All About Quality Management Systems

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

The boards are likewise utilized to electrically link the required leads for each element using conductive copper traces. The part 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 agreed 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 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 process. A multilayer board includes a variety of layers of dielectric product that has been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All of these layers are aligned and then 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 style, the internal layers are often utilized to supply power and ground connections, such as a +5 V aircraft layer and a Ground plane layer as the 2 internal layers, with all other circuit and component connections made on the leading and bottom layers of the board. Very intricate board designs might have a large number of layers to make the different connections for different voltage levels, ground connections, or for linking the numerous leads on ball grid selection devices and other large incorporated circuit plan formats.

There are usually two types of material used to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, normally about.002 inches thick. Core material is similar to a very thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, generally.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are two methods used to develop the desired number of layers. The core stack-up technique, which is an older technology, uses a center layer of pre-preg material with a layer of core material above and another layer of core material below. This mix of one pre-preg layer and 2 core layers would make a 4 layer board.

The film stack-up approach, a newer innovation, 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 final variety of layers needed by the board design, sort of like Dagwood building a sandwich. This method enables the maker flexibility in how the board layer thicknesses are combined to fulfill the ended up product thickness requirements by varying the number of sheets of pre-preg in each layer. Once the material layers are completed, 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 making printed circuit boards follows the actions below for many applications.

The procedure of identifying materials, procedures, and requirements to satisfy the client's specifications for the board style based upon the talks about it Gerber file information offered with the purchase order.

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

The traditional process of exposing the copper and other locations unprotected by the etch withstand film to a chemical that removes the unprotected copper, leaving the protected copper pads and traces in location; newer processes use plasma/laser etching instead of chemicals to eliminate the copper product, allowing finer line meanings.

The procedure of lining up 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 product.

The process of drilling all of the holes for plated through applications; a second drilling process is used for holes that are not to be plated through. Details on hole place 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 placed 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 procedure if possible because it adds expense to the ended up 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 applied; the solder mask safeguards against ecological damage, supplies insulation, protects against solder shorts, and protects traces that run between pads.

The procedure of finish the pad locations with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering process that will take place at a later date after the parts have been positioned.

The procedure of applying the markings for part designations and part describes to the board. May be used to simply the top or to both sides if elements are mounted on both top and bottom sides.

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

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

The process of checking for continuity or shorted connections on the boards by methods applying a voltage in between various points on the board and figuring out if a current circulation takes place. Depending upon the board intricacy, this procedure might require a specially created test component and test program to incorporate with the electrical test system used by the board maker.