows it, a second via in parallel removes that single point of failure. It is a recommended rule rather than a hard one. the open rule decks reference

Hint: Ask what happens at the foundry if you break each one.

Decks carry both. Required rules define what can be manufactured at all; recommended rules, such as via doubling and extra spacing, raise yield. A team decides how many recommended violations it accepts, which is a business decision, not a technical one. the open rule decks reference

Hint: It is the opposite of a minimum-width rule: ask what being too wide causes.

Wide metal can lift or dish during polishing and can trap stress. The rule forces slots in it, which is why power straps in a real layout have holes. It constrains the power grid, since a strap must be wide for current but then needs slotting. the open rule decks reference

Hint: The wire is wide because it carries a lot. Ask what the one cut carries.

One cut is a bottleneck in both resistance and current density, and it is a single point of failure if it is malformed. The rule states how many cuts a wire of a given width needs, and routers satisfy it by dropping a via array rather than a single via. the open rule decks reference

Hint: Think about what the lithography can actually resolve on an edge.

A tiny jog does not print as drawn: it rounds away or pinches the shape. Minimum step and notch rules forbid features the process cannot hold, and they are a common output of a script that merges shapes without cleaning up what it produced. the open rule decks reference

Hint: Two shapes too close must go on different masks. Now make it three.

Below the resolution limit a layer is printed with two or more masks, and neighbours must alternate. Three shapes each too close to the other two form a cycle that cannot be two-coloured, so the layout must change. It is a graph problem the router has to respect while it routes. the open rule decks reference

Hint: Each cell passed on its own. Ask what only exists once they touch.

A cell is drawn so that any neighbour is legal in most combinations, but some pairs are not, and some need a gap. Flows handle it with placement padding, with rules forbidding certain neighbours, or by inserting a filler cell between them. the open rule decks reference