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In electronics, printed circuit boards, or PCBs, are utilized to mechanically support electronic parts 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 style may have all thru-hole elements on the leading or part side, a mix of thru-hole and surface mount on the top side only, a mix of thru-hole and surface install components on the top and surface mount parts on the bottom or circuit side, or surface install components on the top and bottom sides of the board.
The boards are also used to electrically connect the required leads for each component using conductive copper traces. The part pads and connection traces are engraved from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are designed as single agreed copper pads and traces on one side of the board only, double agreed copper pads and traces on the leading and bottom sides of the board, or multilayer designs with copper pads and traces on the 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 product, 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 production process. A multilayer board includes a number 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 aligned 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 four layer board design, the internal layers are often used to offer 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 element connections made on the top and bottom layers of the board. Extremely complicated board designs may have a large number of layers to make the various connections for different voltage levels, ground connections, or for connecting the lots of leads on ball grid range gadgets and other big incorporated circuit bundle formats.
There are generally two types of material utilized to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, usually about.002 inches thick. Core material resembles a very thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, typically.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 preferred number of layers. The core stack-up approach, which is an older innovation, utilizes a center layer of pre-preg product with a layer of core product 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 method, 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 final number of layers required by the board style, sort of like Dagwood building a sandwich. This method permits the maker flexibility in how the board layer densities are integrated to satisfy the ended up item density requirements by varying the variety of sheets of pre-preg in each layer. As soon as the material layers are completed, 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 making printed circuit boards follows the steps below for the majority of applications.
The procedure of determining materials, processes, and requirements to fulfill the consumer's specifications for the board design based upon the Gerber file info supplied with the order.
The procedure of transferring the Gerber file information for a layer onto an etch resist film that is put on the conductive copper layer.
The standard procedure of exposing the copper and other locations unprotected by the etch resist movie to a chemical that removes the unguarded copper, leaving the safeguarded copper pads and traces in location; newer procedures use plasma/laser etching instead of chemicals to remove the copper product, permitting finer line meanings.
The procedure 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 process of drilling all the holes for plated through applications; a 2nd drilling process is utilized for holes that are not to be plated through. Info on hole place and size is contained 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 location but the hole is not to be plated through. Avoid this procedure if possible due to the fact that it adds expense to the completed board.
The procedure 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, offers insulation, safeguards against solder shorts, and safeguards traces that run between pads.
The process of covering the pad locations with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering process that will happen at a later date after the parts have been placed.
The procedure of using the markings for component classifications and component details to the board. May be applied to simply the top side or to both sides if elements are installed on both top and bottom sides.
The procedure of separating numerous boards from a panel of similar boards; this process likewise enables cutting notches or slots into the board if needed.
A visual assessment of the boards; also can be the process of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.
The procedure of looking for connection or shorted connections on the boards by methods using a voltage between numerous points on the board and identifying if a current flow takes place. Relying on the board intricacy, this process might require a specifically designed test fixture and test program to integrate with the electrical test system utilized by the board producer.