ISO 9001 Certification Consultants
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 element leads in thru-hole applications. A board style may have all thru-hole elements on the leading or component side, a mix of thru-hole and surface mount on the top only, a mix of thru-hole and surface install elements on the top side and surface mount elements on the bottom or circuit side, or surface mount elements on the leading and bottom sides of the board.
The boards are also used to electrically connect the required leads for each component using conductive copper traces. The element 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 just, 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 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 etched away to form the real copper pads and connection traces on the board surfaces as part of the board manufacturing procedure. A multilayer board consists of a variety of layers of dielectric product that has actually been impregnated with adhesives, and these layers are utilized to separate the layers of copper plating. All these layers are aligned 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 four layer board style, the internal layers are frequently used to offer power and ground connections, such as a +5 V aircraft layer and a Ground plane layer as the 2 internal layers, with all other circuit and element connections made on the top and bottom layers of the board. Extremely complex board styles might have a a great deal of layers to make the various connections for various voltage levels, ground connections, or for connecting the lots of leads on ball grid variety devices and other big incorporated circuit package formats.
There are generally two kinds of material used to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, generally about.002 inches thick. Core product resembles a really thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, generally.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are two approaches utilized to develop the wanted number 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 material below. This combination of one pre-preg layer and 2 core layers would make a 4 layer board.
The movie stack-up technique, a more recent innovation, would have core product as the center layer followed by layers of pre-preg and copper material developed above and listed below to form the final variety of layers needed by the board style, sort of like Dagwood developing a sandwich. This technique enables the maker versatility in how the board layer densities are integrated to fulfill the completed product density requirements by varying the variety of sheets of pre-preg in each layer. Once 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 process of producing printed circuit boards follows the steps below for many applications.
The process of identifying materials, procedures, and requirements to fulfill the customer's requirements for the board design based on the Gerber file information offered with the order.
The process of moving 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 areas unprotected by the etch withstand film to a chemical that gets rid of the vulnerable copper, leaving the safeguarded copper pads and traces in location; more recent procedures use plasma/laser etching instead of chemicals to get rid of the copper product, 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 2nd drilling process is used for holes that are not to be plated through. Details on hole location 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 placed in an electrically charged bath of copper.
This is required when holes are to be drilled through a copper area however the hole is not to be plated through. Prevent this procedure if possible due to the fact that it includes expense to the completed board.
The procedure of using a protective masking product, a solder mask, over the bare copper traces or over the copper that has had a thin layer of solder applied; the solder mask protects versus ecological damage, offers insulation, safeguards against solder shorts, and safeguards traces that run in between pads.
The procedure of finish the pad locations with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering procedure that will happen at a later date after the components have been placed.
The process of applying the markings for element classifications and component describes to the board. May be applied to just the top side or to both sides if components are mounted on both leading and bottom sides.
The procedure of separating numerous boards from a panel of identical boards; this process likewise enables cutting notches or slots into the board if needed.
A visual evaluation 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 procedure of checking for continuity or shorted connections on the boards by ways applying a voltage in between different points on the board and figuring out if a current flow takes place. Relying on the board intricacy, this process might require a specially created test fixture and test program to integrate with the electrical test system used by the board maker.