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 install applications or through rilled holes in the board and copper pads for soldering the part leads in thru-hole applications. A board design might have all thru-hole elements on the leading or part side, a mix of thru-hole and surface area mount on the top side only, a mix of thru-hole and surface mount elements on the top and surface mount parts on the bottom or circuit Reference site side, or surface mount elements on the top and bottom sides of the board.
The boards are also utilized to electrically link the needed leads for each part using conductive copper traces. The element 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 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 consist of 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 surface areas 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 of 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 typical 4 layer board style, the internal layers are often utilized to supply power and ground connections, such as a +5 V plane layer and a Ground plane layer as the 2 internal layers, with all other circuit and element connections made on the leading and bottom layers of the board. Really intricate board designs might have a large number of layers to make the different connections for various voltage levels, ground connections, or for connecting the many leads on ball grid range gadgets and other big incorporated circuit bundle formats.
There are usually 2 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 type, normally about.002 inches thick. Core material is similar to a very thin double sided board because it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, generally.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are two techniques utilized to build up the wanted number of layers. The core stack-up method, which is an older innovation, uses a center layer of pre-preg product with a layer of core material above and another layer of core material 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 material as the center layer followed by layers of pre-preg and copper material built up above and listed below to form the last number of layers required by the board style, sort of like Dagwood developing a sandwich. This method permits the manufacturer versatility in how the board layer densities are combined to fulfill the completed product density requirements by differing the variety of sheets of pre-preg in each layer. As soon as the material layers are finished, 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 a lot of applications.
The process of identifying products, processes, and requirements to meet the consumer's requirements for the board design based on the Gerber file details supplied with the purchase order.
The process of transferring the Gerber file data for a layer onto an etch resist film that is put on the conductive copper layer.
The traditional 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 secured copper pads and traces in place; newer processes utilize plasma/laser etching rather of chemicals to remove the copper material, enabling finer line definitions.
The process of lining up the conductive copper and insulating dielectric layers and pushing them under heat to activate the adhesive in the dielectric layers to form a strong board product.
The process of drilling all the holes for plated through applications; a second drilling process is utilized for holes that are not to be plated through. Info on hole area and size is included 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 positioned 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 process if possible due to the fact that it adds cost 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 applied; the solder mask safeguards against ecological damage, supplies insulation, protects versus solder shorts, and safeguards traces that run between pads.
The process of coating the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering procedure that will take place at a later date after the elements have been positioned.
The procedure of applying the markings for part classifications and part details to the board. Might be applied to simply 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 identical boards; this procedure also permits cutting notches or slots into the board if required.
A visual evaluation of the boards; likewise 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 ways applying a voltage between different points on the board and figuring out if a current circulation takes place. Depending upon the board intricacy, this process may need a specially designed test fixture and test program to integrate with the electrical test system used by the board maker.