TQM Systems Review



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

The boards are also utilized to electrically connect the required leads for each element using conductive copper traces. The part 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 just, double sided with copper pads and traces on the leading and bottom sides of the board, or multilayer styles 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 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 procedure. A multilayer board includes a number of layers of dielectric material that has actually been fertilized with adhesives, and these layers are utilized to separate the layers of copper plating. All these layers are aligned 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 normal 4 layer board design, the internal layers are typically used to offer 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 element connections made on the leading and bottom layers of the board. Very complex board styles may have a large number of layers to make the different connections for different voltage levels, ground connections, or for linking the many leads on ball grid variety devices and other big incorporated circuit plan formats.

There are usually 2 kinds of product used to build 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 material resembles an extremely thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, usually.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are 2 techniques used to develop the preferred number of layers. The core stack-up method, which is an older innovation, uses 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 technique, a newer technology, would have core product as the center layer followed by layers of pre-preg and copper product developed above and listed below to form the last variety of layers required by the board design, sort of like Dagwood constructing a sandwich. This method allows the producer versatility in how the board layer thicknesses are integrated to fulfill the completed product thickness requirements by varying the variety of sheets of pre-preg in each layer. When the material 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 manufacturing printed circuit boards follows the steps below for a lot of applications.

The procedure of identifying products, processes, and requirements to satisfy the consumer's requirements for the board design based on the Gerber file information provided with the purchase order.

The procedure of transferring the Gerber file data for a layer onto an etch withstand film that is placed 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 unprotected copper, leaving the safeguarded copper pads and traces in place; newer procedures utilize plasma/laser etching rather of chemicals to eliminate 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 activate the adhesive in the dielectric layers to form a strong board product.

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 placed in an electrically charged bath of copper.

This is needed when holes are to be drilled through a copper location but the hole is not to be plated through. Avoid this process if possible since it includes 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 actually had a thin layer of solder applied; the solder mask protects versus environmental damage, offers insulation, safeguards against solder shorts, and safeguards traces that run 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 occur at a later date after the parts have actually been positioned.

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

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

A visual inspection 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 checking for continuity or shorted connections on the boards by methods applying a voltage in between numerous points on the board and figuring out if a present circulation occurs. Depending upon the board intricacy, this process may need a specifically created test component and test program to ISO 9001 Accreditation incorporate with the electrical test system used by the board manufacturer.