Quality Systems Review



In electronic devices, printed circuit boards, or PCBs, are used to mechanically support electronic components which have their connection leads soldered onto copper pads in surface area install applications or through rilled holes in the board and copper pads for soldering the part 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 side only, a mix of thru-hole and surface area mount parts on the top side and surface install elements on the bottom or circuit side, or surface install elements on the leading and bottom sides of the board.

The boards are also utilized to electrically connect the required leads for each element using conductive copper traces. The component pads and connection traces are engraved 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 just, double agreed copper pads and traces on the leading and bottom sides of the board, or multilayer designs 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 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 real copper pads and connection traces on the board surface areas as part of the board production procedure. A multilayer board includes a variety of layers of dielectric product that has actually been fertilized with adhesives, and these layers are used to Click here separate the layers of copper plating. All 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 technologies.

In a normal 4 layer board style, the internal layers are typically utilized to supply power and ground connections, such as a +5 V plane layer and a Ground plane layer as the two internal layers, with all other circuit and part connections made on the top and bottom layers of the board. Very complex board styles may have a large number of layers to make the various connections for different voltage levels, ground connections, or for linking the numerous leads on ball grid selection devices and other big integrated circuit plan formats.

There are normally 2 types of product used to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet form, generally about.002 inches thick. Core product resembles a really thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, generally.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are 2 approaches used to develop the preferred variety of layers. The core stack-up method, which is an older innovation, uses a center layer of pre-preg material with a layer of core material above and another layer of core product below. This mix of one pre-preg layer and two core layers would make a 4 layer board.

The movie stack-up technique, a more recent technology, would have core material as the center layer followed by layers of pre-preg and copper product built up above and below to form the last number of layers required by the board style, sort of like Dagwood constructing a sandwich. This technique allows the producer flexibility in how the board layer thicknesses are combined to satisfy the completed product density requirements by differing the variety of sheets of pre-preg in each layer. Once the product layers are finished, 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 a lot of applications.

The process of determining products, processes, and requirements to meet the customer's requirements for the board style based upon the Gerber file info offered with the order.

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

The conventional process of exposing the copper and other areas unprotected by the etch withstand movie to a chemical that removes the unguarded copper, leaving the protected copper pads and traces in location; more recent procedures use plasma/laser etching rather of chemicals to get rid of the copper material, permitting finer line meanings.

The procedure of lining up the conductive copper and insulating dielectric layers and pushing them under heat to activate the adhesive in the dielectric layers to form a strong board material.

The process of drilling all the holes for plated through applications; a second drilling procedure is utilized for holes that are not to be plated through. Details on hole place and size is contained 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 placed in an electrically charged bath of copper.

This is required when holes are to be drilled through a copper area however the hole is not to be plated through. Prevent this procedure if possible because it includes expense to the finished board.

The process of using 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, provides insulation, safeguards versus solder shorts, and protects traces that run in between pads.

The procedure of covering the pad locations with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering procedure that will happen at a later date after the parts have actually been positioned.

The process of using the markings for component designations and component details to the board. Might be used to just the top or to both sides if parts are mounted on both leading and bottom sides.

The process of separating numerous boards from a panel of identical boards; this process also allows cutting notches or slots into the board if required.

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

The process of checking for connection or shorted connections on the boards by ways applying a voltage between different points on the board and identifying if a current circulation occurs. Depending upon the board intricacy, this process may need a specially designed test component and test program to integrate with the electrical test system used by the board producer.