In electronics, printed circuit boards, or PCBs, are utilized to mechanically support electronic parts 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 might have all thru-hole components on the top or component side, a mix of thru-hole and surface area mount on the top side only, a mix of thru-hole and surface area mount parts on the top side and surface area mount elements on the bottom or circuit side, or surface install elements on the leading and bottom sides of the board.
The boards are likewise used to electrically link the required leads for each component 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 created as single agreed copper pads and traces on one side of the board just, double agreed copper pads and traces on the top 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 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 surfaces as part of the board manufacturing procedure. A multilayer board consists of a number of layers of dielectric product that has been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All these layers are aligned 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 common four layer board style, the internal layers are frequently used to offer power and ground connections, such as a +5 V plane layer and a Ground aircraft layer as the 2 internal layers, with all other circuit and part connections made on the top and bottom layers of the board. Very complicated board designs might have a large number of layers to make the different connections for various voltage levels, ground connections, or for linking the numerous leads on ball grid array gadgets and other large integrated circuit plan formats.
There are typically 2 types of material utilized to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet form, 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, typically.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two methods utilized to build up the preferred number of layers. The core stack-up approach, which is an older technology, uses a center layer of pre-preg material with a layer of core material above and another layer of core material listed below. This mix of one pre-preg layer and two core layers would make a 4 layer board.
The movie stack-up method, a more recent innovation, would have core product as the center layer followed by layers of pre-preg and copper product developed above and below to form the final number of layers needed by the board style, sort of like Dagwood constructing a sandwich. This method permits the manufacturer flexibility in how the board layer thicknesses are combined to meet the ended up product density requirements by differing the variety of sheets of pre-preg in each layer. As soon as the material layers are completed, the entire stack goes through 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 process of making printed circuit boards follows the steps listed below for many applications.
The process of identifying materials, procedures, and requirements to fulfill the client's requirements for the board style based on the Gerber file information provided with the order.
The procedure of transferring the Gerber file information for a layer onto an etch resist film that is put on the conductive copper layer.
The conventional procedure of exposing the copper and other areas unprotected by the etch resist film to a chemical that removes the unprotected copper, leaving the protected copper pads and traces in place; newer processes utilize plasma/laser etching instead of chemicals to eliminate the copper product, permitting finer line meanings.
The process of lining up the conductive copper and insulating dielectric layers and pushing them under heat to activate the adhesive in the dielectric layers to form a strong board material.
The process of drilling all of the holes for plated through applications; a second drilling process is used for holes that are not to be plated through. Information on hole place and size is consisted of in the drill drawing file.
The process of using 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 but the hole is not to be plated through. Avoid this process if possible due to the fact that it adds expense to the finished 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 versus ecological damage, supplies insulation, secures against solder shorts, and secures traces that run in between pads.
The process of covering the pad areas with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering procedure that will occur at a later date after the elements have actually been positioned.
The process of applying the markings for element designations and element describes to the board. Might be used to just the top or to both sides if components are installed on both leading and bottom sides.
The process of separating multiple boards from a panel of similar boards; this process likewise enables cutting notches or slots into the board if required.
A visual examination of the boards; also can be the process of examining 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 using a voltage in between various points on the board and identifying if an existing flow occurs. Depending upon the board complexity, this process may need a specially created test component and test program to integrate with the electrical test system utilized by the board manufacturer.