In electronic devices, printed circuit boards, or PCBs, are utilized to mechanically support electronic components 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 might have all thru-hole components on the leading or part side, a mix of thru-hole and surface install on the top just, a mix of thru-hole and surface area install components on the top and surface area mount components on the bottom or circuit side, or surface mount components on the top and bottom sides of the board.
The boards are likewise utilized to electrically link 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 created as single sided with copper pads and traces on one side of the board only, double agreed copper pads and traces on the top 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 material, 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 manufacturing process. A multilayer board consists of a number of layers of dielectric material that has actually been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All of these layers are aligned 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 innovations.
In a common four layer board style, the internal layers are often used to supply power and ground connections, such as a +5 V airplane layer and a Ground airplane layer as the two internal layers, with all other circuit and element connections made on the top and bottom layers of the board. Really complex board styles might have a a great deal of layers to make the numerous connections for various voltage levels, ground connections, or for linking the numerous leads on ball grid array gadgets and other big integrated circuit bundle formats.
There are normally two kinds of material used to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet kind, usually about.002 inches thick. Core material resembles a really thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, usually.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are two techniques used to develop the desired variety 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 material above and another layer of core material listed below. This mix of ISO 9001 one pre-preg layer and 2 core layers would make a 4 layer board.
The movie stack-up approach, a more recent innovation, would have core product as the center layer followed by layers of pre-preg and copper material developed above and below to form the final number of layers needed by the board design, sort of like Dagwood building a sandwich. This technique allows the manufacturer flexibility in how the board layer thicknesses are combined to fulfill the finished item density requirements by varying the number of sheets of pre-preg in each layer. Once 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 steps listed below for most applications.
The process of determining products, processes, and requirements to satisfy the consumer's specs for the board design based on the Gerber file details provided with the order.
The process of transferring the Gerber file data for a layer onto an etch withstand film that is placed on the conductive copper layer.
The traditional procedure of exposing the copper and other locations unprotected by the etch withstand film to a chemical that eliminates the vulnerable copper, leaving the protected copper pads and traces in place; more recent procedures utilize plasma/laser etching rather of chemicals to eliminate the copper product, permitting finer line meanings.
The process of aligning the conductive copper and insulating dielectric layers and pressing them under heat to activate the adhesive in the dielectric layers to form a strong board product.
The procedure of drilling all of the holes for plated through applications; a second drilling process is utilized for holes that are not to be plated through. Details on hole place and size is included in the drill drawing file.
The procedure of using copper plating to the pads, traces, and drilled through holes that are to be plated through; boards are placed in an electrically charged bath of copper.
This is required when holes are to be drilled through a copper area but the hole is not to be plated through. Avoid this procedure if possible due to the fact that it includes expense to the completed board.
The procedure of using 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 safeguards versus ecological damage, supplies insulation, protects against solder shorts, and safeguards traces that run in between pads.
The procedure of finishing the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering process that will occur at a later date after the components have actually been put.
The process of applying the markings for part classifications and part outlines to the board. May be applied to simply the top side or to both sides if parts are mounted on both top and bottom sides.
The procedure of separating multiple boards from a panel of identical boards; this process also enables cutting notches or slots into the board if required.
A visual examination of the boards; likewise can be the procedure of checking 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 methods applying a voltage between numerous points on the board and figuring out if an existing circulation occurs. Depending upon the board complexity, this procedure might need a specially designed test component and test program to integrate with the electrical test system utilized by the board maker.