generally green in color but can have different colors: green, red, blue, white, black. Only the outer layers need to be stencil covered with solder mask, the inner copper layers are protected by the adjacent substrate layers. The soldering mask soldermask is made of a fluid substance
much higher component density because the component paths on the 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 stencil more than six layers of copper has been concurrent with the adoption
provide electrical connections on that conductive layer. Another manufacturing process adds plated or metallized holes that allow interconnections between layers. PCBs mechanically support electronic components using pads for bonding the component stencil terminals and electrically connect them using traces of one or more layers of copper sheets laminated on and/or between layers