PCB routing is the core link of circuit board design, directly determining the electrical performance, stability and production yield of PCBs. Auto-routing and manual routing, as two mainstream routing methods, have their own advantages and limitations: auto-routing is efficient and time-saving for simple circuits, while manual routing ensures precision and reliability for high-demand signal and structural design. The key to high-quality and efficient PCB design lies in combining the two methods rationally, taking their strengths and avoiding weaknesses based on design requirements and circuit characteristics. This paper elaborates on the core application strategies of the combined use of PCB auto-routing and manual routing, providing practical reference for circuit design engineers.

1. Core Characteristics of Auto-Routing and Manual Routing

1.1 Advantages and Limitations of Auto-Routing

Auto-routing relies on professional EDA software algorithms to complete wiring automatically, with the core advantages of high efficiency and time-saving, which can quickly complete the routing of large-scale ordinary circuits, reduce repetitive manual operations, and is suitable for the initial routing of simple PCBs or auxiliary routing of low-priority signal lines.

Its limitations are obvious: it is difficult to meet the high requirements of signal integrity, EMC and impedance control, and the automatically routed lines are prone to irrational layouts such as excessive bends, long transmission paths and cross-layer chaos; at the same time, it cannot flexibly adapt to the structural constraints of PCB boards (such as mounting holes, component spacing) and special industry routing specifications, often requiring a lot of subsequent modification.

1.2 Advantages and Limitations of Manual Routing

Manual routing is operated by engineers according to design specifications and circuit characteristics, with the core advantages of high precision and strong controllability. It can flexibly optimize the routing path for key signal lines (such as high-speed signals, differential signals, power lines), strictly follow the rules of impedance matching, signal isolation and short-distance transmission, and ensure the electrical performance and EMC performance of the PCB; it can also adapt to the structural constraints of the board and industry-specific requirements, and the routed lines are neat and in line with production and assembly standards.

Its main limitation is low efficiency and high labor cost, which takes a long time for the routing of large-scale PCBs with numerous signal lines, and has high professional requirements for engineers, requiring proficient mastery of routing specifications and EDA software operations.

2. Core Principles of Combined Routing Application

The combined application of auto-routing and manual routing follows the core principle of "manual priority for key parts, auto-assistance for ordinary parts; manual planning first, auto-execution later", which balances design efficiency and routing quality, and avoids the single defect of either method.

Priority of key signal manual routing: Give priority to manual routing for high-speed signals, differential pairs, power lines, clock signals and other key lines that affect the core performance of the PCB, to ensure strict compliance with electrical performance requirements.

Ordinary signal auto-routing assistance: Use auto-routing for low-priority ordinary signal lines (such as low-speed I/O lines, ground wires with no strict requirements) to improve overall design efficiency.

Pre-planning before auto-routing: Complete the manual planning of the PCB in advance, including component layout, key line path reservation, layer stack design and routing rule setting (such as line width, line spacing, via limit), to provide a reasonable constraint framework for auto-routing and reduce subsequent modification work.

Manual optimization after auto-routing: For the lines completed by auto-routing, conduct manual inspection and optimization in a targeted manner, modify the irrational routing paths, eliminate potential signal interference problems, and ensure the consistency of the overall routing specifications.