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 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 side just, a mix of thru-hole and surface area install components on the top side and surface area install parts on the bottom or circuit side, or surface mount parts on the leading and bottom sides of the board.
The boards are also utilized to electrically link the required leads for each element using conductive copper traces. The element pads and connection traces are engraved 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 just, double agreed copper pads and traces on the leading 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 etched away to form the real copper pads and connection traces on the board surface areas as part of the board manufacturing procedure. 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 of 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 common 4 layer board design, the internal layers are frequently utilized to supply power and ground connections, such as a +5 V aircraft 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. Extremely intricate board designs may have a a great deal of layers to make the various connections for various voltage levels, ground connections, or for linking the lots of leads on ball grid array devices and other large integrated circuit package formats.
There are typically 2 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, usually about.002 inches thick. Core product is similar to an extremely thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, usually.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are 2 approaches utilized to develop the preferred 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 combination of one pre-preg layer and two core layers would make a 4 layer board.
The movie stack-up technique, a more recent innovation, would have core product as the center layer followed by layers of pre-preg and copper product developed above and below to form the last variety of layers required by the board style, sort of like Dagwood developing a sandwich. This technique permits the maker flexibility in how the board layer densities are integrated to meet the completed item thickness 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 triggers the adhesive in the pre-preg to bond the core and pre-preg layers together into a single entity.
The process of producing printed circuit boards follows the actions listed below for most applications.
The process of determining materials, processes, and requirements to meet the customer's specifications for the board style based upon the Gerber file details provided with the purchase order.
The procedure 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 areas unprotected by the etch withstand film to a chemical that gets rid of the unguarded copper, leaving the safeguarded copper pads and traces in location; newer processes use plasma/laser etching rather of chemicals to remove the copper material, permitting finer line definitions.
The procedure of aligning the conductive copper and insulating dielectric layers and pressing them under heat to activate the adhesive in the dielectric layers to form a strong board material.
The procedure of drilling all of the ISO 9001 Accreditation
holes for plated through applications; a 2nd drilling process is utilized for holes that are not to be plated through. Information on hole location and size is included 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 put in an electrically charged bath of copper.
This is needed 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 adds expense to the completed board.
The process of using a protective masking product, a solder mask, over the bare copper traces or over the copper that has had a thin layer of solder used; the solder mask safeguards versus environmental damage, supplies insulation, protects versus solder shorts, and safeguards traces that run 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 elements have been positioned.
The procedure of using the markings for part designations and element outlines to the board. Might be applied to just the top side or to both sides if parts are installed on both top and bottom sides.
The procedure of separating multiple boards from a panel of similar boards; this procedure likewise permits cutting notches or slots into the board if required.
A visual evaluation 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 techniques.
The procedure of checking for continuity or shorted connections on the boards by methods applying a voltage in between different points on the board and determining if a present circulation occurs. Depending upon the board complexity, this procedure may require a specifically designed test component and test program to incorporate with the electrical test system used by the board manufacturer.