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 area mount 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 component side, a mix of thru-hole and surface area install on the top only, a mix of thru-hole and surface area mount parts on the top and surface area install 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 needed leads for each part 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 designed as single agreed copper pads and traces on one side of the board only, double agreed copper pads and traces on the top and bottom sides of the board, or multilayer designs 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 etched 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 material 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 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 common 4 layer board design, the internal layers are typically used to offer power and ground connections, such as a +5 V plane layer and a Ground airplane layer as the 2 internal layers, with all other circuit and part connections made on the leading and bottom layers of the board. Very complex board designs may have a large number of layers to make the different connections for various voltage levels, ground connections, or for linking the numerous leads on ball grid selection devices and other large integrated circuit bundle formats.
There are generally 2 types of material used to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet form, typically about.002 inches thick. Core material is similar to a very thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, typically.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are two methods utilized to build up the desired variety of layers. The core stack-up approach, which is an older technology, utilizes a center layer of pre-preg product with a layer of core product above and another layer of core material listed below. This combination of one pre-preg layer and 2 core layers would make a 4 layer board.
The movie stack-up technique, a more recent innovation, 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 required by the board style, sort of like Dagwood building a sandwich. This technique permits the maker flexibility in how the board layer thicknesses are integrated to satisfy the ended up item density requirements by differing the variety of sheets of pre-preg in each layer. Once the material 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 the majority of applications.
The process of figuring out products, processes, and requirements to meet the consumer's specs for the board design based on the Gerber file details offered with the purchase order.
The process of transferring the Gerber file information for a layer onto an etch withstand movie that is placed on the conductive copper layer.
The traditional procedure of exposing the copper and other areas unprotected by the etch resist film to a chemical that gets rid of the vulnerable copper, leaving the safeguarded copper pads and traces in location; newer procedures use plasma/laser etching instead of chemicals to eliminate the copper material, allowing finer line definitions.
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 solid board product.
The procedure of drilling all the holes for plated through applications; a 2nd drilling process is utilized for holes that are not to be plated through. Details on hole area and size is contained 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 put 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 procedure if possible since it adds cost to the finished board.
The process of using a protective masking material, a solder mask, over the bare copper traces or over the copper that has had a thin layer of solder used; ISO 9001 consultants
the solder mask secures against ecological damage, supplies insulation, protects versus solder shorts, and protects traces that run in between pads.
The procedure of covering 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 components have been put.
The process of applying the markings for part classifications and part describes to the board. May be applied to just the top side or to both sides if components are installed on both top and bottom sides.
The process of separating numerous boards from a panel of similar boards; this process likewise enables cutting notches or slots into the board if needed.
A visual evaluation of the boards; also can be the process of inspecting wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.
The procedure of looking for continuity or shorted connections on the boards by ways using a voltage between various points on the board and determining if a current flow occurs. Relying on the board complexity, this process might need a specially designed test fixture and test program to incorporate with the electrical test system used by the board manufacturer.