The Functional Aspects of a Present-day Quality System

Apr 15, 2019  
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 mount applications or through rilled holes in the board and copper pads for soldering the element leads in thru-hole applications. A board style may have all thru-hole components on the leading or element side, a mix of thru-hole and surface area install on the top side just, a mix of thru-hole and surface install components on the top and surface install components on the bottom or circuit side, or surface area install parts on the leading and bottom sides of the board.

The boards are also utilized to electrically link the required leads for each part utilizing 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 number 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 real copper pads and connection traces on the board surfaces as part of the board manufacturing process. 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 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 common four layer board design, the internal layers are often used to supply power and ground connections, such as a +5 V aircraft layer and a Ground plane layer as the 2 internal layers, with all other circuit and part connections made on the leading and bottom layers of the board. Very complicated board designs might have a large number of layers to make the different connections for different voltage levels, ground connections, or for connecting the numerous leads on ball grid variety gadgets and other large integrated circuit bundle formats.

There are typically two kinds of product used to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet form, usually about.002 inches thick. Core ISO 9001 product resembles a very thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, generally.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are two techniques utilized to build up the wanted variety of layers. The core stack-up approach, which is an older innovation, utilizes a center layer of pre-preg material with a layer of core material above and another layer of core material listed below. This combination of one pre-preg layer and two core layers would make a 4 layer board.

The movie stack-up method, a newer innovation, would have core product as the center layer followed by layers of pre-preg and copper material developed above and listed below to form the final number of layers required by the board style, sort of like Dagwood building a sandwich. This technique enables the maker versatility in how the board layer densities are combined to satisfy the completed item density requirements by differing the number of sheets of pre-preg in each layer. As soon as the product layers are finished, 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 making printed circuit boards follows the actions below for many applications.

The process of figuring out materials, processes, and requirements to meet the client's specs for the board design based upon the Gerber file information offered with the purchase order.

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

The standard process of exposing the copper and other areas unprotected by the etch withstand film to a chemical that eliminates the vulnerable copper, leaving the protected copper pads and traces in place; newer processes use plasma/laser etching instead of chemicals to get rid of the copper material, allowing finer line meanings.

The process 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 solid board product.

The process 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. Info on hole place and size is consisted of in the drill drawing file.

The procedure of using 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 however the hole is not to be plated through. Avoid this process if possible due to the fact that it includes cost 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 safeguards against ecological damage, supplies insulation, safeguards versus solder shorts, and protects traces that run in between pads.

The process 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 take place at a later date after the elements have been positioned.

The procedure of using the markings for component designations and component outlines to the board. May be used to just the top side or to both sides if parts are installed on both top and bottom sides.

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

A visual assessment 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 techniques.

The process of looking for continuity or shorted connections on the boards by ways using a voltage in between various points on the board and determining if a current circulation takes place. Relying on the board intricacy, this procedure may need a specifically created test component and test program to incorporate with the electrical test system used by the board maker.