ISO 9001 Accreditation 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 mount 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 component side, a mix of thru-hole and surface area install on the top side only, a mix of thru-hole and surface area mount elements 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 likewise utilized to electrically connect the required leads for each element utilizing conductive copper traces. The part pads and connection traces are etched from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are designed 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 designs 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 etched away to form the real copper pads and connection traces on the board surfaces as part of the board manufacturing procedure. A multilayer board consists of a number of layers of dielectric material that has been fertilized with adhesives, and these layers are utilized to separate the layers of copper plating. All these layers are lined up 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 typical 4 layer board style, the internal layers are frequently used to supply power and ground connections, such as a +5 V airplane layer and a Ground aircraft layer as the 2 internal layers, with all other circuit and part connections made on the leading and bottom layers of the board. Extremely complex board designs might 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 large integrated circuit package formats.
There are usually 2 kinds of material used to build a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, normally about.002 inches thick. Core material is similar to a very thin double sided board because it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, typically.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two approaches used to build up the wanted variety of layers. The core stack-up approach, which is an older innovation, utilizes a center layer of pre-preg material with a layer of core material above and another layer of core product listed below. This mix of one pre-preg layer and two core layers would make a 4 layer board.
The movie stack-up method, a newer technology, would have core product as the center layer followed by layers of pre-preg and copper material developed above and below to form the last number of layers needed by the board design, sort of like Dagwood developing a sandwich. This approach allows the manufacturer flexibility in how the board layer thicknesses are integrated to meet the finished item thickness requirements by differing the number of sheets of pre-preg in each layer. When the product layers are finished, the whole stack is subjected to 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 manufacturing printed circuit boards follows the actions listed below for the majority of applications.
The procedure of identifying materials, procedures, and requirements to meet the customer's specs for the board style based upon the Gerber file info provided with the purchase order.
The process of transferring the Gerber file data for a layer onto an etch resist film that is placed on the conductive copper layer.
The conventional procedure of exposing the copper and other locations unprotected by the etch resist movie to a chemical that removes the unprotected copper, leaving the safeguarded copper pads and traces in place; newer procedures use plasma/laser etching rather of chemicals to get rid of the copper product, allowing finer line definitions.
The process of lining up the conductive copper and insulating dielectric layers and pushing them under heat to activate 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 process is utilized for holes that are not to be plated through. Info on hole area and size is included in the drill drawing file.
The process 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. Prevent this process if possible because it includes cost 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 against ecological damage, supplies insulation, safeguards against solder shorts, and protects 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 eventual wave soldering or reflow soldering procedure that will take place at a later date after the elements have actually been placed.
The process of applying the markings for component designations and part outlines to the board. May be used to simply the top side or to both sides if components are mounted on both top and bottom sides.
The process of separating numerous boards from a panel of similar boards; this process likewise permits cutting notches or slots into the board if needed.
A visual assessment of the boards; likewise can be the procedure of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other approaches.
The procedure of checking for connection or shorted connections on the boards by means using a voltage in between numerous points on the board and identifying if a current circulation takes place. Depending upon the board complexity, this procedure may require a specially developed test fixture and test program to integrate with the electrical test system used by the board manufacturer.