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 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 components on the leading or element side, a mix of thru-hole and surface area mount on the top side only, a mix of thru-hole and surface install components on the top side and surface mount elements on the bottom or circuit side, or surface mount elements on the top and bottom sides of the board.
The boards are also utilized to electrically link the required leads for each element utilizing conductive copper traces. The component 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 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 material, such as FR-4 epoxy fiberglass, with copper plating on one or both sides. This copper plating is engraved 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 number of layers of dielectric material that has been fertilized with adhesives, and these layers are utilized to separate the layers of copper plating. All these layers are lined up and after that bonded into a single board structure under heat and ISO 9001 pressure. Multilayer boards with 48 or more layers can be produced with today's technologies.
In a typical 4 layer board design, the internal layers are frequently used to offer power and ground connections, such as a +5 V plane layer and a Ground aircraft layer as the 2 internal layers, with all other circuit and component connections made on the leading and bottom layers of the board. Really complex board styles might have a a great deal of layers to make the numerous connections for different voltage levels, ground connections, or for linking the many leads on ball grid range gadgets and other large integrated circuit bundle formats.
There are typically two types of product utilized to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, typically about.002 inches thick. Core material is similar to a really thin double sided board because it has a dielectric product, 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 design, there are two approaches utilized to build up the wanted number of layers. The core stack-up approach, which is an older technology, uses a center layer of pre-preg product with a layer of core product above and another layer of core product below. This mix of one pre-preg layer and two core layers would make a 4 layer board.
The film stack-up method, a newer innovation, would have core product as the center layer followed by layers of pre-preg and copper product developed above and listed below to form the last number of layers required by the board design, sort of like Dagwood constructing a sandwich. This method permits the producer flexibility in how the board layer thicknesses are combined to meet the finished product density requirements by differing the number of sheets of pre-preg in each layer. As soon as the material layers are finished, the entire 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 below for the majority of applications.
The process of determining materials, processes, and requirements to fulfill the customer's requirements for the board style based upon the Gerber file information offered with the order.
The procedure of transferring the Gerber file data for a layer onto an etch resist film that is placed on the conductive copper layer.
The traditional procedure of exposing the copper and other locations unprotected by the etch withstand film to a chemical that removes the unguarded copper, leaving the safeguarded copper pads and traces in location; more recent processes use plasma/laser etching instead of chemicals to eliminate the copper material, permitting finer line meanings.
The process of lining up the conductive copper and insulating dielectric layers and pressing them under heat to activate the adhesive in the dielectric layers to form a solid board material.
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. Details on hole place and size is consisted of 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 put 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. Avoid this process if possible since it includes 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 applied; the solder mask safeguards against ecological damage, supplies insulation, secures versus solder shorts, and protects 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 process that will happen at a later date after the elements have actually been placed.
The process of applying the markings for element designations and part details to the board. Might be used to simply the top or to both sides if components are installed on both leading and bottom sides.
The process of separating several boards from a panel of identical boards; this procedure also enables cutting notches or slots into the board if needed.
A visual evaluation of the boards; also can be the process of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.
The procedure of looking for connection or shorted connections on the boards by ways using a voltage in between different points on the board and identifying if a present circulation happens. Depending upon the board intricacy, this procedure may require a specifically designed test fixture and test program to incorporate with the electrical test system utilized by the board manufacturer.