In electronics, printed circuit boards, or PCBs, are used to mechanically support electronic elements which have their connection leads soldered onto copper pads in surface install 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 top or component side, a mix of thru-hole and surface install on the top just, a mix of thru-hole and surface area install parts on the top and surface mount parts on the bottom or circuit side, or surface area install parts on the leading and bottom sides of the board.
The boards are also used to electrically link 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 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 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 product, 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 surface areas as part of the board manufacturing procedure. A multilayer board consists of a number of layers of dielectric material that has actually been impregnated with adhesives, and these layers are utilized to separate the layers of copper plating. All these layers are aligned 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 common four layer board design, the internal layers are typically utilized to offer 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 element connections made on the top and bottom layers of the board. Extremely complex board designs might have a a great deal of layers to make the different connections for different voltage levels, ground connections, or for linking the numerous leads on ball grid array devices and other large integrated circuit package formats.
There are generally two types of material utilized to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, usually about.002 inches thick. Core material resembles an extremely thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, normally.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are 2 methods utilized to build up the desired number of layers. The core stack-up method, which is an older innovation, utilizes a center layer of pre-preg material with a layer of core material above and another layer of core material below. This mix of one pre-preg layer and two 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 product developed above and listed below to form the final number of layers needed by the board design, sort of like Dagwood constructing a sandwich. This approach enables the maker versatility in how the board layer densities are integrated to fulfill the completed product density requirements by varying the variety of sheets of pre-preg in each layer. When the material layers are completed, the whole stack undergoes heat and pressure that causes the adhesive in the pre-preg to bond the ISO 9001 Accreditation Consultants core and pre-preg layers together into a single entity.
The procedure of making printed circuit boards follows the steps listed below for many applications.
The process of determining products, procedures, and requirements to fulfill the client's specifications for the board design based upon the Gerber file details provided with the purchase order.
The procedure of transferring the Gerber file information for a layer onto an etch resist movie that is put on the conductive copper layer.
The traditional procedure of exposing the copper and other locations unprotected by the etch resist film to a chemical that eliminates the vulnerable copper, leaving the secured copper pads and traces in location; newer processes use plasma/laser etching rather of chemicals to eliminate the copper product, permitting 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 process 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 location 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 positioned in an electrically charged bath of copper.
This is needed when holes are to be drilled through a copper location but the hole is not to be plated through. Prevent this procedure if possible because it adds expense to the completed board.
The process of applying a protective masking product, 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 versus environmental damage, provides insulation, safeguards against solder shorts, and secures traces that run between pads.
The process of covering the pad locations 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 positioned.
The procedure of using the markings for element classifications and element lays out to the board. Might be applied to just the top side or to both sides if elements are installed on both leading 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 needed.
A visual evaluation of the boards; likewise can be the procedure of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The process of checking for connection or shorted connections on the boards by ways using a voltage between numerous points on the board and determining if an existing circulation occurs. Depending upon the board intricacy, this process might need a specifically designed test component and test program to integrate with the electrical test system utilized by the board manufacturer.