Also been seeing these errors, maybe it's related?  

@nikolacollins Hi Please to check your Design Rule (The Via diameter), the Via parameters should much the Design Rule or you will keep having these DRC errors. 

Both are set to 0.61mm. It looks like the design rule value has weird mil rounding.


@nikolacollins @JLCPCBsupport Add vias must has top and bottom copper layers

@UserSupport, I have seen exactly the same via dimension error. What happened is that I was working on a PCB with the canvas units set to mm right from the start. Until almost complete, all DRC checks passed ok. I then had to adjust some traces for which I changed the canvas units to mil. Checking the Design Rules showed the via diameter to be 24mil. After that, I changed the canvas units back to mm and then ran a DRC which showed this via dimension error. I then changed the units back to mil and opened the Design Rules and noted that the dimensions quoted in mil were no longer exact. The via diameter which had showed 24mil now showed 24.016mil. The clearance width had also changed from an exact value to a very slightly larger value. Resetting the via diameter and clearances back to their original whole number values, swapping canvas units back to mm and rerunning a DRC then cleared the via diameter DRC errors. The error is caused because switching between mm/mil/mm or mil/mm/mil creates a rounding error which is not detected and corrected. This error cost me about an hour of wasted time trying to understand the cause and how to "fix" an error that should never have occurred. The problems with rounding errors has been the subject of several Feature Requests and Bug Reports for several years now and really needs to be properly dealt with.

@andyfierman It is unit converting precision issue, there is no a good to solve yet.

Yes, I understand the issue. But other EDA tools must have the same problem so how do they fix it? It is obvious to a human what is wrong so surely all that is needed is to create a process that follows the same rules as a human would. If the base units in EasyEDA are mil then internally, EasyEDA is always working in mil. Internally EasyEDA works to maybe 0.01mil or maybe higher precision. Suppose you then define the smallest distance value in mil to be 0.1mil. So the user is only allowed to defined dimensions in mil to a resolution of 0.1mil. All dimensions that are in the Design Rules are checked against minimum values. For example, tracks, clearances, pads, vias and holes are checked against minimum diameters. When the canvas units are changed to mm and the user inputs a value in mm, that value has to be converted internally to mil. If the converted value in mil is less than the DRC value in mil then the DRC value in mil must be used for the user dimension and not the converted value. The DRC value that has been substituted for the converted user value must also then be converted from mil to mm and the user notified that their value has been  rounded up this new value to meet the minimum DRC values in mil. The user must accept that any mm values they enter that, when converted at full precision into mil are less than the internal DRC values in mil, will be recalculated back into mm from the minimum DRC values in mil. These corrections only affect user entered values that when converted into mil end up below the minimum DRC values so things like setting a grid to 5mm and a snap to 0.1mm should not be subject to the conversion and correction process. I think this should solve the problem. Maybe a flow chart would help?

@JLCPCBsupport I didn't realize I've been missing bottom copper areas. That resolved my via problem, thank you. @andyfierman Thanks for the tips on how to workaround the DRC errors.