Ohmforge Gerber & Drill Viewer with DRC-lite

What it is for

Before you order a circuit board you want to see what the fabricator will see: the copper, solder mask and silkscreen as they come out of your design tool, the holes, and the board size. This tool opens the fabrication data itself – a ZIP of Gerber layers and Excellon drill files from KiCad, Altium, Eagle, EasyEDA or any CAM tool – renders it and measures it.

You get a board image for the top or bottom side, SVG files of both sides and of every layer, a drill table, the narrowest drawn trace, a sampled copper clearance and copper area, and a short DRC: annular rings of plated holes and the distance from every hole to the board edge. A board model with the outline and the mounting holes is ready for the enclosure generator. It is a quick check, not your fabricator's CAM review.

Worked example

The first example is a 50 × 30 mm two-layer sensor board exported KiCad-style with X2 attributes. All 8 files are recognised from their .FileFunction attribute: outline, top silkscreen, both masks, both copper layers and plated and non-plated drills. The result: 50 × 30 mm, 1496.5 mm² (rounded corners), 18 holes and 1 slot. The drill table lists six 0.3 mm plated vias, eight 1 mm header holes, one 1.2 mm plated slot and four 3.2 mm non-plated mounting holes.

The narrowest trace is 0.25 mm, the smallest annular ring 0.15 mm (0.6 mm via pads on 0.3 mm drills) and the closest hole sits 1.9 mm from the edge. The bottom copper is 88.6 % ground plane, the top 19 %. With the default rules every check passes.

Now tighten the rules to a 0.25 mm clearance and a 0.2 mm annular ring. The summary changes to 9 checks need attention: three pairs of copper islands are about 0.23 mm (± 0.025 mm) apart, and the six vias have rings of 0.15 mm.

The second example is the same board written Eagle-style: inch units, old syntax, no attributes. The layers are recognised from file names such as .cmp and .sol, the board is again 50 × 30 mm, and 7 checks fail: six vias with only 0.05 mm of ring and a hole 0.249 mm from the edge.

How to read the result

Board size comes from the closed contour of the outline layer, measured along the line centres. If there is no closed contour, a warning says the size is only a bounding box.

Detected by tells you whether a layer was identified by an X2 attribute or by its file name. A wrong guess usually means an unusual file name; Ohmforge's viewer lets you change the layer function.

Clearance and copper area are sampled on a grid, shown in the report (0.025 mm here); treat a value within one grid step of your rule as borderline, not as a failure. Trace width, annular ring and hole-to-edge values are exact for drawn traces and flashed pads.

Tips and common mistakes

• Upload the whole ZIP your design tool writes; single files work too, and a separate drill file has its own field.
• Set the four rules to your fabricator's published capabilities; the defaults are typical, not universal.
• A plated hole without a flashed pad is reported. Holes of unknown plating without copper count as non-plated.
• Mounting-hole candidates are holes between 2 and 4.5 mm; change the range if you use M4 or M2 screws.

FAQ

Which Gerber features are supported?

Standard and macro apertures, arcs, regions, dark and clear polarity, step and repeat, block apertures, rotation, mirroring and scaling, X2 attributes and the common deprecated commands of older files.

Why does the clearance differ slightly from my design tool?

It is measured on a raster of the copper, so it is accurate to about one grid step. A smaller sampling grid gives a finer answer.

Does it replace a real DRC?

No. It checks drawn traces, island gaps, rings and edge distances, not nets, drill-to-copper spacing or impedance.

Can I make an enclosure from it?

Yes. Download the board model or the Ohmforge project, or open Instruments → Gerber viewer… in Ohmforge and choose Use the outline for the enclosure.