In electronic devices, printed circuit boards, or PCBs, are utilized 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 part leads in thru-hole applications. A board design may have all thru-hole components on the top or component side, a mix of thru-hole and surface area mount on the top just, a mix of thru-hole and surface install elements on the top side and surface mount elements on the bottom or circuit side, or surface area mount components on the pop over here leading and bottom sides of the board.
The boards are also utilized to electrically link the required leads for each component 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 only, double agreed copper pads and traces on the top 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 engraved 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 product that has been impregnated with adhesives, and these layers are utilized to separate the layers of copper plating. All of these layers are lined up 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 normal 4 layer board style, the internal layers are frequently used to provide power and ground connections, such as a +5 V airplane 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. 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 connecting the many leads on ball grid variety gadgets and other large incorporated circuit package formats.
There are usually 2 kinds of material used to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet form, generally about.002 inches thick. Core product 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, usually.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are 2 techniques utilized to build up the desired 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 listed below. This combination of one pre-preg layer and two core layers would make a 4 layer board.
The film stack-up method, a newer technology, would have core product as the center layer followed by layers of pre-preg and copper product built up above and below to form the last number of layers needed by the board design, sort of like Dagwood constructing a sandwich. This technique enables the manufacturer versatility in how the board layer densities are combined to meet the ended up item density requirements by varying the variety of sheets of pre-preg in each layer. When the product layers are completed, the whole 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 steps below for a lot of applications.
The process of figuring out materials, procedures, and requirements to fulfill the client's requirements for the board design based upon the Gerber file info supplied with the order.
The process of transferring the Gerber file data for a layer onto an etch resist film that is put on the conductive copper layer.
The standard process of exposing the copper and other locations unprotected by the etch resist film to a chemical that gets rid of the vulnerable copper, leaving the protected copper pads and traces in place; more recent processes use plasma/laser etching instead of chemicals to eliminate the copper material, permitting finer line meanings.
The process of aligning 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 process of drilling all the holes for plated through applications; a second drilling procedure is utilized for holes that are not to be plated through. Information on hole area and size is consisted of 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 positioned 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. Avoid this process if possible due to the fact that it adds 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 safeguards against environmental damage, provides insulation, protects against solder shorts, and protects traces that run in between pads.
The process of finish 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 elements have actually been positioned.
The process of using the markings for component classifications and component outlines to the board. May be used to just the top side or to both sides if elements are installed on both leading and bottom sides.
The process 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 assessment of the boards; also can be the process of inspecting wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The procedure of checking for continuity or shorted connections on the boards by methods applying a voltage between numerous points on the board and determining if an existing circulation takes place. Depending upon the board complexity, this process might require a specially developed test component and test program to integrate with the electrical test system used by the board maker.