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 install applications or through rilled holes in the board and copper pads for soldering the element leads in thru-hole applications. A board design might have all thru-hole components on the leading or part side, a mix of thru-hole and surface install on the top side only, a mix of thru-hole and surface mount elements on the top side and surface area install components on the bottom or circuit side, or surface install elements on the top and bottom sides of the board.
The boards are also used to electrically link the needed leads for each element utilizing conductive copper traces. The element pads and connection traces are engraved from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are designed 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 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 material, such as FR-4 epoxy fiberglass, with copper plating on one or both sides. This copper plating is etched away to form the actual copper pads and connection traces on the board surfaces as part of the board production procedure. A multilayer board includes a number of layers of dielectric material that has been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All 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 normal four layer board design, the internal layers are often utilized to provide 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 element connections made on the leading and bottom layers of the board. Very complicated board styles may have a large number of layers to make the various connections for various voltage levels, ground connections, or for linking the lots of leads on ball grid selection devices and other large integrated circuit package formats.
There are generally two kinds of material used to construct a multilayer board. Pre-preg material 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 an extremely thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, typically.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are two approaches utilized to develop the preferred number of layers. The core stack-up technique, which is an older technology, 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 two core layers would make a 4 layer board.
The movie stack-up method, a more recent innovation, 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 last variety of layers required by check my reference the board design, sort of like Dagwood constructing a sandwich. This approach permits the producer flexibility in how the board layer thicknesses are integrated to meet the ended up product thickness requirements by differing the variety of sheets of pre-preg in each layer. As soon as the material layers are finished, the entire stack goes through 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 below for the majority of applications.
The process of figuring out materials, procedures, and requirements to fulfill the consumer's specifications for the board style based upon the Gerber file details supplied with the purchase order.
The process of moving the Gerber file data for a layer onto an etch resist movie 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 removes the unprotected copper, leaving the secured copper pads and traces in place; more recent procedures use plasma/laser etching instead of chemicals to remove the copper material, allowing finer line definitions.
The process 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 solid board material.
The procedure of drilling all of the holes for plated through applications; a 2nd drilling process is used for holes that are not to be plated through. Details on hole place and size is included in the drill drawing file.
The process 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 because it includes expense to the ended up board.
The process of using 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 secures versus ecological damage, provides insulation, safeguards versus solder shorts, and secures traces that run between pads.
The process of finish the pad locations with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering process that will take place at a later date after the components have been positioned.
The process of applying the markings for part designations and component outlines to the board. Might be used to simply the top side or to both sides if components are installed on both leading and bottom sides.
The procedure of separating numerous boards from a panel of similar boards; this procedure also permits cutting notches or slots into the board if needed.
A visual inspection of the boards; likewise can be the process of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.
The process of looking for continuity or shorted connections on the boards by means using a voltage between various points on the board and determining if an existing flow happens. Depending upon the board complexity, this process might require a specifically created test component and test program to integrate with the electrical test system utilized by the board maker.