In electronic devices, printed circuit boards, or PCBs, are used to mechanically support electronic parts 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 element leads in thru-hole applications. A board style might have all thru-hole components on the leading or component side, a mix of thru-hole and surface area install on the top side only, a mix of thru-hole and surface mount elements on the top and surface area install elements on the bottom or circuit side, or surface area install components 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 created 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 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 product, 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 surfaces as part of the board manufacturing procedure. A multilayer board includes a variety 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 and 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 typical four layer board design, the internal layers are frequently utilized to offer 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 component connections made on the leading and bottom layers of the board. Very complex board styles may have a a great deal of layers to make the numerous connections for different voltage levels, ground connections, or for connecting the many leads on ball grid array devices and other large incorporated circuit package formats.
There are generally 2 kinds of product utilized to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, normally about.002 inches thick. Core product resembles 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 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are 2 methods used to build up the desired 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 mix of one pre-preg layer and two core layers would make a 4 layer board.
The film stack-up technique, 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 final variety of layers needed by the board style, sort of like Dagwood building a sandwich. This method enables the maker versatility in how the board layer thicknesses are combined to satisfy the completed item thickness requirements by differing the variety of sheets of pre-preg in each layer. When 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 producing printed circuit boards follows the actions listed below for a lot of applications.
The process of identifying materials, procedures, and requirements to satisfy the consumer's specifications for the board style based upon the Gerber file details supplied with the purchase order.
The procedure of transferring the Gerber file data for a layer onto an etch withstand movie that is placed on the conductive copper layer.
The conventional process of exposing the copper and other locations unprotected by the etch resist film to a chemical that removes the unguarded copper, leaving the safeguarded copper pads and traces in place; more recent processes utilize plasma/laser etching rather of chemicals to remove the copper material, enabling finer line definitions.
The process of aligning 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 material.
The procedure of drilling all of the holes for plated through applications; a 2nd drilling procedure is used for holes that are not to be plated through. Info on hole place and size is consisted of in the drill drawing file.
The procedure 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 process if possible because it adds expense to the completed board.
The procedure of using a protective masking material, a solder mask, over the bare copper traces or over the copper that has had a thin layer of solder used; the solder mask protects versus ecological damage, provides insulation, secures versus solder shorts, and secures traces that run in between pads.
The process of covering the pad areas with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering process that will take place at a later date after the elements have actually been positioned.
The procedure of using the markings for component classifications and part lays out to the board. Might be used to simply the top side or to both sides if components are mounted on both top and bottom sides.
The process of separating multiple boards from a panel of identical boards; this process also permits cutting notches or slots into the board if required.
A visual examination of the boards; also can be the process of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The process of looking for continuity or shorted connections on the boards by ways using a voltage between different points on the board and figuring out if a current flow occurs. Relying on the board intricacy, this process might require ISO 9001 consultants a specially designed test fixture and test program to incorporate with the electrical test system utilized by the board maker.