The printed circuit is a support, generally a plate, intended to gather electronics components, in order to carry out a more complex system.

Manufacture

The printed circuit (also called “PCB” for Printed Circuit Board ) is a plate manufactured starting from materials composite (in the past Bakélite, then resin epoxy) and doubled of a fine layer of Cuivre. This plate, of very variable lengths and widths, has a thickness about the millimetre (standard = 16/10 mm), such FR-4).

The layer of copper, by photographic transfer of the electrical circuit with a Insoleuse and, dissolution of the copper surplus, allows the manufacture of electrical circuits the request. After drilling of the holes of passage, it makes it possible to establish by brazing (commonly called welding with the tin) the components electronic S (Diode S, resistances, condensing, Transistor S, integrated circuits, etc). They will then be connected by the conducting bands thus created. This plate forms an electronic subsystem then. This type of printed circuit is known as full-course.

The dissolution of copper can be realized by perchloride of iron liquid, or a mixture of hydrochloric acid, Cuprous chloride and hydrogen peroxide (what with the advantage of recycling copper dissolves, then in the form of cuprous chloride, as a solvent for a following engraving).

Bakelite (of color chestnut) can support only two layers, for the majority of the old electronic devices (i.e 1960 - 1970), only one layer of copper is present, the components are positioned on the other side of the plate.

With the appearance of increasingly complex circuits, the techniques of engraving evolved/moved. The printed circuits saw the number of their layers multiplying (the layers are added two by two). The connections between the tracks of the various layers and the components are ensured by tiny Rivet S drivers called vias. In a mother chart of microcomputer for example, the layers are six, even more. A layer is reserved for the mass or food 0  V, one with the food 5  V, the others are distributed according to the needs. When complexity is really raised and that the cost can be regarded as secondary, one can meet to 30 layers.

Examples of use

Almost all the fields of electronics now use printed circuits:

• microcomputer;
• Printing;
• Computer;
• equipment electric household appliances, Hi-fi;
• chart which one finds in the plays of arcade;
• etc

Certain components of computer are (by construction) printed circuits:

• the Mother chart;
• the bars memories;
• the expander cards of microcomputer NCV/ISA.

Evolutions

With the decrease of the manufacturing costs, the number of layers used by printed circuits intended for general public applications does not cease increasing. Whereas in the years 1990, auto industry considered that only printed circuits full-course were industrially acceptable, it is not any more surprising (in 2005) to meet circuits with four layers in the apparatuses general public, and from 10 to 14 layers for specific applications. Generally, one alternates layers conveying the signals and of the more homogeneous layers (plan of mass and plan of food) in order to distribute the supply voltages on all the chart and to improve electromagnetic compatibility (in summary, CEM). The various layers are inter-connected by metallized holes called vias. Recent techniques make it possible to carry out one-eyed vias (not crossing all the layers) and even of the buried vias (not leading to the external layers).

With the need for reduction of the size, the printed circuit planéiforme can be an obstacle with integration. One thus observes the use of flexible printed circuits which can be traced on a flexible support (generally with only one or two layers of copper). An environment where the flexible circuit is current is that of the cameras where that makes it possible to circumvent the constraints of placement which are imposed by optics and the industrial design. But of the reasons of cost can also lead the industrialists to choose this technology of flexible circuits: although more expensive to manufacture, they offer the undeniable advantage of not requiring any system of connector industry for the interconnection between various charts, consequently saving the labor and the matter of this operation, and making reliable the unit.

The detail of the techniques of printed circuit evolved/moved with the appearance of the CMS (assembled Composant surfaces of it) which made it possible to reduce the size of the components considerably. So the miniaturization induced the increase in the Fréquence S of use, the reduction in the tensions used and the heat produced by the passage of the electric current, but this imposed specific adaptations as the increase in the median number of crossings but also the appearance of crossings “in-pad” (made with the Laser), i.e. integrated in the beach where the component comes to be brazed. This technique also makes it possible to avoid an escape of welding to the assembly of the components.

In certain extreme cases, the support can leave ordinary completely (while taking again the same principles). For example, certain military or space applications which are subjected to thermal environments very testing using printed circuits in ceramic.

See too

• BATH OF GRAVAGE

• Realization of circuits print

Related articles

• Routing

• Graveuse horizontal
• Insoleuse
• Drilling machine
• electric Slotting
• Test

Random links:

Universal format of disc | Communication and information technologies for education | Edward Brophy | Higashine | County of Fannin (Texas)