In electronics, printed circuit boards, or PCBs, are used to mechanically support electronic elements which have their connection leads soldered onto copper pads in surface mount applications or through rilled holes in the board and copper pads for soldering the element leads in thru-hole applications. A board design might have all thru-hole components on the top or part side, a mix of thru-hole and surface mount on the top just, a mix of thru-hole and surface install elements on the top and surface area mount parts on the bottom or circuit side, or surface area install components on the top and bottom sides of the board.
The boards are likewise utilized to electrically connect the needed leads for each element utilizing conductive copper traces. The component pads and connection traces are engraved from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are created 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 styles with copper pads and traces on the 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 surfaces as part of the board production process. A multilayer board includes a variety of layers of dielectric product that has actually been impregnated with adhesives, and these layers are used to separate ISO 9001 Certification Consultants the layers of copper plating. All 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 four layer board design, the internal layers are frequently utilized to supply power and ground connections, such as a +5 V aircraft layer and a Ground airplane layer as the 2 internal layers, with all other circuit and component connections made on the top and bottom layers of the board. Extremely intricate board styles may have a large number of layers to make the various connections for various voltage levels, ground connections, or for connecting the many leads on ball grid array gadgets and other large integrated circuit bundle formats.
There are generally two types of material utilized to build a multilayer board. Pre-preg product 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 because it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, normally.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two methods utilized to build up the preferred number of layers. The core stack-up approach, 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 listed below. This combination of one pre-preg layer and 2 core layers would make a 4 layer board.
The film stack-up technique, 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 below to form the final variety of layers needed by the board design, sort of like Dagwood constructing a sandwich. This method enables the manufacturer versatility in how the board layer densities are integrated to fulfill the finished item density requirements by differing the variety of sheets of pre-preg in each layer. When the product layers are finished, the whole 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 actions listed below for many applications.
The procedure of determining materials, procedures, and requirements to meet the client's specifications for the board design based on the Gerber file info supplied with the purchase order.
The procedure of transferring the Gerber file information for a layer onto an etch resist film that is put on the conductive copper layer.
The standard procedure of exposing the copper and other locations unprotected by the etch resist movie to a chemical that removes the unprotected copper, leaving the protected copper pads and traces in location; newer processes utilize plasma/laser etching rather of chemicals to eliminate the copper product, allowing finer line meanings.
The procedure of aligning the conductive copper and insulating dielectric layers and pressing 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 used for holes that are not to be plated through. Info on hole place 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 location but the hole is not to be plated through. Avoid this process if possible because it includes cost to the completed 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 secures versus environmental damage, supplies insulation, protects versus solder shorts, and safeguards traces that run between pads.
The process of finish the pad locations with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering procedure that will take place at a later date after the components have been placed.
The procedure of applying the markings for component designations and element describes to the board. Might be applied to just the top or to both sides if elements are installed on both top and bottom sides.
The process of separating multiple boards from a panel of identical boards; this process also allows cutting notches or slots into the board if needed.
A visual inspection of the boards; likewise can be the procedure of inspecting wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The process of checking for connection or shorted connections on the boards by methods using a voltage in between various points on the board and figuring out if an existing flow occurs. Depending upon the board intricacy, this procedure may require a specially designed test fixture and test program to incorporate with the electrical test system used by the board manufacturer.