In electronics, printed circuit boards, or PCBs, are utilized to mechanically support electronic parts 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 part leads in thru-hole applications. A board design might have all thru-hole elements on the top or part side, a mix of thru-hole and surface area install on the top side just, a mix of thru-hole and surface area install parts on the top and surface area install components on the bottom or circuit side, or surface mount elements on the top and bottom sides of the board.
The boards are likewise utilized to electrically link the needed leads for each component using conductive copper traces. The element pads and connection traces are engraved from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are created as single sided with copper pads and traces on one side of the board only, 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 variety 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 engraved away to form the real copper pads and connection traces on the board surface areas as part of the board manufacturing process. A multilayer board consists of a variety of layers of dielectric product that has 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 four layer board design, the internal layers are frequently used to provide power and ground connections, such as a +5 V airplane layer and a Ground aircraft layer as the two internal layers, with all other circuit and part connections made on the leading and bottom layers of the board. Very complicated board designs might have a large number of layers to make the different connections for various voltage levels, ground connections, or for connecting the many leads on ball grid range devices and other large integrated circuit bundle formats.
There are generally 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 kind, normally about.002 inches ISO 9001 thick. Core product resembles a really thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, normally.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are 2 approaches utilized to build up the desired variety of layers. The core stack-up method, which is an older innovation, utilizes a center layer of pre-preg material with a layer of core material above and another layer of core material below. This combination of one pre-preg layer and two core layers would make a 4 layer board.
The movie 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 needed by the board design, sort of like Dagwood developing a sandwich. This method enables the maker flexibility in how the board layer densities are combined to meet the finished item thickness requirements by varying the variety of sheets of pre-preg in each layer. Once the product layers are completed, the whole stack is subjected to 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 procedure of producing printed circuit boards follows the actions listed below for the majority of applications.
The process of figuring out materials, processes, and requirements to satisfy the client's specifications for the board design based on the Gerber file information provided with the order.
The procedure of transferring the Gerber file data for a layer onto an etch resist film that is placed on the conductive copper layer.
The standard process of exposing the copper and other areas unprotected by the etch withstand movie to a chemical that removes the vulnerable copper, leaving the protected copper pads and traces in place; newer procedures use plasma/laser etching instead of chemicals to get rid of the copper product, enabling finer line meanings.
The process 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 process 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. Information on hole area and size is contained 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 positioned in an electrically charged bath of copper.
This is needed when holes are to be drilled through a copper area however the hole is not to be plated through. Prevent this process if possible because it adds cost to the completed board.
The procedure of applying a protective masking product, a solder mask, over the bare copper traces or over the copper that has had a thin layer of solder used; the solder mask safeguards against environmental damage, offers insulation, safeguards against solder shorts, and safeguards 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 eventual wave soldering or reflow soldering procedure that will happen at a later date after the components have been placed.
The process of applying the markings for part classifications and element details to the board. Might be applied to just the top or to both sides if elements are mounted 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 required.
A visual evaluation of the boards; likewise can be the procedure of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.
The procedure of looking for continuity or shorted connections on the boards by methods applying a voltage between different points on the board and identifying if a current flow occurs. Depending upon the board complexity, this procedure might need a specifically developed test component and test program to integrate with the electrical test system utilized by the board maker.