TQM Systems Update



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 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 elements on the top or element side, a mix of thru-hole and surface mount on the top side just, a mix of thru-hole and surface area mount parts on the top and surface mount parts on the bottom or circuit side, or surface mount parts on the leading and bottom sides of the board.

The boards are also utilized to electrically connect the needed leads for each part 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 just, double sided with 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 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 etched away to form the actual copper pads and connection traces on the board surface areas as part of the board production process. A multilayer board includes a variety of layers of dielectric material that has been fertilized with adhesives, and these layers are used 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 style, the internal layers are frequently utilized to supply power and ground connections, such as a +5 V airplane layer and a Ground airplane layer as the 2 internal layers, with all other circuit and component connections made on the top and bottom layers of the board. Really intricate board styles may have a large number of layers to make the various connections for different voltage levels, ground connections, or for linking the many leads on ball grid range gadgets and other large integrated circuit bundle formats.

There are generally two types of material used to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet form, generally about.002 inches thick. Core material resembles a very 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 material with 1 ounce copper layer on each side. In a multilayer board style, there are two techniques utilized to build up the desired number of layers. The core stack-up method, which is an older innovation, uses a center layer of pre-preg product with a layer of core product above and another layer of core product below. This combination of one pre-preg layer and two core layers would make a 4 layer board.

The movie stack-up technique, a newer innovation, would have core product as the center layer followed by layers of pre-preg and copper product developed above and listed below to form the last variety of layers required by the board style, sort of like Dagwood constructing a sandwich. This approach allows the manufacturer flexibility in how the board layer densities are combined to fulfill the completed product density requirements by differing the variety of sheets of pre-preg in each layer. As soon as the product layers are finished, the whole stack is subjected to 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 actions listed below for most applications.

The process of identifying products, processes, and requirements to meet the consumer's requirements 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 withstand movie that is put on the conductive copper layer.

The standard procedure of exposing the copper and other areas unprotected by the etch resist film to a chemical that removes the vulnerable copper, leaving the protected copper pads and traces in place; newer processes use plasma/laser etching rather of chemicals to Reference site remove the copper product, enabling finer line meanings.

The process 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 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. Info on hole location and size is included in the drill drawing file.

The process of using copper plating to the pads, traces, and drilled through holes that are to be plated through; boards are positioned 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. Avoid this process if possible due to the fact that it includes expense to the ended up 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 versus environmental damage, provides insulation, secures versus solder shorts, and protects traces that run between pads.

The process 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 occur at a later date after the elements have actually been put.

The process of using the markings for part designations and part describes to the board. May be applied to just the top side or to both sides if components are installed on both leading and bottom sides.

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

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

The procedure of looking for continuity or shorted connections on the boards by means applying a voltage between various points on the board and identifying if a current flow occurs. Depending upon the board intricacy, this process may require a specifically designed test fixture and test program to integrate with the electrical test system utilized by the board manufacturer.