Quality Management Systems Examination

In electronics, printed circuit boards, or PCBs, are used 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 component leads in thru-hole applications. A board style might have all thru-hole parts on the top or component side, a mix of thru-hole and surface mount on the top See more side only, a mix of thru-hole and surface mount elements on the top and surface install components on the bottom or circuit side, or surface install components on the leading and bottom sides of the board.

The boards are likewise utilized to electrically connect the needed leads for each part utilizing conductive copper traces. The part 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 sided with 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 product, 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 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 lined up 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 4 layer board design, the internal layers are frequently used to supply power and ground connections, such as a +5 V plane layer and a Ground plane layer as the 2 internal layers, with all other circuit and element connections made on the leading and bottom layers of the board. Really complex board styles may have a a great deal of layers to make the various connections for various voltage levels, ground connections, or for linking the numerous leads on ball grid array gadgets and other big incorporated circuit plan formats.

There are usually two kinds of material utilized to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet form, normally about.002 inches thick. Core material resembles an extremely thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, generally.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are two methods used to develop the preferred number 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 product listed below. This mix of one pre-preg layer and 2 core layers would make a 4 layer board.

The movie stack-up technique, a newer innovation, would have core product as the center layer followed by layers of pre-preg and copper material developed above and below to form the last variety of layers needed by the board design, sort of like Dagwood constructing a sandwich. This technique permits the manufacturer flexibility in how the board layer densities are combined to meet the finished item thickness requirements by differing the variety of sheets of pre-preg in each layer. When the material layers are completed, the whole stack undergoes 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 manufacturing printed circuit boards follows the actions below for most applications.

The process of determining products, processes, and requirements to satisfy the client's specifications for the board style based upon the Gerber file information provided with the order.

The procedure of moving the Gerber file information for a layer onto an etch withstand movie that is put on the conductive copper layer.

The conventional procedure of exposing the copper and other areas unprotected by the etch resist movie to a chemical that gets rid of the vulnerable copper, leaving the protected copper pads and traces in location; more recent procedures utilize plasma/laser etching rather of chemicals to eliminate the copper material, allowing finer line definitions.

The process of lining up the conductive copper and insulating dielectric layers and pressing them under heat to activate 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 second drilling process is used for holes that are not to be plated through. Details on hole location and size is included 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 needed when holes are to be drilled through a copper area but the hole is not to be plated through. Prevent this procedure if possible because it includes expense to the ended up board.

The process of 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 secures against ecological damage, offers insulation, secures against solder shorts, and protects traces that run between pads.

The procedure of finishing 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 parts have actually been placed.

The process of using the markings for element designations and component describes to the board. Might be applied to just the top side or to both sides if elements are mounted on both top and bottom sides.

The procedure of separating multiple boards from a panel of identical boards; this process likewise enables cutting notches or slots into the board if needed.

A visual inspection of the boards; likewise can be the process of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.

The process of looking for connection or shorted connections on the boards by ways applying a voltage between different points on the board and figuring out if a current flow takes place. Depending upon the board intricacy, this process may need a specifically created test component and test program to incorporate with the electrical test system utilized by the board producer.
2019-04-15 / Posted in