In electronic devices, printed circuit boards, See more 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 component leads in thru-hole applications. A board design might have all thru-hole parts on the top or element side, a mix of thru-hole and surface install on the top just, a mix of thru-hole and surface install parts on the top and surface mount components on the bottom or circuit side, or surface area mount elements on the leading and bottom sides of the board.
The boards are also utilized to electrically connect the required 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 designed as single sided with copper pads and traces on one side of the board just, 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 consist of 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 surface areas as part of the board manufacturing process. A multilayer board consists of a number of layers of dielectric material that has been fertilized with adhesives, and these layers are utilized 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 innovations.
In a normal 4 layer board design, the internal layers are typically utilized to offer power and ground connections, such as a +5 V plane layer and a Ground plane layer as the two internal layers, with all other circuit and component connections made on the top and bottom layers of the board. Really complicated board styles might have a a great deal of layers to make the different connections for different voltage levels, ground connections, or for connecting the many leads on ball grid selection devices and other large incorporated circuit bundle formats.
There are normally 2 kinds of product used to build a multilayer board. Pre-preg product 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 because it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, generally.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are 2 approaches used to build up the wanted variety of layers. The core stack-up method, which is an older technology, 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 film stack-up approach, a more recent technology, would have core product as the center layer followed by layers of pre-preg and copper product developed above and below to form the final variety of layers required by the board design, sort of like Dagwood building a sandwich. This approach permits the producer flexibility in how the board layer thicknesses are integrated to satisfy the finished item thickness requirements by varying the number of sheets of pre-preg in each layer. As soon as the material layers are finished, the entire 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 procedure of producing printed circuit boards follows the actions listed below for a lot of applications.
The process of determining products, processes, and requirements to meet the consumer's specs for the board design based on the Gerber file info offered with the order.
The procedure of transferring the Gerber file information for a layer onto an etch resist movie that is put on the conductive copper layer.
The conventional process of exposing the copper and other areas unprotected by the etch resist film to a chemical that removes the unprotected copper, leaving the safeguarded copper pads and traces in place; newer processes utilize plasma/laser etching instead of chemicals to eliminate the copper product, 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 2nd drilling process is used for holes that are not to be plated through. Information on hole place and size is contained in the drill drawing file.
The procedure 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 required 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 includes cost to the ended up board.
The process of using a protective masking product, a solder mask, over the bare copper traces or over the copper that has had a thin layer of solder applied; the solder mask secures against environmental damage, supplies insulation, secures versus solder shorts, and safeguards traces that run 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 occur at a later date after the elements have been positioned.
The process of applying the markings for component classifications and element outlines to the board. May be used to just the top or to both sides if components are installed on both leading and bottom sides.
The process of separating several boards from a panel of similar boards; this procedure likewise allows cutting notches or slots into the board if required.
A visual evaluation of the boards; also can be the procedure of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The process of looking for connection or shorted connections on the boards by means using a voltage in between various points on the board and identifying if a current circulation takes place. Depending upon the board intricacy, this procedure may need a specifically designed test component and test program to incorporate with the electrical test system utilized by the board maker.