Whenever I plot my layout to gerber files, and then drop the zip into an online gerber viewer (I’ve tried three different viewers now), they show me random solder mask anomalies like this:
Here’s what the solder mask looks like in the layout (everything else turned off) in this area:
The way I fix the issue is to reload the footprints and then refill the zones. Then generate new gerber plots and look again. What usually happens is that the anomalies move to a different footprint. I’ve even tried reloading all footprints. It doesn’t seem to matter - the anomalies just show up somewhere else. I’m wondering if it’s not just a bug in the plotter code and reloading footprints doesn’t really do anything - the plotter just puts anomalies in a different random location.
The anomalies seem to be in the paste layer, not in the mask layer. Paste is grey in the online viewer while the mask openings without paste are golden/yellow, uncovering the copper below, like in the through hole pads. Some online viewers have had problems with rounded corners in pads, maybe this is similar.
A bunch of the online viewers also use the same underlying code.
Have you tried the ucamco viewer?
They are a company that actually makes the machines that make gerber plotters, which suggest they probably have a more reliable gerber viewer. https://gerber.ucamco.com/
Actually Ucamco governs the Gerber standard, so it’s the most authoritative source for anything related to Gerber.
The KiCad project founder J.P. Charras has some relations to Ucamco and I would believe KiCad is above average in handling gerbers. See Post-v5 new features and development news.
