The Design and Advantages of Cutting-edge QM Systems

Apr 15, 2019  
In electronic devices, printed circuit boards, or PCBs, are used to mechanically support electronic elements which have their connection leads soldered onto copper pads in surface mount applications or through rilled holes in ISO 9001 the board and copper pads for soldering the part leads in thru-hole applications. A board design may have all thru-hole elements on the top or component side, a mix of thru-hole and surface area mount on the top side just, a mix of thru-hole and surface install parts on the top and surface install parts on the bottom or circuit side, or surface area install elements on the leading and bottom sides of the board.

The boards are likewise utilized to electrically link the needed leads for each component utilizing conductive copper traces. The element 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 only, 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 the 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 etched away to form the actual copper pads and connection traces on the board surfaces as part of the board manufacturing procedure. A multilayer board includes a variety of layers of dielectric material that has been fertilized with adhesives, and these layers are utilized to separate the layers of copper plating. All these layers are lined up 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 typical four layer board design, the internal layers are typically used to offer power and ground connections, such as a +5 V plane layer and a Ground airplane layer as the two internal layers, with all other circuit and part connections made on the leading and bottom layers of the board. Extremely intricate board designs might have a large number of layers to make the numerous connections for different voltage levels, ground connections, or for connecting the many leads on ball grid selection gadgets and other large integrated circuit package formats.

There are generally 2 kinds of material utilized to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet type, normally about.002 inches thick. Core product resembles 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, normally.030 density dielectric product with 1 ounce copper layer on each side. In a multilayer board design, there are 2 methods utilized to develop the desired 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 product above and another layer of core material listed 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 below to form the last number of layers required by the board design, sort of like Dagwood building a sandwich. This approach allows the manufacturer versatility in how the board layer densities are combined to fulfill the completed item thickness requirements by varying the number of sheets of pre-preg in each layer. When the product layers are completed, the whole 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 many applications.

The procedure of figuring out products, procedures, and requirements to meet the customer's requirements for the board style based on the Gerber file information supplied 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 standard procedure of exposing the copper and other areas unprotected by the etch withstand film to a chemical that removes the unguarded copper, leaving the protected copper pads and traces in place; more recent processes use plasma/laser etching instead of chemicals to eliminate the copper material, allowing finer line meanings.

The process of lining up the conductive copper and insulating dielectric layers and pushing them under heat to activate the adhesive in the dielectric layers to form a strong board product.

The process of drilling all the holes for plated through applications; a second drilling process is used for holes that are not to be plated through. Details on hole place and size is included 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 needed when holes are to be drilled through a copper area however the hole is not to be plated through. Avoid this process if possible due to the fact that it adds expense to the completed board.

The process of applying a protective masking product, a solder mask, over the bare copper traces or over the copper that has actually had a thin layer of solder used; the solder mask secures versus ecological damage, supplies insulation, protects against solder shorts, and safeguards traces that run in between pads.

The process of finishing the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering process that will happen at a later date after the components have actually been put.

The procedure of using the markings for part classifications and element details 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 numerous boards from a panel of identical boards; this process also permits cutting notches or slots into the board if needed.

A visual inspection of the boards; likewise can be the process of inspecting wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.

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 circulation takes place. Relying on the board intricacy, this process might need a specifically created test fixture and test program to integrate with the electrical test system used by the board maker.