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 mount applications or through rilled holes in the board and copper pads for soldering the part leads in thru-hole applications. A board design might have all thru-hole components 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 mount components on the top and surface mount parts on the bottom or circuit side, or surface area install elements on the leading and bottom sides of the board.
The boards are likewise utilized to electrically connect the required leads for each part using conductive See more copper traces. The part pads and connection traces are etched from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are designed as single agreed copper pads and traces on one side of the board only, double agreed copper pads and traces on the top 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 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 production procedure. A multilayer board includes a number of layers of dielectric product that has been fertilized with adhesives, and these layers are used 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 common 4 layer board design, the internal layers are often used to provide power and ground connections, such as a +5 V aircraft layer and a Ground aircraft layer as the 2 internal layers, with all other circuit and element connections made on the top and bottom layers of the board. Really complex board designs might have a large number of layers to make the numerous connections for different voltage levels, ground connections, or for linking the many leads on ball grid range devices and other large integrated circuit package formats.
There are generally 2 types of product used to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, 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, usually.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two approaches used to develop the wanted number of layers. The core stack-up method, 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 material below. This mix of one pre-preg layer and 2 core layers would make a 4 layer board.
The film stack-up approach, a more recent technology, would have core product as the center layer followed by layers of pre-preg and copper material developed above and below to form the last number of layers required by the board style, sort of like Dagwood constructing a sandwich. This approach allows the manufacturer versatility in how the board layer densities are combined to meet the ended up product density requirements by varying the number of sheets of pre-preg in each layer. Once 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 actions below for most applications.
The process of figuring out products, procedures, and requirements to fulfill the customer's specs for the board style based upon the Gerber file information offered with the order.
The process of transferring the Gerber file information for a layer onto an etch resist movie that is placed 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 removes the unguarded copper, leaving the secured copper pads and traces in place; more recent processes use plasma/laser etching rather of chemicals to get rid of the copper product, permitting finer line definitions.
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 strong board material.
The process of drilling all of the holes for plated through applications; a second drilling procedure is used for holes that are not to be plated through. Details on hole location 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 positioned in an electrically charged bath of copper.
This is needed when holes are to be drilled through a copper area however the hole is not to be plated through. Avoid this process if possible due to the fact that it includes cost to the completed board.
The process of using 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 safeguards versus environmental damage, supplies insulation, protects against solder shorts, and protects traces that run 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 process that will take place at a later date after the parts have actually been positioned.
The process of applying the markings for part designations and component details to the board. Might 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 similar boards; this process likewise permits cutting notches or slots into the board if needed.
A visual examination of the boards; likewise can be the process of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The procedure of checking for connection or shorted connections on the boards by methods applying a voltage between various points on the board and identifying if a current circulation takes place. Relying on the board intricacy, this process may need a specifically designed test fixture and test program to integrate with the electrical test system utilized by the board producer.