The Rudiments Concerning Quality Management Systems




In electronics, printed circuit boards, or PCBs, are used to mechanically support electronic elements 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 design might have all thru-hole elements on the top or part side, a mix of thru-hole and surface mount on the top only, a mix of thru-hole and surface install components on the top side and surface area mount elements on the bottom or circuit side, or surface mount elements on the leading and bottom sides of the board.

The boards are also utilized to electrically link the required leads for each element using conductive copper traces. The element pads and connection traces are etched 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 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 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 procedure. A multilayer board includes a variety of layers of dielectric material that has actually been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All these layers are aligned 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 typically used to supply power and ground connections, such as a +5 V aircraft 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. Really complex board designs may have a a great deal of layers to make the numerous connections for various voltage levels, ground connections, or for connecting the lots of leads on ball grid selection gadgets and other large integrated circuit bundle formats.

There are generally two types of material used to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet kind, normally about.002 inches thick. Core product is similar to a very thin double sided board because it has a dielectric product, such as epoxy fiberglass, with a copper layer See more here deposited on each side, typically.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are two methods used to build up the desired number of layers. The core stack-up approach, which is an older technology, uses a center layer of pre-preg product with a layer of core material above and another layer of core material 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 technology, would have core product as the center layer followed by layers of pre-preg and copper material built up above and listed below to form the final number of layers needed by the board design, sort of like Dagwood constructing a sandwich. This method enables the manufacturer flexibility in how the board layer densities are combined 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 finished, 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 manufacturing printed circuit boards follows the steps below for most applications.

The procedure of figuring out materials, procedures, and requirements to satisfy the customer's requirements for the board design based on the Gerber file information offered with the purchase order.

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

The conventional procedure of exposing the copper and other areas unprotected by the etch withstand movie to a chemical that eliminates the unguarded copper, leaving the protected copper pads and traces in place; more recent processes use plasma/laser etching rather of chemicals to remove the copper product, enabling finer line meanings.

The procedure 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 strong board product.

The procedure of drilling all the holes for plated through applications; a 2nd drilling procedure is used for holes that are not to be plated through. Information on hole location 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 positioned in an electrically charged bath of copper.

This is needed when holes are to be drilled through a copper location however the hole is not to be plated through. Prevent this procedure if possible since it includes cost to the ended up board.

The process of applying a protective masking product, 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, supplies insulation, safeguards versus solder shorts, and safeguards traces that run between pads.

The procedure of finishing the pad areas with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering process that will take place at a later date after the elements have been positioned.

The procedure of using the markings for component designations and component details to the board. May be used to just the top or to both sides if components are mounted on both top and bottom sides.

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

A visual assessment of the boards; likewise can be the procedure of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.

The procedure of checking for connection or shorted connections on the boards by means applying a voltage between various points on the board and figuring out if an existing circulation occurs. Relying on the board complexity, this process might need a specially developed test fixture and test program to incorporate with the electrical test system utilized by the board maker.