In electronics, printed circuit boards, or PCBs, are used to mechanically support electronic elements 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 style might have all thru-hole elements on the top or element side, a mix of thru-hole and surface area mount on the top only, a mix of thru-hole and surface install elements on the top side and surface area install components on the bottom or circuit side, or surface install elements on the leading and bottom sides of the board.
The boards are also used to electrically connect the required leads for each component utilizing conductive copper traces. The element pads and connection traces are etched from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are developed as single sided with copper pads and traces on one side of the board only, double sided with copper pads and traces on the leading 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 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 real copper pads and connection traces on the board surface areas as part of the board manufacturing process. A multilayer board includes a number 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 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 style, the internal layers are typically used to offer power and ground connections, such as a +5 V aircraft layer and a Ground plane layer as the 2 internal layers, with all other circuit and component connections made on the leading and bottom layers of the board. Very complex 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 selection devices and other large integrated circuit bundle formats.
There are generally two types of product used to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, normally about.002 inches thick. Core product is similar to an extremely thin double sided board in that it has a dielectric material, 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 style, there are 2 ISO 9001 Accreditation Consultants techniques used to develop the desired variety 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 below. This mix of one pre-preg layer and two core layers would make a 4 layer board.
The movie stack-up technique, a newer technology, would have core product as the center layer followed by layers of pre-preg and copper product developed above and below to form the final number of layers needed by the board design, sort of like Dagwood developing a sandwich. This method enables the manufacturer flexibility in how the board layer densities are integrated to meet the ended up item thickness requirements by differing the number of sheets of pre-preg in each layer. When the material layers are finished, the whole stack undergoes 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 process of manufacturing printed circuit boards follows the steps below for most applications.
The process of identifying materials, procedures, and requirements to fulfill the customer's specifications for the board style based upon the Gerber file information offered with the purchase order.
The procedure of moving the Gerber file information for a layer onto an etch withstand film that is placed on the conductive copper layer.
The conventional process of exposing the copper and other areas unprotected by the etch resist movie to a chemical that gets rid of the vulnerable copper, leaving the secured copper pads and traces in location; newer procedures utilize plasma/laser etching rather of chemicals to eliminate the copper product, allowing finer line definitions.
The procedure of aligning 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 material.
The process of drilling all the holes for plated through applications; a 2nd drilling procedure is used for holes that are not to be plated through. Information on hole location and size is contained 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 needed when holes are to be drilled through a copper location but the hole is not to be plated through. Avoid this procedure if possible because it adds cost 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 had a thin layer of solder applied; the solder mask safeguards against ecological damage, offers insulation, protects versus solder shorts, and protects traces that run between pads.
The procedure of finishing 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 been placed.
The process of using the markings for element classifications and component describes to the board. May be used to simply the top or to both sides if elements are mounted on both top and bottom sides.
The procedure of separating multiple boards from a panel of similar boards; this procedure also permits cutting notches or slots into the board if required.
A visual evaluation of the boards; also can be the process of examining wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The procedure of looking for continuity or shorted connections on the boards by methods applying a voltage between various points on the board and identifying if a present flow occurs. Depending upon the board complexity, this process might need a specifically developed test component and test program to incorporate with the electrical test system utilized by the board producer.