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 part leads in thru-hole applications. A board design may have all thru-hole components on the top or element side, a mix of thru-hole and surface install on the top just, ISO 9001 Accreditation a mix of thru-hole and surface area install components on the top and surface area mount parts on the bottom or circuit side, or surface install components on the top and bottom sides of the board.
The boards are also utilized to electrically link 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 created as single sided with copper pads and traces on one side of the board only, double sided with 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 consist of 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 manufacturing process. A multilayer board includes a variety of layers of dielectric product that has 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 technologies.
In a common four layer board style, the internal layers are typically utilized to offer power and ground connections, such as a +5 V airplane layer and a Ground aircraft layer as the two internal layers, with all other circuit and component connections made on the top and bottom layers of the board. Really complicated board styles might have a large number of layers to make the different connections for different voltage levels, ground connections, or for connecting the many leads on ball grid selection gadgets and other large incorporated circuit bundle formats.
There are usually two kinds of product used to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet form, normally about.002 inches thick. Core material is similar to a really thin double sided board because it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, normally.030 thickness dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are two methods used to build up the wanted 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 product above and another layer of core material below. This combination of one pre-preg layer and 2 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 material built up above and listed below to form the last number of layers required by the board style, sort of like Dagwood developing a sandwich. This method allows the manufacturer versatility in how the board layer thicknesses are combined to fulfill the completed item thickness requirements by varying the number of sheets of pre-preg in each layer. Once the material layers are completed, 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 actions below for most applications.
The process of figuring out materials, processes, and requirements to meet the customer's specs for the board design based upon the Gerber file information offered with the purchase order.
The process of transferring the Gerber file information for a layer onto an etch resist film that is placed on the conductive copper layer.
The standard process of exposing the copper and other locations unprotected by the etch resist movie to a chemical that gets rid of the unguarded copper, leaving the secured copper pads and traces in location; newer processes use plasma/laser etching rather of chemicals to eliminate 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 of the holes for plated through applications; a second drilling process is used for holes that are not to be plated through. Information on hole location and size is included 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 but the hole is not to be plated through. Avoid this procedure if possible since it adds expense to the finished board.
The process of applying a protective masking product, 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 secures against environmental damage, supplies insulation, safeguards versus solder shorts, and safeguards traces that run in between pads.
The process of coating the pad locations with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering process that will occur at a later date after the parts have actually been put.
The procedure of applying the markings for part classifications and component describes to the board. Might be used to simply the top or to both sides if parts are installed on both leading and bottom sides.
The process of separating numerous boards from a panel of identical boards; this process likewise permits cutting notches or slots into the board if needed.
A visual inspection of the boards; likewise can be the procedure of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The procedure of looking for connection or shorted connections on the boards by methods using a voltage in between various points on the board and determining if a current circulation happens. Depending upon the board intricacy, this procedure may need a specifically designed test fixture and test program to incorporate with the electrical test system used by the board manufacturer.