QM Systems Assessment

In electronics, printed circuit boards, or PCBs, are used to mechanically support electronic parts 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 part leads in thru-hole applications. A board style might have all thru-hole elements on the leading or component side, a mix of thru-hole and surface area install on the top side only, a mix of thru-hole and surface area mount elements on the top and surface mount components on the bottom or circuit side, or surface area mount parts on the leading and bottom sides of the board.

The boards are likewise utilized to electrically connect the required leads for each element utilizing conductive copper traces. The element pads 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 agreed 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 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 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 fertilized with adhesives, and these layers are utilized to separate the layers of copper plating. All of 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 typically used to supply power and ground connections, such as a +5 V aircraft layer and a Ground aircraft 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 might have a a great deal of layers to make the numerous connections for various voltage levels, ground connections, or for connecting the many leads on ball grid selection gadgets and other big integrated circuit bundle formats.

There are usually two types of product used to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet kind, generally 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 transferred on each side, generally.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are two techniques utilized to develop the desired number of layers. The core stack-up technique, which is an older technology, uses a center layer of pre-preg material with a layer of core material above and another layer of core product below. This mix of one pre-preg layer and 2 core layers would make a 4 layer board.

The film stack-up method, a more recent innovation, would have core material as the center layer followed by layers of pre-preg and copper product built up above and listed below to form the last variety of layers required by the board style, sort of like Dagwood developing a sandwich. This method permits the producer versatility in how the board layer thicknesses are combined to fulfill the completed item density requirements by differing the number of sheets of pre-preg in each layer. When the material layers are finished, the whole stack is subjected to 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 procedure of manufacturing printed circuit boards follows the actions below for many applications.

The procedure of determining materials, processes, and requirements to fulfill the client's requirements for the board style based on the Gerber file details provided with the order.

The process of transferring the Gerber file information for a layer onto an etch resist movie that is put on the conductive copper layer.

The standard procedure of exposing the copper and other areas unprotected by the etch withstand film to a chemical that gets rid of the vulnerable copper, leaving the More interesting details here safeguarded copper pads and traces in place; newer procedures utilize plasma/laser etching instead of chemicals to remove the copper product, enabling finer line meanings.

The process of lining up the conductive copper and insulating dielectric layers and pressing them under heat to trigger the adhesive in the dielectric layers to form a solid board material.

The process of drilling all the holes for plated through applications; a second drilling procedure is used for holes that are not to be plated through. Information on hole location 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 positioned in an electrically charged bath of copper.

This is needed when holes are to be drilled through a copper location however the hole is not to be plated through. Prevent this procedure if possible since it adds expense to the ended up board.

The procedure of applying 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 protects against ecological damage, supplies insulation, protects versus solder shorts, and secures traces that run between pads.

The procedure of coating the pad locations with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering procedure that will occur at a later date after the parts have actually been put.

The procedure of applying the markings for part designations and component lays out to the board. May be applied to just the top side or to both sides if parts are mounted on both leading and bottom sides.

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

A visual inspection of the boards; also can be the process of checking 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 between numerous points on the board and figuring out if a current flow takes place. Depending upon the board intricacy, this procedure may need a specially created test component and test program to incorporate with the electrical test system used by the board maker.