Modern Quality System Features



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

The boards are also utilized to electrically connect the needed leads for each part 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 developed as single agreed 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 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 real copper pads and connection traces on the board surface areas as part of the board manufacturing procedure. A multilayer board consists of a number of layers of dielectric material that has actually been fertilized with adhesives, and these layers are used to separate the layers of copper plating. All of these layers are lined up 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 airplane layer and a Ground airplane layer as the two internal layers, with all other circuit and part connections made on the leading and bottom layers of the board. Very complex board styles might have a large number of layers to make the various connections for various voltage levels, ground connections, or for linking the many leads on ball grid array gadgets and other big integrated circuit plan formats.

There are typically two kinds of product utilized to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet kind, generally about.002 inches thick. Core product is similar to a really thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, usually.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two techniques utilized to develop the preferred variety of layers. The core stack-up technique, 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 mix of one pre-preg layer and two core layers would make a 4 layer board.

The movie stack-up approach, 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 listed below to form the final variety of layers needed by the board style, sort of like Dagwood developing a sandwich. This method allows the manufacturer versatility in how the board layer thicknesses are integrated to satisfy the ended up item thickness requirements by differing the variety of sheets of pre-preg in each layer. As soon as the material layers are finished, the whole stack undergoes 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 listed below for the majority of applications.

The procedure of determining materials, procedures, and requirements to meet the consumer's specs for the board style based upon the Gerber file info provided with the purchase order.

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

The traditional procedure of exposing the copper and other areas unprotected by the etch withstand movie to a chemical that removes the vulnerable copper, leaving the secured copper pads and traces in location; newer procedures utilize plasma/laser etching instead of chemicals to get rid of the copper material, allowing finer line meanings.

The procedure 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 material.

The process of drilling all of the holes for plated through applications; a 2nd drilling process is utilized for holes that are not to be plated through. Details on hole place and size is contained in the drill drawing file.

The process 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 needed when holes are to be drilled through a copper area however the hole is not to be plated through. Avoid this process if possible due to the fact that it includes cost to the completed board.

The process of using a protective masking product, a solder mask, over the bare copper traces or over the copper that has actually had a thin layer of Reference site solder applied; the solder mask protects versus ecological damage, provides insulation, safeguards against solder shorts, and safeguards traces that run between pads.

The process of finish the pad locations with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering procedure that will happen at a later date after the elements have been placed.

The procedure of applying the markings for component designations and component outlines to the board. May be applied to simply the top or to both sides if elements are installed on both leading and bottom sides.

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

A visual examination of the boards; likewise can be the procedure of checking 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 methods applying a voltage in between numerous points on the board and identifying if an existing flow happens. Relying on the board intricacy, this procedure may require a specifically created test fixture and test program to integrate with the electrical test system used by the board manufacturer.