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 install applications or through rilled holes in the board and copper pads for soldering the component leads in thru-hole applications. A board style may have all thru-hole parts on the top or element side, a mix of thru-hole and surface area mount on the top just, a mix of thru-hole and surface area install components on the top side and surface area install components on the bottom or circuit side, or surface area install parts on the leading and bottom sides of the board.
The boards are also utilized to electrically link the required leads for each component utilizing conductive copper traces. The element pads and connection traces are engraved 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 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 product, 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 manufacturing procedure. A multilayer board consists of a variety of layers of dielectric material that has actually been impregnated with adhesives, and these layers are utilized 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 with today's technologies.
In a typical 4 layer board style, the internal layers are often used to offer power and ground connections, such as a +5 V aircraft layer and a Ground airplane layer as the 2 internal layers, with all other circuit and element connections made on the leading and bottom layers of the board. Very complex board designs may have a a great deal of layers to make the different connections for various voltage levels, ground connections, or for linking the many leads on ball grid selection devices and other large integrated circuit bundle formats.
There are usually 2 kinds 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 kind, normally about.002 inches thick. Core product is similar to an extremely thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, normally.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are two methods utilized to build up the preferred variety of layers. The core stack-up technique, which is an older innovation, uses a center layer of pre-preg material 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 approach, a newer innovation, 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 final variety of layers needed by the board style, sort of like Dagwood constructing a sandwich. This technique enables the maker versatility in how the board layer densities are combined to satisfy the ended up item thickness requirements by varying the number of sheets of pre-preg in each layer. Once 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 making printed circuit boards follows the actions listed below for many applications.
The procedure of identifying materials, procedures, and requirements to meet the customer's requirements for the board design ISO 9001 Accreditation Consultants based upon the Gerber file information supplied with the purchase order.
The procedure of moving the Gerber file data for a layer onto an etch withstand movie that is put on the conductive copper layer.
The conventional procedure of exposing the copper and other locations unprotected by the etch withstand movie to a chemical that eliminates the unprotected copper, leaving the secured copper pads and traces in location; newer procedures utilize plasma/laser etching rather of chemicals to eliminate the copper product, permitting finer line meanings.
The process of aligning the conductive copper and insulating dielectric layers and pushing 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 2nd drilling process is used for holes that are not to be plated through. Info on hole area 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 needed when holes are to be drilled through a copper location however the hole is not to be plated through. Avoid this process if possible since it includes cost to the finished board.
The process of applying 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 applied; the solder mask protects against environmental damage, supplies insulation, secures against solder shorts, and safeguards traces that run between pads.
The process of covering the pad locations 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 placed.
The process of using the markings for component designations and component outlines to the board. May be applied to just the top 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 enables cutting notches or slots into the board if required.
A visual examination of the boards; likewise can be the procedure of checking 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 methods applying a voltage between numerous points on the board and determining if a current flow takes place. Depending upon the board intricacy, this process might need a specially developed test fixture and test program to incorporate with the electrical test system used by the board manufacturer.