Is Auto-Routing Really That Useless?

Many engineers have a poor first impression of auto-routing tools: the output is messy, too many vias, obvious detours, and often not as good as manual routing.

This assessment isn't entirely unfounded. Early auto-routing tools often only pursued "connectivity" without understanding engineers' requirements for routing layers, via positions, local aesthetics, and maintainability. But if we change our testing approach — instead of expecting the tool to "guess" the best result from a completely blank project in one shot, but treating it as an iterative routing assistant — the conclusion might be different.

This time we're doing a test closer to real-world work: prepare two DSN files, one complete original project export, one empty-routed version with vias and traces deleted. Then starting directly from the empty DSN, use PcbAutoRouter to re-route and see how long it takes to recover to a level close to the original project.

Test Files

This article uses two resource files:

Original Project DSN: 📐flyback-test-board253.9 KB · 1 次下载

Empty-Routed DSN (vias and traces deleted): 📐flyback-test-board3195.7 KB · 0 次下载

The original DSN is used to observe the final goal: where vias are roughly placed, how critical nets route, and overall routing density level.

The empty-routed DSN is the actual test entry point. It has deleted traces and vias from the original, but retained component placement, net connectivity, board outline, and design rules.

All operations from here start with these two DSN files, without demonstrating how to delete traces or re-export in the EDA tool.

Test Objective

This test doesn't pursue the exaggerated conclusion of "one-click auto-routing beats manual work". Instead, it answers a more practical question:

If a project's layout is already finalized and design rules are correct, can auto-routing quickly recover a usable, clean routing result close to the original project quality?

To make the test fair, the empty-routed DSN retains:

Component positions unchanged
Net connectivity unchanged
Board outline unchanged
Design rules (trace width, spacing, via size) unchanged

While deleting:

All routed traces
Original vias
Manual local routing results

In other words, the auto-routing tool faces a project with "layout complete but routing cleared".

Step 1: First Full Auto-Routing

Directly press F5 on the empty DSN to start full auto-routing.

First routing mainly looks at three things:

Can it quickly achieve 100% connectivity?
Which areas show obvious detours?
Where do vias concentrate?

This step usually doesn't need manual intervention. Let the tool produce a complete result first to judge where the project's routing challenges are.

In this project, first auto-routing completed most connections quickly. The result already shows overall topology: which nets route better on top, where drilling to bottom is needed, which areas are congested due to component density.

Don't rush to judge "looks good or bad" yet. The first result is more like a sketch, telling us which paths the auto-router thinks are easiest.

Step 2: Compare with Original Project DSN

After the first result, compare it with the original project.

Main observations:

Does original project retain fixed vias at certain locations?
Did auto-routing take detours at certain points?
Are there areas with vias too close or too dense?
Do traces pass through unwanted regions?
Do power, ground, and critical nets maintain reasonable paths?

This step is critical. Auto-routing doesn't completely replace engineer judgment; it completes most repetitive routing first, then exposes the few locations that truly need human judgment.

If hand-routing from scratch, engineers must consider all nets simultaneously. But after auto-routing, attention can focus on few unsatisfactory areas.

Comparison shows two main differences:

Fewer ground vias, resulting in detours
Right side test load traces routed differently

Next we focus on fixing these two points.

Step 3: Keep Valuable Results, Delete Unsatisfactory Local Traces

Now enters the iteration phase.

For already reasonable areas in auto-routing results, keep them directly. For obviously detoured or unattractive areas, delete local traces, observe unconnected indicators, then add vias.

PcbAutoRouter supports quick via parameter picking with shortcuts:

Alt + Left Click: Pick parameters from existing pads, traces, or vias
Ctrl + Left Click: Place via
After placing, can continue single-net routing or re-run full auto-routing

Start adding vias to previously deleted areas. With copper pour on bottom layer, many places need just one via. After placing, press F5 for re-auto-routing; excess vias are automatically removed.

This workflow is more practical than traditional "one-click auto-routing then accept or reject everything":

Auto-routing completes overall connectivity
Engineer deletes unsatisfactory local traces
Adjust vias or few critical paths
Re-run auto-routing
Repeat until results match expectations

In actual practice, many local issues don't need redrawing wire by wire. Just delete problem traces and re-run auto-routing; the tool usually re-finds paths based on remaining traces and vias.

