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 design may have all thru-hole elements on the ISO 9001 top or element side, a mix of thru-hole and surface install on the top just, a mix of thru-hole and surface mount parts on the top side and surface area install components on the bottom or circuit side, or surface area mount elements on the top and bottom sides of the board.
The boards are likewise utilized to electrically connect the needed leads for each element using conductive copper traces. The component 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 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 material, 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 process. A multilayer board includes a variety of layers of dielectric material that has been fertilized with adhesives, and these layers are used 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 technologies.
In a normal 4 layer board style, the internal layers are often utilized 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 part connections made on the leading and bottom layers of the board. Really complicated board styles may have a large number of layers to make the various connections for different voltage levels, ground connections, or for connecting the numerous leads on ball grid selection gadgets and other large incorporated circuit bundle formats.
There are typically two types of material used to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, normally about.002 inches thick. Core product resembles an extremely thin double sided board because it has a dielectric product, 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 2 methods utilized to build up the preferred variety of layers. The core stack-up approach, which is an older innovation, uses a center layer of pre-preg product with a layer of core product above and another layer of core material listed below. This combination of one pre-preg layer and 2 core layers would make a 4 layer board.
The film stack-up technique, a newer 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 last number of layers needed by the board design, sort of like Dagwood building a sandwich. This method allows the manufacturer versatility in how the board layer thicknesses are combined to satisfy the finished product density requirements by varying the number of sheets of pre-preg in each layer. Once the material layers are completed, the entire 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 manufacturing printed circuit boards follows the steps listed below for most applications.
The process of figuring out materials, procedures, and requirements to satisfy the client's requirements for the board style based upon the Gerber file details offered with the purchase order.
The process of transferring the Gerber file data for a layer onto an etch resist film that is put on the conductive copper layer.
The conventional process of exposing the copper and other locations unprotected by the etch resist movie to a chemical that removes the unprotected copper, leaving the secured copper pads and traces in place; newer procedures use plasma/laser etching rather of chemicals to get rid of the copper material, permitting finer line definitions.
The procedure of lining up 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 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. Info on hole location and size is consisted of 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 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. Prevent this procedure if possible since it adds expense to the completed board.
The process 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 used; the solder mask secures versus ecological damage, offers insulation, protects versus solder shorts, and safeguards traces that run in between pads.
The process of coating the pad locations with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering procedure that will occur at a later date after the parts have been positioned.
The procedure of using the markings for component designations and element outlines 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 procedure of separating several boards from a panel of similar boards; this process also permits cutting notches or slots into the board if required.
A visual examination of the boards; likewise can be the procedure of inspecting 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 using a voltage in between numerous points on the board and determining if an existing circulation happens. Relying on the board complexity, this process may require a specially developed test component and test program to incorporate with the electrical test system used by the board manufacturer.