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 install applications or through rilled holes in the board and copper pads for soldering the component leads in thru-hole applications. A board style may have all thru-hole parts on the leading or element side, a mix of thru-hole and surface area install on the top side just, a mix of thru-hole and surface install elements on the top side and surface area install elements on the bottom or circuit side, or surface mount elements on the leading and bottom sides of the board.
The boards are likewise used to electrically link the needed leads for each part using conductive copper traces. The element 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 just, double sided with copper pads and traces on the top 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 consist of a core dielectric product, 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 procedure. A multilayer board includes a variety of layers of dielectric material that has actually been impregnated with adhesives, and these layers are used to separate the layers of copper plating. All these layers are aligned then 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 design, the internal layers are frequently used to offer power and ground connections, such as a +5 V plane layer and a Ground airplane layer as the two internal layers, with all other circuit and part connections made on the leading and bottom layers of the board. Really intricate board styles might have a a great deal of layers to make the different connections for different voltage levels, ground connections, or for connecting the lots of leads on ball grid range devices and other large integrated circuit bundle formats.
There are normally two types of product utilized 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 an extremely thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, usually.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are 2 techniques used to develop the desired number of layers. The core stack-up method, which is an older innovation, utilizes a center layer of pre-preg material with a layer of core product above and another layer of core material listed below. This combination of one pre-preg layer and 2 core layers would make a 4 layer board.
The film stack-up technique, a newer technology, would have core material as the center layer followed by layers of pre-preg and copper product built up above and listed below to form the final number of layers needed by the board design, sort of like Dagwood developing a sandwich. This approach allows the producer flexibility in how the board layer thicknesses are integrated to meet the completed item density requirements by differing the number of sheets of pre-preg in each layer. Once the material layers are finished, the entire stack is subjected to 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 producing printed circuit boards follows the actions below for most applications.
The procedure of figuring out products, procedures, and requirements to satisfy the consumer's specifications for the board style based upon the Gerber file details offered with the purchase order.
The procedure of transferring the Gerber file information for a layer onto an etch withstand movie that is placed on the conductive copper layer.
The traditional process of exposing the copper and other locations unprotected by the etch resist film to a chemical that gets rid of the unprotected copper, leaving the protected copper pads and traces in place; more recent procedures utilize plasma/laser etching rather of chemicals to remove the copper product, enabling finer line definitions.
The procedure of aligning 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 2nd drilling procedure is utilized for holes that are not to be plated through. Info on hole location and size is contained 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 positioned in an electrically charged bath of copper.
This is needed when holes are to be drilled through a copper location but the hole is not to be plated through. Prevent this procedure if possible due to the fact that it includes cost 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 actually had a thin layer of solder applied; the solder mask protects versus ecological damage, provides insulation, protects versus solder shorts, and safeguards 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 take place at a later date after the components have actually been put.
The process of using the markings for part designations and component describes to the board. Might be used to simply the top or to both sides if components are installed on both leading and bottom sides.
The procedure 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 assessment of the boards; likewise can be the process of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The procedure of checking for continuity or shorted connections on the boards by methods using a voltage in between different points on the board and identifying if a current circulation occurs. Depending upon the board complexity, this process might require a specifically developed test component and test program to integrate with the electrical test system utilized by the board manufacturer.