In electronic devices, printed circuit boards, or PCBs, are used to mechanically support electronic elements 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 style may have all thru-hole components on the leading or element side, a mix of thru-hole and surface install on the top side only, a mix of thru-hole and surface mount elements on the top side and surface area mount elements on the bottom or circuit side, or surface area mount elements on the top and bottom sides of the board.
The boards are likewise used to electrically link the needed leads for each element 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 designed as single agreed copper pads and traces on one side of the board just, 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 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 production process. A multilayer board consists of a variety of layers of dielectric product that has been impregnated with adhesives, and these layers are utilized to separate the layers of copper plating. All these layers are aligned then bonded into a single board structure under heat and pressure. Multilayer boards with 48 or more layers can be produced with today's innovations.
In a typical four layer board design, the internal layers are typically utilized to offer power and ground connections, such as a +5 V plane layer and a Ground airplane layer as the two 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 different connections for different voltage levels, ground connections, or for linking the numerous leads on ball grid array gadgets and other large integrated circuit plan formats.
There are usually two types of material utilized to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet form, typically 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 deposited on each side, normally.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are two techniques used to build up the wanted variety 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 product above and another layer of core material below. This combination of one pre-preg layer and 2 core layers would make a 4 layer board.
The film stack-up method, a more recent innovation, 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 final number of layers needed by the board design, sort of like Dagwood constructing a sandwich. This technique permits the producer versatility in how the board layer densities are combined to meet the ended up item density requirements by varying the variety of sheets of pre-preg in each layer. As soon as the product layers are completed, the entire stack undergoes 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 actions listed below for many applications.
The procedure of figuring out materials, processes, and requirements to fulfill the consumer's specifications for the board design 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 film that is placed on the conductive copper layer.
The standard process of exposing the copper and other locations unprotected by the etch withstand film to a chemical that removes the unguarded copper, leaving the protected copper pads and traces in location; more recent procedures use plasma/laser etching rather of chemicals to remove the copper material, permitting finer line meanings.
The procedure of lining up the conductive copper and insulating dielectric layers and pushing them under heat to trigger the adhesive in the dielectric layers to form a strong board material.
The procedure of drilling all the holes for plated through applications; a 2nd drilling process is used for holes that are not to be plated through. Details on hole area and size is consisted of in the drill drawing file.
The procedure of applying copper plating to the pads, traces, and drilled through holes that are to be plated through; boards are positioned in an electrically charged bath of copper.
This is needed when holes are to be drilled through a copper area but the hole is not to be plated through. Avoid this process if possible since it adds cost to the finished board.
The procedure of applying 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 protects against environmental damage, supplies insulation, protects against solder shorts, and protects traces that run in between pads.
The process of finishing the pad areas with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering procedure that will occur at a later date after the elements have been put.
The procedure of using the markings for element designations and component outlines to the board. May be applied to simply the top side or to both sides if components are installed on both top 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 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 techniques.
The procedure of looking for connection or shorted connections on the boards by methods applying a voltage in between various points on the board and ISO 9001 identifying if a current flow takes place. Depending upon the board complexity, this procedure might require a specially created test fixture and test program to incorporate with the electrical test system utilized by the board manufacturer.