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 mount applications or through rilled holes in the board and copper pads for soldering the element leads in thru-hole applications. A board design may have all thru-hole elements on the leading or part side, a mix of thru-hole and surface area mount on the top just, a mix of thru-hole and surface area install elements on the top side and surface area install components on the bottom or circuit side, or surface mount parts on the top and bottom sides of the board.
The boards are also used to electrically connect the required leads for each element using conductive copper traces. The part 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 styles with copper pads and traces on 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 material, such as FR-4 epoxy fiberglass, with copper plating on one or both sides. This copper plating is etched away to form the real copper pads and connection traces on the board surfaces as part of the board production process. A multilayer board includes a variety of layers of dielectric product that has actually been fertilized 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 technologies.
In a common 4 layer board design, the internal layers are frequently utilized to provide power and ground connections, such as a +5 V aircraft layer and a Ground aircraft layer as the two internal layers, with all other circuit and part connections made on the top and bottom layers of the board. Very complicated board designs may have a large number of layers to make the various connections for different voltage levels, ground connections, or for connecting the many leads on ball grid range gadgets and other large incorporated circuit bundle formats.
There are usually two types 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 kind, usually about.002 inches thick. Core material resembles a really thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, generally.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are 2 techniques utilized to build up the wanted variety of layers. The core stack-up approach, which is an older innovation, uses a center layer of pre-preg product with a layer of core material above and another layer of core material listed below. This mix of one pre-preg layer and two core layers would make a 4 layer board.
The movie 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 below to form the last variety of layers needed by the board design, sort of like Dagwood developing a sandwich. This technique allows the manufacturer flexibility in how the board layer thicknesses are combined to satisfy the finished product thickness requirements by differing the variety of sheets of pre-preg in each layer. As soon as the product layers are completed, the entire 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 procedure of producing printed circuit boards follows the actions below for the majority of applications.
The procedure of identifying materials, processes, and requirements to fulfill the client's specifications for the board style based upon the Gerber file info offered with the purchase order.
The procedure of moving the Gerber file information for a layer onto an etch withstand movie that is placed on the conductive copper layer.
The traditional process ISO 9001 Certification Consultants of exposing the copper and other locations unprotected by the etch resist movie to a chemical that removes the unguarded copper, leaving the safeguarded copper pads and traces in place; more recent processes utilize plasma/laser etching instead of chemicals to eliminate the copper product, 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 solid board material.
The procedure of drilling all of the holes for plated through applications; a second drilling process is used for holes that are not to be plated through. Information on hole location and size is consisted of 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 placed in an electrically charged bath of copper.
This is required when holes are to be drilled through a copper location but the hole is not to be plated through. Prevent this process if possible because it adds expense to the completed board.
The process of applying 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 used; the solder mask secures against environmental damage, offers insulation, safeguards versus solder shorts, and secures traces that run in between pads.
The procedure 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 occur at a later date after the parts have actually been put.
The procedure of applying the markings for component designations and part lays out to the board. May be used to just the top or to both sides if components are mounted on both top and bottom sides.
The procedure of separating several boards from a panel of similar boards; this process also enables cutting notches or slots into the board if needed.
A visual evaluation 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 methods.
The procedure of looking for connection or shorted connections on the boards by methods applying a voltage between various points on the board and determining if a present circulation occurs. Relying on the board complexity, this procedure may require a specifically designed test fixture and test program to integrate with the electrical test system utilized by the board producer.