Step 4: Fine-Tune Traces

When auto-routing reaches over 90% satisfaction, enter final refinement phase.

This step shouldn't pursue "fully-automatic solving all details". Engineering projects always have local preferences, such as:

Certain trace should route along edge
Certain traces should be neater
Certain via should move slightly
Certain trace should avoid silkscreen or mounting hole area

These can be directly fixed by dragging traces or moving vias. PcbAutoRouter's advantage is that traces adjust automatically after local changes without redoing surrounding nets.

In other words, final phase is more like photo editing: major structure already generated, engineer only does minor tweaks.

Step 5: Compare Results

Finally compare results with original project again.

No need to pursue every trace matching original exactly. PCB routing isn't photo copying; as long as a net meets rules, has reasonable paths, and won't introduce obvious electrical or manufacturing issues, it's considered the same level.

From comparison, major differences have converged to small locals:

After adding ground vias, originally detoured areas basically recover to normal
Right side test load traces, though different paths, have reasonable connectivity and logic
Large copper pours and traces near critical output areas show no obvious anomalies
Overall completion reaches target; remaining is just aesthetics and local habit tweaks

Getting approximately close is sufficient. This test's focus isn't proving auto-routing can replicate every coordinate of the original, but proving it can quickly recover a usable, checkable, further-adjustable result under existing layout and rules.

Actual Time Spent?

In this actual workflow, time was spent on comparison and judgment, not auto-routing calculation itself.

Stage	Approximate Time	Notes
Open original DSN and confirm reference result	~1 minute	Mainly observing via positions, critical paths and overall density
Open empty DSN and first auto-routing	Tens of seconds	Directly press `F5` for initial result
Compare two result images	2-3 minutes	Identify true differences to handle
Delete unsatisfactory local traces and add vias	3-5 minutes	Mainly handling ground vias and detour areas
Re-run full auto-routing	Seconds	Excess vias and local paths rearranged by tool
Final check and minor tweaks	1-2 minutes	Check for obvious unpleasant or unreasonable paths

So in this case, recovering from empty DSN to close to original level takes roughly ten minutes of work. Auto-routing itself is only a small part; the real work is "understand differences, then give the tool a hint".

If the goal is "usable and close to original", this workflow is much easier than manually recovering from scratch. For boards with more nets and complex rules, time increases of course, but work still concentrates on few critical areas, not redrawing every trace.

What is Auto-Routing Really Suitable For?

Through this test, auto-routing tools are most suitable for:

Quickly verify if current layout can be easily routed
Quickly generate initial routing after layout finalization
Quickly recover projects after deleting traces and vias
Auto-complete after deleting local traces
Guide tool toward engineer-expected paths by manually adding few vias
Focus on critical paths, feedback areas, power outputs and test traces, rather than repeatedly handling all signal lines

If treating auto-routing as a black box fully replacing engineers, it easily disappoints. But treating it as a high-speed routing assistant, its value becomes clear.

In this case, auto-routing didn't magically "one-click replicate" the original, but quickly completed most connections. Engineers only needed to check two obvious differences: detours from insufficient ground vias, and right-side test trace path differences. After handling these, letting the tool re-route, the result was already close to original.

This is reasonable division of labor: engineers handle layout, rules, critical paths and final quality; tools handle quick tries, quick connections, quick re-routing.

Conclusion: Not Useless, Just Different Usage

"Is auto-routing really that useless?"

The answer depends on how you use it.

If expecting it to output the exact final routing from a senior engineer in one shot, that's not realistic. PCB routing involves much experience judgment, aesthetic preference and project background; tools can't fully know these.

But using it for "quickly recovering routing after clearing traces and vias", "quick iteration on existing layout", "completing most repetitive routing first", it has tremendous value.

This flyback test board shows: with correct layout and rules, PcbAutoRouter can quickly recover a project with cleared traces/vias to close to original level. Engineers only need focus on few critical vias, detour areas and local tweaks, rather than manually redrawing the entire board.

So auto-routing isn't unusable; it just can't be used with old concepts.

It's more like a repeatedly collaborative routing assistant: you give direction, it handles quick trials; you point out critical locations, it completes the whole. This workflow is where auto-routing truly excels.