Quality Systems Viewpoints

In electronic devices, printed circuit boards, or PCBs, are utilized 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 components on the leading or part side, a mix of thru-hole and surface install on the top just, a mix of thru-hole and surface mount parts on the top and surface area install parts on the bottom or circuit side, or surface area install elements on the leading and bottom sides of the board.

The boards are also used to electrically connect the required leads for each component 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 just, 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 top and bottom of board with a variable variety of internal copper layers with traces and connections.

Single or double sided boards consist of a core dielectric material, 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 surfaces as part of the board production process. A multilayer board consists of a variety of layers of dielectric material that has actually been impregnated with adhesives, and these layers are utilized to separate the layers of copper plating. All of these layers are lined up 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 normal 4 layer board design, the internal layers are often utilized to offer power and ground connections, such as a +5 V plane layer and a Ground airplane layer as the two internal layers, with all other circuit and element connections made on the leading and bottom layers of the board. Really complicated board designs may have a large number of layers to make the different connections for various voltage levels, ground connections, or for linking the many leads on ball grid array devices and other big incorporated circuit bundle formats.

There are normally 2 types of material utilized to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet kind, usually about.002 inches thick. Core material resembles an extremely thin double sided board because it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, normally.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are 2 approaches utilized to develop the desired variety of layers. The core stack-up technique, which is an older innovation, uses a center layer of pre-preg product with a layer of core material above and another layer of core material listed below. This mix of one pre-preg layer and 2 core layers would make a 4 layer board.

The film stack-up approach, a more recent innovation, would have core material as the center layer followed by layers of pre-preg and copper material developed above and listed below to form the last variety of layers needed by the board style, sort of like Dagwood building a sandwich. This approach allows the manufacturer versatility in how the board layer densities are combined to satisfy the ended up product density requirements by differing the variety of sheets of pre-preg in each layer. As soon as the material layers are finished, the entire stack is subjected to 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 steps below for many applications.

The procedure of identifying materials, processes, and requirements to fulfill the client's specifications for the board style based on the Gerber file info provided with the ISO 9001 Accreditation Consultants order.

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

The standard process of exposing the copper and other locations unprotected by the etch resist movie to a chemical that removes the unguarded copper, leaving the secured copper pads and traces in location; newer processes utilize plasma/laser etching rather of chemicals to eliminate the copper material, permitting finer line definitions.

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

The procedure 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 since it adds cost to the completed 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 used; the solder mask safeguards versus ecological damage, supplies insulation, protects against solder shorts, and secures traces that run between pads.

The procedure of finish 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 element classifications and component lays out to the board. May be used to just the top or to both sides if components are mounted on both top and bottom sides.

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

A visual evaluation of the boards; also 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 applying a voltage between various points on the board and identifying if an existing circulation takes place. Depending upon the board complexity, this procedure may need a specially developed test fixture and test program to incorporate with the electrical test system utilized by the board manufacturer.