In electronics, printed circuit boards, or PCBs, are utilized to mechanically support electronic components which have their connection leads soldered onto copper pads in surface 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 leading or part side, a mix of thru-hole and surface mount on the top side only, a mix of thru-hole and surface area install parts on the top side and surface area mount elements on the bottom or circuit side, or surface mount elements on the leading and bottom sides of the board.
The boards are also used to electrically link the needed leads for each component utilizing conductive copper traces. The component 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 only, double agreed copper pads and traces on the leading 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 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 surface areas as part of the board production process. A multilayer board consists of a variety of layers of dielectric product that has actually been fertilized with adhesives, and these layers are utilized 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 typically used to supply 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 element connections made on the leading and bottom layers of the board. Very intricate board designs might have a a great deal of layers to make the numerous connections for different voltage levels, ground connections, or for connecting the numerous leads on ball grid variety devices and other large integrated circuit plan formats.
There are typically two types of material utilized to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, usually 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, usually.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are 2 approaches used to develop the preferred number of layers. The core stack-up approach, which is an older technology, utilizes a center layer of pre-preg material with a layer of core material above and another layer of core product below. This mix of one pre-preg layer and 2 core layers would make a 4 layer board.
The movie stack-up approach, a newer innovation, would have core material as the center layer followed by layers of pre-preg and copper material developed above and listed below to form the final variety of layers needed by the board style, sort of like Dagwood developing a sandwich. This approach allows the manufacturer flexibility in how the board layer thicknesses are combined to meet the completed product thickness requirements by varying the variety 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 procedure of producing printed circuit boards follows the actions below for a lot of applications.
The process of identifying products, procedures, and requirements to meet the consumer's specs for the board style based upon the Gerber file info offered with the purchase order.
The process of transferring the Gerber file information for a layer onto an etch resist film that is placed on the conductive copper layer.
The standard procedure of exposing the copper and other locations unprotected by the etch resist film to a chemical that eliminates the unprotected copper, leaving the secured copper pads and traces in place; more recent processes utilize plasma/laser etching instead of chemicals to get rid of 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 solid board material.
The procedure 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. 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 put 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 procedure if possible 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 had a ISO 9001 Accreditation thin layer of solder used; the solder mask safeguards against environmental damage, offers insulation, secures against solder shorts, and safeguards traces that run in between pads.
The procedure of coating the pad locations 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 parts have actually been put.
The process of using the markings for element designations and component details to the board. May be used to simply the top side or to both sides if components are installed on both leading and bottom sides.
The procedure of separating multiple boards from a panel of identical boards; this procedure likewise permits cutting notches or slots into the board if required.
A visual examination 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 approaches.
The procedure of looking for connection or shorted connections on the boards by methods using a voltage in between numerous points on the board and figuring out if a current circulation occurs. Relying on the board complexity, this procedure may require a specifically developed test fixture and test program to incorporate with the electrical test system utilized by the board producer.