Quality Systems Examination

In electronic devices, 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 component leads in thru-hole applications. A board style may have all thru-hole elements on the leading or component side, a mix of thru-hole and surface area mount on the top side only, a mix of thru-hole and surface area install elements on the top and surface install components on the bottom or circuit side, or surface area install parts on the top and bottom sides of the board.

The boards are also used to electrically connect the required leads for each part utilizing conductive copper traces. The part pads and connection traces are engraved 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 agreed copper pads and traces on the top and bottom sides of the board, or multilayer styles 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 real copper pads and connection traces on the board surface areas as part of the board production procedure. A multilayer board includes a number of layers of dielectric material that has been impregnated with adhesives, and these layers are utilized to separate the layers of copper plating. All of these layers are aligned then bonded into a single board structure See more under heat and pressure. Multilayer boards with 48 or more layers can be produced with today's innovations.

In a typical 4 layer board style, the internal layers are typically utilized to provide power and ground connections, such as a +5 V airplane layer and a Ground plane layer as the 2 internal layers, with all other circuit and part connections made on the top and bottom layers of the board. Really intricate board designs may have a a great deal of layers to make the different connections for various voltage levels, ground connections, or for linking the lots of leads on ball grid range devices and other big incorporated circuit plan formats.

There are usually 2 types of product utilized to construct a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet kind, typically about.002 inches thick. Core product 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 density dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two methods utilized to build up the preferred variety of layers. The core stack-up approach, which is an older technology, uses a center layer of pre-preg product with a layer of core product above and another layer of core material below. This combination of one pre-preg layer and 2 core layers would make a 4 layer board.

The movie stack-up technique, a more recent innovation, would have core material as the center layer followed by layers of pre-preg and copper material built up above and below to form the final variety of layers needed by the board design, sort of like Dagwood constructing a sandwich. This method enables the maker flexibility in how the board layer densities are combined to meet the finished product density requirements by differing the variety of sheets of pre-preg in each layer. As soon as the product layers are completed, the entire stack goes through 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 producing printed circuit boards follows the actions below for a lot of applications.

The process of determining materials, processes, and requirements to satisfy the customer's requirements for the board style based on the Gerber file information provided with the purchase order.

The procedure of moving the Gerber file information for a layer onto an etch withstand movie that is placed on the conductive copper layer.

The standard process of exposing the copper and other areas unprotected by the etch resist movie to a chemical that removes the vulnerable copper, leaving the protected copper pads and traces in location; more recent processes use plasma/laser etching instead of chemicals to remove the copper material, permitting finer line meanings.

The procedure 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 strong board product.

The procedure of drilling all the holes for plated through applications; a second drilling procedure is utilized for holes that are not to be plated through. Details on hole place 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 positioned 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. Avoid this procedure if possible since it adds cost to the completed board.

The process of applying a protective masking material, 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 versus ecological damage, supplies insulation, protects versus solder shorts, and protects traces that run between pads.

The procedure of finishing the pad areas 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 placed.

The procedure of using the markings for part designations and part lays out to the board. May be applied to simply the top or to both sides if parts are installed on both leading and bottom sides.

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

A visual assessment of the boards; likewise can be the process 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 using a voltage in between numerous points on the board and determining if a present circulation occurs. Depending upon the board intricacy, this process may need a specifically created test component and test program to incorporate with the electrical test system used by the board manufacturer.