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 part leads in thru-hole applications. A board style might have all thru-hole components on the leading or part side, a mix of thru-hole and surface mount on the top side only, a mix of thru-hole and surface area install parts on the top side and surface mount components on the bottom or circuit side, or surface area install components on the leading and bottom sides of the board.
The boards are also used to electrically link the required 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 created as single agreed copper pads and traces on one side of the board only, 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 the 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 material, 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 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 of these layers are aligned and then bonded into a single board structure under heat and pressure. Multilayer boards with 48 or more layers can be produced with today's technologies.
In a typical four layer board style, the internal layers are typically utilized to provide 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. Really complicated board designs may have a large number of layers to make the numerous connections for different voltage levels, ground connections, or for connecting the lots of leads on ball grid selection gadgets and other large incorporated circuit package formats.
There are generally 2 kinds of material utilized to build a multilayer board. Pre-preg material 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 really thin double sided board because it has a dielectric product, such as epoxy fiberglass, with a copper layer deposited on each side, normally.030 density dielectric material with 1 ounce copper layer on each side. In a multilayer board style, there are two techniques used to develop the wanted variety of layers. The core stack-up approach, 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 below. This combination of one pre-preg layer and two core layers would make a 4 layer board.
The film stack-up technique, 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 number of layers needed by the board style, sort of like Dagwood building a sandwich. This approach permits the producer flexibility in how the board layer thicknesses are combined to meet the finished item thickness requirements by differing the variety of sheets of pre-preg in each layer. Once the material layers are finished, the entire stack goes through 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 making printed circuit boards follows the actions listed below for the majority of applications.
The procedure of determining materials, processes, and requirements to satisfy the consumer's specifications for the board design based on the Gerber file information offered with the order.
The process of moving the Gerber file data for a layer onto an etch withstand movie that is placed on the conductive copper layer.
The standard procedure of exposing the copper and other locations unprotected by the etch withstand movie to a chemical that removes the vulnerable copper, leaving the safeguarded copper pads and traces in location; newer procedures utilize plasma/laser etching instead of chemicals to get rid of the copper material, permitting finer line definitions.
The procedure of aligning the conductive copper and insulating dielectric layers and pressing them ISO 9001 consultants under heat to activate the adhesive in the dielectric layers to form a solid board material.
The procedure of drilling all the holes for plated through applications; a 2nd drilling process is utilized for holes that are not to be plated through. Information on hole area and size is consisted of 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 put in an electrically charged bath of copper.
This is required when holes are to be drilled through a copper location however the hole is not to be plated through. Avoid this procedure if possible because it includes expense to the ended up board.
The procedure of applying a protective masking material, a solder mask, over the bare copper traces or over the copper that has had a thin layer of solder applied; the solder mask secures against ecological damage, provides insulation, safeguards against solder shorts, and safeguards traces that run in between pads.
The procedure of covering 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 components have actually been placed.
The procedure of applying the markings for part classifications and component describes to the board. May be used to just the top side or to both sides if parts are installed on both top and bottom sides.
The process of separating numerous boards from a panel of similar boards; this procedure likewise enables cutting notches or slots into the board if needed.
A visual examination 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 methods.
The process of checking for continuity or shorted connections on the boards by ways applying a voltage in between numerous points on the board and determining if a present flow occurs. Depending upon the board complexity, this process might require a specifically developed test fixture and test program to integrate with the electrical test system used by the board producer.