In electronics, 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 component leads in thru-hole applications. A board style may have all thru-hole components on the top or part side, a mix of thru-hole and surface area install on the top side only, a mix of thru-hole and surface area install parts on the top side and surface area mount parts on the bottom or circuit side, or surface area mount components on the leading and bottom sides of the board.
The boards are likewise used to electrically connect the required leads for each part utilizing conductive copper traces. The part pads and connection traces are engraved 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 sided with copper pads and traces on the top 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 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 surface areas as part of the board production process. A multilayer board includes a number of layers of dielectric product that has 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 four layer board design, the internal layers are often utilized to supply power and ground connections, such as a +5 V airplane layer and a Ground plane layer as the 2 internal layers, with all other circuit and component connections made on the top and bottom layers of the board. Very intricate board designs might have a large number of layers to make the numerous connections for various voltage levels, ground connections, or for linking the numerous leads on ball grid variety devices and other big incorporated circuit bundle formats.
There are typically two kinds 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 kind, normally about.002 inches thick. Core product is similar to a very thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, typically.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two techniques used to develop the wanted variety of layers. The core stack-up technique, which is an older innovation, uses a center layer of pre-preg material with a layer of core material above and another layer of core product below. This mix of one pre-preg layer and 2 core layers would make a 4 layer board.
The movie stack-up method, a newer innovation, would have core material as the center layer followed by layers of pre-preg and copper material built up above and listed below to form the last number of layers required by the board style, sort of like Dagwood building a sandwich. This approach enables the manufacturer flexibility in how the board layer densities are integrated to meet the completed product density requirements by varying the number of sheets of pre-preg in each layer. As soon as the product layers are finished, 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 procedure of producing printed circuit boards follows the steps below for many applications.
The process of determining materials, processes, and requirements to meet the client's specifications for the board design based upon the Gerber file details supplied with the purchase order.
The procedure of moving the Gerber file information for a layer onto an etch resist movie that is placed on the conductive copper layer.
The traditional ISO 9001 consultants process of exposing the copper and other locations unprotected by the etch resist film to a chemical that gets rid of the unprotected copper, leaving the secured copper pads and traces in location; newer processes utilize plasma/laser etching instead of chemicals to get rid of the copper product, allowing finer line definitions.
The procedure of aligning 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 process is used for holes that are not to be plated through. Details on hole area and size is included 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 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 ended up board.
The process 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 used; the solder mask secures against environmental damage, offers insulation, protects versus solder shorts, and safeguards traces that run between pads.
The procedure of coating the pad locations with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering process that will happen at a later date after the components have been put.
The procedure of using the markings for part classifications and part outlines to the board. Might be applied to simply the top side 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 procedure likewise allows cutting notches or slots into the board if required.
A visual assessment of the boards; likewise can be the procedure of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The process of checking for connection or shorted connections on the boards by means applying a voltage between numerous points on the board and identifying if an existing flow takes place. Relying on the board complexity, this process may require a specially designed test fixture and test program to incorporate with the electrical test system utilized by the board maker.