For signal wires in digital integrated circuits, global routing (Chap. 5) is performed first, and detailed routing next (Chap. 6). However, some types of designs, such as analog circuits and printed circuit boards (PCBs) with gridless (trackless) routing, do not warrant this distinction. Smaller, older designs with only one or two metal layers also fall into this category. When global and detailed routing are not performed separately,
(Secs. 7.1–7.2) directly constructs metal routes for signal connections. Unlike routing with multiple metal layers, area routing emphasizes crossing minimization. Non-Manhattan routing is discussed in Sec. 7.3, and nets that require special treatment, such as clock signals, are discussed in Secs. 7.4–7.5.