TQM Systems Update

Apr 15, 2019



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 element leads in thru-hole applications. A board style might have all thru-hole components on the leading or element side, a mix of thru-hole and surface area install on the top only, a mix of thru-hole and surface install parts on the top side and surface mount elements on the bottom or circuit side, or surface area install components on the leading and bottom sides of the board.

The boards are likewise used to electrically link the required leads for each element utilizing conductive copper traces. The part pads and connection traces are engraved from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are designed as single agreed copper pads and traces on one side of the board just, double agreed copper pads and traces on the top 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 material, 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 production procedure. A multilayer board consists of a number of layers of dielectric product that has actually been fertilized with adhesives, and these layers are utilized to separate the layers of copper plating. All these layers are lined up 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 normal four layer board design, the internal layers are often used to provide power and ground connections, such as a +5 V airplane layer and a Ground plane layer as the two internal layers, with all other circuit and element connections made on the top and bottom layers of the board. Very complicated board designs may have a a great deal of layers to make the numerous connections for different voltage levels, ground connections, or for connecting the many leads on ball grid range devices and other big incorporated circuit bundle formats.

There are usually 2 kinds of product utilized to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet kind, normally about.002 inches thick. Core material resembles a very thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, usually.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are two approaches utilized to develop the preferred 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 product above and another layer of core product listed below. This combination 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 product developed above and listed below to form the last variety of layers needed by the board style, sort of like Dagwood constructing a sandwich. This method permits the manufacturer versatility in how the board layer densities are combined to meet the finished product density requirements by differing the number of sheets of pre-preg in each layer. When the product layers are completed, the whole stack goes through 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 actions below for a lot of applications.

The process of identifying products, processes, and requirements to satisfy the client's requirements for the board style based upon the Gerber file info offered with the purchase order.

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

The traditional procedure of exposing the copper and other areas unprotected by the etch withstand film to a chemical that removes the unprotected 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 product, allowing finer line meanings.

The procedure of aligning the conductive copper and insulating dielectric layers and pushing them under heat to trigger the adhesive in the dielectric layers to form a solid board material.

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. Details on hole location and size is consisted of in the drill drawing file.

The process of using 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 since it adds cost to the ended up board.

The process 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 ISO 9001 consultants solder mask safeguards against ecological damage, supplies insulation, safeguards versus solder shorts, and safeguards traces that run in between pads.

The process of finishing 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 been put.

The procedure of applying the markings for component designations and component outlines to the board. May be used to just the top side or to both sides if components are installed on both leading and bottom sides.

The process of separating multiple boards from a panel of identical boards; this procedure also enables cutting notches or slots into the board if required.

A visual evaluation 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 methods.

The process of looking for connection or shorted connections on the boards by methods using a voltage between different points on the board and figuring out if a current circulation takes place. Depending upon the board intricacy, this procedure might require a specifically designed test fixture and test program to incorporate with the electrical test system utilized by the board manufacturer.