In electronic devices, printed circuit boards, or PCBs, are used to mechanically support electronic parts which have their connection leads soldered onto copper pads in surface area install 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 parts on the top or component side, a mix of thru-hole and surface area install on the top only, a mix of thru-hole and surface area mount elements on the top side and surface area install elements on the bottom or circuit side, or surface area install parts on the top and bottom sides of the board.
The boards are likewise used to electrically connect the needed leads for each component using 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 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 variety 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 actual copper pads and connection traces on the board surfaces as part of the board production procedure. A multilayer board includes a variety of layers of dielectric product that has been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All these layers are aligned 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 ISO 9001 Accreditation Consultants innovations.
In a normal four layer board design, the internal layers are typically utilized to offer power and ground connections, such as a +5 V plane layer and a Ground plane layer as the 2 internal layers, with all other circuit and element connections made on the leading and bottom layers of the board. Very complicated board styles might have a a great deal of layers to make the numerous connections for various voltage levels, ground connections, or for linking the numerous leads on ball grid variety gadgets and other large integrated circuit package formats.
There are normally two kinds 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, usually about.002 inches thick. Core product is similar to a very thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, normally.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are 2 techniques used to develop the preferred number of layers. The core stack-up method, which is an older innovation, utilizes a center layer of pre-preg material with a layer of core material 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 movie stack-up approach, a more recent technology, would have core material as the center layer followed by layers of pre-preg and copper material built up above and below to form the last number of layers needed by the board style, sort of like Dagwood building a sandwich. This technique permits the manufacturer flexibility in how the board layer densities are combined to fulfill the completed item thickness requirements by differing the number 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 process of producing printed circuit boards follows the steps listed below for the majority of applications.
The procedure of figuring out materials, procedures, and requirements to satisfy the consumer's specs for the board style based upon the Gerber file info supplied with the purchase order.
The procedure of transferring the Gerber file information for a layer onto an etch withstand film that is placed on the conductive copper layer.
The conventional procedure of exposing the copper and other areas unprotected by the etch withstand film to a chemical that removes the unguarded copper, leaving the protected copper pads and traces in place; more recent processes use plasma/laser etching rather of chemicals to remove the copper material, enabling finer line definitions.
The process 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 product.
The procedure 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. Information on hole place and size is included 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 needed when holes are to be drilled through a copper area however the hole is not to be plated through. Prevent this procedure if possible because it adds expense 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 had a thin layer of solder used; the solder mask secures versus environmental damage, supplies insulation, safeguards versus solder shorts, and protects traces that run in 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 process that will occur at a later date after the components have actually been put.
The process of applying the markings for component classifications and element describes to the board. May be applied to simply the top side or to both sides if parts are installed on both top and bottom sides.
The procedure of separating multiple boards from a panel of similar boards; this procedure also allows 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 techniques.
The procedure of checking for continuity or shorted connections on the boards by means using a voltage in between different points on the board and determining if a current circulation happens. Depending upon the board complexity, this procedure might need a specifically created test component and test program to integrate with the electrical test system used by the board maker.