In electronics, printed circuit boards, or PCBs, are used to mechanically support electronic components 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 element leads in thru-hole applications. A board style may have all thru-hole elements on the top or component side, a mix of thru-hole and surface area mount on the top only, a mix of thru-hole and surface install elements on the top and surface area mount elements on the bottom or circuit side, or surface area install elements 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 component pads and connection traces are engraved from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are created as single sided with copper pads and traces on one side of the board just, double sided with 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 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 surfaces as part of the board manufacturing procedure. A multilayer board includes a number of layers of dielectric material that has been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All these layers are lined up 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 style, the internal layers are frequently utilized to supply power and ground connections, such as a +5 V airplane layer and a Ground airplane layer as the two internal layers, with all other circuit and part connections made on the leading and bottom layers of the board. Extremely complicated board designs might have a a great deal of layers to make the numerous connections for various voltage levels, ground connections, or for connecting the lots of leads on ball grid array gadgets and other big integrated circuit package formats.
There are generally 2 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, normally about.002 inches thick. Core product resembles a very thin double sided board because 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 methods utilized to build up the desired number of layers. The core stack-up technique, which is an older innovation, uses a center layer of pre-preg product 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 movie stack-up method, a newer innovation, would have core material as the center layer followed by layers of pre-preg and copper material built up above and below to form the final number of layers needed by the board design, sort of like Dagwood building a sandwich. This method allows the maker flexibility in how the board layer thicknesses are combined to fulfill the completed item thickness requirements by varying the number of sheets of pre-preg in each layer. As soon as the material layers are finished, 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 making printed circuit boards follows the steps listed below for many applications.
The procedure of determining materials, processes, and requirements to fulfill the customer's specifications for the board style based upon the Gerber file info offered with the purchase order.
The procedure of transferring the Gerber file data for a layer onto an etch withstand movie that is put on the conductive copper layer.
The standard process of exposing the copper and other areas unprotected by the etch withstand movie to a chemical that eliminates the unprotected copper, leaving the protected copper pads and traces in location; more recent processes utilize plasma/laser etching rather of chemicals to eliminate the copper product, allowing 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 product.
The process of drilling all of the holes for plated through applications; a 2nd drilling procedure is utilized for holes that are not to be plated through. Details on hole place and size is contained 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 placed in an electrically charged bath of copper.
This is required when holes are to be drilled through a copper location however the hole is not to be plated through. Avoid this procedure if possible ISO 9001 Accreditation Consultants since it adds expense to the completed board.
The process of applying a protective masking product, a solder mask, over the bare copper traces or over the copper that has actually had a thin layer of solder applied; the solder mask secures versus ecological damage, offers insulation, protects against solder shorts, and secures traces that run between pads.
The procedure of finishing the pad locations with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering procedure that will happen at a later date after the parts have actually been put.
The process of using the markings for component designations and component outlines to the board. Might be applied to simply the top side or to both sides if parts are installed on both top and bottom sides.
The process of separating numerous boards from a panel of similar boards; this process likewise allows cutting notches or slots into the board if needed.
A visual assessment 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 looking for continuity or shorted connections on the boards by methods using a voltage between different points on the board and figuring out if a present circulation happens. Depending upon the board intricacy, this process might need a specifically developed test fixture and test program to incorporate with the electrical test system utilized by the board maker.