In electronic devices, printed circuit boards, or PCBs, are utilized to mechanically support electronic parts 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 part leads in thru-hole applications. A board style may have all thru-hole elements on the top or part side, a mix of thru-hole and surface mount on the top only, a mix of thru-hole and surface mount components on the top side and surface mount parts on the bottom or circuit side, or surface install elements on the leading and bottom sides of the board.
The boards are likewise utilized to electrically connect the needed leads for each part 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 only, double agreed 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 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 surfaces as part of the board production procedure. A multilayer board consists of a variety 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 of these layers are lined up and after that 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 normal 4 layer board style, the internal layers are typically used to provide power and ground connections, such as a +5 V aircraft layer and a Ground plane layer as the two internal layers, with all other circuit and component connections made on the leading and bottom layers of the board. Really complicated board styles might have a a great deal of layers to make the numerous connections for various voltage levels, ground connections, or for connecting the numerous leads on ball grid variety devices and other large incorporated circuit package formats.
There are generally two kinds of product used to build 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 is similar to a very thin double sided board because it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, normally.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are two techniques utilized to develop the wanted number of layers. The core stack-up approach, which is an older innovation, utilizes a center layer of pre-preg product with a layer of core product above and another layer of core product below. This mix of one pre-preg layer and two core layers would make a 4 layer board.
The movie stack-up approach, a newer technology, would have core product as the center layer followed by layers of pre-preg and copper material developed above and below to form the last number of layers required by the board style, sort of like Dagwood developing a sandwich. This method permits the producer versatility in how the board layer densities are combined to fulfill the completed item density requirements by differing the variety of sheets of pre-preg in each layer. Once the material layers are completed, the whole 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 making printed circuit boards follows the steps listed below for the majority of applications.
The process of identifying products, processes, and requirements to meet the consumer's specifications for the board style based upon the Gerber file info supplied with the order.
The procedure of moving the Gerber file information for a layer onto an etch withstand film that is placed on the conductive copper layer.
The conventional procedure of exposing the copper and other areas unprotected by the etch withstand film to a chemical that removes the unguarded copper, leaving the secured copper pads and traces in location; newer procedures use plasma/laser etching instead of chemicals to get rid of the copper product, enabling finer line meanings.
The procedure of lining up the conductive copper and insulating dielectric layers and pushing them under heat to trigger the adhesive in the dielectric layers to form a solid board material.
The procedure of drilling all of the holes for plated through applications; a 2nd drilling process is utilized for holes that are not to be plated through. Information on hole location 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 put in an electrically charged bath of copper.
This is needed when holes are to be drilled through a copper location however the hole is not to be plated through. Avoid this procedure if possible due to the fact that it adds 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 had a thin layer of solder applied; the solder mask safeguards versus ecological damage, offers insulation, secures versus solder shorts, and secures traces that run in between pads.
The process of finishing the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering process that will take place at a later date after the parts have been positioned.
The process of using the markings for part classifications and component describes to the board. May be applied to just the top side or to both sides ISO 9001 Accreditation Consultants if elements 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 needed.
A visual assessment of the boards; also 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 continuity or shorted connections on the boards by methods applying a voltage between numerous points on the board and identifying if a current flow takes place. Depending upon the board intricacy, this process might need a specifically designed test component and test program to integrate with the electrical test system used by the board manufacturer.