QM Systems - Their Format and Features

In electronic devices, printed circuit boards, or See more PCBs, are used to mechanically support electronic parts which have their connection leads soldered onto copper pads in surface area mount applications or through rilled holes in the board and copper pads for soldering the component leads in thru-hole applications. A board design might have all thru-hole elements on the leading or component side, a mix of thru-hole and surface area install on the top just, a mix of thru-hole and surface area mount elements on the top and surface install components on the bottom or circuit side, or surface install elements on the top and bottom sides of the board.

The boards are likewise utilized to electrically link the required leads for each component utilizing conductive copper traces. The component 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 just, double sided with copper pads and traces on the leading 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 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 actual copper pads and connection traces on the board surfaces as part of the board production process. A multilayer board includes a variety of layers of dielectric product that has actually been impregnated with adhesives, and these layers are utilized 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 technologies.

In a normal 4 layer board style, the internal layers are typically utilized 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. Really complex board styles may have a large number of layers to make the different connections for various voltage levels, ground connections, or for connecting the many leads on ball grid selection gadgets and other large integrated circuit plan formats.

There are typically 2 types of product utilized to construct a multilayer board. Pre-preg material is thin layers of fiberglass pre-impregnated with an adhesive, and remains in sheet type, usually about.002 inches thick. Core product is similar to a really thin double sided board in that it has a dielectric material, such as epoxy fiberglass, with a copper layer deposited on each side, typically.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board style, there are two approaches utilized to build up the desired number of layers. The core stack-up technique, 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 mix of one pre-preg layer and 2 core layers would make a 4 layer board.

The film stack-up approach, a more recent innovation, would have core product as the center layer followed by layers of pre-preg and copper product developed above and listed below to form the final number of layers needed by the board style, sort of like Dagwood developing a sandwich. This method permits the manufacturer versatility in how the board layer thicknesses are combined to fulfill the completed product thickness requirements by differing the number of sheets of pre-preg in each layer. As soon as the product layers are finished, the entire stack goes through heat and pressure that causes the adhesive in the pre-preg to bond the core and pre-preg layers together into a single entity.

The procedure of producing printed circuit boards follows the actions listed below for most applications.

The process of determining products, procedures, and requirements to meet the consumer's specifications for the board style based on the Gerber file details provided with the purchase order.

The process of transferring the Gerber file information for a layer onto an etch withstand film that is put on the conductive copper layer.

The traditional procedure of exposing the copper and other areas unprotected by the etch withstand film to a chemical that eliminates the vulnerable copper, leaving the safeguarded copper pads and traces in place; more recent procedures use plasma/laser etching instead of chemicals to eliminate the copper product, allowing finer line meanings.

The procedure of aligning the conductive copper and insulating dielectric layers and pushing them under heat to trigger the adhesive in the dielectric layers to form a strong board material.

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. Details on hole place and size is consisted of 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 positioned 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. Avoid this procedure if possible due to the fact that it includes cost to the completed 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 used; the solder mask safeguards versus environmental damage, supplies insulation, safeguards versus solder shorts, and safeguards traces that run between pads.

The procedure of coating the pad areas 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 positioned.

The process of applying the markings for component classifications and component describes to the board. May be used to simply the top or to both sides if components are mounted on both top and bottom sides.

The process of separating numerous boards from a panel of identical boards; this procedure also allows cutting notches or slots into the board if needed.

A visual inspection 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 procedure of looking for continuity or shorted connections on the boards by methods using a voltage in between various points on the board and identifying if a present flow happens. Relying on the board intricacy, this procedure might need a specially created test fixture and test program to integrate with the electrical test system used by the board manufacturer.
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