In electronics, printed circuit boards, or PCBs, are used to mechanically support electronic elements which have their connection leads soldered onto copper pads in surface area install 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 parts on the leading or part side, a mix of thru-hole and surface install on the top just, a mix of thru-hole and surface mount components on the top side and surface area install components on the bottom or circuit side, or surface area mount elements on the top and bottom sides of the board.
The boards are also used to electrically connect the required leads for each element utilizing conductive copper traces. The part pads and connection traces are etched 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 sided with copper pads and traces on the leading and bottom sides of the board, or multilayer styles 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 consist of a core dielectric material, such as FR-4 epoxy fiberglass, with copper plating on one or both sides. This copper plating is engraved away to form the real 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 ISO 9001 Accreditation Consultants of dielectric product that has actually been impregnated with adhesives, and these layers are utilized 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 technologies.
In a normal four layer board style, the internal layers are frequently used to supply power and ground connections, such as a +5 V aircraft layer and a Ground plane layer as the two internal layers, with all other circuit and component connections made on the leading and bottom layers of the board. Really intricate board designs may have a large number of layers to make the numerous connections for different voltage levels, ground connections, or for linking the lots of leads on ball grid range devices and other large integrated circuit package formats.
There are usually 2 types of material used to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, typically about.002 inches thick. Core product resembles a really thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, normally.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are two techniques utilized to develop the preferred number of layers. The core stack-up approach, 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 combination 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 material developed above and below to form the final variety of layers needed by the board design, sort of like Dagwood constructing a sandwich. This method allows the maker versatility in how the board layer thicknesses are combined to fulfill the finished product density requirements by varying the number of sheets of pre-preg in each layer. When the product layers are completed, the entire 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 procedure of producing printed circuit boards follows the steps below for many applications.
The procedure of determining products, processes, and requirements to satisfy the customer's specifications for the board design based on the Gerber file info offered with the order.
The process of moving the Gerber file information for a layer onto an etch resist film that is put on the conductive copper layer.
The traditional procedure of exposing the copper and other areas unprotected by the etch resist movie to a chemical that removes the unprotected copper, leaving the safeguarded copper pads and traces in place; newer procedures utilize plasma/laser etching rather of chemicals to remove the copper material, enabling finer line definitions.
The procedure 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 material.
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 area 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 area but the hole is not to be plated through. Avoid this process if possible because it includes cost 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 had a thin layer of solder applied; the solder mask secures against environmental damage, supplies insulation, protects against solder shorts, and safeguards traces that run between pads.
The procedure of coating the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering procedure that will take place at a later date after the components have been put.
The procedure of applying the markings for component classifications and element describes to the board. Might be used to simply the top side or to both sides if parts are mounted on both leading and bottom sides.
The procedure of separating numerous boards from a panel of identical boards; this process also allows 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 methods.
The process of checking for connection or shorted connections on the boards by methods applying a voltage between numerous points on the board and figuring out if a present circulation happens. Relying on the board complexity, this procedure might need a specifically developed test component and test program to incorporate with the electrical test system utilized by the board producer.