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 components on the top or component side, a mix of thru-hole and surface install on the top only, a mix of thru-hole and surface mount parts on the top side and surface area install components on the bottom or circuit side, or surface area mount elements on the leading and bottom sides of the board.
The boards are likewise utilized to electrically connect the required leads for each element utilizing conductive copper traces. The component pads and connection traces are engraved 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 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 material, 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 surfaces as part of the board manufacturing procedure. A multilayer board includes a variety of layers of dielectric product that has been fertilized with adhesives, and these layers are used to separate the layers of copper plating. All of these layers are aligned and after that 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 frequently used to supply power and ground connections, such as a +5 V airplane layer and a Ground airplane layer as the 2 internal layers, with all other circuit and part connections made on the top and bottom layers of the board. Very intricate board styles might have a a great deal of layers to make the numerous connections for various voltage levels, ground connections, or for linking the many leads on ball grid array devices and other big incorporated circuit package formats.
There are generally two types of material used to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet kind, generally about.002 inches thick. Core material is similar to a very thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, generally.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are two methods used to build up the desired variety of layers. The core stack-up method, which is an older innovation, uses 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 two core layers would make a 4 layer board.
The movie stack-up approach, a newer innovation, would have core material as the center layer followed by layers of pre-preg and copper product built up above and below to form the last number of layers required by the board style, sort of like Dagwood developing a sandwich. This technique enables the maker flexibility in how the board layer thicknesses are combined to fulfill the completed product density requirements by varying the number of sheets of pre-preg in each layer. When the product layers are completed, the entire stack goes through 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 process of making printed circuit boards follows the steps below for many applications.
The process of identifying products, processes, and requirements to fulfill the consumer's specifications for the board style based on the Gerber file details provided with the purchase order.
The procedure of moving the Gerber file data for a layer onto an etch resist film that is put on the conductive copper layer.
The standard process of exposing the copper and other locations unprotected by the etch resist movie to a chemical that removes the unguarded copper, leaving the safeguarded copper pads and traces in place; more recent procedures use 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 pressing them under heat to trigger the adhesive in the dielectric layers to form a solid board material.
The process of drilling all the holes for plated through applications; a second drilling process is used for holes that are not to be plated through. Info on hole area and size is consisted of 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 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 due to the fact that it adds expense to the completed board.
The process 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 applied; the solder mask secures versus ecological damage, supplies insulation, safeguards against solder shorts, and safeguards traces that run between pads.
The process of coating the pad locations with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering process that will occur at a later date after the components have been put.
The process of using the markings for part classifications and element lays out to the board. May be applied to just the top side or to both sides if parts are installed on both leading and bottom sides.
The process of separating numerous boards from a panel of similar boards; this process also enables cutting notches or slots into the board if needed.
A visual examination of the boards; also can be the procedure of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other ISO 9001 techniques.
The process of looking for continuity or shorted connections on the boards by means applying a voltage between numerous points on the board and identifying if a present circulation happens. Depending upon the board complexity, this process may require a specially created test component and test program to incorporate with the electrical test system utilized by the board maker.