The ECO Flow
An engineering change order applies a controlled late-stage netlist or layout modification while preserving already-closed parts of the design.
The best ECO is the smallest change that fixes the root cause and can be proven consistent across logic, layout, and signoff views.
A hold ECO may insert a delay cell on a short data path using a nearby spare site, then reroute only the affected nets.
Physical Design flow
Follow each stage in sequence. Every stage produces information needed by the next.
The ECO Flow—visualized
This technical view uses the actual structures and relationships associated with this stage, followed by its key terms.
Understand every concept
Late-stage changes
What it is: Late-stage changes is a core concept within The ECO Flow. It describes the information, structure, or analysis engineers use at this stage of the Physical Design flow.
Why it matters: Understanding it helps you interpret the stage correctly, avoid incorrect assumptions, and connect the result to the next implementation or signoff step.
Where it fits: This topic belongs to module 11, The ECO Flow, and its output supports the stages that follow.
Practical example: Engineer workflow: Classify the change as functional, setup, hold, DRC, or power related. A hold ECO may insert a delay cell on a short data path using a nearby spare site, then reroute only the affected nets.
Timing ECO
What it is: Timing ECO is a core concept within The ECO Flow. It describes the information, structure, or analysis engineers use at this stage of the Physical Design flow.
Why it matters: Understanding it helps you interpret the stage correctly, avoid incorrect assumptions, and connect the result to the next implementation or signoff step.
Where it fits: This topic belongs to module 11, The ECO Flow, and its output supports the stages that follow.
Practical example: Engineer workflow: Select spare cells, sizing, buffering, rerouting, or metal-only logic. A hold ECO may insert a delay cell on a short data path using a nearby spare site, then reroute only the affected nets.
Metal-only implementation
What it is: Metal-only implementation is a core concept within The ECO Flow. It describes the information, structure, or analysis engineers use at this stage of the Physical Design flow.
Why it matters: Understanding it helps you interpret the stage correctly, avoid incorrect assumptions, and connect the result to the next implementation or signoff step.
Where it fits: This topic belongs to module 11, The ECO Flow, and its output supports the stages that follow.
Practical example: Engineer workflow: Implement and legalize the local modification. A hold ECO may insert a delay cell on a short data path using a nearby spare site, then reroute only the affected nets.
Work through it step by step
- 1
Late-stage changes
Classify the change as functional, setup, hold, DRC, or power related.
- 2
Timing ECO
Select spare cells, sizing, buffering, rerouting, or metal-only logic.
- 3
Metal-only implementation
Implement and legalize the local modification.
- 4
Late-stage changes
Run equivalence, extraction, timing, DRC, and LVS checks.
Explore each topic
01Late-stage changes
Understand the concept, connect it to the ASIC flow, study the report or behavior it produces, and apply it in a guided exercise. Check the result against the module goal before moving forward.
02Timing ECO
Understand the concept, connect it to the ASIC flow, study the report or behavior it produces, and apply it in a guided exercise. Check the result against the module goal before moving forward.
03Metal-only implementation
Understand the concept, connect it to the ASIC flow, study the report or behavior it produces, and apply it in a guided exercise. Check the result against the module goal before moving forward.
Completion checklist
- ✓ Logical intent is preserved
- ✓ Changed routes are legal
- ✓ All timing corners are rechecked
- ✓ Netlist and layout remain equivalent
Practise with open-source tools
These are official third-party GitHub projects selected for this learning path.