In electronics, printed circuit boards, or PCBs, are utilized to mechanically support electronic parts which have their connection leads soldered onto copper pads in surface install 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 components on the top or element side, a mix of thru-hole and surface area mount on the top side just, a mix of thru-hole and surface area mount elements on the top side and surface mount parts on the bottom or circuit side, or surface area mount components on the top and bottom sides of the board.
The boards are also utilized to electrically link the required leads for each component using conductive copper traces. The component pads and connection traces are engraved from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are designed as single sided with copper pads and traces on one side of the board only, double agreed copper pads and traces on the leading 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 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 process. A multilayer board consists of 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 of these layers are lined up and after that 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 used to offer power and ground connections, such as a +5 V aircraft 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 complex board designs might have a large number of layers to make the different connections for various voltage levels, ground connections, or for linking the many leads on ball grid variety devices and other large integrated circuit plan formats.
There are usually two types of product used to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, usually about.002 inches thick. Core material is similar to a very thin double sided board because it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, generally.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are two approaches used to develop the wanted variety of layers. The core stack-up approach, which is an older innovation, utilizes a center layer of pre-preg material with a layer of core product above and another layer of core product listed below. This mix of one pre-preg layer and 2 core layers would make a 4 layer board.
The movie stack-up technique, a more recent technology, would have core material as the center layer followed by layers of pre-preg and copper product built up above and listed below to form the last number of layers needed by the board style, sort of like Dagwood developing a sandwich. This approach enables the producer flexibility in how the board layer thicknesses are combined to satisfy the completed product density requirements by differing the number of sheets of pre-preg in each layer. Once the product layers are finished, the entire 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 manufacturing printed circuit boards follows the steps listed below for many applications.
The procedure of identifying materials, processes, and requirements to meet the client's specifications for the board design based on the Gerber file details supplied 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 traditional process of exposing the copper and other locations unprotected by the etch resist movie to a chemical that removes the unguarded copper, leaving the protected copper pads and traces in place; newer procedures utilize plasma/laser etching instead of chemicals to remove the copper material, allowing finer line definitions.
The process of aligning the conductive copper and insulating dielectric layers and pressing them under heat to trigger the adhesive in the dielectric layers to form a solid board product.
The process of drilling all the holes for plated through applications; a second drilling process is utilized for holes that are not to be plated through. Details on hole place and size is included 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 placed in an electrically charged bath of copper.
This is required when holes are to be drilled through a copper area but the hole is not to be plated through. Prevent this process if possible because it adds expense to the ended up 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 applied; the solder mask secures against environmental damage, offers insulation, secures against solder shorts, and secures traces that run between pads.
The procedure of finish the pad areas with a thin layer of solder See more to prepare the board for the ultimate wave soldering or reflow soldering procedure that will happen at a later date after the parts have actually been placed.
The procedure of using the markings for part designations and part outlines to the board. May be used to just the top or to both sides if components are installed on both leading and bottom sides.
The procedure of separating multiple boards from a panel of similar boards; this procedure also permits cutting notches or slots into the board if needed.
A visual inspection 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 checking for continuity or shorted connections on the boards by means using a voltage in between numerous points on the board and determining if a present flow occurs. Relying on the board complexity, this procedure might require a specifically designed test component and test program to incorporate with the electrical test system utilized by the board maker.