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 mount applications or through rilled holes in the board and copper pads for soldering the component leads in thru-hole applications. A board design might have all thru-hole elements on the top or part side, a mix of thru-hole and surface install on the top side only, a mix of thru-hole and surface mount parts on the top side and surface mount parts on the bottom or circuit side, or surface install parts on the top and bottom sides of the board.
The boards are likewise utilized to electrically connect the needed leads for each part utilizing conductive copper traces. The part pads and connection traces are etched from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are designed 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 styles 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. ISO 9001 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 layers of dielectric material that has been impregnated with adhesives, and these layers are utilized to separate the layers of copper plating. All these layers are lined up and 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 four layer board style, the internal layers are often used to offer power and ground connections, such as a +5 V aircraft layer and a Ground aircraft layer as the 2 internal layers, with all other circuit and component connections made on the top and bottom layers of the board. Really complex board styles may have a a great deal of layers to make the different connections for different voltage levels, ground connections, or for connecting the numerous leads on ball grid selection gadgets and other big integrated circuit bundle formats.
There are normally two kinds of product used to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet form, generally about.002 inches thick. Core product resembles an extremely thin double sided board because it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, usually.030 density 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 approach, which is an older technology, utilizes a center layer of pre-preg material with a layer of core material 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 approach, a more recent innovation, would have core product as the center layer followed by layers of pre-preg and copper product developed above and listed below to form the last variety of layers needed by the board design, sort of like Dagwood constructing a sandwich. This technique permits the maker versatility in how the board layer densities are integrated to satisfy the ended up item thickness requirements by differing the variety of sheets of pre-preg in each layer. As soon as 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 process of making printed circuit boards follows the actions below for a lot of applications.
The process of figuring out products, procedures, and requirements to satisfy the client's specifications for the board design based on the Gerber file info provided with the order.
The process of moving the Gerber file information for a layer onto an etch withstand movie that is placed on the conductive copper layer.
The traditional procedure of exposing the copper and other areas unprotected by the etch resist movie to a chemical that eliminates the unprotected copper, leaving the safeguarded copper pads and traces in location; more recent procedures use plasma/laser etching rather of chemicals to get rid of the copper material, enabling finer line definitions.
The process of lining up the conductive copper and insulating dielectric layers and pushing them under heat to trigger the adhesive in the dielectric layers to form a strong board material.
The process of drilling all the holes for plated through applications; a second drilling process is utilized for holes that are not to be plated through. Information on hole location and size is included 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 location but the hole is not to be plated through. Avoid this procedure if possible because it adds expense to the completed board.
The procedure of applying 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, offers insulation, safeguards against solder shorts, and safeguards traces that run in between pads.
The procedure of coating the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering procedure that will take place at a later date after the components have actually been put.
The process of using the markings for part designations and component lays out to the board. May be applied to just the top or to both sides if elements are mounted on both leading and bottom sides.
The procedure of separating multiple boards from a panel of similar boards; this procedure likewise permits cutting notches or slots into the board if required.
A visual assessment of the boards; likewise can be the process of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The procedure of checking for continuity or shorted connections on the boards by means applying a voltage between numerous points on the board and figuring out if an existing circulation occurs. Depending upon the board intricacy, this procedure might need a specially created test component and test program to integrate with the electrical test system utilized by the board maker.