QM Systems - Their Structure and Benefits

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

The boards are likewise used to electrically link the needed leads for each component using conductive copper traces. The element pads and connection traces are etched from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are designed as single sided with 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 styles 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 consist of a core dielectric product, such as FR-4 epoxy fiberglass, with copper plating on one or both sides. This copper plating is etched away to form the real copper pads and connection traces on the board surface areas as part of the board production process. A multilayer board includes a variety of layers of dielectric material that ISO 9001 consultants has been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All these layers are aligned 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 4 layer board style, the internal layers are frequently utilized to provide power and ground connections, such as a +5 V plane layer and a Ground airplane layer as the two internal layers, with all other circuit and part connections made on the top and bottom layers of the board. Really intricate 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 array devices and other large integrated circuit package formats.

There are usually 2 kinds 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 form, typically about.002 inches thick. Core material is similar to an extremely thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, usually.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are two approaches used to develop the wanted number of layers. The core stack-up approach, which is an older technology, utilizes a center layer of pre-preg product 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 approach, a newer innovation, 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 final number of layers needed by the board design, sort of like Dagwood developing a sandwich. This method permits the producer flexibility in how the board layer densities are combined to meet the finished item density requirements by differing the number of sheets of pre-preg in each layer. Once the material layers are finished, the entire stack undergoes 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 process of producing printed circuit boards follows the steps below for many applications.

The process of figuring out products, procedures, and requirements to fulfill the customer's specifications for the board design based on the Gerber file information offered with the order.

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

The conventional procedure of exposing the copper and other areas unprotected by the etch withstand movie to a chemical that removes the vulnerable copper, leaving the protected copper pads and traces in place; more recent processes utilize plasma/laser etching rather of chemicals to remove the copper material, permitting finer line definitions.

The process of aligning 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 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. Information on hole area and size is contained 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 needed when holes are to be drilled through a copper area but the hole is not to be plated through. Avoid this procedure if possible due to the fact that it adds expense to the ended up board.

The procedure 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 versus environmental damage, offers insulation, protects versus solder shorts, and safeguards traces that run in between pads.

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

The process of applying the markings for element classifications and element lays out to the board. May be applied to just the top or to both sides if parts are mounted on both top and bottom sides.

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

A visual inspection of the boards; likewise can be the procedure of inspecting wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.

The process of looking for connection or shorted connections on the boards by ways applying a voltage in between various points on the board and identifying if a current flow takes place. Depending upon the board complexity, this process might require a specifically created test fixture and test program to integrate with the electrical test system used by the board producer.