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 mount applications or through rilled holes in the board and copper pads for soldering the component leads in thru-hole applications. A board design may have all thru-hole parts on the leading or part side, a mix of thru-hole and surface mount on the top only, a mix of thru-hole and surface install parts on the top side and surface install parts on the bottom or circuit side, or surface area mount components on the top and bottom sides of the board.
The boards are likewise used to electrically link the required leads for each part 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 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 engraved away to form the real copper pads and connection traces on the board surfaces as part of the board manufacturing process. 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 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 technologies.
In a normal 4 layer board design, the internal layers are typically utilized to provide power and ground connections, such as a +5 V airplane layer and a Ground plane layer as the two internal layers, with all other circuit and component connections made on the leading and bottom layers of the board. Really intricate board designs might have a large number of layers to make the various connections for various voltage levels, ground connections, or for connecting the numerous leads on ball grid variety devices and other big integrated circuit bundle formats.
There are normally 2 kinds 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 kind, typically about.002 inches thick. Core product is similar to a very thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer transferred on each side, generally.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are 2 techniques used to develop the preferred number of layers. The core stack-up approach, which is an older innovation, utilizes a center layer of pre-preg product 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 approach, a newer technology, would have core material as the center layer followed by layers of pre-preg and copper product developed above and below to form the last variety of layers needed by the board style, sort of like Dagwood building a sandwich. This method enables the producer flexibility in how the board layer thicknesses are integrated to fulfill the finished item density requirements by differing the variety of sheets of pre-preg in each layer. When the product 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 process of manufacturing printed circuit boards follows the steps below for the majority of applications.
The procedure of identifying materials, processes, and requirements to fulfill the customer's requirements for the board design based upon the Gerber file details 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 conventional process of exposing the copper and other locations unprotected by the etch withstand movie to a chemical that removes the unguarded copper, leaving the protected copper pads and traces in location; newer processes use plasma/laser etching instead of chemicals to get rid of the copper material, allowing finer line meanings.
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 solid board product.
The process of drilling all of the holes for plated through applications; a 2nd drilling procedure is used for holes that are not to be plated through. ISO 9001 Accreditation Consultants Information on hole location and size is consisted of 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 positioned 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 procedure if possible since it adds expense to the completed 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 applied; the solder mask protects against ecological damage, provides insulation, protects versus solder shorts, and safeguards traces that run in between pads.
The procedure of covering the pad areas with a thin layer of solder to prepare the board for the eventual wave soldering or reflow soldering procedure that will occur at a later date after the elements have been positioned.
The process of using the markings for part designations and part outlines to the board. May be applied to simply the top or to both sides if components are installed on both top and bottom sides.
The procedure of separating numerous boards from a panel of identical boards; this process also permits cutting notches or slots into the board if needed.
A visual assessment of the boards; likewise can be the procedure of inspecting wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.
The process of checking for connection or shorted connections on the boards by ways applying a voltage between various points on the board and determining if a current flow takes place. Relying on the board complexity, this procedure might require a specially developed test fixture and test program to integrate with the electrical test system used by the board manufacturer.