In electronic devices, printed circuit boards, or PCBs, are utilized to mechanically support electronic components 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 component leads in thru-hole applications. A board design may have all thru-hole parts on the top or element side, a mix of thru-hole and surface install on the top only, a mix of thru-hole and surface area mount parts on the top side and surface mount elements on the bottom or circuit side, or surface install elements on the top and bottom sides of the board.
The boards are likewise utilized to electrically connect the needed 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 designed as single agreed copper pads and traces on one side of the board only, double sided with copper pads and traces on the leading and bottom sides of the board, or multilayer designs with copper pads and traces on the top and bottom of board with a variable variety of internal copper layers with traces and connections.
Single or double sided boards include 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 actual copper pads and connection traces on the board surface areas as part of the board manufacturing process. A multilayer board consists of a variety of layers of dielectric product that has actually been impregnated with adhesives, and these layers are utilized 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 normal 4 layer board design, the internal layers are typically used to supply power and ground connections, such as a +5 V aircraft layer and a Ground airplane layer as the two internal layers, with all other circuit and component connections made on the top and bottom layers of the board. Extremely complicated board styles may have a a great deal of layers to make the numerous connections for various voltage levels, ground connections, or for connecting the lots of leads on ball grid variety gadgets and other big incorporated circuit bundle formats.
There are usually two types of product utilized to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet kind, normally about.002 inches thick. Core material resembles a very thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, typically.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are two techniques utilized to develop the preferred number 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 below. This combination of one pre-preg layer and two core layers would make a 4 layer board.
The film stack-up method, a more recent technology, 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 final variety of layers required by the board design, sort of like Dagwood building a sandwich. This method enables the manufacturer flexibility in how the board layer densities are combined to satisfy the finished product density requirements by varying the variety of sheets of pre-preg in each layer. As soon ISO 9001 Accreditation as the product layers are finished, 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 process of manufacturing printed circuit boards follows the actions below for a lot of applications.
The process of identifying products, processes, and requirements to meet the customer's requirements for the board design based upon the Gerber file details supplied with the purchase order.
The procedure of moving the Gerber file data for a layer onto an etch resist film that is put 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 vulnerable copper, leaving the safeguarded copper pads and traces in location; more recent procedures use plasma/laser etching instead of chemicals to get rid of the copper product, allowing finer line definitions.
The procedure of lining up 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 second drilling process is utilized for holes that are not to be plated through. Details on hole location and size is consisted of in the drill drawing file.
The procedure 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 but the hole is not to be plated through. Avoid this process if possible since it adds 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 protects against environmental damage, provides insulation, safeguards versus solder shorts, and safeguards traces that run in between pads.
The process of finish the pad locations 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 been put.
The procedure of applying the markings for component classifications and element describes to the board. May be applied to simply the top or to both sides if components are installed on both leading and bottom sides.
The process of separating multiple boards from a panel of identical boards; this procedure likewise allows cutting notches or slots into the board if required.
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 methods.
The procedure of checking for connection or shorted connections on the boards by means using a voltage in between different points on the board and determining if an existing flow occurs. Relying on the board intricacy, this procedure might need a specifically developed test component and test program to integrate with the electrical test system used by the board maker.