There is currently no "Expose Copper" option for Copper Areas. There is also no option to convert a Copper Area into any other form of copper feature that does offer the "Expose Copper" option. Your project is private so only you can see it. If you can post an example of what you want to achieve then we may be able to suggest a workaround. :)

Thanks for the reply. I created a very simple example of what I'm trying to do: [https://easyeda.com/audiomath/example-project-need-solder-mask-removed](https://easyeda.com/audiomath/example-project-need-solder-mask-removed) These units often must be modified in the field, so we don't know in advance the style or location of the SMD capacitors that get soldered between the exposed traces and the ground plane, so it makes sense that there be no solder mask at all on the bottom.

Go to the solder mask layer on the layers and object window and select to edit it then you can edit no solder mask regions similar to how you edit copper regions

@audiomath alternaterly there is a expose copper option in the track properties pane you can also use that