Insights Into Quality Systems



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

The boards are likewise utilized to electrically connect the needed leads for each part 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 created as single agreed copper pads and traces on one side of the board just, double agreed copper pads and traces on the leading and bottom sides of the board, or multilayer designs 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 include 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 actual copper pads and connection traces on the board surfaces as part of the board production procedure. A multilayer board consists of a variety 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 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 style, the internal layers are often used to offer 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. Extremely complex 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 range devices and other large integrated circuit package formats.

There are typically 2 types of material utilized to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, normally about.002 inches thick. Core material resembles a very thin double sided board because it has a dielectric product, such as epoxy fiberglass, with a copper layer investigate this site transferred on each side, usually.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are 2 approaches utilized to develop the wanted number of layers. The core stack-up approach, which is an older technology, utilizes a center layer of pre-preg material with a layer of core material above and another layer of core product below. This combination of one pre-preg layer and 2 core layers would make a 4 layer board.

The movie stack-up method, a more recent technology, would have core material as the center layer followed by layers of pre-preg and copper product built up above and below to form the final variety of layers required by the board design, sort of like Dagwood constructing a sandwich. This technique allows the maker flexibility in how the board layer densities are combined to meet the finished product density requirements by differing the variety of sheets of pre-preg in each layer. As soon as the product layers are finished, the whole stack goes through 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 process of manufacturing printed circuit boards follows the actions listed below for the majority of applications.

The process of determining materials, processes, and requirements to satisfy the customer's specs for the board style based on the Gerber file info offered with the purchase order.

The process of transferring the Gerber file information 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 withstand movie to a chemical that gets rid of the vulnerable copper, leaving the protected copper pads and traces in place; newer procedures use plasma/laser etching rather of chemicals to eliminate the copper material, permitting 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 strong board product.

The process of drilling all the holes for plated through applications; a second drilling process is utilized for holes that are not to be plated through. Details on hole location and size is included 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 location however the hole is not to be plated through. Prevent this process if possible because it adds cost to the completed board.

The procedure of applying 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 ecological damage, provides insulation, secures against solder shorts, and protects traces that run between pads.

The procedure of covering the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering procedure that will take place at a later date after the elements have been put.

The procedure of applying the markings for element classifications and component lays out to the board. Might be applied to simply the top or to both sides if parts are mounted on both leading and bottom sides.

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

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

The procedure of looking for connection or shorted connections on the boards by ways applying a voltage between different points on the board and identifying if a present flow occurs. Depending upon the board complexity, this procedure may need a specifically designed test fixture and test program to incorporate with the electrical test system used by the board maker.