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 design may have all thru-hole parts on the leading or part side, a mix of thru-hole and surface area install on the top side just, a mix of thru-hole and surface install components on the top and surface install parts on the bottom or circuit side, or surface area install elements on the leading and bottom sides of the board.
The boards are also utilized to electrically connect the required leads for each component 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 designed as single agreed copper pads and traces on one side of the board just, 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 number of internal copper layers with traces and connections.
Single or double sided boards include a core dielectric product, such as FR-4 epoxy fiberglass, with copper plating on one or both sides. This copper plating is etched away to form the actual copper pads and connection traces on the board surfaces as part of the board production process. A multilayer board consists of a variety 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 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 4 layer board design, the internal layers are often used to provide power and ground connections, such as a +5 V airplane layer and a Ground plane layer as the 2 internal layers, with all other circuit and part connections made on the top and bottom layers of the board. Extremely complex board styles might have a a great deal of layers to make the numerous connections for different voltage levels, ground connections, or for linking the numerous leads on ball grid range gadgets and other large integrated circuit bundle formats.
There are generally two types of material used to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet kind, generally about.002 inches thick. Core product is similar to a really thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, normally.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are two methods used to develop the preferred number 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 material below. This combination of one pre-preg layer and 2 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 material developed above and below to form the last variety of layers required by the board design, sort of like Dagwood developing a sandwich. This technique enables the maker flexibility in how the board layer densities are combined to fulfill the finished item density requirements by varying the variety of sheets of pre-preg in each layer. Once the product layers are completed, the entire stack undergoes 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 process of producing printed circuit boards follows the steps listed below for the majority of applications.
The procedure of determining materials, processes, and requirements to fulfill the customer's requirements for the board design based on the Gerber file information provided with the purchase order.
The process of transferring the Gerber file information for a layer onto an etch withstand film that is put on the conductive copper layer.
The traditional process of exposing the copper and other locations unprotected by the etch withstand movie to a chemical that eliminates the unguarded copper, leaving the safeguarded copper pads and traces in place; more recent procedures use plasma/laser etching instead of chemicals to eliminate the copper material, allowing 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 solid board product.
The process of drilling all of the holes for plated through applications; a second drilling procedure is utilized for holes that are not to be plated through. Info on hole area and size is consisted of in the drill drawing file.
The procedure of applying copper plating to the pads, traces, and ISO 9001 Accreditation Consultants 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 area but the hole is not to be plated through. Prevent this procedure if possible due to the fact that it adds expense to the completed board.
The procedure 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 applied; the solder mask safeguards versus ecological damage, offers insulation, protects against solder shorts, and protects traces that run between pads.
The process of finishing the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering procedure that will happen at a later date after the parts have actually been put.
The process of applying the markings for element designations and element details to the board. Might be used to just the top side or to both sides if components are mounted on both leading and bottom sides.
The procedure of separating multiple boards from a panel of similar boards; this procedure 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 techniques.
The procedure of looking for continuity or shorted connections on the boards by ways applying a voltage between various points on the board and determining if a current flow happens. Depending upon the board complexity, this process might require a specifically designed test fixture and test program to incorporate with the electrical test system used by the board manufacturer.