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 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 elements on the top or component side, a mix of thru-hole and surface area install on the top only, a mix of thru-hole and surface area install components on the top and surface area install parts on the bottom or circuit side, or surface mount parts on the leading and bottom sides of the board.
The boards are also used to electrically link the needed leads for each part utilizing conductive copper traces. The part pads and connection traces are engraved from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are developed as single agreed 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 the top and bottom of board with a variable number of internal copper layers with traces and connections.
Single or double sided boards include a core dielectric material, such as FR-4 epoxy fiberglass, with copper plating on one or both sides. This copper plating is etched away to form the real copper pads and connection traces on the board surface areas as part of the board production procedure. A multilayer board includes a variety of Reference site layers of dielectric product that has been fertilized with adhesives, and these layers are used to separate the layers of copper plating. All of 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 normal 4 layer board style, the internal layers are typically utilized to provide power and ground connections, such as a +5 V aircraft layer and a Ground plane layer as the 2 internal layers, with all other circuit and part connections made on the leading and bottom layers of the board. Really complicated board designs may have a large number of layers to make the numerous connections for different voltage levels, ground connections, or for linking the numerous leads on ball grid variety gadgets and other large integrated circuit plan formats.
There are usually two kinds of material utilized to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet kind, normally about.002 inches thick. Core product is similar to an extremely thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, generally.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are 2 methods used to build up the desired variety of layers. The core stack-up technique, which is an older technology, uses a center layer of pre-preg material with a layer of core material above and another layer of core product below. This combination of one pre-preg layer and 2 core layers would make a 4 layer board.
The film stack-up method, a more recent innovation, would have core product as the center layer followed by layers of pre-preg and copper product built up above and below to form the last variety of layers needed by the board design, sort of like Dagwood constructing a sandwich. This approach allows the maker flexibility in how the board layer densities are combined to meet the ended up product density requirements by differing the number of sheets of pre-preg in each layer. When the product layers are finished, the entire stack is subjected to 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 process of producing printed circuit boards follows the actions below for the majority of applications.
The procedure of identifying materials, processes, and requirements to fulfill the client's requirements for the board design based on the Gerber file info supplied with the purchase order.
The process of transferring the Gerber file information for a layer onto an etch withstand movie that is placed on the conductive copper layer.
The standard process of exposing the copper and other locations unprotected by the etch withstand film to a chemical that gets rid of the unguarded copper, leaving the secured copper pads and traces in location; more recent processes use plasma/laser etching rather of chemicals to remove the copper product, enabling finer line meanings.
The process 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 solid board product.
The process of drilling all the holes for plated through applications; a second drilling procedure is used for holes that are not to be plated through. Information on hole area 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 positioned in an electrically charged bath of copper.
This is required when holes are to be drilled through a copper area however the hole is not to be plated through. Avoid this process if possible since it includes cost to the ended up board.
The process of applying a protective masking material, a solder mask, over the bare copper traces or over the copper that has had a thin layer of solder used; the solder mask secures against environmental damage, provides insulation, protects against solder shorts, and secures traces that run in between pads.
The procedure of covering the pad areas with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering procedure that will take place at a later date after the components have been put.
The process of using the markings for element classifications and component lays out to the board. May be used to simply the top or to both sides if elements are mounted on both top and bottom sides.
The procedure of separating multiple boards from a panel of identical boards; this procedure likewise permits cutting notches or slots into the board if needed.
A visual assessment of the boards; likewise can be the procedure of inspecting wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The procedure of checking for connection or shorted connections on the boards by methods using a voltage in between various points on the board and determining if an existing flow takes place. Relying on the board intricacy, this procedure might need a specially created test fixture and test program to incorporate with the electrical test system utilized by the board manufacturer.