A printed circuit board is a structural element that consists of a dielectric base and copper conductors, which are deposited on the base in the form of metallized sections. It provides the connection of all radio-electronic elements of the circuit.
The printed circuit board has a number of advantages compared to volumetric (hinged) mounting using cables and wires:
- high-density mounting of radio components and their connections, resulting in a significant reduction in the dimensions and weight of the product;
- obtaining conductors and shielding surfaces, as well as radioelements in a single technological cycle;
- stability, repeatability of characteristics such as capacitance, conductivity, inductance;
- high speed and noise immunity of circuits;
- resistance to mechanical and climatic influences;
- standardization and unification of technological and design solutions;
- reliability of nodes, blocks and the device itself as a whole;
- increased manufacturability as a result of complex automation of assembly work and control and adjustment actions;
- lowlabor intensity, material intensity and cost.
The PCB also has disadvantages, but there are very few of them: limited maintainability and high complexity of adding design changes.
The elements of such boards include: a dielectric base, a metallized coating, which is a pattern of printed conductors, contact pads; fixing and mounting holes.
Requirements for these products GOST
- Printed circuit boards must have a dielectric base uniform in color, which must be monolithic in structure, not contain internal bubbles, shells, foreign inclusions, cracks, chips, delaminations. However, single scratches, metal inclusions, traces of a single removal of an unetched area are allowed, as well as a manifestation of the structure that does not change the electrical parameters of the product, does not reduce the allowable distance between the elements of the pattern.
- The pattern is clear, with a smooth edge, without swelling, tearing, delamination, tool marks. Minor local mordants are allowed, but not more than five dots per square decimeter, provided that the rest of the track width complies with the minimum allowable; scratches up to six millimeters long and up to 25 microns deep.
To improve corrosion characteristics and increase solderability, the surface of the board is coated with an electrolytic composition, which must be continuous, without delamination, ruptures and burns. Fixing and mounting holes are requiredposition according to the drawing. It is allowed to have deviations determined by the accuracy class of the board. In order to improve the reliability of soldering, a layer of copper is sprayed onto all internal surfaces of the mounting holes, the thickness of which must be at least 25 microns. This process is called hole plating.
What are PCB grades? This concept means the accuracy classes of manufacturing boards, they are provided for by GOST 23751-86. Depending on the density of the pattern, the printed circuit board has five accuracy classes, the choice of which is determined by the level of technical equipment of the enterprise. The first and second classes do not require high-precision equipment and are considered cheap to manufacture. The fourth and fifth grades require special materials, specialized equipment, perfect cleanliness in production facilities, air conditioning, and temperature maintenance. Domestic enterprises mass-produce printed circuit boards of the third accuracy class.
