A Peek Into Quality Management Systems



In electronics, printed circuit boards, or PCBs, are utilized to mechanically support electronic elements which have their connection leads soldered onto copper pads in surface area mount 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 parts on the leading or element side, a mix of thru-hole and surface install on the top side just, a mix of thru-hole and surface area install components on the top side and surface area mount elements on the bottom or circuit side, or surface area install components on the top and bottom sides of the board.

The boards are also used to electrically link the required leads for each element using 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 agreed copper pads and traces on the leading and bottom sides of the board, or multilayer styles 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 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 surface areas as part of the board manufacturing procedure. A multilayer board includes a variety of layers of dielectric material 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 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 style, the internal layers are often used to provide 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 top and bottom layers of the board. Very complicated board styles might have a a great deal of layers to make the various connections for various voltage levels, ground connections, or for connecting the many leads on ball grid array gadgets and other big integrated circuit bundle formats.

There are typically two kinds of product utilized to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, typically about.002 inches thick. Core product is similar to a very thin double sided board in that it has a dielectric material, 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 build up the wanted variety of layers. The core stack-up approach, which is an older technology, utilizes 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 film stack-up approach, a newer technology, would have core product as the center layer followed by layers of pre-preg and copper product built up above and below to form the last variety of layers needed by the board design, sort of like Dagwood building a sandwich. This method permits the maker versatility in how the board layer densities are integrated to meet the completed product density requirements by varying the variety of sheets of pre-preg in each layer. Once the product layers are finished, the entire stack undergoes 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 manufacturing printed circuit boards follows the actions below for most applications.

The process of determining materials, procedures, and requirements to fulfill the customer's requirements for the board design based on the Gerber file info provided with the purchase order.

The process of transferring the Gerber file data for a layer onto an etch withstand movie that is put on the conductive copper layer.

The standard process of exposing the copper and other locations unprotected by the etch withstand movie to a chemical that gets rid of the vulnerable copper, leaving the protected copper pads and traces in place; newer procedures utilize plasma/laser etching instead of chemicals to get rid of the copper material, enabling finer line meanings.

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 product.

The process of drilling all the holes for plated through applications; a second drilling process is used for holes that are not to be plated through. Information on hole area 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 positioned 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 process if possible since 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 safeguards against environmental damage, provides insulation, safeguards versus solder shorts, and protects traces that run between pads.

The procedure of covering the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering process that will happen at a later date after the components have been positioned.

The process of applying the markings for component classifications and part lays out to the board. May be used to simply the top side or to both sides if elements are mounted on both top and bottom sides.

The procedure of separating numerous boards from a panel of similar boards; this procedure also enables cutting notches or slots into the board if needed.

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

The procedure of looking for connection or shorted connections on the boards by means using a voltage between different See more points on the board and figuring out if a current flow happens. Depending upon the board intricacy, this procedure may need a specially designed test fixture and test program to incorporate with the electrical test system utilized by the board maker.