ISO 9001 Certification Consultants
In electronic devices, printed circuit boards, or PCBs, are used to mechanically support electronic components 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 leading or part side, a mix of thru-hole and surface area mount on the top just, a mix of thru-hole and surface mount elements on the top side and surface area install elements on the bottom or circuit side, or surface area mount components on the leading and bottom sides of the board.
The boards are likewise utilized to electrically link the needed 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 created 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 styles with copper pads and traces on top and bottom of board with a variable number 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 real copper pads and connection traces on the board surfaces as part of the board manufacturing process. A multilayer board consists of a number of layers of dielectric material that has actually been impregnated with adhesives, and these layers are utilized to separate the layers of copper plating. All 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 technologies.
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 2 internal layers, with all other circuit and part connections made on the leading and bottom layers of the board. Really intricate board designs may have a large number of layers to make the numerous connections for different voltage levels, ground connections, or for linking the numerous leads on ball grid range devices and other big incorporated circuit bundle formats.
There are usually two kinds 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 form, typically about.002 inches thick. Core product is similar to a very thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, generally.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two approaches utilized 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 material above and another layer of core material below. This combination of one pre-preg layer and two core layers would make a 4 layer board.
The movie stack-up approach, a newer technology, would have core material as the center layer followed by layers of pre-preg and copper material developed above and below to form the last number of layers required by the board design, sort of like Dagwood developing a sandwich. This approach permits the maker flexibility in how the board layer densities are integrated to fulfill the completed product density requirements by differing the variety of sheets of pre-preg in each layer. As soon as the product 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 manufacturing printed circuit boards follows the steps listed below for most applications.
The process of identifying materials, processes, and requirements to satisfy the consumer's specs for the board design based upon the Gerber file information provided with the order.
The process of moving the Gerber file data for a layer onto an etch withstand movie that is put on the conductive copper layer.
The traditional process of exposing the copper and other locations unprotected by the etch resist movie to a chemical that removes the vulnerable copper, leaving the safeguarded copper pads and traces in location; newer procedures utilize plasma/laser etching instead of chemicals to remove the copper material, allowing finer line definitions.
The process of lining up the conductive copper and insulating dielectric layers and pressing 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 second drilling procedure is utilized for holes that are not to be plated through. Information on hole location and size is consisted of in the drill drawing file.
The process of applying 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 required when holes are to be drilled through a copper location however the hole is not to be plated through. Prevent this process if possible due to the fact that it includes expense to the completed board.
The procedure of applying a protective masking product, 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 against environmental damage, offers insulation, protects versus solder shorts, and secures traces that run in between pads.
The process 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 happen at a later date after the parts have been put.
The process of applying the markings for element designations and part describes to the board. May be applied to simply the top or to both sides if elements are installed on both top and bottom sides.
The process of separating multiple boards from a panel of identical boards; this procedure likewise allows cutting notches or slots into the board if needed.
A visual inspection of the boards; likewise can be the process of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other methods.
The procedure of checking for connection or shorted connections on the boards by means applying a voltage between numerous points on the board and figuring out if a current flow occurs. Depending upon the board intricacy, this procedure might require a specially developed test component and test program to integrate with the electrical test system used by the board producer.