prevent solder shorts, the coating is called a solder mask. Soldermask is generally green stencil in color but can have different colors: green, red, blue, white, black. Only the outer layers need to be covered with solder mask, the inner copper layers are protected by the adjacent substrate layers. The soldering mask soldermask is made
insulating layers. A basic printed circuit consists of a flat sheet of insulating material FR4, Rogers or Polyamide for flexible circuits, and a layer of copper foil, laminated to the substrate. Chemical etching stencil divides the copper into separate conductive lines called tracks or circuit paths, pads for connections, metallized holes (vias)
because the component paths on the stencil inner layers would occupy the space between the components. The increase in the need for multilayer printed circuit boards with more than two, four and especially more than six layers of copper has been concurrent with the adoption of surface mount technology. "Through holes" components are