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 install applications or through rilled holes in the board and copper pads for soldering the part leads in thru-hole applications. A board style might have all thru-hole components on the leading or part side, a mix of thru-hole and surface mount on the top just, a mix of thru-hole and surface area mount parts on the top side and surface install parts on the bottom or circuit side, or surface area install elements on the leading and bottom sides of the board.
The boards are also used to electrically connect the needed leads for each element utilizing conductive copper traces. The element pads and connection traces are etched 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 agreed copper pads and traces on the top and bottom sides of the board, or multilayer styles with copper pads and traces on the 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 process. A multilayer board includes a variety of layers of dielectric product that has been blog impregnated with adhesives, and these layers are used to separate the layers of copper plating. All 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 innovations.
In a typical 4 layer board style, the internal layers are typically used to provide power and ground connections, such as a +5 V plane layer and a Ground aircraft layer as the two internal layers, with all other circuit and part connections made on the top and bottom layers of the board. Very intricate board styles may have a a great deal of layers to make the various connections for various voltage levels, ground connections, or for connecting the lots of leads on ball grid variety devices and other big integrated circuit package formats.
There are generally 2 types of material used 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 material, such as epoxy fiberglass, with a copper layer transferred on each side, generally.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two techniques utilized to develop the desired number of layers. The core stack-up technique, which is an older innovation, 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 2 core layers would make a 4 layer board.
The movie stack-up method, a more recent innovation, would have core product as the center layer followed by layers of pre-preg and copper product built up above and below to form the last variety of layers needed by the board design, sort of like Dagwood developing a sandwich. This approach enables the producer versatility in how the board layer thicknesses are combined to meet the completed product density requirements by varying the number of sheets of pre-preg in each layer. When 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 steps listed below for many applications.
The procedure of identifying materials, processes, and requirements to fulfill the client's requirements for the board style based upon the Gerber file details provided with the order.
The procedure of moving the Gerber file data for a layer onto an etch resist movie 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 removes the unguarded copper, leaving the safeguarded copper pads and traces in location; more recent processes use plasma/laser etching rather of chemicals to get rid of the copper material, allowing 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 solid board product.
The procedure of drilling all of the holes for plated through applications; a second drilling procedure is used for holes that are not to be plated through. Information on hole location and size is included in the drill drawing file.
The process of applying 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 required when holes are to be drilled through a copper location however the hole is not to be plated through. Prevent this process if possible because it adds cost to the finished board.
The procedure of using 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 applied; the solder mask safeguards versus environmental damage, offers insulation, secures versus solder shorts, and protects 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 elements have been positioned.
The process of applying the markings for component designations and part outlines to the board. May be applied to simply the top or to both sides if components are mounted on both top and bottom sides.
The process of separating multiple boards from a panel of similar boards; this process likewise enables cutting notches or slots into the board if required.
A visual evaluation of the boards; likewise can be the process of inspecting wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The procedure of looking for connection or shorted connections on the boards by means applying a voltage in between various points on the board and figuring out if a current circulation takes place. Relying on the board intricacy, this procedure might need a specially designed test fixture and test program to incorporate with the electrical test system utilized by the board producer.