Flatten

To flatten a layout is to replace every stamp with a copy of the shapes inside it, until one drawing holds only raw outlines.

Mask writers, some rule decks, and many board exports want that single pile of geometry. Flattening is the form a shop can read when it will not open the cell tree. It is also how the one place to edit disappears. After a flatten, fixing a via means hunting through ten thousand squares. A chip that listed 40 cells can end as one cell named chip_flat, with the shape count jumping from 2,000 to 2,000,000.

Three copies of the L drawn as raw outlines. The middle copy has an extra mark the others do not.

Each stamp that gets exploded was an instance. The tree that gets destroyed is hierarchy. Board flows often flatten early, because a footprint is placed once and the copper is then edited as art. Chip flows flatten late, if they flatten at all, and they keep the masters until tapeout. The shapes inside an instance can be inspected without destroying the tree. Flatten when a downstream tool requires the raw outlines, and keep a hierarchical copy beside that export.

The accounts are hierarchy and flattening and cells and instances.