In electronic devices, printed circuit boards, or PCBs, are utilized to mechanically support electronic parts 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 style might have all thru-hole elements on the leading 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 parts on the top and surface area install elements on the bottom or circuit side, or surface area mount elements on the leading and bottom sides of the board.
The boards are also used to electrically connect the needed leads for each component using conductive copper traces. The part 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 just, 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 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 material, 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 surfaces as part of the board production process. A multilayer board consists of a number of layers of dielectric material that has been fertilized with adhesives, and these layers are used to separate the layers of copper plating. All these layers are aligned 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 innovations.
In a common 4 layer board design, the internal layers are typically utilized to supply power and ground connections, such as a +5 V airplane layer and a Ground airplane layer as the 2 internal layers, with all other circuit and element connections made on the top and bottom layers of the board. Extremely complex board designs may have a large number of layers to make the numerous connections for various voltage levels, ground connections, or for linking the numerous leads on ball grid selection devices and other big incorporated circuit package formats.
There are typically 2 kinds 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 form, generally about.002 inches thick. Core product is similar to a very thin double sided board because it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, normally.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are 2 techniques utilized to build up the preferred number of layers. The core stack-up method, which is an older technology, utilizes a center layer of pre-preg product with a layer of core material above and another layer of core product listed below. This combination of one pre-preg layer and two core layers would make a 4 layer board.
The film stack-up method, a more recent 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 final variety of layers required by the board style, sort of like Dagwood developing a sandwich. This approach permits the manufacturer versatility in how the board layer densities are integrated to satisfy the finished item density requirements by differing the variety of sheets of pre-preg in each layer. Once 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 many applications.
The process of determining products, processes, and requirements to fulfill the client's requirements for the board design based on the Gerber file information offered with the purchase order.
The procedure of moving the Gerber file information for a layer onto an etch resist movie that is put on the conductive copper layer.
The standard process of exposing the copper and other locations unprotected by the etch withstand movie to a chemical that eliminates the unprotected copper, leaving the ISO 9001 Certification Consultants safeguarded copper pads and traces in place; more recent procedures use plasma/laser etching instead of chemicals to eliminate the copper product, permitting finer line definitions.
The process 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 process of drilling all the holes for plated through applications; a second drilling procedure is used for holes that are not to be plated through. Info on hole location and size is consisted of in the drill drawing file.
The procedure 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 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 since it includes cost to the finished board.
The procedure of applying 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 against ecological damage, offers insulation, secures versus solder shorts, and secures traces that run between pads.
The procedure 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 parts have actually been positioned.
The procedure of applying the markings for part classifications and component lays out to the board. May be used to simply the top side or to both sides if parts are installed on both top and bottom sides.
The procedure of separating numerous boards from a panel of identical boards; this procedure likewise allows cutting notches or slots into the board if needed.
A visual evaluation of the boards; also can be the procedure of checking wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The process of looking for continuity or shorted connections on the boards by means using a voltage between numerous points on the board and identifying if a current flow occurs. Relying on the board complexity, this procedure might need a specially developed test fixture and test program to incorporate with the electrical test system used by the board manufacturer.