Printed circuit board. PrintedCircuitBoard (PCB) refers to selectively assembling and installing holes on the insulated substrates, connecting wires and assembling pads of electronic components to achieve the electrical connection between components. Printed circuit board is one of the most important components in electronic products. From household appliances, communication equipment, weapon equipment to aerospace equipment, any electronic device is inseparable from printed circuit boards. In the development of electronic products, the design of printed boards, the compilation and manufacture of the documents are the main factors that affect the success of the products. It can be said that the quality and cost of the whole product are directly affected by the design and manufacturing quality of the printed board. The development direction of printed circuit technology is high density, high accuracy, high reliability, large area and fine line. It depends on the continuous improvement and development of printing technology, chemical technology, precision machining, optical technology, CAD technology and new materials and other technologies.
A qualified printed circuit board is composed of pad, through hole, installation hole, location hole, printing line, component surface, welding surface, solder mask and screen printing layer. It has double functions of conductive line and insulating baseplate.
Printed circuit board
(1) weld plate.
Pad, also known as the connecting disk, refers to the metal part of the printed wire around the weld hole, which is used for welding the external leads, usually through the treatment of copper clad laminate. There are some pads on the PCB copper clad copper foil is itself after spraying a layer of solder resist is formed; there are some pads on the PCB using dip dip tin, silver, pewter plating and other measures. The size and shape of the pads have a direct effect on the quality of the solder joints, the quality of PCB and the beauty of the solder joints.
(2) through holes.
A hole is a small metal hole connected up and down two layers of printed wire on a double side PCB, usually filled with metal or coated with a metal layer. The process of coating metal in an over hole is called metallization. The over hole can be used as a welding plate or only as a connection hole, depending on its role in the circuit.
(3) installation holes.
The installation holes are small holes for fixing large components and installing PCB, and the specific size depends on the actual needs.
(4) the positioning hole.
The positioning hole is a small hole for PCB processing and detection and localization, usually adopts three positioning method, the pore size depends on the assembly process to determine. Sometimes it can be replaced by an installation hole.
(5) printed line.
Connecting circuit printed line is essentially the PCB components, it is on the copper clad copper foil connection circuit according to the actual requirements, through a series of etching while leaving the reticular small line. The printed wire on the finished PCB is usually coated with a layer of green or brown solder resistance to prevent oxidation and rust.
(6) component surface.
The component surface is also known as the assembly surface of the component, which is used to install the components on the PCB. On one side PCB, there is no printed line (copper foil) on the side of the component surface. On the double PCB, there are parts of the logo, such as graphics and characters, which are printed with components.
(7) welding surface.
The welding surface is also called the printed sheet surface, which is used to weld the pin of the components on the PCB, usually without any mark.
(8) solder resistance layer.
As the name implies, the solder layer is the layer that hinders the welding, and the green (or brown) layer on the PCB is the insulating layer. The solder barrier protects the printed copper wires from being oxidized and prevents the components from being welded to the wrong place.
(9) silk screen.
The screen is used to mark the position of the components on the PCB, mostly white, and is printed with characters and symbols on the resistance layer of PCB. As the method of silk printing is used in the manufacturing process, it is called the silk screen.