In electronic devices, 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 component leads in thru-hole applications. A board design might have all thru-hole elements on the top or component side, a mix of thru-hole and See more surface area install on the top only, a mix of thru-hole and surface install components on the top and surface mount parts on the bottom or circuit side, or surface mount elements 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 element pads and connection traces are engraved from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are designed as single sided with copper pads and traces on one side of the board only, double agreed copper pads and traces on the top 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 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 manufacturing procedure. A multilayer board consists of a number 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 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 typical four layer board design, the internal layers are typically used to offer power and ground connections, such as a +5 V plane layer and a Ground plane layer as the 2 internal layers, with all other circuit and part connections made on the top and bottom layers of the board. Extremely intricate board styles might have a a great deal of layers to make the various connections for various voltage levels, ground connections, or for connecting the many leads on ball grid range gadgets and other big integrated circuit plan formats.
There are normally 2 types of material utilized to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet kind, usually about.002 inches thick. Core product resembles a very thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, typically.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are two approaches used to build up the desired variety of layers. The core stack-up technique, which is an older technology, utilizes a center layer of pre-preg product 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 film stack-up method, a more recent innovation, would have core product as the center layer followed by layers of pre-preg and copper product developed above and below to form the last variety of layers needed by the board design, sort of like Dagwood building a sandwich. This method allows the maker versatility in how the board layer thicknesses are combined to satisfy the finished product density requirements by varying the variety of sheets of pre-preg in each layer. As soon as the material layers are finished, the entire stack is subjected to 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 producing printed circuit boards follows the actions listed below for most applications.
The procedure of identifying products, processes, and requirements to fulfill the client's specifications for the board design based upon the Gerber file information offered with the order.
The procedure of moving the Gerber file information for a layer onto an etch resist film that is placed on the conductive copper layer.
The conventional procedure of exposing the copper and other locations unprotected by the etch resist movie to a chemical that gets rid of the unprotected copper, leaving the secured copper pads and traces in place; newer processes use plasma/laser etching instead of chemicals to eliminate the copper material, permitting finer line meanings.
The procedure of aligning the conductive copper and insulating dielectric layers and pressing them under heat to trigger the adhesive in the dielectric layers to form a strong board product.
The process of drilling all the holes for plated through applications; a second drilling process is used for holes that are not to be plated through. Information on hole place and size is included 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 placed in an electrically charged bath of copper.
This is required when holes are to be drilled through a copper area however the hole is not to be plated through. Prevent this procedure if possible since it includes 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 versus environmental damage, supplies insulation, safeguards against solder shorts, and secures traces that run between pads.
The procedure of covering the pad locations with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering procedure that will occur at a later date after the components have been placed.
The procedure of applying the markings for part classifications and part describes to the board. May be used to simply the top or to both sides if parts are mounted on both top and bottom sides.
The procedure of separating numerous 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 inspecting 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 methods applying a voltage between different points on the board and determining if a current circulation takes place. Relying on the board intricacy, this process may require a specially developed test component and test program to incorporate with the electrical test system used by the board producer.