In electronic devices, printed circuit boards, or PCBs, are used 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 part leads in thru-hole applications. A board style may have all thru-hole parts on the top or element side, a mix of thru-hole and surface install on the top just, a mix of thru-hole and surface area mount components on the top and surface mount parts on the bottom or circuit side, or surface area mount elements on the top and bottom sides of the board.
The boards are also utilized to electrically link the needed leads for each element utilizing conductive copper traces. The part 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 top 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 real copper pads and connection traces on the board surface areas as part of the board manufacturing process. A multilayer board includes a number 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 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 common four layer board design, the internal layers are often used to provide power and ground connections, such as a +5 V aircraft layer and a Ground plane layer as the 2 internal layers, with all other circuit and element connections made on the top and bottom layers of the board. Really complex board styles may have a a great deal of layers to make the different connections for different voltage levels, ground connections, or for linking the many leads on ball grid array gadgets and other big integrated circuit bundle formats.
There are generally 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 form, normally about.002 inches thick. Core product resembles an extremely thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, generally.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are 2 methods used to develop the wanted variety of layers. The core stack-up method, 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 material listed below. This mix of one pre-preg layer and two core layers would make a 4 layer board.
The movie stack-up method, a more recent technology, would have core material as the center layer followed by layers of pre-preg and copper product built up above and listed below to form the last number of layers required by the board design, sort of like Dagwood building a sandwich. This technique enables the maker versatility in how the board layer densities are combined to satisfy the ended up item thickness requirements by differing the number of sheets of pre-preg in each layer. As soon as 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 producing printed circuit boards follows the ISO 9001 actions listed below for most applications.
The process of determining products, procedures, and requirements to fulfill the customer's requirements for the board design based upon the Gerber file details offered with the order.
The process of transferring the Gerber file data for a layer onto an etch withstand movie that is placed on the conductive copper layer.
The conventional procedure of exposing the copper and other areas unprotected by the etch withstand film to a chemical that removes the vulnerable copper, leaving the safeguarded copper pads and traces in place; newer procedures use plasma/laser etching instead of chemicals to eliminate the copper product, allowing 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 strong board product.
The procedure of drilling all the holes for plated through applications; a 2nd drilling procedure is utilized for holes that are not to be plated through. Information on hole area and size is contained in the drill drawing file.
The process of applying 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 required when holes are to be drilled through a copper location however the hole is not to be plated through. Avoid this process if possible because 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 actually had a thin layer of solder used; the solder mask safeguards against environmental damage, provides insulation, protects against solder shorts, and protects traces that run between pads.
The process of coating the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering procedure that will occur at a later date after the parts have actually been put.
The process of using the markings for component designations and component outlines to the board. Might be applied to just the top side or to both sides if components are installed on both top 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 required.
A visual assessment 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 techniques.
The procedure of looking for continuity or shorted connections on the boards by means using a voltage in between different points on the board and determining if an existing circulation occurs. Relying on the board intricacy, this procedure might need a specifically designed test fixture and test program to integrate with the electrical test system utilized by the board producer.