Printed Circuits Boards Design And Technology Pdf
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- Printed circuit boards: A review on the perspective of sustainability
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- PRINTED CIRCUIT BOARD (PCB) DESIGN
- Printed circuit board
Components are generally soldered onto the PCB to both electrically connect and mechanically fasten them to it.
Printed circuit boards: A review on the perspective of sustainability
Components are generally soldered onto the PCB to both electrically connect and mechanically fasten them to it. Printed circuit boards are used in all but the simplest electronic products.
They are also used in some electrical products, such as passive switch boxes. Alternatives to PCBs include wire wrap and point-to-point construction , both once popular but now rarely used. PCBs require additional design effort to lay out the circuit, but manufacturing and assembly can be automated.
Electronic computer-aided design software is available to do much of the work of layout. Mass-producing circuits with PCBs is cheaper and faster than with other wiring methods, as components are mounted and wired in one operation.
Large numbers of PCBs can be fabricated at the same time, and the layout only has to be done once. PCBs can also be made manually in small quantities, with reduced benefits. PCBs can be single-sided one copper layer , double-sided two copper layers on both sides of one substrate layer , or multi-layer outer and inner layers of copper, alternating with layers of substrate. Multi-layer PCBs allow for much higher component density, because circuit traces on the inner layers would otherwise take up surface space between components.
The rise in popularity of multilayer PCBs with more than two, and especially with more than four, copper planes was concurrent with the adoption of surface mount technology. However, multilayer PCBs make repair, analysis, and field modification of circuits much more difficult and usually impractical. A basic PCB consists of a flat sheet of insulating material and a layer of copper foil , laminated to the substrate. Chemical etching divides the copper into separate conducting lines called tracks or circuit traces , pads for connections, vias to pass connections between layers of copper, and features such as solid conductive areas for electromagnetic shielding or other purposes.
The tracks function as wires fixed in place, and are insulated from each other by air and the board substrate material. The surface of a PCB may have a coating that protects the copper from corrosion and reduces the chances of solder shorts between traces or undesired electrical contact with stray bare wires. For its function in helping to prevent solder shorts, the coating is called solder resist or solder mask.
A printed circuit board can have multiple copper layers. A two-layer board has copper on both sides; multi layer boards sandwich additional copper layers between layers of insulating material. Conductors on different layers are connected with vias , which are copper-plated holes that function as electrical tunnels through the insulating substrate.
Through-hole component leads sometimes also effectively function as vias. After two-layer PCBs, the next step up is usually four-layer. Often two layers are dedicated as power supply and ground planes , and the other two are used for signal wiring between components. A board may use both methods for mounting components.
PCBs with only through-hole mounted components are now uncommon. Surface mounting is used for transistors , diodes , IC chips , resistors and capacitors. Through-hole mounting may be used for some large components such as electrolytic capacitors and connectors. The pattern to be etched into each copper layer of a PCB is called the "artwork".
The etching is usually done using photoresist which is coated onto the PCB, then exposed to light projected in the pattern of the artwork. The resist material protects the copper from dissolution into the etching solution. The etched board is then cleaned. A PCB design can be mass-reproduced in a way similar to the way photographs can be mass-duplicated from film negatives using a photographic printer.
In multi-layer boards, the layers of material are laminated together in an alternating sandwich: copper, substrate, copper, substrate, copper, etc. Only the outer layers need be coated; the inner copper layers are protected by the adjacent substrate layers. FR-4 glass epoxy is the most common insulating substrate. Another substrate material is cotton paper impregnated with phenolic resin , often tan or brown.
When a PCB has no components installed, it is less ambiguously called a printed wiring board PWB or etched wiring board.
However, the term "printed wiring board" has fallen into disuse. In informal usage, the term "printed circuit board" most commonly means "printed circuit assembly" with components. The IPC preferred term for assembled boards is circuit card assembly CCA ,  and for assembled backplanes it is backplane assemblies. For example, expansion card. A PCB may be printed with a legend identifying the components, test points, or identifying text.
Originally, silkscreen printing was used for this purpose, but today other, finer quality printing methods are usually used. Normally the legend does not affect the function of the PCBA. A minimal PCB for a single component, used for prototyping , is called a breakout board.
