In electronics, printed circuit boards, or PCBs, are used to mechanically support electronic parts which have their connection leads soldered onto copper pads in surface area install applications or through rilled holes in the board and copper pads for soldering the part leads in thru-hole applications. A board design might have all thru-hole elements on the leading or part side, a mix of thru-hole and surface mount on the top side just, a mix of thru-hole and surface area install elements on the top and surface mount components on the bottom or circuit side, or surface area mount elements on the leading and bottom sides of the board.
The boards are likewise used to electrically connect the needed 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 designed as single sided with copper pads and traces on one side of the board just, 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 top and bottom of board with a variable number 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 etched 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 includes a number of layers of dielectric material 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 4 layer board ISO 9001 design, the internal layers are often utilized to supply power and ground connections, such as a +5 V aircraft layer and a Ground aircraft layer as the 2 internal layers, with all other circuit and part connections made on the leading and bottom layers of the board. Extremely intricate board styles might have a large number of layers to make the numerous connections for various voltage levels, ground connections, or for linking the many leads on ball grid array gadgets and other big incorporated circuit plan formats.
There are usually two types of material used to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet form, normally about.002 inches thick. Core material is similar to a very thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, usually.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are two techniques utilized to develop the desired variety of layers. The core stack-up method, which is an older technology, uses 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 technique, a newer technology, 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 last number of layers required by the board design, sort of like Dagwood constructing a sandwich. This technique allows the maker flexibility in how the board layer thicknesses are integrated to meet the completed item density requirements by varying the variety of sheets of pre-preg in each layer. As soon as the material 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 making printed circuit boards follows the steps listed below for most applications.
The procedure of figuring out materials, procedures, and requirements to fulfill the client's specifications for the board style based upon the Gerber file details supplied with the order.
The procedure of moving the Gerber file information for a layer onto an etch withstand movie that is put on the conductive copper layer.
The conventional process of exposing the copper and other locations unprotected by the etch withstand film to a chemical that eliminates the vulnerable copper, leaving the secured copper pads and traces in location; more recent procedures use plasma/laser etching instead of chemicals to remove the copper product, allowing finer line meanings.
The process of aligning the conductive copper and insulating dielectric layers and pressing them under heat to activate the adhesive in the dielectric layers to form a solid board product.
The procedure of drilling all the holes for plated through applications; a second drilling procedure is used for holes that are not to be plated through. Information on hole area and size is contained 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. Prevent this process if possible due to the fact that it includes expense to the finished board.
The process of applying a protective masking material, 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 versus environmental damage, offers insulation, safeguards versus solder shorts, and protects 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 procedure that will happen at a later date after the parts have been placed.
The process of applying the markings for part classifications and component outlines to the board. Might be applied to just the top side or to both sides if elements are installed on both top and bottom sides.
The process of separating multiple boards from a panel of similar boards; this process also 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 techniques.
The procedure of looking for connection or shorted connections on the boards by means using a voltage in between different points on the board and identifying if a current circulation happens. Depending upon the board intricacy, this procedure may need a specifically created test component and test program to integrate with the electrical test system used by the board maker.