TQM Systems Update



In electronics, printed circuit boards, or PCBs, are used 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 element leads in thru-hole applications. A board design may have all thru-hole components on the top or component side, a mix of thru-hole and surface area mount on the top just, a mix of thru-hole and surface area install parts on the top side and surface area install components on the bottom or circuit side, or surface mount elements 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 component pads and connection traces are etched from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are designed 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 styles 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 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 real copper pads and connection traces on the board surfaces as part of the board production procedure. A multilayer board includes a number of layers of dielectric material that has actually been fertilized with adhesives, and these layers are used to separate the layers of copper plating. All these layers are aligned 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 design, the internal layers are often utilized to provide power and ground connections, such as a +5 V aircraft layer and a Ground plane layer as the two internal layers, with all other circuit and part connections made on the leading and bottom layers of the board. Very intricate board styles might have a large number of layers to make the numerous connections for various voltage levels, ground connections, or for linking the many leads on ball grid selection devices and other large integrated circuit plan formats.

There are typically two kinds of material used to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet form, typically about.002 inches thick. Core product is similar to 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 product with 1 ounce copper layer on each side. In a multilayer board style, there are two methods used to develop the preferred variety of layers. The core stack-up approach, which is an older technology, uses a center layer of pre-preg product with a layer of core material above and another layer of core product below. This combination of one pre-preg layer and 2 core layers would make a 4 layer board.

The movie stack-up approach, a more recent innovation, would have core material as the center layer followed by layers of pre-preg and copper product developed above and listed below to form the final number of layers required by the board design, sort of like Dagwood developing a sandwich. This technique permits the manufacturer flexibility in how the board layer densities are combined to satisfy the completed product thickness requirements by differing the variety of sheets of pre-preg in each layer. As soon as the material layers are completed, the whole 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 procedure of producing printed circuit boards follows the steps below for many applications.

The procedure of identifying products, procedures, and requirements to meet the consumer's requirements for the board style based upon the Gerber file information offered with the order.

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

The traditional process of exposing the copper and other areas unprotected by the etch resist movie to a chemical that removes the unguarded copper, leaving the protected copper pads and traces in location; newer procedures use plasma/laser etching instead of chemicals to eliminate the copper product, enabling finer line definitions.

The procedure of aligning the conductive copper and insulating dielectric layers and pushing them under heat to activate Click here the adhesive in the dielectric layers to form a solid board material.

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 place and size is contained 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 positioned in an electrically charged bath of copper.

This is required when holes are to be drilled through a copper location but the hole is not to be plated through. Avoid this process if possible due to the fact that it includes expense to the completed board.

The process of using a protective masking product, 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 safeguards against ecological damage, provides insulation, secures against solder shorts, and protects 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 take place at a later date after the components have actually been put.

The process of using the markings for component designations and component details to the board. Might be applied to just the top or to both sides if components are installed on both top and bottom sides.

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

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

The process of checking for continuity or shorted connections on the boards by ways using a voltage between various points on the board and identifying if a present circulation takes place. Depending upon the board intricacy, this procedure may need a specially designed test component and test program to integrate with the electrical test system used by the board producer.