In electronic devices, printed circuit boards, or PCBs, are used 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 element leads in thru-hole applications. A board style might have all thru-hole parts on the top or element 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 side and surface area mount components on the bottom or circuit side, or surface area mount parts on the leading 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 component 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 sided with copper pads and traces on the leading 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. 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 procedure. A multilayer board includes a variety of layers of dielectric product that has been fertilized 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 common four layer board design, the internal layers are frequently utilized to provide power and ground connections, such as a +5 V plane layer and a Ground airplane layer as the 2 internal layers, with all other circuit and component connections made on the leading and bottom layers of the board. Very complex board designs may have a large number of layers to make the different connections for different voltage levels, ground connections, or for ISO 9001 Accreditation connecting the numerous leads on ball grid variety gadgets and other big integrated circuit plan formats.
There are usually two kinds of material utilized to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, normally about.002 inches thick. Core material resembles a really thin double sided board because it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, typically.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two techniques used to develop the desired number of layers. The core stack-up approach, which is an older technology, utilizes a center layer of pre-preg product with a layer of core material above and another layer of core product below. This combination of one pre-preg layer and two core layers would make a 4 layer board.
The film stack-up method, a newer technology, 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 final number of layers needed by the board style, sort of like Dagwood building a sandwich. This technique enables the producer versatility in how the board layer thicknesses are combined to meet the finished product thickness requirements by varying the variety of sheets of pre-preg in each layer. When the product layers are completed, the entire 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 procedure of producing printed circuit boards follows the steps below for the majority of applications.
The process of identifying materials, processes, and requirements to meet the client's specs for the board style based on the Gerber file details offered with the purchase order.
The procedure of moving the Gerber file information for a layer onto an etch resist movie that is placed on the conductive copper layer.
The traditional process of exposing the copper and other locations unprotected by the etch resist film to a chemical that removes the unguarded copper, leaving the protected copper pads and traces in location; newer procedures utilize plasma/laser etching instead of chemicals to eliminate the copper material, enabling finer line meanings.
The procedure of lining up 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 procedure is utilized 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 placed 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. Avoid this procedure if possible since it includes expense to the finished 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 against ecological damage, provides insulation, protects versus solder shorts, and secures traces that run between pads.
The process of covering the pad locations with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering procedure that will occur at a later date after the components have been placed.
The process of applying the markings for component designations and element describes to the board. Might be used to just the top side or to both sides if parts are installed on both top and bottom sides.
The process of separating multiple boards from a panel of similar boards; this process also allows cutting notches or slots into the board if required.
A visual inspection of the boards; also can be the process of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.
The procedure of checking for connection or shorted connections on the boards by means using a voltage between various points on the board and determining if an existing flow occurs. Relying on the board intricacy, this process may need a specifically designed test fixture and test program to integrate with the electrical test system utilized by the board maker.