The Basics Of TQM Systems

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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 install applications or through rilled holes in the board and copper pads for soldering the part leads in thru-hole applications. A board design may have all thru-hole components on the top or part side, a mix of thru-hole and surface area install on the top only, a mix of thru-hole and surface install components on the top and surface area install parts on the bottom or circuit side, or surface install parts on the leading and bottom sides of the board.

The boards are also utilized to electrically connect the needed leads for each component 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 designed as single agreed copper pads and traces on one side of the board just, 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 include a core dielectric product, such as FR-4 epoxy fiberglass, with copper plating on one or both sides. This copper plating is engraved away to form the actual copper pads and connection traces on the board surfaces as part of the board production procedure. A multilayer board consists of a number of layers of dielectric product that has been fertilized with adhesives, and these layers are used to separate the layers of copper plating. All of these layers are aligned 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 often utilized to provide power and ground connections, such as a +5 V aircraft 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. Extremely intricate board styles might 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 array devices and other large integrated circuit plan formats.

There are generally 2 kinds of product utilized to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet form, typically about.002 inches thick. Core material is similar to an extremely thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, usually.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are two methods used to build up the desired variety of layers. The core stack-up technique, 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 listed below. This mix of one pre-preg layer and 2 core layers would make a 4 layer board.

The movie stack-up method, a more recent technology, would have core product as the center layer followed by layers of pre-preg and copper material developed above and below to form the final variety of layers needed by the board style, sort of like Dagwood developing a sandwich. This technique permits the producer versatility in how the board layer thicknesses are integrated to fulfill the ended up product density requirements by differing the number of sheets of pre-preg in each layer. As soon as the material layers are completed, the entire 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 listed below for the majority of applications.

The procedure of figuring out products, procedures, and requirements to fulfill the customer's specs for the board design based on the Gerber file details supplied with the purchase order.

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

The standard process of exposing the copper and other locations unprotected by the etch withstand film to a chemical that eliminates the unprotected copper, leaving the secured copper pads and traces in place; newer procedures use plasma/laser etching instead of chemicals to eliminate the copper material, enabling finer line meanings.

The procedure of lining up 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 material.

The procedure of drilling all the holes for plated through applications; a 2nd drilling process is used for holes that are not to be plated through. Information on hole area 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 put 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. Prevent this process if possible because it adds cost to the finished board.

The procedure 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, protects versus solder shorts, and safeguards traces that run in 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 procedure that will happen at a later date after the elements have been positioned.

The procedure of using the markings for element classifications and part describes to the board. May be used to simply the top or to both sides if components are installed on both top and bottom sides.

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

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

The process of looking for continuity or shorted connections on the boards by methods using a voltage in between different points on the board and identifying if a present circulation occurs. Depending upon the board intricacy, this procedure may require a specially created test fixture and test program to incorporate with the electrical test system used by the board manufacturer.

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