In electronic devices, printed circuit boards, or PCBs, are used 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 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 just, a mix of thru-hole and surface area mount components on the top and surface area mount components on the bottom or circuit side, or surface install elements on the top and bottom sides of the board.
The boards are also used to electrically connect the required leads for each component using conductive See more 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 sided with 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 the top and bottom of board with a variable variety 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 real copper pads and connection traces on the board surface areas as part of the board production procedure. A multilayer board consists of 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 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 design, the internal layers are frequently utilized to provide power and ground connections, such as a +5 V airplane layer and a Ground aircraft layer as the 2 internal layers, with all other circuit and part connections made on the leading and bottom layers of the board. Really complex board designs might have a large number of layers to make the numerous connections for various voltage levels, ground connections, or for linking the lots of leads on ball grid variety devices and other large incorporated circuit bundle 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 type, normally about.002 inches thick. Core product is similar to 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 design, there are two techniques used to build up the preferred number of layers. The core stack-up method, 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 product listed below. This mix of one pre-preg layer and two core layers would make a 4 layer board.
The film stack-up approach, a more recent innovation, would have core product as the center layer followed by layers of pre-preg and copper material built up above and listed below to form the final number of layers required by the board style, sort of like Dagwood building a sandwich. This method enables the maker versatility in how the board layer densities are integrated to meet the completed item density requirements by differing the number of sheets of pre-preg in each layer. As soon as the product layers are finished, the whole stack undergoes 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 making printed circuit boards follows the actions listed below for the majority of applications.
The procedure of figuring out products, procedures, and requirements to meet the client's specifications for the board style based on the Gerber file info offered with the purchase order.
The process of moving the Gerber file data for a layer onto an etch withstand film that is placed on the conductive copper layer.
The conventional procedure of exposing the copper and other locations unprotected by the etch resist film to a chemical that eliminates the vulnerable copper, leaving the safeguarded copper pads and traces in place; newer procedures use 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 activate 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 second drilling procedure is utilized for holes that are not to be plated through. Info on hole location 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 put 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 adds expense to the finished 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 thin layer of solder applied; the solder mask secures against ecological damage, offers insulation, protects versus solder shorts, and safeguards traces that run in between pads.
The process of covering the pad locations with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering procedure that will happen at a later date after the parts have been placed.
The procedure of using the markings for component classifications and component describes to the board. Might be applied to just the top side or to both sides if elements are mounted on both top and bottom sides.
The procedure of separating numerous boards from a panel of similar boards; this procedure likewise allows cutting notches or slots into the board if needed.
A visual assessment of the boards; also can be the procedure of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.
The procedure of looking for connection or shorted connections on the boards by means applying a voltage between different points on the board and determining if an existing circulation 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 used by the board maker.