Quality Systems Synopsis



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

The boards are likewise utilized to electrically link the needed leads for each part using conductive copper traces. The component pads and connection traces are etched from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are created 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 variety 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 etched away to form the real copper pads and connection traces on the board surfaces as part of the board manufacturing process. A multilayer board includes a variety of layers of dielectric product that has been impregnated 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 typical 4 layer board design, the internal layers are typically used to supply power and ground connections, such as a +5 V aircraft layer and a Ground airplane layer as the two internal layers, with all other circuit and element connections made on the top and bottom layers of the board. Really complicated board styles may have a large number of layers to make the numerous connections for various voltage levels, ground connections, or for linking the many leads on ball grid array devices and other large incorporated circuit bundle formats.

There are generally 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 type, generally about.002 inches thick. Core material resembles a very thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, generally.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are 2 techniques utilized to develop the desired variety of layers. The core stack-up technique, which is an older innovation, utilizes a center layer of pre-preg product with a layer of core material 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 film 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 last variety of layers required by the board design, sort of like Dagwood building a sandwich. This method permits the manufacturer versatility in how the board layer densities are combined to satisfy the completed product thickness requirements by differing the variety of sheets of pre-preg in each layer. When the product 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 listed below for a lot of applications.

The process of identifying materials, procedures, and requirements to satisfy the consumer's specs for the board design based on the Gerber file information supplied with the purchase order.

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

The conventional procedure of exposing the copper and other areas agree with unprotected by the etch withstand movie to a chemical that eliminates the unprotected copper, leaving the safeguarded copper pads and traces in place; newer procedures utilize plasma/laser etching instead of chemicals to remove the copper product, permitting 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 strong board product.

The process of drilling all of the holes for plated through applications; a second drilling procedure is used for holes that are not to be plated through. Info on hole place 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 however the hole is not to be plated through. Avoid this procedure if possible since it includes expense 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 protects versus ecological damage, offers insulation, protects versus solder shorts, and safeguards 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 take place at a later date after the parts have actually been put.

The process of using the markings for part designations and element 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 process of separating several boards from a panel of similar boards; this procedure likewise allows cutting notches or slots into the board if needed.

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 techniques.

The process of looking for connection or shorted connections on the boards by means applying a voltage between different points on the board and identifying if a present circulation occurs. Depending upon the board intricacy, this process may require a specially created test component and test program to incorporate with the electrical test system utilized by the board maker.