In electronic devices, printed circuit boards, or PCBs, are utilized to mechanically support electronic components 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 style might have all thru-hole components on the leading or component side, a mix of thru-hole and surface install on the top just, a mix of thru-hole and surface area mount elements on the top side and surface mount elements on the bottom or circuit side, or surface area mount elements on the top and bottom sides of the board.
The boards are likewise used to electrically connect the needed leads for each component 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 created 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 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 surfaces as part of the board production process. A multilayer board consists of a variety of layers of dielectric material that has been fertilized 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 innovations.
In a typical four layer board design, the internal layers are typically used to provide 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. Extremely complicated 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 array devices and other big integrated circuit package formats.
There are typically two types of material used to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, typically 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 deposited on each side, generally.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are 2 methods utilized to develop the desired number of layers. The core stack-up method, which is an older innovation, uses a center layer of pre-preg product with a layer of core material above and another layer of core material listed below. This combination of one pre-preg layer and two core layers would make a 4 layer board.
The film stack-up technique, a newer technology, would have core product as the center layer followed by layers of pre-preg and copper product built up above and listed below to form the final number of layers required by the board style, sort of like Dagwood building a sandwich. This method enables the maker versatility in how the board layer densities are integrated to satisfy the finished item thickness requirements by differing the number of sheets of pre-preg in each layer. When the material layers are completed, the whole 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 below for the majority of applications.
The process of determining products, processes, and requirements to fulfill the customer's specs for the board design based upon the Gerber file info offered with the purchase order.
The process of moving the Gerber file data for a layer onto an etch withstand movie that is placed on the conductive copper layer.
The conventional procedure of exposing the copper and other locations unprotected by the etch resist film to a chemical that eliminates the unprotected copper, leaving the safeguarded copper pads and traces in location; more recent procedures utilize plasma/laser etching rather of chemicals to get rid of the copper material, allowing finer line meanings.
The process of lining up the conductive copper and insulating dielectric layers and pressing them under heat to activate the adhesive in the dielectric layers to form a strong board product.
The process of drilling all of the holes for plated through applications; a second drilling process is used for holes that are not to be plated through. Information on hole place 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 placed 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. Avoid this process if possible because it adds cost to the completed 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 See more solder used; the solder mask secures against environmental damage, provides insulation, safeguards versus solder shorts, and protects traces that run between pads.
The procedure of coating the pad areas with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering process that will happen at a later date after the parts have been put.
The procedure of applying the markings for component designations and element outlines to the board. Might be applied to just 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 similar boards; this procedure also permits cutting notches or slots into the board if needed.
A visual evaluation of the boards; likewise can be the procedure of inspecting wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The process of looking for connection or shorted connections on the boards by means using a voltage between numerous points on the board and figuring out if a current circulation occurs. Relying on the board intricacy, this procedure might require a specially developed test component and test program to incorporate with the electrical test system utilized by the board maker.