In electronic devices, printed circuit boards, or PCBs, are used to mechanically support electronic parts which have their connection leads soldered onto copper pads in surface mount 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 mount on the top only, a mix of thru-hole and surface install components on the top and surface area mount 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 needed leads for each element utilizing conductive copper traces. The part pads and connection traces are engraved from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are developed as single agreed copper pads and traces on one side of the board just, double sided with copper pads and traces on the leading and bottom sides of the board, or multilayer styles with copper pads and traces on 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 product, 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 production process. A multilayer board consists of a variety of layers of dielectric product that has actually 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 style, the internal layers are typically used to offer 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 element connections made on the top and bottom layers of the board. Really complex board designs might have a large number of layers to make the various connections for various voltage levels, ground connections, or for connecting the numerous leads on ball grid variety devices and other big incorporated circuit bundle formats.
There are normally 2 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 kind, typically about.002 inches thick. Core product resembles an extremely thin double sided board because it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, normally.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are two approaches utilized to develop the wanted number 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 product 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 movie stack-up method, a newer innovation, would have core product as the center layer followed by layers of pre-preg and copper material built up above and below to form the final number of layers required by the board style, sort of like Dagwood building a sandwich. This approach permits the manufacturer versatility in how the board layer densities are integrated to satisfy the completed product density requirements by differing the number of sheets of pre-preg in each layer. Once the material layers are completed, the entire 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 making printed circuit boards follows the steps listed below for many applications.
The procedure of determining products, processes, and requirements to satisfy the consumer's requirements for the board design based upon the Gerber file info offered with the purchase order.
The procedure of transferring the Gerber file information for a layer onto an etch resist film that is placed on the conductive copper layer.
The traditional process of exposing the copper and other locations unprotected by the etch resist film to a chemical that gets rid of the unguarded copper, leaving the protected copper pads and traces in place; newer processes utilize plasma/laser etching instead of chemicals to eliminate the copper material, enabling finer line definitions.
The procedure of aligning the conductive copper and insulating dielectric layers and pushing them under heat to trigger the adhesive in the dielectric layers to form a strong board material.
The procedure of drilling all the holes for plated through applications; a 2nd drilling procedure is used for holes that are not to be plated through. Info on hole area and size is contained 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 needed when holes are to be drilled through a copper area but the hole is not to be plated through. Avoid this procedure if possible due to the fact that it adds expense to the finished board.
The process of using a protective masking product, a solder mask, over the bare copper traces or over the copper that has actually had a thin layer of solder used; the solder mask secures against ecological damage, provides insulation, safeguards versus solder shorts, and secures traces that run in between pads.
The process of covering the pad locations with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering process that will occur at a later date after the elements have been put.
The process of using the markings for component classifications and part details to the board. May be applied to just the top side or to both sides if components are mounted on both top and bottom sides.
The procedure of separating multiple boards from a panel of identical boards; this process also permits 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 procedure of checking for connection or shorted connections on the boards by methods using a voltage in between different points on the board and determining if a current circulation happens. Depending upon the board complexity, this procedure might require a specifically created test fixture and test program to integrate with the electrical test system utilized by the board manufacturer.