The purpose of a breakout board is to "break out" the leads of a component on separate terminals so that manual connections to them can be made easily. Breakout boards are especially used for surface-mount components or any components with fine lead pitch. Advanced PCBs may contain components embedded in the substrate, such as capacitors and integrated circuits, to reduce the amount of space taken up by components on the surface of the PCB while improving electrical characteristics.
The first PCBs used through-hole technology, mounting electronic components by leads inserted through holes on one side of the board and soldered onto copper traces on the other side. Boards may be single-sided, with an unplated component side, or more compact double-sided boards, with components soldered on both sides.
Horizontal installation of through-hole parts with two axial leads such as resistors, capacitors, and diodes is done by bending the leads 90 degrees in the same direction, inserting the part in the board often bending leads located on the back of the board in opposite directions to improve the part's mechanical strength , soldering the leads, and trimming off the ends.
Leads may be soldered either manually or by a wave soldering machine. Through-hole manufacture adds to board cost by requiring many holes to be drilled accurately, and it limits the available routing area for signal traces on layers immediately below the top layer on multi-layer boards, since the holes must pass through all layers to the opposite side. Once surface-mounting came into use, small-sized SMD components were used where possible, with through-hole mounting only of components unsuitably large for surface-mounting due to power requirements or mechanical limitations, or subject to mechanical stress which might damage the PCB e.
Through-hole devices mounted on the circuit board of a mids Commodore 64 home computer. A box of drill bits used for making holes in printed circuit boards. While tungsten-carbide bits are very hard, they eventually wear out or break. Drilling is a considerable part of the cost of a through-hole printed circuit board. Surface-mount technology emerged in the s, gained momentum in the early s and became widely used by the mids. Components were mechanically redesigned to have small metal tabs or end caps that could be soldered directly onto the PCB surface, instead of wire leads to pass through holes.
Components became much smaller and component placement on both sides of the board became more common than with through-hole mounting, allowing much smaller PCB assemblies with much higher circuit densities. Surface mounting lends itself well to a high degree of automation, reducing labor costs and greatly increasing production rates compared with through-hole circuit boards.
Components can be supplied mounted on carrier tapes. Surface mount components can be about one-quarter to one-tenth of the size and weight of through-hole components, and passive components much cheaper.
However, prices of semiconductor surface mount devices SMDs are determined more by the chip itself than the package, with little price advantage over larger packages, and some wire-ended components, such as 1N small-signal switch diodes, are actually significantly cheaper than SMD equivalents. Each trace consists of a flat, narrow part of the copper foil that remains after etching.
Its resistance , determined by its width, thickness, and length, must be sufficiently low for the current the conductor will carry. Power and ground traces may need to be wider than signal traces. In a multi-layer board one entire layer may be mostly solid copper to act as a ground plane for shielding and power return. For microwave circuits, transmission lines can be laid out in a planar form such as stripline or microstrip with carefully controlled dimensions to assure a consistent impedance.
In radio-frequency and fast switching circuits the inductance and capacitance of the printed circuit board conductors become significant circuit elements, usually undesired; conversely, they can be used as a deliberate part of the circuit design, as in distributed-element filters , antennae , and fuses , obviating the need for additional discrete components. The European Union bans the use of lead among other heavy metals in consumer items, a piece of legislature called the RoHS , for Restriction of Hazardous Substances, directive.
PCBs to be sold in the EU must be RoHS-compliant, meaning that all manufacturing processes must not involve the use of lead, all solder used must be lead-free, and all components mounted on the board must be free of lead, mercury, cadmium, and other heavy metals. Laminates are manufactured by curing under pressure and temperature layers of cloth or paper with thermoset resin to form an integral final piece of uniform thickness. The size can be up to 4 by 8 feet 1. Varying cloth weaves threads per inch or cm , cloth thickness, and resin percentage are used to achieve the desired final thickness and dielectric characteristics.
The cloth or fiber material used, resin material, and the cloth to resin ratio determine the laminate's type designation FR-4, CEM-1, G, etc. There are quite a few different dielectrics that can be chosen to provide different insulating values depending on the requirements of the circuit. Thermal expansion is an important consideration especially with ball grid array BGA and naked die technologies, and glass fiber offers the best dimensional stability.
