In electronics, printed circuit boards, or PCBs, are utilized 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 part leads in thru-hole applications. A board style may have all thru-hole elements on the leading or element side, a mix of thru-hole and surface mount on the top just, a mix of thru-hole and surface mount parts on the top and surface install 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 required leads for each component 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 only, 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 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 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 product that has actually been fertilized with adhesives, and these layers are used 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 typically utilized to offer power and ground connections, such as a +5 V airplane layer and a Ground plane layer as the two internal layers, with all other circuit and component connections made on the leading and bottom layers of the board. Extremely complicated board styles might have a large number of layers to make the various connections for different voltage levels, ground connections, or for linking the many leads on ball grid selection gadgets and other big integrated circuit package formats.
There are typically two kinds of material utilized to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet form, normally about.002 inches thick. Core product is similar to a very thin double sided board in that 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 style, there are two methods used to build up the preferred number of layers. The core stack-up method, which is an older innovation, utilizes 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 two core layers would make a 4 layer board.
The movie stack-up technique, a newer 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 final number of layers needed by the board style, sort of like Dagwood building a sandwich. This technique allows the manufacturer flexibility in how the board layer densities are combined to satisfy the finished item density requirements by differing the variety of sheets of pre-preg in each layer. Once the material 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 process of manufacturing printed circuit boards follows the actions below for a lot of applications.
The process of figuring out materials, procedures, and requirements to fulfill the client's specifications for the board design based on the Gerber file details provided with the purchase order.
The procedure of transferring the Gerber file data for a layer onto an etch withstand film that is placed on the conductive copper layer.
The standard procedure of exposing the copper and other areas unprotected by the etch withstand movie to a chemical that gets rid of the unprotected copper, leaving the safeguarded copper pads and traces in location; more recent procedures utilize plasma/laser etching rather of chemicals to remove the copper product, permitting finer line meanings.
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 procedure of drilling all the holes for plated through applications; a second drilling procedure is utilized for holes that are not to be plated through. Details on hole area 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 placed in an electrically charged bath of copper.
This is needed when holes are to be drilled through a copper area however the hole is not to be plated through. Avoid this process if possible due to the fact that it includes expense to the ended up board.
The process of using a protective masking material, a solder mask, over the bare copper traces or over the copper that has actually had a thin layer of solder used; the solder mask safeguards against environmental damage, provides insulation, secures against solder shorts, and secures traces that run in between pads.
The process of covering the pad areas 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 elements have been positioned.
The procedure of using the markings for part classifications and element describes to the board. May be used to simply the top or to both sides if parts are installed on both top and bottom sides.
The procedure of separating numerous boards from a panel of identical boards; this procedure likewise enables cutting notches or slots into the board if needed.
A visual inspection of the boards; also can be the procedure of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.
The process of looking for connection or shorted connections on the boards by means using a voltage in between numerous points on the board and determining if a present circulation occurs. Depending upon the board intricacy, this procedure may need a specifically developed test component and test program to incorporate with the electrical test system used by the board manufacturer.