What file type is used for pcb schematic drawings

​To preserve, edit, and communicate these schematics, specialized software tools (Electronic Design Automation or EDA tools) are used. And these tools rely on specific file types to store, share, and interpret schematic data. But what exactly are those file types, and how do they function in the broader landscape of PCB design?

PCB Schematic Drawings

Before diving into file formats, it’s important to understand the role and structure of a schematic.

A schematic diagram is a graphical representation of an electrical circuit. Unlike a physical layout that shows the exact positions of components, a schematic focuses on function. It uses standardized symbols to represent components like resistors, capacitors, ICs, and connections between them.

A good schematic allows engineers to:

Understand the design’s logic

Simulate circuit behavior

Troubleshoot errors

Collaborate across teams

Transition to PCB layout design

Because of these functions, schematics must be saved in formats that preserve component information, connectivity, and annotations — and that’s where various file types come into play.

Native Schematic File Formats: Tool-Specific Types

Each EDA software suite has its own native file format for schematic drawings. These proprietary formats are typically binary or XML-based, and they are fully editable within their respective environments.

1. .SCH – Used by Multiple EDA Tools

.SCH is a common file extension used in several design tools, but it’s not universal in format. It simply denotes a schematic file, and its structure depends on the tool that created it.

Tools that use .SCH:

EAGLE (Autodesk) – .sch holds the schematic drawing.

Altium Designer – Also uses .SchDoc, which is technically different from EAGLE’s .sch.

KiCad – Older versions used .sch before switching to a new format in v6.

Each of these .sch files is formatted differently, despite the common extension. They are typically not interchangeable unless converted.

2. .SchDoc – Altium Designer

Altium Designer, a professional-grade EDA suite, uses .SchDoc (Schematic Document) as its native schematic file type. It contains detailed information about component placement, electrical nets, and hierarchical structures. Features include:

Embedded symbols and attributes

Annotation layers

Multi-sheet designs

Versioning and history tracking

Altium projects also include .PrjPcb project files that manage multiple .SchDoc and .PcbDoc files.

3. .kicad_sch – KiCad (v6 and later)

KiCad, an open-source EDA tool, uses the .kicad_sch file format in its recent versions. Unlike the older flat .sch format, .kicad_sch is based on a hierarchical and more human-readable structure.

Benefits include:

Version control-friendly (text-based)

Supports annotation, netlists, and component fields

Flexible for large designs

Each schematic sheet in a KiCad project corresponds to its own .kicad_sch file.

4. .dsn – OrCAD and Allegro

.dsn files are used by Cadence tools such as OrCAD Capture and Allegro. These files store the schematic logic and are closely tied to .opj (project) files.

Features include:

Hierarchical design capability

Embedded constraints and rules

Export support for SPICE simulation and PCB layout

This format is binary, making it less accessible outside the OrCAD ecosystem.

Exchange and Interoperability File Formats

Sometimes, you need to move schematic data between different software tools or share it with collaborators who use different platforms. That’s where exchange formats come in.

1. .EDIF (Electronic Design Interchange Format)

EDIF is an industry-standard file format designed to facilitate data exchange between EDA tools. It can store schematic and layout data, and its scope includes both logical and physical representations.

File extensions:

.edf

.edn

.edi

Although EDIF is text-based and flexible, it’s somewhat outdated and not widely used in newer tools, having been replaced in many contexts by more modern standards or proprietary exchange formats.

2. .XML / .JSON (Modern Interchange Formats)

Some EDA tools and open-source workflows have started supporting schematic exports in XML or JSON formats.

For example:

EasyEDA supports exporting designs to JSON.

LibrePCB uses XML for all design files, including schematics.

These formats offer:

Readability for version control and scripting

Ease of transformation into other formats using custom parsers

Flexibility in modern web-based EDA tools

These are not yet standardized across the industry, but their accessibility makes them appealing for custom workflows.

Simulation-Oriented Schematic File Formats

While schematic files are primarily used for PCB layout preparation, they’re also essential for simulation. Some tools allow you to export schematics in formats tailored for SPICE-based circuit simulators.

1. .cir / .sp (SPICE Netlists)

SPICE simulation tools like LTspice, NGSpice, and PSpice often use:

.cir (Circuit)

.sp (SPICE)

These are not schematic drawing formats in the visual sense but are generated from schematics. They define the same electrical behavior using a netlist syntax.

2. .asc – LTspice

LTspice uses .asc (ASCII Schematic) files to store schematic drawings for simulations. These files are editable and contain both graphical and electrical data.

The .asc format is specific to LTspice but widely used in analog and mixed-signal design simulations.

Documentation and Visual Export Formats

For sharing schematics with non-technical users or integrating them into documents, engineers often export schematic drawings into visual or markup-friendly formats.

1. .PDF

Schematic drawings are often exported as PDFs for review, printing, or collaboration. This format ensures that the visual layout is preserved, and files can include bookmarks for navigation.

Pros:

Universally viewable

Lightweight

Maintains visual fidelity

Cons:

Not editable for schematic logic

No embedded electrical data

2. .SVG / .PNG / .JPG

These image formats are useful for web publishing, documentation, or presentations. Exporting a schematic to .SVG (vector) or .PNG (raster) allows engineers to share designs without exposing editable logic.

SVG is preferred for high-resolution, scalable documentation, while PNG or JPG is easier for basic image embedding.

Netlist Files: The Bridge Between Schematic and Layout

A netlist is not a schematic drawing, but it is often generated from a schematic file to describe how components are electrically connected. It plays a crucial role in transferring schematic logic to PCB layout tools.

Common Netlist Formats:

.net – Generic netlist format used in many tools

.xml – XML-based netlist for easier parsing

.cmp – Component list with reference and footprint info

.xnet – Advanced netlist format for signal integrity tools

These files may accompany schematic files when moving a design to another tool for layout or analysis.