In electronic devices, printed circuit boards, or PCBs, are utilized to mechanically support electronic components 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 element leads in thru-hole applications. A board design may have all thru-hole parts on the leading or component side, a mix of thru-hole and surface area install on the top side just, a mix of thru-hole and surface mount components on the top and surface area install elements on the bottom or circuit side, or surface area install components on the top and bottom sides of the board.
The boards are also utilized to electrically connect the required leads for each component using conductive copper traces. The element pads and connection traces are etched from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are developed as single agreed 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 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 real copper pads and connection traces on the board surface areas as part of the board production process. A multilayer board includes a variety of layers of dielectric material that has been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All of these layers are lined up 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 common four layer board design, the internal layers are frequently used to supply power and ground connections, such as a +5 V airplane layer and a Ground aircraft layer as the 2 internal layers, with all other circuit and part connections made on the top and bottom layers of the board. Extremely complicated board styles might have a a great deal of layers to make the various connections for various voltage levels, ground connections, or for connecting the numerous leads on ball grid range devices and other large integrated circuit package formats.
There are normally 2 kinds of product used to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, usually about.002 inches thick. Core material resembles a very thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, typically.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are two approaches used to build up the preferred number of layers. The core stack-up technique, which is an older technology, utilizes a center layer of pre-preg material with a layer of core material above and another layer of core product 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 product as the center layer followed by layers of pre-preg and copper product built up above and listed below to form the final number of layers required by the board style, sort of like Dagwood developing a sandwich. This technique permits the maker versatility in how the board layer thicknesses are integrated to satisfy the finished item density requirements by varying the variety of sheets of pre-preg in each layer. As soon as the product layers are finished, 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 manufacturing printed circuit boards follows the steps listed below for many applications.
The process of figuring out products, procedures, and requirements to satisfy the consumer's requirements for the board style based upon the Gerber file info supplied with the purchase order.
The process of transferring the Gerber file data for a layer onto an etch withstand movie that is placed on the conductive copper layer.
The conventional procedure of exposing the copper and other locations unprotected by the etch withstand movie to a chemical that removes the vulnerable copper, leaving the protected copper pads and traces in place; newer processes utilize plasma/laser etching rather of chemicals to eliminate the copper product, allowing finer line definitions.
The procedure 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 material.
The procedure of drilling all the holes for plated through applications; a 2nd drilling procedure is utilized for holes that are not to be plated through. Info on hole area and size is contained 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 put in an electrically charged bath of copper.
This is required when holes are to be drilled through a copper location however the hole is not to be plated through. Prevent this process if possible due to the fact that it includes expense to the ended up board.
The process 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 applied; the solder mask protects against ecological damage, supplies insulation, secures against solder shorts, and secures traces that run in between pads.
The process of finish the pad areas 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 parts have been placed.
The process of using the markings for element classifications and element details to the board. May 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 multiple boards from a panel of similar boards; this process also allows cutting notches or slots into the board if needed.
A visual examination 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 process of checking for continuity or shorted connections on the boards by means applying a voltage in between various points on the board and determining if a present circulation occurs. Relying on the board intricacy, this procedure may need a specifically designed test component and test program to incorporate with the electrical test system utilized by the board producer.