In electronic devices, printed circuit boards, or PCBs, are utilized 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 component leads in thru-hole applications. A board design might have all thru-hole parts on the top or part side, a mix of thru-hole and surface mount on the top just, a mix of thru-hole and surface area mount parts on the top and surface mount components on the bottom or circuit side, or surface area install components on the top and bottom sides of the board.
The boards are also utilized to electrically connect the needed leads for each element utilizing conductive copper traces. The element pads and connection traces are engraved 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 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 real 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 been fertilized with adhesives, and these layers are used 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 innovations.
In a normal 4 layer board design, the internal layers are often used 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 part connections made on the top and bottom layers of the board. Extremely intricate board designs might have a large number of layers to make the various connections for various voltage levels, ground connections, or for connecting the numerous leads on ball grid array gadgets and other big incorporated circuit package formats.
There are usually 2 kinds of material utilized to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet form, generally about.002 inches thick. Core material resembles an extremely thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, usually.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two techniques utilized to build up the desired variety of layers. The core stack-up method, 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 product below. This combination of one pre-preg layer and two core layers would make a 4 layer board.
The film stack-up approach, a more recent technology, would have core material as the center layer followed by layers of pre-preg and copper product built up above and below to form the last variety of layers needed by the board style, sort of like Dagwood constructing a sandwich. This method permits the producer versatility in how the board layer thicknesses are combined to satisfy the ended up item density requirements by differing the variety of sheets of pre-preg in each layer. Once the product layers are finished, the whole stack is subjected to 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 producing printed circuit boards follows the actions below for many applications.
The procedure of identifying materials, processes, and requirements to fulfill the consumer's specifications for the board design based upon the Gerber file details supplied with the order.
The process of transferring the Gerber file data for a layer onto an etch resist movie that is put on the conductive copper layer.
The traditional procedure of exposing the copper and other locations unprotected by the etch resist film to a chemical that eliminates the unguarded copper, leaving the protected copper pads and traces in location; more recent processes use plasma/laser etching rather of chemicals to remove the copper product, enabling 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 product.
The process of drilling all of the holes for plated through applications; a 2nd drilling procedure is used for holes that are not to be plated through. Details on hole location and size is included in the drill drawing file.
The process of using 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. Prevent this procedure if possible since it adds expense to the completed board.
The procedure of using a protective masking product, a solder mask, over the bare copper traces or over the copper that has actually had a thin layer of solder applied; the solder mask protects versus environmental damage, provides insulation, secures versus solder shorts, and protects traces that run in between pads.
The procedure of finishing the pad locations 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 procedure of applying the markings for element classifications and part details to the board. Might be used to just the top side or to both sides if elements ISO 9001 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 needed.
A visual evaluation 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 approaches.
The process of checking for connection or shorted connections on the boards by means using a voltage between numerous points on the board and determining if a present circulation takes place. Depending upon the board intricacy, this process may need a specially created test fixture and test program to integrate with the electrical test system utilized by the board producer.