In electronics, printed circuit boards, or PCBs, are used to mechanically support electronic elements 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 style may have all thru-hole elements on the leading or component side, a mix of thru-hole and surface mount on the top only, a mix of thru-hole and surface install components 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 also utilized to electrically link the required leads for each part utilizing conductive copper traces. The element pads and connection traces are etched from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are developed as single agreed copper pads and traces on one side of the board just, double agreed copper pads and traces on the leading 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 consist of 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 process. A multilayer board includes a variety of layers of dielectric product that has been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All of these layers are aligned and after that 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 design, the internal layers are typically utilized to offer power and ground connections, such as a +5 V plane layer and a Ground airplane layer as the 2 internal layers, with all other circuit and element connections made on the top and bottom layers of the board. Extremely complicated board designs may have a large number of layers to make the various connections for various voltage levels, ground connections, or for connecting the lots of leads on ball grid selection devices and other large integrated circuit bundle formats.
There are normally 2 types of product used to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet form, generally about.002 inches thick. Core material resembles a very thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, normally.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are 2 techniques used to develop the preferred number of layers. The core stack-up technique, which is an older technology, utilizes a center layer of pre-preg material with a layer of core product above and another layer of core product listed below. This combination of one pre-preg layer and 2 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 last number of layers required by the board design, sort of like Dagwood constructing a sandwich. This technique allows the producer versatility in how the board layer densities are integrated to satisfy the finished product thickness requirements by varying the number of sheets of pre-preg in each layer. Once 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 Reference site of manufacturing printed circuit boards follows the actions below for many applications.
The procedure of determining products, processes, and requirements to meet the consumer's specifications for the board design based upon the Gerber file details offered with the order.
The process of moving the Gerber file information for a layer onto an etch resist film that is placed on the conductive copper layer.
The standard process of exposing the copper and other locations 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 instead of chemicals to get rid of the copper product, enabling finer line definitions.
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 strong board product.
The process of drilling all the holes for plated through applications; a 2nd drilling process is utilized for holes that are not to be plated through. Information on hole place and size is included 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 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 procedure if possible due to the fact that it includes expense to the ended up board.
The process of applying 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 safeguards against environmental damage, supplies insulation, protects against solder shorts, and protects traces that run between pads.
The process 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 occur at a later date after the parts have actually been put.
The process of using the markings for component designations and element describes to the board. May be applied to just the top or to both sides if parts are mounted on both leading and bottom sides.
The procedure of separating multiple boards from a panel of identical boards; this process also 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 checking for connection or shorted connections on the boards by ways using a voltage in between numerous points on the board and figuring out if a present circulation occurs. Relying on the board intricacy, this procedure may require a specifically created test fixture and test program to incorporate with the electrical test system used by the board manufacturer.