ISO 9001 Certification Consultants
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 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 leading or element side, a mix of thru-hole and surface area mount on the top side just, a mix of thru-hole and surface area install parts on the top and surface mount elements on the bottom or circuit side, or surface area mount parts on the top and bottom sides of the board.
The boards are also utilized to electrically link the needed leads for each part 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 designed 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 designs with copper pads and traces on the top and bottom of board with a variable variety 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 manufacturing process. A multilayer board includes a variety of layers of dielectric material that has been impregnated with adhesives, and these layers are used 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 innovations.
In a common four layer board style, the internal layers are often utilized 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 leading and bottom layers of the board. Very complex board styles may 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 array devices and other big incorporated circuit package 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 remains in sheet form, generally about.002 inches thick. Core material is similar to a very thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, typically.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are 2 techniques utilized to develop the desired number of layers. The core stack-up approach, which is an older innovation, uses a center layer of pre-preg product with a layer of core product above and another layer of core material below. This mix of one pre-preg layer and two core layers would make a 4 layer board.
The film stack-up method, a more recent 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 final variety of layers needed by the board design, sort of like Dagwood developing a sandwich. This approach enables the producer versatility in how the board layer densities are combined to fulfill the ended up product thickness requirements by differing the variety of sheets of pre-preg in each layer. Once the material layers are completed, the whole 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 steps listed below for many applications.
The process of figuring out materials, processes, and requirements to fulfill the consumer's specs for the board design based upon the Gerber file info supplied with the order.
The procedure of transferring the Gerber file information for a layer onto an etch withstand movie that is put on the conductive copper layer.
The conventional process of exposing the copper and other locations unprotected by the etch resist film to a chemical that eliminates the unprotected copper, leaving the secured copper pads and traces in location; more recent processes utilize plasma/laser etching instead of chemicals to get rid of the copper product, allowing finer line definitions.
The process of aligning the conductive copper and insulating dielectric layers and pushing them under heat to activate 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. Information on hole location 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 placed 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 procedure if possible because it includes expense to the completed board.
The procedure 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 protects versus ecological damage, provides insulation, safeguards versus solder shorts, and secures traces that run between pads.
The procedure of finishing the pad locations with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering procedure that will take place at a later date after the components have been placed.
The process of applying the markings for component classifications and element describes to the board. Might be applied to simply the top side or to both sides if parts are installed on both top and bottom sides.
The procedure of separating numerous boards from a panel of identical boards; this procedure likewise enables cutting notches or slots into the board if needed.
A visual examination of the boards; also can be the process of checking 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 methods applying a voltage in between numerous points on the board and figuring out if a current flow happens. Relying on the board complexity, this process may require a specifically designed test fixture and test program to incorporate with the electrical test system used by the board producer.