ExpressPCB expands whole-board design rule checking

ExpressPCB has released version 3.4 of its Plus printed circuit board design software, extending design rule checking to spacing between all objects on a layout. The update also introduces a revised fault-reporting interface, restores component downloads through SnapMagic and allows existing ExpressPCB Classic designs to use the expanded checking functions.

The free update, announced on 19 October by ExpressPCB’s parent company ASC Sunstone Circuits, addresses the identification of layout errors before a board is submitted for manufacturing. Earlier versions checked spacing between objects and polygon fills, while the new design rule checker, or DRC, examines spacing relationships throughout the layout.

PCB design rules define the geometrical limits within which copper features, components and other board elements must be placed. These limits can include minimum conductor spacing, track widths, clearances around holes and restrictions associated with mechanical features. Their values depend on the chosen manufacturing process and the electrical requirements of the completed circuit.

As component density increases, spacing violations can become difficult to identify through visual inspection alone. Copper tracks may pass close to pads, vias or other conductors, while dense component footprints can leave little routing space. A layout that appears acceptable at a normal viewing scale may contain features that cannot be manufactured consistently or that violate the electrical clearances required by the design.

Design rule checking provides a systematic method for identifying these conflicts. The software compares the positions and dimensions of layout objects against the selected constraints and reports conditions that require attention. The process can reveal errors before fabrication data is generated, although the results depend on the completeness and suitability of the rules applied.

The redesigned DRC interface in ExpressPCB Plus 3.4 allows users to examine individual violations. Selecting a reported item automatically centres and zooms the layout view on its location, while the interface provides a summary of the identified problem. The complete report can be exported as a text file for review, communication or retention with the design documentation.

Linking a reported fault to its physical position can make dense layouts easier to examine. A designer can inspect the neighbouring tracks, pads and copper regions before deciding how to modify the geometry. Resolving one spacing violation may require rerouting conductors or moving a component, with the subsequent design changes potentially affecting other parts of the circuit.

The expanded checks also change the treatment of certain warnings during the ordering process. Objects outside the board outline no longer automatically prevent an order from proceeding. Where only spacing violations remain, users can review the reported conditions and choose to override them before submitting the design.

That override does not establish that a board containing unresolved violations will manufacture successfully. A narrow gap may be achievable under one fabrication process but unsuitable for another, while an electrical clearance needed for a particular operating voltage may be more restrictive than the minimum geometry a fabricator can produce.

Manufacturability and electrical suitability therefore require separate consideration. A board can meet a fabricator’s minimum track and spacing specifications while still containing an unsuitable current path, inadequate insulation clearance or a component arrangement that creates problems during assembly or operation.

ExpressPCB Plus 3.4 also restores component downloads through SnapMagic, formerly SnapEDA, within the schematic and layout environments. The library integration allows users to obtain component symbols and footprints without constructing each item manually, with the available content depending on the component and its associated library information.

Schematic symbols represent electrical connections and functions, while PCB footprints describe the physical pads and other features required to mount components. Both must correspond to the actual part being used. A downloaded footprint with incorrect dimensions, pad numbering or mechanical clearance can create assembly problems even if the DRC finds no spacing violations.

The update adds support for multi-section schematic symbols. Devices containing repeated functions or several distinct circuit sections can be represented across different parts of a schematic while remaining associated with one physical component. This arrangement can improve the organisation of complex circuit diagrams without changing the underlying electrical connections.

Library improvements also include restricted, or keep-out, layers for imported SnapMagic and Eagle parts. These identify areas where particular board objects should not be placed. The expanded DRC can flag tracks and vias entering such regions, helping users identify conflicts associated with component dimensions, mechanical movement or other restrictions.

Keep-out information complements electrical spacing rules because a component may require clearance for reasons unrelated to conductor separation. Mechanical housings, mounting structures and other physical features can occupy space beyond the component’s solder pads. The correct restrictions depend on the manufacturer’s mechanical drawing and the way the component is installed.

ExpressPCB Plus 3.4 can also represent imported footprints containing slots, cutouts and non-plated holes. These features are placed on the layout milling layer, allowing the design to retain mechanical information required by components or the surrounding assembly.

The software’s ability to represent these features must be distinguished from the fabrication services available through its integrated ordering route. ASC Sunstone Circuits states that slots, cutouts and non-plated holes are not offered through the ExpressPCB service. Designs requiring them must instead be ordered through Sunstone’s separate fabrication service.

This distinction is particularly relevant when a component has mounting tabs, unusual leads or mechanical requirements that cannot be represented by conventional plated holes. A layout can contain the necessary manufacturing information, but the selected fabrication process must support the required mechanical operations and tolerances.

Users retaining designs in ExpressPCB Classic can import their layouts into Plus and run the new DRC against them. The imported files can also access the expanded library functionality and restricted layers, providing a route for checking older designs using the updated software.

The release moves ExpressPCB Plus to .NET 8 and includes changes intended to improve reliability when opening large schematic files. Several component footprints and symbols have also been updated, with details available in the manufacturer’s release notes.

ExpressPCB Plus 3.4 is available as a free download, and existing users can install it over the current version. The software retains its integrated ordering workflow, while the expanded DRC and library functions provide additional checks before manufacturing. Electrical verification, component selection and confirmation of the fabricator’s capabilities remain necessary parts of the design process.