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 install applications or through rilled holes in the board and copper pads for soldering the component leads in thru-hole applications. A board style might have all thru-hole elements on the leading or part side, a mix of thru-hole and surface area mount on the top side only, a mix of thru-hole and surface mount parts on the top and surface area install parts on the bottom or circuit side, or surface area install components on the top and bottom sides of the board.
The boards are also used to electrically connect the required leads for each component using conductive copper traces. The element pads and connection traces are etched from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are created as single Click here sided with copper pads and traces on one side of the board just, double sided with copper pads and traces on the top 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 material, such as FR-4 epoxy fiberglass, with copper plating on one or both sides. This copper plating is engraved 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 fertilized with adhesives, and these layers are utilized to separate the layers of copper plating. All these layers are aligned and then 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 normal 4 layer board design, the internal layers are typically used to supply power and ground connections, such as a +5 V plane layer and a Ground airplane layer as the 2 internal layers, with all other circuit and element connections made on the top and bottom layers of the board. Very intricate board designs might have a large number of layers to make the numerous connections for various voltage levels, ground connections, or for linking the numerous leads on ball grid selection gadgets and other large integrated circuit bundle formats.
There are typically two types of material used to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, usually about.002 inches thick. Core product is similar to an extremely 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 style, there are two methods used to build up the preferred variety of layers. The core stack-up technique, 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 product listed below. This combination of one pre-preg layer and 2 core layers would make a 4 layer board.
The film stack-up approach, a more recent technology, would have core material as the center layer followed by layers of pre-preg and copper product built up above and listed below to form the final variety of layers needed by the board design, sort of like Dagwood constructing a sandwich. This method permits the manufacturer versatility in how the board layer densities are combined to satisfy the completed product thickness requirements by varying the variety of sheets of pre-preg in each layer. As soon as the material layers are completed, the entire stack undergoes 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 producing printed circuit boards follows the actions listed below for the majority of applications.
The procedure of identifying products, processes, and requirements to meet the client's requirements for the board design based on the Gerber file information provided with the order.
The procedure of transferring the Gerber file information for a layer onto an etch resist movie that is put on the conductive copper layer.
The traditional procedure of exposing the copper and other areas unprotected by the etch withstand movie to a chemical that eliminates the unprotected copper, leaving the protected copper pads and traces in location; newer procedures utilize plasma/laser etching rather of chemicals to eliminate the copper material, permitting finer line definitions.
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 product.
The procedure of drilling all of the holes for plated through applications; a 2nd drilling procedure is used for holes that are not to be plated through. Info on hole place and size is included 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 placed in an electrically charged bath of copper.
This is needed when holes are to be drilled through a copper location but the hole is not to be plated through. Prevent this procedure if possible due to the fact that it adds cost to the finished board.
The procedure 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 protects against ecological damage, provides insulation, safeguards against solder shorts, and protects traces that run in between pads.
The process 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 take place at a later date after the components have actually been positioned.
The process of applying the markings for element designations and part details to the board. Might be applied to just the top or to both sides if elements are installed on both top and bottom sides.
The procedure of separating several boards from a panel of similar boards; this process likewise enables cutting notches or slots into the board if needed.
A visual inspection of the boards; also can be the procedure of inspecting wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The process of checking for continuity or shorted connections on the boards by methods using a voltage in between various points on the board and figuring out if a current flow takes place. Depending upon the board complexity, this process may require a specifically developed test fixture and test program to incorporate with the electrical test system used by the board manufacturer.