In electronics, printed circuit boards, or PCBs, are used to mechanically support electronic components which have their connection leads soldered onto copper pads in surface area install applications or through rilled holes in the board and copper pads for soldering the element leads in thru-hole applications. A board design may have all thru-hole parts on the top or part side, a mix of thru-hole and surface mount on the top just, a mix of thru-hole and surface area mount components on the top and surface area install elements on the bottom or circuit side, or surface area install elements on the top and bottom sides of the board.
The boards are also used to electrically connect the required leads for each part utilizing conductive copper traces. The element pads and connection traces are engraved from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are designed as single agreed copper pads and traces on one side of the board only, double agreed copper pads and traces on the leading and bottom sides of the board, or multilayer styles with copper pads and traces on the top and bottom of board with a variable variety 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 real copper pads and connection traces on the board surface areas as part of the board production process. A multilayer board consists of a number of layers of dielectric material that has actually been impregnated with adhesives, and these layers are utilized to separate the layers of copper plating. All these layers are lined up then 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 typical 4 layer board style, the internal layers are typically used to provide power and ground connections, such as a +5 V airplane layer and a Ground aircraft layer as the two internal layers, with all other circuit and element connections made on the top and bottom layers of the board. Very complicated board styles may have a a great deal of layers to make the various connections for various voltage levels, ground connections, or for linking the lots of leads on ball grid array devices and other large integrated circuit package formats.
There are generally two types of material utilized to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet form, usually about.002 inches thick. Core material is similar to a really thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, usually.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are two approaches used to build up the wanted number of layers. The core stack-up method, which is an older technology, uses a center layer of pre-preg material with a layer of core product above and another layer of core material below. This combination of one pre-preg layer and two core layers would make a 4 layer board.
The film stack-up method, a more recent innovation, would have core material as the center layer followed by layers of pre-preg and copper material built up above and listed below to form the final variety of layers needed by the board style, sort of like Dagwood developing a sandwich. This approach allows the producer versatility in how the board layer densities are combined to meet the finished product density requirements by differing the number of sheets of pre-preg in each layer. When the material layers are finished, the whole stack goes through heat and pressure that triggers the adhesive in the pre-preg to bond the core and pre-preg layers together into a single entity.
The procedure of manufacturing printed circuit boards follows the actions below for many applications.
The procedure of identifying products, procedures, and requirements to fulfill the client's requirements for the board design based upon the Gerber file info provided with the order.
The procedure of transferring the Gerber file information for a layer onto an etch withstand movie that is placed on the conductive copper layer.
The conventional process of exposing the copper and other areas unprotected by the etch resist film to a chemical that eliminates the unguarded copper, leaving the protected copper pads and traces in location; more recent processes utilize plasma/laser etching rather of chemicals to eliminate the copper material, allowing finer line meanings.
The procedure of lining up 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 See more here process of drilling all the holes for plated through applications; a second drilling process is used for holes that are not to be plated through. Details on hole location and size is contained in the drill drawing file.
The procedure of applying copper plating to the pads, traces, and drilled through holes that are to be plated through; boards are positioned in an electrically charged bath of copper.
This is needed when holes are to be drilled through a copper location but the hole is not to be plated through. Prevent this procedure if possible because it adds expense to the completed board.
The procedure 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 used; the solder mask protects versus environmental damage, offers insulation, safeguards versus solder shorts, and protects traces that run between pads.
The procedure 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 happen at a later date after the components have actually been placed.
The process of applying the markings for element designations and component lays out to the board. Might be applied to simply the top or to both sides if components are mounted on both leading and bottom sides.
The procedure of separating several boards from a panel of identical boards; this procedure also enables cutting notches or slots into the board if needed.
A visual inspection of the boards; likewise can be the process of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.
The process of checking for continuity or shorted connections on the boards by means using a voltage between different points on the board and determining if a present flow happens. Relying on the board intricacy, this procedure might require a specially developed test component and test program to integrate with the electrical test system used by the board producer.