FR-4 is by far the most common material used today. The board stock with unetched copper on it is called "copper-clad laminate". With decreasing size of board features and increasing frequencies, small nonhomogeneities like uneven distribution of fiberglass or other filler, thickness variations, and bubbles in the resin matrix, and the associated local variations in the dielectric constant, are gaining importance.
The circuitboard substrates are usually dielectric composite materials. The composites contain a matrix usually an epoxy resin and a reinforcement usually a woven, sometimes nonwoven, glass fibers, sometimes even paper , and in some cases a filler is added to the resin e. The reinforcement type defines two major classes of materials: woven and non-woven. Woven reinforcements are cheaper, but the high dielectric constant of glass may not be favorable for many higher-frequency applications.
The substrates are characterized by several key parameters, chiefly thermomechanical glass transition temperature , tensile strength , shear strength , thermal expansion , electrical dielectric constant , loss tangent , dielectric breakdown voltage , leakage current , tracking resistance At the glass transition temperature the resin in the composite softens and significantly increases thermal expansion; exceeding T g then exerts mechanical overload on the board components - e.
Below T g the thermal expansion of the resin roughly matches copper and glass, above it gets significantly higher. As the reinforcement and copper confine the board along the plane, virtually all volume expansion projects to the thickness and stresses the plated-through holes. Repeated soldering or other exposition to higher temperatures can cause failure of the plating, especially with thicker boards; thick boards therefore require a matrix with a high T g.
The materials used determine the substrate's dielectric constant. This constant is also dependent on frequency, usually decreasing with frequency. As this constant determines the signal propagation speed , frequency dependence introduces phase distortion in wideband applications; as flat a dielectric constant vs frequency characteristics as is achievable is important here.
The impedance of transmission lines decreases with frequency, therefore faster edges of signals reflect more than slower ones. Dielectric breakdown voltage determines the maximum voltage gradient the material can be subjected to before suffering a breakdown conduction, or arcing, through the dielectric. Tracking resistance determines how the material resists high voltage electrical discharges creeping over the board surface. Loss tangent determines how much of the electromagnetic energy from the signals in the conductors is absorbed in the board material.
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PCB Inclusive : 0. PCB 6, 8, 10 Layers Inclusive : 0. Observance of this Design-Aid will ensure quick and problem-free processing of your circuit board order. This will help you reduce costs in two ways: first, through error-free manufacture of your boards correct tolerances, avoiding misunderstandings, etc. The ideal solution for correct layer orientation: Please make sure you provide an indication of the layer definitions in the copper , such as a caption: "TOP" in the top layer, "BOT" in the bottom layer.
However, we shall discuss those aspects of the design connected to choice of technology, components, PWB layout and production on PCB/hybrid circuit level. .
PRINTED CIRCUIT BOARD (PCB) DESIGN
The printed circuit board is a complex construct made of a wide variety of materials, produced by a multitude of processes and it is used for a wide range of applications. Understanding these dependencies and the possibilities of influencing PCB design are a necessary skill to develop and manufacture reliable PCBs. The process includes a proper specification of the requirements and requires the cooperation of all disciplines involved. We would like to invite you to an introduction to the application of a modern test procedure for bare boards, the Interconnect Stress Test IST. The webinar is of interest to developers, quality managers, purchasing and management.
Printed circuit board
At Elmgrove Technologies , we have been a respected provider of printed circuit board design services since We keep pace with the continual advancements in the field of electronic design and utilize leading edge software packages to create layouts that are functionally accurate and optimized for manufacturing and assembly. Our policy is to establish open lines of communication with our clients; this allows us to respond quickly to client needs and accelerate turnaround times. We have the ability to manage any type of project, from simple designs to those with complex arrangements and a high mix of features. By applying the principles of design-for-manufacturability and design-for-assembly, we transform your schematic into a circuit board layout that is functionally sound yet economical to produce.
Providing local, regional and global services for advanced PCBs and flex circuits, including technology development, quick turns and volume production. From the in house qualification of advanced laminate materials, signal integrity analysis, DFx and global manufacturing, Sanmina is the recognized leading manufacturer of advanced printed circuit boards. For both high speed and high reliability PCB fabrication, Sanmina will work with you to develop advanced PCBs with unique requirements. Services Learn More.
Printed Circuit Boards: Design, Fabrication, Assembly and Testing. Tata McGraw-Hill gaspdg.org The HDI technology allows shorter traces on the board by reducing the amount of.