Composition of printed circuit boards
The standard PCB is a circuit board with no components, and the raw material of the board is made of heat-insulated, non-boastful material. The small circuit material seen on the surface of the circuit board is copper foil. These lines are called wiring lines or conductors of the circuit board. Printed circuit boards use copper boxes instead of wires to complete the electrical connection between the components on the circuit board. Circuit board insert element hole is called a pad and is used to place elements, as well as solder pin fixing elements and complete electrical connections.
Printed circuit board mainly consists of three layers: copper foil layer, screen printing layer and printed material layer. Each layer is composed of solder pad, wiring, through hole and copper coating.
The copper foil layer, also known as the signal layer or line layer, is a tool for conducting components between components. The number of layers of copper foil determines the number of layers of the circuit board. There is only one copper foil layer is a single-sided board, and there are two copper box layers are dual panels. Screen printing layer is the screen printing layer, which is located at the top of the printed board. It is for the convenience of the installation and debugging of the circuit or the standardization requirements of the company, and the code names and text string icons printed on the circuit board, etc. Such as components of the outline of the number of manufacturers and other content. In addition, the screen printing layer also plays the role of protecting the steel foil layer. The printing material layer is also called the substrate, its function is to separate each copper foil layer with the printed material layer, plays the role of insulation and support the whole circuit board.
The pad is mainly used to complete the electrical connection between the component pin and the wire. It is also used to help weld the component pin during welding. The wiring plays the role of the conductor in the actual circuit. The wiring is connected to the pad of the element to complete the task of electrical connection on the whole circuit board. The through hole allows more than two layers of copper foil to conduct each other. Larger through holes are usually designed for component plugins, and non-through holes are used for surface mount positioning and assembly of fixed screws. Copper coating is to fill a certain area of the circuit board with copper foil, which can improve the circuit performance and anti-interference.
In addition, during welding, not all copper surfaces are welded. In order to avoid the problem of short-circuiting between lines that do not require welding, a layer of copper foil on the non-pad of the circuit board will be printed to insulate the tin from the copper surface. This material is called welding resistance ink. Welding ink can be divided into green oil, red oil and blue oil.
Because the copper surface is easily oxidized in the general environment, it can not be tin or solder poor, so the copper surface to be welded will be coated with an auxiliary welding film to improve solderability.