In electronics, printed circuit boards, or PCBs, are utilized 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 element leads in thru-hole applications. A board design may have all thru-hole elements on the top or part side, a mix of thru-hole and surface mount on the top only, 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 part pads and connection traces are etched 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 sided with copper pads and traces on the leading and bottom sides of the board, or multilayer styles with copper pads and traces on top and bottom of board with a variable variety 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 manufacturing process. A multilayer board includes a number 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 and 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 style, the internal layers are often used to offer power and ground connections, such as a +5 V airplane layer and a Ground plane layer as the two internal layers, with all other circuit and part connections made on the top and bottom layers of the board. Very complex board designs may have a a great deal of layers to make the numerous connections for various voltage levels, ground connections, or for linking the many leads on ball grid range devices and other large incorporated circuit plan formats.
There are normally 2 types of product utilized to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet kind, typically about.002 inches thick. Core product resembles a really 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 material with 1 ounce copper layer on each side. In a multilayer board design, there are two techniques utilized to develop the desired number of layers. The core stack-up approach, which is an older technology, uses a center layer of pre-preg material with a layer of core product 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 innovation, would have core product as the center layer followed by layers of pre-preg and copper product developed above and below to form the final number of layers required by the board style, sort of like Dagwood building a sandwich. This method permits the producer versatility in how the board layer thicknesses are integrated to fulfill the completed item thickness requirements by differing the variety of sheets of pre-preg in each layer. When the material layers are completed, 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 process of making printed circuit boards follows the actions listed below for a lot of applications.
The process of determining materials, procedures, and requirements to satisfy the client's requirements for the board style based upon the Gerber file details supplied with the order.
The procedure of moving the Gerber file information for a layer onto an etch resist movie that is placed on the conductive copper layer.
The conventional procedure of exposing the copper and other areas unprotected by the etch withstand film to a chemical that gets rid of the unguarded copper, leaving the protected copper pads and traces in location; newer processes use plasma/laser etching rather of chemicals to eliminate the copper product, permitting finer line meanings.
The procedure of lining up the conductive copper and insulating dielectric layers and pushing them under heat to activate 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 process is used for holes that are not to be plated through. Info on hole area and size is consisted of in the drill drawing file.
The procedure 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 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 due to the fact that it adds expense to the finished board.
The process of applying a protective masking product, a solder mask, over ISO 9001 Accreditation the bare copper traces or over the copper that has had a thin layer of solder applied; the solder mask secures versus environmental damage, provides insulation, protects against solder shorts, and protects traces that run between pads.
The procedure of finishing the pad locations 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 classifications and component lays out to the board. May be used to simply the top or to both sides if elements are mounted on both top and bottom sides.
The procedure of separating several boards from a panel of similar boards; this procedure also allows 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 process of looking for continuity or shorted connections on the boards by ways using a voltage in between various points on the board and figuring out if an existing flow takes place. Depending upon the board intricacy, this procedure may need a specially developed test component and test program to integrate with the electrical test system utilized by the board producer.