In electronic devices, printed circuit boards, or PCBs, are used to mechanically support electronic parts 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 part leads in thru-hole applications. A board design might have all thru-hole components on the leading or element side, a mix of thru-hole and surface area install on the top just, a mix of thru-hole and surface mount components on the top and surface install elements on the bottom or circuit side, or surface area install elements on the top and bottom sides of the board.
The boards are likewise utilized to electrically link the required leads for each part using 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 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 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 surface areas 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 used to separate the layers of copper plating. All of these layers are aligned 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 normal four layer board style, the internal layers are typically used to offer power and ground connections, such as a +5 V plane 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. Extremely complex board styles may have a large number of layers to make the different connections for different voltage levels, ground connections, or for linking the lots of leads on ball grid array devices and other large integrated circuit package formats.
There are normally 2 kinds of material used to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, generally about.002 inches thick. Core material resembles a very thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, typically.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two approaches used to develop the desired variety of layers. The core stack-up approach, which is an older technology, uses a center layer of pre-preg product with a layer of core product 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 innovation, would have core material as the center layer followed by layers of pre-preg and copper material developed above and below to form the final number of layers needed by the board style, sort of like Dagwood developing a sandwich. This technique enables the producer versatility in how the board layer densities are combined to fulfill the ended up product thickness requirements by varying the number of sheets of pre-preg in each layer. Once the material layers are finished, the entire 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 producing printed circuit boards follows the steps listed below for most applications.
The procedure of figuring out products, procedures, and requirements to fulfill the client's specs for the board design based upon the Gerber file details provided with the order.
The procedure of moving the Gerber file data for a layer onto an etch resist film that is put on the conductive copper layer.
The traditional process of exposing the copper and other locations unprotected by the etch withstand movie to a chemical that removes 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 product, enabling finer line definitions.
The process of aligning 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 product.
The procedure of drilling all of the holes for plated through applications; a 2nd drilling procedure is utilized 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 area however the hole is not to be plated through. Avoid this procedure if possible because it adds expense to the ended up board.
The procedure of using a protective masking material, a solder mask, over the bare copper traces or over the copper that has actually had a thin layer of solder used; the solder mask safeguards versus ecological damage, supplies insulation, secures versus solder shorts, and safeguards traces that run in between pads.
The procedure of finish the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering process that will happen at a later date after the parts have been put.
The procedure of using the markings for component designations and part describes to the board. May be applied to just the top side or to both sides if parts are mounted on both top and bottom sides.
The process of separating numerous boards from a panel of similar boards; this procedure also permits cutting notches or slots into the board if needed.
A visual evaluation of the boards; also can be the procedure of checking 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 in between different points on the board and figuring out if ISO 9001 Accreditation a present circulation takes place. Depending upon the board intricacy, this process might require a specifically created test fixture and test program to integrate with the electrical test system utilized by the board manufacturer.