Quality Systems Opinions



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

The boards are likewise utilized to electrically link the required leads for each element utilizing conductive copper traces. The component pads at yahoo and connection traces are etched from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are created as single agreed copper pads and traces on one side of the board only, 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 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 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 process. A multilayer board includes a number of layers of dielectric product that has actually been fertilized with adhesives, and these layers are utilized to separate the layers of copper plating. All of these layers are aligned 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 typical four layer board style, the internal layers are typically utilized to provide 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. Really complex board styles may have a large number of layers to make the numerous connections for different voltage levels, ground connections, or for connecting the many leads on ball grid variety gadgets and other big incorporated circuit plan formats.

There are normally two kinds of product utilized to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, generally about.002 inches thick. Core product resembles an extremely thin double sided board in that it has a dielectric product, 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 style, there are two approaches used 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 product 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 technique, a more recent technology, would have core product as the center layer followed by layers of pre-preg and copper product developed above and below to form the last variety of layers needed by the board design, sort of like Dagwood constructing a sandwich. This technique enables the producer versatility in how the board layer densities are combined to fulfill the completed item density requirements by differing the number of sheets of pre-preg in each layer. As soon as the product layers are completed, the entire stack is subjected to 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 listed below for a lot of applications.

The process of identifying materials, processes, and requirements to satisfy the consumer's requirements for the board style based upon the Gerber file details offered with the order.

The procedure of transferring the Gerber file data for a layer onto an etch resist film that is placed on the conductive copper layer.

The conventional process of exposing the copper and other locations unprotected by the etch withstand film to a chemical that removes the unguarded copper, leaving the protected copper pads and traces in location; more recent processes utilize plasma/laser etching rather of chemicals to get rid of the copper product, permitting finer line meanings.

The procedure 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 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 included 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 area however the hole is not to be plated through. Avoid this process if possible since it adds expense to the completed 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 environmental damage, offers insulation, protects versus solder shorts, and secures traces that run between pads.

The procedure of covering the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering process that will happen at a later date after the parts have actually been placed.

The process of using the markings for component classifications and part outlines to the board. May be used to simply 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; likewise can be the process of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.

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