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 mount applications or through rilled holes in the board and copper pads for soldering the component leads in thru-hole applications. A board design may have all thru-hole parts on the top or component side, a mix of thru-hole and surface mount on the top side only, a mix of thru-hole and surface install parts on the top and surface area install elements on the bottom or circuit side, or surface area mount parts on the leading and bottom sides of the board.
The boards are also used to electrically connect the needed leads for each element 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 developed as single sided with copper pads and traces on one side of the board only, double sided with copper pads and traces on the top and bottom sides of the board, or multilayer designs 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 material, 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 surfaces as part of the board production procedure. A multilayer board ISO 9001 Accreditation Consultants includes a number of layers of dielectric product that has actually been impregnated 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 technologies.
In a common 4 layer board style, the internal layers are frequently used to provide power and ground connections, such as a +5 V plane layer and a Ground plane layer as the two internal layers, with all other circuit and part connections made on the leading and bottom layers of the board. Really intricate board designs may have a large number of layers to make the different connections for different voltage levels, ground connections, or for connecting the numerous leads on ball grid variety devices and other big integrated circuit package formats.
There are generally two kinds of product used to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, usually about.002 inches thick. Core material 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, typically.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are two techniques used to develop the preferred number of layers. The core stack-up approach, which is an older technology, uses a center layer of pre-preg product with a layer of core material above and another layer of core product below. This mix of one pre-preg layer and two core layers would make a 4 layer board.
The film stack-up technique, a more recent innovation, would have core material as the center layer followed by layers of pre-preg and copper product built up above and listed below to form the last number of layers needed by the board style, sort of like Dagwood developing a sandwich. This technique permits the manufacturer flexibility in how the board layer thicknesses are combined to fulfill the completed product thickness requirements by differing the number of sheets of pre-preg in each layer. As soon as the material layers are finished, the whole stack goes through 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 process of producing printed circuit boards follows the steps below for a lot of applications.
The process of identifying materials, processes, and requirements to fulfill the client's requirements for the board design based on the Gerber file details supplied with the purchase order.
The process of moving the Gerber file information for a layer onto an etch resist film that is put on the conductive copper layer.
The conventional process of exposing the copper and other locations unprotected by the etch resist movie to a chemical that removes the vulnerable copper, leaving the safeguarded copper pads and traces in location; more recent processes utilize plasma/laser etching instead of chemicals to eliminate the copper material, enabling finer line meanings.
The procedure of aligning the conductive copper and insulating dielectric layers and pressing 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 2nd drilling process is used for holes that are not to be plated through. Info on hole location and size is included 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 required when holes are to be drilled through a copper location however the hole is not to be plated through. Prevent this procedure if possible due to the fact that it adds expense to the completed board.
The procedure 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 safeguards versus environmental damage, provides insulation, protects versus solder shorts, and secures 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 process that will take place at a later date after the elements have actually been put.
The process of applying the markings for element designations and component lays out to the board. Might be applied to just the top side or to both sides if parts are installed on both top and bottom sides.
The process of separating several boards from a panel of similar boards; this procedure also allows cutting notches or slots into the board if needed.
A visual examination 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 methods.
The process of looking for connection or shorted connections on the boards by methods using a voltage between various points on the board and figuring out if a current flow occurs. Relying on the board intricacy, this process may require a specifically designed test fixture and test program to incorporate with the electrical test system utilized by the board maker.