TQM Systems Comment

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 install applications or through rilled holes in the board and copper pads for soldering the component leads in thru-hole applications. A board style may have all thru-hole elements on the top or component side, a mix of thru-hole and surface area install on the top just, a mix of thru-hole and surface mount components on the top and surface area install components on the bottom or circuit side, or surface area mount parts on the leading and bottom sides of the board.

The boards are likewise used to electrically connect the required 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 designed 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 styles 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 engraved away to form the real copper pads and connection traces on the board surfaces as part of the board manufacturing process. A multilayer board consists of a number of layers of dielectric product that has been impregnated with adhesives, and these layers are utilized to separate the layers of copper plating. All of 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 technologies.

In a typical 4 layer board design, the internal layers are often utilized to provide 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 component connections made on the leading and bottom layers of the board. Very complex board designs might have a a great deal of layers to make the various connections for different voltage levels, ground connections, or for linking the many leads on ball grid array devices and other big integrated circuit bundle formats.

There are usually 2 types 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 kind, usually 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 transferred on each side, normally.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are two approaches used to build up the preferred number 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 ISO 9001 Certification Consultants listed below. This mix of one pre-preg layer and 2 core layers would make a 4 layer board.

The film stack-up method, a more recent innovation, 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 last variety of layers needed by the board design, sort of like Dagwood developing a sandwich. This method allows the manufacturer flexibility in how the board layer thicknesses are integrated to fulfill 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 whole 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 steps listed below for a lot of applications.

The procedure of determining materials, processes, and requirements to satisfy the client's specifications for the board design based upon the Gerber file info provided with the purchase order.

The process of moving the Gerber file data for a layer onto an etch resist film that is placed on the conductive copper layer.

The standard procedure of exposing the copper and other areas unprotected by the etch resist movie to a chemical that gets rid of the unguarded copper, leaving the safeguarded copper pads and traces in location; newer processes use plasma/laser etching rather of chemicals to remove the copper product, permitting finer line definitions.

The procedure of aligning 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 material.

The procedure of drilling all of the holes for plated through applications; a 2nd drilling process is used for holes that are not to be plated through. Details on hole area and size is contained in the drill drawing file.

The procedure of using 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. Prevent this process if possible due to the fact that it adds expense to the completed 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 protects against ecological damage, provides insulation, secures against solder shorts, and secures traces that run between pads.

The procedure of coating the pad locations 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 components have actually been put.

The procedure of using the markings for element classifications and component lays out to the board. Might be used to just the top side or to both sides if elements are installed on both leading and bottom sides.

The process of separating several boards from a panel of identical boards; this procedure likewise permits cutting notches or slots into the board if required.

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

The procedure of looking for connection or shorted connections on the boards by methods using a voltage between numerous points on the board and determining if a current flow occurs. Depending upon the board intricacy, this process may need a specially created test fixture and test program to integrate with the electrical test system utilized by the board maker.