【Semiconductor】🧩 14. What Makes a PDK Compatible with OpenLane?

— Why SKY130 Works Smoothly and GF180 Becomes Difficult

topics: [“openlane”, “asic”, “pdk”, “sky130”, “gf180”]

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🧭 Introduction

When working with OpenLane, you inevitably encounter the following questions:

• Why does SKY130 flow relatively smoothly?
• Why is GF180 Open PDK often harder to use in the same way?
• Is this a configuration problem—or a PDK issue?

In this article, we frame the answer as a difference in design assumptions.

To state the conclusion upfront:

GF180 is not “bad.”
Rather, the design world implicitly assumed by OpenLane
differs from the design world GF180 is optimized for.

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🧱 What Kind of Flow Is OpenLane? (Assumptions)

OpenLane is a digital-only, fully automated flow that integrates:

• RTL → logic synthesis
• Automatic place & route (P&R)
• Automatic STA / DRC / LVS
• GDS generation

into a single, end-to-end pipeline.

The key point is:

OpenLane is not a framework that generalizes all PDKs

Instead, the flow implicitly assumes
a certain PDK structure and design philosophy.

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📋 PDK Conditions OpenLane Effectively Requires

PDKs that work “smoothly” with OpenLane tend to share common traits.

1. OpenPDK-Compatible Structure

• Well-organized libs.ref / libs.tech
• Existing OpenLane configuration files (e.g., config.tcl)
• Standard-cell–centric view hierarchy

2. Digital Standard-Cell Assumptions

• Synthesis → P&R → STA flows consistently
• No primary dependence on high-voltage or special-purpose cells

3. Designed for Automation

• Minimal human intervention required
• Flow assumes and absorbs certain “PDK behaviors”

These are implicit assumptions, not formally specified requirements.

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✅ Why SKY130 Works Well with OpenLane

The SKY130 PDK provides:

• OpenPDK-compatible structure
• A strong focus on digital standard cells
• Extensive use in education and PoC contexts

In other words:

The design world assumed by OpenLane
aligns closely with the design world SKY130 was built for

As a result, even with imperfect tuning,
the flow often completes successfully.

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🧠 Design Assumptions of GF180 Open PDK

GF180MCU Open PDK is optimized with a different philosophy.

Characteristics of GF180

• High-voltage support (5V / 10V class)
• Mixed-signal and analog use cases
• Product-oriented, real-chip design focus
• High design freedom

From a PDK standpoint, this is entirely healthy and correct.

However:

It is not primarily designed for
fully automated, digital-only, one-click flows

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⚠ Why GF180 Becomes Difficult with OpenLane

This is not a binary “works / does not work” issue.

• Basic PDK setup and tests may succeed
• But achieving an RTL → GDS automatic flow
  with the same ease as SKY130 is often difficult

The reasons include:

• Partial mismatch with OpenLane’s assumed PDK structure
• High-voltage and special cells conflicting with automation
• Design decisions that the flow cannot automatically resolve

In short, this is:

Not a configuration failure,
but a mismatch in design assumptions

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❗ On the Statement “GF180 Cannot Be Used with OpenLane”

This article frames the issue as follows:

• ❌ “GF180 cannot be used with OpenLane at all”
• ⭕ “GF180 has a narrower applicability

  for OpenLane-style fully automated digital flows”

This distinction matters.

GF180 excels in a different design domain,
and this neither diminishes GF180 nor OpenLane.

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🎯 Use Cases Where GF180 Excels

GF180 is well suited for:

• High-voltage drivers
• Mixed-signal circuits
• Custom-driven design flows
• Product-oriented designs with strong human control

👉 Designer-driven design world

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⚙ Use Cases Where OpenLane Excels

OpenLane is strongest in:

• Education
• Proof-of-concept designs
• Digital-only implementations
• Validation of automated flows

👉 Flow-driven design world

There is no superiority here—
only different roles.

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🧭 The Correct Decision Axis for Designers

The most important judgment is:

• Do not force a PDK to fit a tool
• Do not force a tool onto a PDK
• First check whether the design assumptions align

Choosing a PDK means choosing
not just a process, but a design philosophy

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📝 Summary

• OpenLane is a digital automation flow
• Compatible PDKs share implicit assumptions
• SKY130 aligns well with those assumptions
• GF180 is optimized for a different design world
• “Difficulty” reflects boundary conditions, not failure

With this understanding, designers can:

• Avoid overestimating OpenLane
• Avoid misunderstanding PDKs
• Make sound architectural decisions

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🧩 Closing

At this point, we have safely established three pillars:

1. OpenLane1: make it run once
2. OpenLane2: manage the environment
3. OpenLane × PDK: understand the assumptions

This is not a tool tutorial,
but a discussion about where designers stand.

When assumptions align,
tools will always work in your favor.