In electronic devices, printed circuit boards, or PCBs, are utilized to mechanically support electronic parts 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 part leads in thru-hole applications. A board design may have all thru-hole elements on the top or component side, a mix of thru-hole and surface area install on the top side only, a mix of thru-hole and surface area mount parts on the top and surface area install components on the bottom or circuit side, or surface install components on the leading 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 component pads and connection traces are etched from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are developed as single sided with copper pads and traces on one side of the board only, double sided with copper pads and traces on the leading and bottom sides of the board, or multilayer designs 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 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 surfaces as part of the board manufacturing process. A multilayer board includes a variety of layers of dielectric product that has actually been fertilized with adhesives, and these layers are utilized to separate the layers of copper plating. All of 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 technologies.
In a normal four layer board style, the internal layers are often utilized to supply power and ground connections, such as a +5 V airplane layer and a Ground plane layer as the two internal layers, with all other circuit and element connections made on the top and bottom layers of the board. Very complicated board designs might have a a great deal of layers to make the various connections for different voltage levels, ground connections, or for connecting the many leads on ball grid variety devices and other large integrated circuit plan formats.
There are generally 2 kinds of product used to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet kind, usually about.002 inches thick. Core material resembles an extremely thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, normally.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are 2 methods used to build up the desired number of layers. The core stack-up technique, which is an older technology, uses a center layer of pre-preg material with a layer of core product above and another layer of core product below. This mix 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 product as the center layer followed by layers of pre-preg and copper product developed above and listed below to form the last variety of layers needed by the board design, sort of like Dagwood constructing a sandwich. This technique enables the producer versatility in how the board layer thicknesses are integrated to meet the ended up product density requirements by varying the number of sheets of pre-preg in each layer. As soon as the material layers are completed, the entire stack is subjected to 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 making printed circuit boards follows the actions below for many applications.
The procedure of determining materials, procedures, and requirements to meet the customer's specs for the board design based upon the Gerber file details supplied with the purchase order.
The procedure of moving the Gerber file data 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 areas unprotected by the etch resist film to a chemical that removes the vulnerable copper, leaving the secured copper pads and traces in place; newer procedures use plasma/laser etching rather of chemicals to eliminate the copper material, permitting finer line definitions.
The process of lining up 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 product.
The process 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. Info on hole area and size is contained 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 put 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 procedure if possible because it includes cost to the finished board.
The process of ISO 9001 consultants applying 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 protects versus ecological damage, provides insulation, protects against solder shorts, and secures traces that run in between pads.
The process of coating the pad locations with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering procedure that will occur at a later date after the elements have been positioned.
The procedure of applying the markings for part classifications and component details to the board. Might be used to just the top or to both sides if components are installed on both leading and bottom sides.
The process of separating several boards from a panel of similar boards; this procedure likewise permits cutting notches or slots into the board if required.
A visual assessment 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 process of checking for connection or shorted connections on the boards by ways using a voltage in between various points on the board and figuring out if a present flow takes place. Relying on the board complexity, this process might require a specially designed test fixture and test program to incorporate with the electrical test system utilized by the board manufacturer.