In electronics, printed circuit boards, or PCBs, are utilized to mechanically support electronic elements which have their connection leads soldered onto copper pads in surface area mount applications or through rilled holes in the board and copper pads for soldering the part leads in thru-hole applications. A board style may have all thru-hole components on the leading or element side, a mix of thru-hole and surface area mount on the top side just, a mix of thru-hole and surface install components on the top side and surface area mount components on the bottom or circuit side, or surface area mount elements on the top and bottom sides of the board.
The boards are likewise used to electrically connect the required leads for each element using conductive copper traces. The component pads and connection traces are etched from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are created as single sided with copper pads and traces on one side of the board just, double sided with copper pads and traces on the top and bottom sides of the board, or multilayer designs with copper pads and traces on top and bottom of board with a variable number of internal copper layers with traces and connections.
Single or double sided boards consist of a core dielectric product, such as FR-4 epoxy fiberglass, with copper plating on one or both sides. This copper plating is engraved away to form the actual copper pads and connection traces on the board surface areas as part of the board production procedure. A multilayer board consists of a number of layers of dielectric product that has actually been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All of these layers are lined up and after that bonded into a single board structure under heat and pressure. Multilayer boards with 48 or more layers can be produced with today's technologies.
In a common four layer board design, the internal layers are frequently used to supply power and ground connections, such as a +5 V airplane layer and a Ground aircraft layer as the 2 internal layers, with all other circuit and element connections made on the top and bottom layers of the board. Extremely intricate board designs may have a large number of layers to make the various connections for various voltage levels, ground connections, or for connecting the lots of leads on ball grid range gadgets and other big integrated circuit bundle formats.
There are typically two types of material used to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet kind, typically about.002 inches thick. Core material is similar to a very thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, usually.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are 2 techniques used to build up the preferred variety of layers. The core stack-up method, which is an older innovation, uses a center layer of pre-preg material with a layer of core material above and another layer of core product listed below. This combination of one pre-preg layer and two core layers would make a 4 layer board.
The film stack-up approach, a more recent technology, would have core product as the center layer followed by layers of pre-preg and copper product developed above and below to form the final number of layers required by the board style, sort of like Dagwood developing a sandwich. This method permits the maker versatility in how the board layer densities are integrated to fulfill the ended up product density requirements by varying the variety of sheets of pre-preg in each layer. When the material layers are finished, the whole stack goes through heat and pressure that causes the adhesive in the pre-preg to bond the core and pre-preg layers together into a single entity.
The procedure of producing printed circuit boards follows the actions listed below for most applications.
The procedure of determining materials, procedures, and requirements to fulfill the consumer's specifications for the board style based upon the Gerber file info supplied with the purchase order.
The process of moving the Gerber file data for Reference site a layer onto an etch resist film that is placed on the conductive copper layer.
The conventional procedure of exposing the copper and other locations unprotected by the etch withstand film to a chemical that eliminates the unguarded copper, leaving the secured copper pads and traces in location; newer procedures use plasma/laser etching rather of chemicals to get rid of the copper product, enabling finer line meanings.
The procedure of aligning the conductive copper and insulating dielectric layers and pressing them under heat to trigger the adhesive in the dielectric layers to form a strong board product.
The procedure of drilling all the holes for plated through applications; a second drilling procedure is used for holes that are not to be plated through. Details on hole place and size is contained in the drill drawing file.
The process of applying copper plating to the pads, traces, and drilled through holes that are to be plated through; boards are put in an electrically charged bath of copper.
This is needed when holes are to be drilled through a copper location however the hole is not to be plated through. Prevent this process if possible due to the fact that it includes expense to the completed board.
The process of using a protective masking product, a solder mask, over the bare copper traces or over the copper that has had a thin layer of solder applied; the solder mask safeguards against ecological damage, provides insulation, safeguards against solder shorts, and safeguards traces that run in between pads.
The process of finish the pad locations with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering process that will take place at a later date after the components have actually been put.
The process of applying the markings for element designations and part details to the board. May be used to just the top or to both sides if parts are mounted on both leading and bottom sides.
The process of separating multiple boards from a panel of identical boards; this process likewise permits cutting notches or slots into the board if required.
A visual examination of the boards; also can be the procedure of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.
The procedure of looking for continuity or shorted connections on the boards by ways applying a voltage in between various points on the board and identifying if a present flow takes place. Depending upon the board complexity, this process might require a specially designed test component and test program to integrate with the electrical test system used by the board producer.