In electronic devices, printed circuit boards, or PCBs, are used 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 may have all thru-hole components on the top or element side, a mix of thru-hole and surface area install on the top side just, a mix of thru-hole and surface install elements on the top side and surface mount elements on the bottom or circuit side, or surface install elements on the top and bottom sides of the board.
The boards are likewise utilized to electrically link the needed leads for each element utilizing conductive copper traces. The component 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 agreed 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 number of internal copper layers with traces and connections.
Single or double sided boards include a core dielectric product, such as FR-4 epoxy fiberglass, with copper plating on one or both sides. This copper plating is engraved away to form the actual copper pads and connection traces on the board surface areas as part of the board production process. A multilayer board consists of a variety of layers of dielectric product 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 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 common four layer board design, the internal layers are frequently utilized 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 element connections made on the top and bottom layers of the board. Really intricate board designs might have a a great deal of layers to make the different connections for different voltage levels, ground connections, or for connecting the many leads on ball grid array devices and other large incorporated circuit bundle formats.
There are generally two types of product used to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet form, usually about.002 inches thick. Core material is similar to a very thin double sided board because it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, generally.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are 2 techniques utilized to develop the wanted 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 mix of one pre-preg layer and two core layers would make a 4 layer board.
The movie stack-up approach, a more recent technology, would have core material as the center layer followed by layers of pre-preg and copper material built up above and listed below to form the final number of layers required by the board style, sort of like Dagwood developing a sandwich. This technique allows the manufacturer versatility in how the board layer thicknesses are combined to fulfill the finished product density requirements by varying the number of sheets of pre-preg in each layer. When the material layers are completed, the entire 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 process of making printed circuit boards follows the actions below for a lot of applications.
The procedure of determining materials, processes, and requirements to meet the client's specs for the board design based upon the Gerber file details offered with the purchase 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 conventional process of exposing the copper and other locations unprotected by the etch resist movie to a chemical that eliminates the unprotected copper, leaving the safeguarded copper pads and traces in location; more recent processes use plasma/laser etching rather of chemicals to remove the copper product, allowing finer line definitions.
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 solid board product.
The procedure of drilling all of the holes for plated through applications; a 2nd drilling process is utilized for holes that are not to be plated through. Information on hole place and size is consisted of 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 positioned in an electrically charged bath of copper.
This is required when holes are to be drilled through a copper area but the hole is not to be plated through. Avoid this process if possible because it adds cost to the ended up board.
The procedure of using 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, offers insulation, secures against solder shorts, and protects traces that run in between pads.
The process of finish 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 parts have been positioned.
The process of using the markings for element classifications and component lays out to the board. Might be applied to just the top side or to both sides if components are installed on both leading and bottom sides.
The procedure of separating several boards from a panel of identical boards; this process 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 methods.
The process of checking for connection or shorted connections on the boards by means applying a voltage between various points on the board and identifying if a current circulation occurs. Depending upon the board intricacy, this procedure might require a specifically created test component and test program to integrate with the electrical test system utilized by the board manufacturer.