When we open the keyboard of a general-purpose computer, we see a soft film (flexible insulating substrate) printed with a silver-white (silver paste) conductive pattern and a health pattern. Because of the general screen printing method to obtain this pattern, we call this printed circuit board flexible silver paste printed circuit board. And we go to the computer city to see a variety of computer host board, graphics cards, network cards, modems, sound cards and household appliances on the printed circuit board is different. The substrate used is made of paper base (usually used for single side) or glass cloth base (often used for double side and multi-layer), pre-pregassed phenolic or epoxy resin, one or both surface layers are glued to a copper-coated sheet and then laminate and cure. This circuit board covered with copper sheet plate, we call it a rigid plate. Then made into a printed circuit board, we call it a rigid printed circuit board. Single-sided printed circuit graphics we call single-sided printed circuit board, double-sided printed circuit graphics, and then through the metallization of holes to form a double-sided printed circuit board, we call it a double panel. If the printed circuit board with a double-sided inner layer, two single-sided outer layer or two double-sided inner layer and two single-sided outer layer is used, the printed circuit board with the positioning system and the insulating binder material alternately together and the conductive graphics are interconnected according to the design requirements becomes a four-layer and six-layer printed circuit board, also known as a multi-layer printed circuit board. There are now more than 100 layers of functional printed circuit boards.