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 component leads in thru-hole applications. A board style may have all thru-hole elements 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 mount elements on the top side and surface mount components on the bottom or circuit side, or surface area mount parts 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 part pads and connection traces are etched 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 only, double sided with copper pads and traces on the top and bottom sides of the board, or multilayer designs 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 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 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 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 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 technologies.
In a normal four layer board style, the internal layers are frequently used to provide power and ground connections, such as a +5 V airplane layer and a Ground aircraft layer as the two internal layers, with all other circuit and component connections made on the leading and bottom layers of the board. Extremely complicated board designs may have a large number of layers to make the various connections for various voltage levels, ground connections, or for connecting the numerous leads on ball grid selection gadgets and other big incorporated circuit bundle formats.
There are typically 2 types 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, normally about.002 inches thick. Core product resembles an extremely thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, usually.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are 2 techniques utilized to build up the wanted variety 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 product below. This combination of one pre-preg layer and 2 core layers would make a 4 layer board.
The film stack-up method, a newer innovation, 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 variety of layers required by the board style, sort of like Dagwood constructing a sandwich. This technique permits the maker versatility in how the board layer thicknesses are integrated to satisfy the ended up product density requirements by differing the variety 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 producing printed circuit boards follows the steps listed below for a lot of applications.
The process of figuring out materials, processes, and requirements to fulfill the customer's requirements for the board style based on the Gerber file info offered with the purchase order.
The procedure of moving the Gerber file information for a layer onto an etch withstand movie that is placed on the conductive copper layer.
The traditional process of exposing the copper and other locations unprotected by the etch resist movie to a chemical that eliminates the unprotected copper, leaving the protected copper pads and traces in location; more recent procedures use 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 strong 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. Information on hole area 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 positioned in an electrically charged bath of copper.
This is needed when holes are to be drilled through a copper location but the hole is not to be plated through. Avoid this procedure if possible since it includes expense to the finished board.
The procedure of using a protective masking product, a solder mask, over the bare copper traces or over the copper that has actually had a thin layer of solder used; the solder mask safeguards against ecological damage, offers insulation, safeguards against solder shorts, and secures traces that run between pads.
The procedure of coating the pad locations with a thin layer of solder to prepare the board for the eventual wave soldering or ISO 9001 Accreditation reflow soldering process that will take place at a later date after the elements have actually been placed.
The procedure of applying the markings for element classifications and element lays out to the board. Might be used to just the top side 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 allows cutting notches or slots into the board if needed.
A visual evaluation of the boards; also can be the process of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The procedure of checking for connection or shorted connections on the boards by ways using a voltage in between numerous points on the board and determining if a current flow happens. Depending upon the board complexity, this process may need a specifically created test component and test program to integrate with the electrical test system utilized by the board manufacturer.