Quality Management Systems Comment



In electronics, printed circuit boards, or PCBs, are utilized to mechanically support electronic components 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 part leads in thru-hole applications. A board style may have all thru-hole elements on the leading or part side, a mix of thru-hole and surface area install on the top side just, a mix of thru-hole and surface area install components on the top side and surface mount parts on the bottom or circuit side, or surface area mount parts 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 developed 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 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 engraved away to form the real copper pads and connection traces on the board surface areas as part of the board production procedure. A multilayer board consists of 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 of 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 common 4 layer board style, the internal layers are frequently used to provide power and ground connections, such as a +5 V aircraft layer and a Ground aircraft layer as the two internal layers, with all other circuit and component connections made on the leading and bottom layers of the board. Extremely complicated board designs might have a large number of layers to make the different connections for various voltage levels, ground connections, or for connecting the numerous leads on ball grid variety gadgets and other big integrated circuit bundle formats.

There are normally two types of product used to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet form, normally about.002 inches thick. Core product 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, typically.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are 2 approaches utilized to develop the wanted variety of layers. The core stack-up technique, which is an older technology, uses a center layer of pre-preg product with a layer of core product above and another layer of core product listed below. This mix of one pre-preg layer and two core layers would make a 4 layer board.

The film stack-up method, a newer technology, would have core product as the center layer followed by layers of pre-preg and copper product built up above and listed below to form the last variety of layers needed by the board style, sort of like Dagwood constructing a sandwich. This technique allows the producer versatility in how the board layer densities are combined to meet the finished item density requirements by varying the variety of sheets of pre-preg in each layer. Once the material 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 process of producing printed circuit boards follows the actions below for most applications.

The process of figuring out materials, processes, and requirements to fulfill the customer's specs for the board style based on the Gerber file details offered with the purchase order.

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

The traditional procedure of exposing the copper and other areas unprotected by the etch resist movie to a chemical that eliminates the unguarded copper, leaving the protected copper pads and traces in location; newer procedures utilize plasma/laser etching rather of chemicals to remove the copper material, allowing finer line definitions.

The procedure of aligning 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 process of drilling all the holes for plated through applications; a second drilling procedure is used for holes that are not to be plated through. Information on hole place and size is consisted of 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 needed when holes are to be drilled through a copper location however the hole is not to be plated through. Avoid this process if possible because it includes 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 actually had a thin layer of solder used; the solder mask protects against ecological damage, offers insulation, protects against solder shorts, and safeguards traces that run between pads.

The procedure of coating the pad areas with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering process that will occur at a later date after the components have ISO 9001 consultants been positioned.

The process of applying the markings for element classifications and component lays out to the board. May be applied to just the top or to both sides if parts are mounted on both leading and bottom sides.

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

A visual examination 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 techniques.

The process of looking for continuity or shorted connections on the boards by means using a voltage between numerous points on the board and figuring out if a current flow occurs. Relying on the board intricacy, this process might require a specially developed test fixture and test program to incorporate with the electrical test system utilized by the board manufacturer.
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