At the second level of electronic packaging, components are mounted on a platform known as a printed wiring board (PWB) or printed circuit board (PCB). The board is either single-sided, double-sided, or multi-layered, depending on the number of components and the interconnection density. Components are interconnected to one another by the conductors embedded among the layers of the board or on its surface. Power and ground are provided to the components by point-to-point conductors in a single- or double-sided PWB or through planes embedded in the layers of a multi-layer board. A typical PWB serves an electronic system mechanically, electrically, and thermally. Mechanically, it provides support for the components and the conductors and a thermal conduction path for the heat dissipated by the components. Electrically, the PWB provides an insulator for the conductors. Because moisture absorption and chemical attack degrade material properties, the chemical properties also need to be considered.