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 install applications or through rilled holes in the board and copper pads for soldering the element leads in thru-hole applications. A board style may have all thru-hole parts on the top or element side, a mix of thru-hole and surface mount on the top side just, a mix of thru-hole and surface area install components on the top side and surface mount elements on the bottom or circuit side, or surface install elements on the leading and bottom sides of the board.
The boards are likewise utilized to electrically connect the needed leads for each part utilizing conductive copper traces. The part pads and connection traces are engraved 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 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 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 engraved away to form the actual copper pads and connection traces on the board surface areas as part of the board manufacturing procedure. A multilayer board includes a number of layers of dielectric product that has actually been fertilized with adhesives, and these layers are used to separate 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 innovations.
In a ISO 9001 typical four layer board design, the internal layers are typically utilized to provide power and ground connections, such as a +5 V aircraft 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. Very intricate board styles may have a a great deal of layers to make the different connections for various voltage levels, ground connections, or for connecting the lots of leads on ball grid array devices and other big integrated circuit bundle formats.
There are generally 2 types of material utilized to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, typically about.002 inches thick. Core product is similar to a very thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred 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 technique, which is an older technology, uses 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 two core layers would make a 4 layer board.
The film stack-up approach, a newer 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 number of layers required by the board design, sort of like Dagwood developing a sandwich. This technique permits the producer versatility in how the board layer thicknesses are combined to fulfill the completed product thickness requirements by differing the variety of sheets of pre-preg in each layer. When the product layers are finished, the whole stack goes through 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 procedure of making printed circuit boards follows the actions listed below for the majority of applications.
The procedure of determining materials, procedures, and requirements to satisfy the customer's requirements for the board style based upon the Gerber file info offered with the purchase order.
The process of transferring the Gerber file data for a layer onto an etch resist movie that is put on the conductive copper layer.
The conventional procedure of exposing the copper and other locations unprotected by the etch withstand film to a chemical that eliminates the vulnerable copper, leaving the protected copper pads and traces in place; newer procedures use plasma/laser etching rather of chemicals to get rid of the copper material, allowing 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 solid board material.
The process of drilling all the holes for plated through applications; a second drilling procedure is used for holes that are not to be plated through. Details on hole place 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 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. Avoid this procedure if possible because it includes expense 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 applied; the solder mask secures versus environmental damage, provides insulation, safeguards against solder shorts, and safeguards 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 ultimate wave soldering or reflow soldering process that will take place at a later date after the parts have been put.
The procedure of using the markings for component classifications and component lays out to the board. May be used to simply the top side or to both sides if elements are installed on both leading and bottom sides.
The process of separating several boards from a panel of similar boards; this procedure also permits cutting notches or slots into the board if required.
A visual evaluation of the boards; also can be the procedure of inspecting wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The process of checking for connection or shorted connections on the boards by ways using a voltage in between different points on the board and figuring out if an existing flow occurs. Depending upon the board complexity, this process may require a specially developed test component and test program to incorporate with the electrical test system utilized by the board producer.