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 area mount applications or through rilled holes in the board and copper pads for soldering the element leads in thru-hole applications. A board design may have all thru-hole elements on the top or part side, a mix of thru-hole and surface install on the top side just, a mix of thru-hole and surface area install components on the top and surface install elements on the bottom or circuit side, or surface area mount elements on the leading and bottom sides of the board.
The boards are also used to electrically link the needed leads for each component using conductive copper traces. The part pads and connection traces are etched from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are created as single agreed copper pads and traces on one side of the board just, double sided with copper pads and traces on the leading and bottom sides of the board, or multilayer styles 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 include 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 surfaces as part of the board manufacturing procedure. A multilayer board includes a variety of layers of dielectric material that has been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All of these layers are aligned 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 innovations.
In a common four layer board style, the internal layers are often utilized to offer power and ground connections, such as a +5 V aircraft layer and a Ground airplane layer as the two internal layers, with all other circuit and component connections made on the leading and bottom layers of the board. Extremely complex board designs might have a a great deal of layers to make the various connections for various voltage levels, ground connections, or for linking the many leads on ball grid range devices and other big integrated circuit package formats.
There are typically two kinds of material used to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet form, typically about.002 inches thick. Core material resembles an extremely thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, generally.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two approaches utilized to develop the preferred number of layers. The core stack-up method, which is an older technology, utilizes a center layer of pre-preg material with a layer of core product above and another layer of core material below. This mix of one pre-preg layer and two core layers would make a 4 layer board.
The film stack-up technique, a more recent innovation, would have core material as the center layer followed by layers of pre-preg and copper product developed above and listed below to form the last variety of layers required by the board style, sort of like Dagwood constructing a sandwich. This technique enables the maker versatility in how the board layer thicknesses are combined to fulfill the ended up item thickness requirements by varying the variety of sheets of pre-preg in each layer. As soon as the ISO 9001 product layers are finished, the entire stack goes through 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 procedure of producing printed circuit boards follows the steps below for most applications.
The procedure of determining products, procedures, and requirements to satisfy the consumer's specs for the board style based upon the Gerber file info offered with the order.
The process of transferring the Gerber file information for a layer onto an etch resist movie that is placed on the conductive copper layer.
The traditional process of exposing the copper and other locations unprotected by the etch resist film to a chemical that eliminates the vulnerable copper, leaving the safeguarded copper pads and traces in place; newer procedures use plasma/laser etching instead of chemicals to get rid of the copper material, allowing finer line definitions.
The process of lining up the conductive copper and insulating dielectric layers and pressing them under heat to activate the adhesive in the dielectric layers to form a solid board product.
The procedure of drilling all the holes for plated through applications; a second drilling process is used for holes that are not to be plated through. Info on hole place and size is consisted of 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 however the hole is not to be plated through. Prevent this procedure if possible since it adds expense 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 used; the solder mask secures versus environmental damage, provides insulation, protects against solder shorts, and secures traces that run in between pads.
The procedure of finish 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 components have actually been placed.
The procedure of applying the markings for element designations and part describes to the board. Might be used to just the top side or to both sides if elements are mounted on both leading and bottom sides.
The procedure of separating several boards from a panel of similar boards; this process also enables cutting notches or slots into the board if needed.
A visual examination of the boards; likewise can be the process of inspecting 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 means using a voltage in between various points on the board and identifying if an existing flow occurs. Relying on the board intricacy, this process may require a specifically developed test component and test program to incorporate with the electrical test system utilized by the board maker.