In electronic devices, printed circuit boards, or PCBs, are used to mechanically support electronic elements which have their connection leads soldered onto copper pads in surface mount applications or through rilled holes in the board and copper pads for soldering the part leads in thru-hole applications. A board style might have all thru-hole elements 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 install components on the top and surface mount elements 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 element using conductive copper traces. The element 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 just, double agreed 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 production process. A multilayer board includes a variety of layers of dielectric material that has actually been fertilized with adhesives, and these layers are used 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 ISO 9001 with today's technologies.
In a common four layer board design, the internal layers are frequently used to offer power and ground connections, such as a +5 V aircraft layer and a Ground aircraft layer as the 2 internal layers, with all other circuit and element connections made on the top and bottom layers of the board. Really complicated board styles may have a a great deal of layers to make the numerous connections for different voltage levels, ground connections, or for connecting the numerous leads on ball grid variety devices and other big incorporated circuit package formats.
There are generally two kinds of material used to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet kind, usually about.002 inches thick. Core product is similar to a very thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, generally.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are two techniques utilized to build up the preferred number of layers. The core stack-up method, which is an older innovation, utilizes a center layer of pre-preg material with a layer of core material 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 film stack-up method, 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 last number of layers needed by the board design, sort of like Dagwood developing a sandwich. This technique enables the producer flexibility in how the board layer thicknesses are combined 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 whole stack is subjected to 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 producing printed circuit boards follows the actions listed below for many applications.
The procedure of identifying products, procedures, and requirements to meet the customer's specs for the board design based upon the Gerber file info offered with the purchase order.
The procedure of moving the Gerber file data for a layer onto an etch resist movie that is placed on the conductive copper layer.
The conventional process of exposing the copper and other locations unprotected by the etch resist movie to a chemical that removes the unguarded copper, leaving the protected copper pads and traces in place; newer procedures utilize plasma/laser etching instead of chemicals to get rid of the copper material, allowing finer line meanings.
The process of lining up the conductive copper and insulating dielectric layers and pressing them under heat to trigger the adhesive in the dielectric layers to form a solid board product.
The procedure of drilling all of the holes for plated through applications; a second drilling procedure 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 using 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 required when holes are to be drilled through a copper location but the hole is not to be plated through. Prevent this procedure if possible due to the fact that it includes 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 actually had a thin layer of solder used; the solder mask safeguards versus environmental damage, offers insulation, protects against solder shorts, and secures traces that run in between pads.
The process of coating the pad areas 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 components have actually been put.
The process of applying the markings for component designations and element describes to the board. May be used to simply the top side or to both sides if components are installed on both top and bottom sides.
The procedure of separating several boards from a panel of identical boards; this process likewise permits cutting notches or slots into the board if needed.
A visual inspection of the boards; also can be the procedure of inspecting wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The process of checking for connection or shorted connections on the boards by ways applying a voltage in between various points on the board and determining if a present circulation happens. Depending upon the board complexity, this procedure might require a specifically designed test component and test program to incorporate with the electrical test system used by the board producer.