The Fundamentals Concerning Quality Systems



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

The boards are likewise used to electrically link the required leads for each element 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 designed 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 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 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 includes a number of layers of dielectric product that has been impregnated with adhesives, and these layers are utilized to separate the layers of copper plating. All these layers are lined up 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 common four layer board style, the internal layers are frequently used to offer power and ground connections, such as a +5 V airplane layer and a Ground plane layer as the two internal layers, with all other circuit and part connections made on the top and bottom layers of the board. Extremely complex board styles might have a large number of layers to make the different connections for various voltage levels, ground connections, or for linking the numerous leads on ball grid variety gadgets and other large integrated circuit package formats.

There are normally two 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 form, normally about.002 inches thick. Core material resembles 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 material with 1 ounce copper layer on each side. In a multilayer board style, there are two approaches used to develop the desired number of layers. The core stack-up approach, which is an older technology, utilizes a center layer of pre-preg product with a layer of core material above and another layer of core product below. This mix of one pre-preg layer and two core layers would make a 4 layer board.

The movie stack-up approach, a more recent innovation, would have core product as the center layer followed by layers of pre-preg and copper product developed above and below to form the final variety of layers required by the board style, sort of like Dagwood building a sandwich. This approach enables the producer flexibility in how the board layer densities are combined to meet the ended up item thickness requirements by differing the number of sheets of pre-preg in each layer. When 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 steps below for the majority of applications.

The procedure of identifying products, procedures, and requirements to fulfill the consumer's specifications for the board design based upon the Gerber file information supplied with the order.

The process of moving the Gerber file information for a layer onto See more an etch withstand film that is put on the conductive copper layer.

The conventional process of exposing the copper and other locations unprotected by the etch resist movie to a chemical that removes the vulnerable copper, leaving the safeguarded copper pads and traces in location; more recent procedures utilize plasma/laser etching rather of chemicals to eliminate the copper product, permitting finer line meanings.

The process 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 solid board material.

The procedure of drilling all of the holes for plated through applications; a 2nd drilling procedure is utilized 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 area however the hole is not to be plated through. Prevent this procedure if possible because it adds cost to the completed board.

The procedure of applying 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 applied; the solder mask secures against environmental damage, supplies insulation, secures versus solder shorts, and safeguards traces that run in 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 process that will take place at a later date after the parts have actually been positioned.

The procedure of applying the markings for component designations and element details to the board. Might be applied to just the top side or to both sides if components are mounted on both leading and bottom sides.

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

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

The procedure of looking for continuity or shorted connections on the boards by methods applying a voltage in between various points on the board and identifying if a present flow occurs. Relying on the board complexity, this procedure may need a specifically created test component and test program to integrate with the electrical test system utilized by the board manufacturer.