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 part leads in thru-hole applications. A board design might have all thru-hole components on the leading or part side, a mix of thru-hole and surface install on the top side only, a mix of thru-hole and surface install components on the top side and surface install parts on the bottom or circuit side, or surface area mount elements on the top and bottom sides of the board.
The boards are also used to electrically connect the required leads for each component utilizing 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 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 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 surface areas as part of the board manufacturing process. A multilayer board includes a number of layers of dielectric product that has actually been fertilized with adhesives, and these layers are utilized 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 typical four layer board design, the internal layers are typically utilized to supply power and ground connections, such as a +5 V airplane layer and a Ground airplane layer as the two internal layers, with all other circuit and element connections made on the top and bottom layers of the board. Extremely intricate board designs may have a large number of layers to make the different connections for various voltage levels, ground connections, or for connecting the many leads on ball grid array devices and other big incorporated circuit bundle formats.
There are typically 2 types 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, normally about.002 inches thick. Core material is similar to an extremely thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, usually.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two methods used to build up the wanted number of layers. The core stack-up technique, which is an older innovation, uses a center layer of pre-preg product with a layer of core material above and another layer of core product below. This mix of one pre-preg layer and 2 core layers would make a 4 layer board.
The film stack-up approach, a newer 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 variety of layers required by the board style, sort of like Dagwood constructing a sandwich. This approach enables the producer versatility in how the board layer densities are integrated to satisfy the completed product thickness requirements by differing the number of sheets of pre-preg in each layer. When the material layers are completed, the whole stack is subjected to heat and pressure that triggers 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 a lot of applications.
The process of determining products, procedures, and requirements to fulfill the customer's requirements for the board style based upon the Gerber file details offered with the purchase order.
The process of moving the Gerber file information for a layer onto an etch resist film that is put 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 gets rid of the unguarded copper, leaving the protected copper pads and traces in location; more recent procedures utilize 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 pushing them under heat to activate the adhesive in the dielectric layers to form a strong board material.
The process of drilling all the holes for plated through applications; a 2nd drilling process is utilized for holes original site that are not to be plated through. Information on hole location and size is contained 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 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. Avoid this process if possible because it includes cost to the ended up board.
The procedure of applying 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 protects versus ecological damage, provides insulation, protects versus solder shorts, and protects traces that run between pads.
The procedure of finishing the pad locations with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering procedure that will take place at a later date after the parts have been put.
The procedure of applying the markings for component classifications and component details to the board. Might be used to just the top side or to both sides if components are mounted on both top and bottom sides.
The process of separating numerous boards from a panel of identical boards; this process likewise allows cutting notches or slots into the board if needed.
A visual inspection of the boards; also can be the procedure of checking 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 means using a voltage between numerous points on the board and determining if a current flow happens. Relying on the board intricacy, this process might require a specifically created test component and test program to integrate with the electrical test system used by the board maker.