The term "soldermask" is also known as "solder mask", "solder resist" or just "mask".Default Behavior
By default, all Surface Mount (SMT) pads and Through-Hole (THT) pads already have a soldermask defined, so there is no need for the user to add it.
The soldermask term may confuse some users into thinking that they need to place a mask over the entire board to prevent copper from being exposed, this is incorrect when you work in a PCB Layout software such as Ultiboard. Think of this as a negative image
, places where you see an object will be exposed (for soldering or just bare copper), and places where you do not see any object will be covered by the protective coating material that will prevent copper to be exposed or soldered.
The next image is a visual copy of the Soldermask Layer in Ultiboard. All objects that you see in green represent places where copper will be exposed to solder (mostly footprint pins). The black background is where in reality the soldermask coating material will be applied to prevent copper from being exposed, hence, the negative image