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 element leads in thru-hole applications. A board style may have all thru-hole parts on the top or component side, a mix of thru-hole and surface area mount on the top just, a mix of thru-hole and surface mount elements on the top side and surface install parts on the bottom or circuit side, or surface install elements on the top and bottom sides of the board.
The boards are also utilized to electrically connect the needed leads for each part utilizing conductive copper traces. The component pads and connection traces are engraved from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are designed as single agreed copper pads and traces on one side of the board only, 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 number 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 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 consists of a variety of layers of dielectric material that has been impregnated with adhesives, and these layers are utilized to separate the layers of copper plating. All of these layers are aligned 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 common four layer board style, the internal layers are often used to supply 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 part connections made on the top and bottom layers of the board. Extremely complex board designs might have a large number of layers to make the numerous connections for various voltage levels, ground connections, or for connecting the lots of leads on ball grid array devices and other big incorporated circuit package formats.
There are normally two kinds of material utilized to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet form, generally about.002 inches thick. Core material is similar to a really thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, usually.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are two techniques used to build up the desired variety of layers. The core stack-up approach, which is an older technology, uses a center layer of pre-preg product with a layer of core product above and another layer of core product listed below. This combination of one pre-preg layer and two core layers would make a 4 layer board.
The movie stack-up technique, a more recent innovation, would have core product as the center layer followed by layers of pre-preg and copper material developed above and listed below to form the last number of layers needed by the board design, sort of like Dagwood developing a sandwich. This method permits the maker versatility in how the board layer densities are combined to fulfill the finished item thickness requirements by varying the variety of sheets of pre-preg in each layer. As soon as the product layers are completed, the whole stack undergoes 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 process of producing printed circuit boards follows the actions below for most applications.
The process of identifying products, procedures, and requirements to fulfill the customer's specifications for the board style based on the Gerber file information provided with the purchase order.
The procedure of transferring the Gerber file data for a layer onto an etch withstand film that is put on the conductive copper layer.
The conventional procedure of exposing the copper and other locations unprotected by the etch withstand film to a chemical that gets rid of the unprotected copper, leaving the protected copper pads and traces in place; newer procedures utilize plasma/laser etching rather of chemicals to remove the copper material, enabling finer line meanings.
The procedure of lining up the conductive copper and insulating dielectric layers and pressing them under heat to trigger the adhesive in the dielectric layers to form a solid board product.
The procedure of drilling all of the holes for plated through applications; a second drilling process is utilized for holes that are not to be plated through. Information on hole area and size is contained 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 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 includes cost to the ended up board.
The procedure of using 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 applied; the solder mask protects 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 process that will take place at a later date after the elements have been placed.
The process of applying the markings for element designations and part lays out to the board. Might be applied to simply the top side or to both sides if components are mounted on both leading and bottom sides.
The procedure of separating multiple boards from a panel of identical boards; this procedure also allows cutting notches or slots into the board if required.
A visual evaluation ISO 9001 Accreditation Consultants 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 methods.
The process of checking for continuity or shorted connections on the boards by ways using a voltage between different points on the board and determining if an existing flow takes place. Relying on the board complexity, this process might require a specifically designed test fixture and test program to integrate with the electrical test system utilized by the board producer.