What is SPEF, and what does it actually represent?
From PDVerse MMMC Interview Masterclass · pdVerse Mentor Series
Direct answer
SPEF (Standard Parasitic Exchange Format) is the file format used to hand off extracted interconnect parasitics — resistance, ground capacitance, and coupling capacitance for every net — from the extraction tool to the timing engine. It's the recorded data, not the policy for what condition it represents.
Mentor explanation
It helps to separate two ideas that sound similar: SPEF data is the actual extracted numbers for the wires as routed. An RC corner configuration is the methodology decision about which extraction condition (or which technology assumptions) you're asking for. You could have several different SPEFs, each one representing a different RC corner. SPEF answers "here are the parasitics for this net, as extracted." RC corner answers "under what interconnect assumption should this extraction have been generated?" They work together, but they're not the same thing.
Interview trap
Assuming that because a SPEF loaded without a fatal error, every net in it is correctly and completely annotated. Loading is not the same as verifying coverage.
Key takeaways
- SPEF (Standard Parasitic Exchange Format) is the file format used to hand off extracted interconnect parasitics — resistance, ground capacitance, and coupling capacitance for every net — from the extraction tool to the timing engine.
- It's the recorded data, not the policy for what condition it represents.
Self-check: can you answer this aloud?
Try a 45-second answer using this structure:
- State the direct answer.
- Explain the timing or physical reason.
- Name one caveat.
- Say how you would verify it in a real flow.
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