A Peek Into Quality Systems

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

The boards are also used to electrically link the required leads for each component using conductive copper traces. The component pads and connection traces are engraved 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 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 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 surface areas as part of the board production process. A multilayer board consists of a number of layers of dielectric material that has actually been impregnated with adhesives, and these layers are utilized to separate the layers of copper plating. All these layers are aligned and then bonded into a single board structure under heat and pressure. Multilayer boards with 48 or more layers can be produced with today's innovations.

In a common 4 layer board design, the internal layers are frequently used to supply power and ground connections, such as a +5 V plane layer and a Ground plane layer as the two internal layers, with all other circuit and component connections made on the leading and bottom layers of the board. Extremely complicated board styles might have a large number of layers to make the different connections for various voltage levels, ground connections, or for connecting the lots of leads on ball grid selection gadgets and other large integrated circuit plan formats.

There are generally two types of product utilized 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 product resembles a really 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 product with 1 ounce copper layer on each side. In a multilayer board style, 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 material with a layer of core material above and another layer of core material below. This mix of one pre-preg layer and 2 core layers would make a 4 layer board.

The film stack-up approach, a more recent technology, would have core material as the center layer followed by layers of pre-preg and copper material developed above and listed below to form the last variety of layers needed by the board design, sort of like Dagwood building a sandwich. This method enables the producer versatility in how the board layer densities are combined to fulfill 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 whole 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 manufacturing printed circuit boards follows the steps below for many applications.

The procedure of identifying materials, processes, and requirements to meet the consumer's specifications for the board style based on the Gerber file information supplied with the 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 film to a chemical that eliminates the vulnerable copper, leaving the secured copper pads and traces in place; more recent processes use plasma/laser etching instead of chemicals to eliminate the copper material, enabling finer line definitions.

The process of lining up the conductive copper and insulating dielectric layers and pushing them under heat to activate the adhesive in the dielectric layers to form a strong board product.

The procedure of drilling all the holes for plated through applications; a 2nd drilling procedure is used for holes that are not to be plated through. Details on hole area and size is contained 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 area but the hole is not to be plated through. Prevent this process if possible because it adds cost to the ended up board.

The process of applying a protective masking product, a solder mask, over the bare copper traces or over the copper that has had a thin layer of solder used; the solder mask protects versus ecological damage, supplies insulation, safeguards versus solder shorts, and safeguards traces that run between pads.

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

The procedure of using the markings for part classifications and component details to the board. Might be applied to just 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 identical boards; this process also enables cutting notches or slots into the board if needed.

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

The process of looking for connection or shorted connections on the boards by means using a voltage in between numerous points on the board and figuring out if a present circulation happens. Depending upon the board complexity, this procedure might need a specifically created test fixture and test program to integrate with the electrical test system used by the board maker.