In electronics, printed circuit boards, or PCBs, are used 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 element leads in thru-hole applications. A board style may have all thru-hole parts on the leading or element side, a mix of thru-hole and surface area mount on the top side just, a mix of thru-hole and surface mount parts on the top side and surface install elements on the bottom or circuit side, or surface install components on the leading and bottom sides of the board.
The boards are also used 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 developed as single agreed 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 designs 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 include a core dielectric material, 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 number of layers of dielectric product that has been impregnated with adhesives, and these layers are utilized to separate the layers of copper plating. All of 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 style, the internal layers are frequently used to supply power and ground connections, such as a +5 V plane layer and a Ground aircraft layer as the two internal layers, with all other circuit and part connections made on the leading and bottom layers of the board. Very intricate board designs may have a large number of layers to make the numerous connections for different voltage levels, ground connections, or for connecting the many leads on ball grid array devices and other large integrated circuit package formats.
There are typically 2 kinds of material used to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet kind, generally about.002 inches thick. Core material is similar to an extremely thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, typically.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are two approaches utilized to build up the wanted number of layers. The core stack-up technique, which is an older innovation, uses a center layer of pre-preg material with a layer of core product above and another layer of core product listed below. This mix of 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 product developed above and listed below to form the final variety of layers needed by the board design, sort of like Dagwood building a sandwich. This technique permits the producer flexibility in how the board layer densities are integrated to satisfy the completed item thickness requirements by differing the variety of sheets of pre-preg in each layer. As soon as the product layers are finished, 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 manufacturing printed circuit boards follows the steps listed below for a lot of applications.
The process of figuring out products, processes, and requirements to fulfill the client's requirements for the board style based on the Gerber file information offered with the purchase order.
The procedure of transferring the Gerber file data for a layer onto an etch resist film that is placed on the conductive copper layer.
The traditional procedure of exposing the copper and other areas unprotected by the etch resist film to a chemical that removes the vulnerable copper, leaving the secured copper pads and traces in location; more recent procedures utilize plasma/laser etching rather of chemicals to remove the copper material, allowing finer line definitions.
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 solid board product.
The process of drilling all the holes for plated through applications; a 2nd drilling procedure is utilized for holes that are not to be plated through. Information on hole location and size is consisted of in the drill drawing file.
The procedure of applying copper plating to the pads, traces, and drilled through holes that are to be plated through; boards are put 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. Avoid this procedure if possible due to the fact that it includes cost to the ended up board.
The procedure of applying 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 protects against environmental damage, provides insulation, protects against solder shorts, and secures traces that run between pads.
The procedure of finish 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 elements have been put.
The procedure of using the markings for element designations and part lays out to the board. May be applied to simply the top or to both sides ISO 9001 if parts are mounted on both top and bottom sides.
The procedure of separating numerous boards from a panel of identical boards; this procedure also allows cutting notches or slots into the board if required.
A visual examination of the boards; likewise can be the procedure of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The procedure of checking for continuity or shorted connections on the boards by means applying a voltage in between numerous points on the board and determining if a current circulation occurs. Depending upon the board intricacy, this procedure might require a specifically created test fixture and test program to integrate with the electrical test system used by the board manufacturer.