CONTENTS * INTRODUCTION * HISTORY * TYPES * APPLICATIONS * ADVANTAGES * DIS-ADVANTAGES * TOP PCBs MANUFACTURERS IN INDIA * MATERIALS USED IN MANUFACTURING PCBs * MANUFACTURING PROCESS * SOLDER RESIST * TEST * PROTECTION AND PACKAGING

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Case Based Assignment
TOPIC:- Printed Circuit Board (PCB)

Submitted To:- Submitted By:-
Harneek sani Group members Suraj kumar sahni (A 36) Sumeet jha (B 21) Aaditya baidwan (A 11) Section – JE101

Introduction
A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board(PWB) or etched wiring board. Printed circuit boards are used in virtually all but the simplest commercially produced electronic devices.
A PCB populated with electronic components is called a printed circuit assembly (PCA), printed circuit board assembly or PCB Assembly (PCBA). In informal use the term "PCB" is used both for bare and assembled boards, the context clarifying the meaning.
Alternatives to PCBs include wire wrap and point-to-point construction. PCBs must initially be designed and laid out, but become cheaper, faster to make, and potentially more reliable for high-volume production since production and soldering of PCBs can be automated. Much of the electronics industry's PCB design, assembly, and quality control needs are set by standards published by the IPC organization.

Fig. Part of a 1983 Sinclair ZX Spectrum computer board; a populated PCB, showing the conductive traces, vias (the through-hole paths to the other surface), and some mounted electrical components.

History
Development of the methods used in modern printed circuit boards started early in the 20th century. In 1903, a German inventor, Albert Hanson, described flat foil conductors laminated to an insulating board, in multiple layers. Thomas Edison experimented with chemical methods of plating conductors onto linen paper in 1904. Arthur Berry in 1913 patented a print-and-etch method in Britain, and in the United States Max Schoop obtained a patent to flame-spray metal onto a board through a patterned mask. Charles Durcase in 1927 patented a method of electroplating circuit patterns.
The Austrian engineer Paul Eisler invented the printed circuit while working in England around 1936 as part of a radio set. Around 1943 the USA began to use the technology on a large scale to make proximity fuse for use in World War II. After the war, in 1948, the USA released the invention for commercial use. Printed circuits did not become commonplace in consumer electronics until the mid-1950s, after the Auto-Sembly process was developed by the United States Army.
Before printed circuits (and for a while after their invention), point-to-point construction was used. For prototypes, or small production runs, wire wrap or turret board can be more efficient. Predating the printed circuit invention, and similar in spirit, was John Sargrove's 1936–1947 Electronic Circuit Making Equipment (ECME) which sprayed metal onto a Bakalite plastic board. The ECME could produce 3 radios per minute.
During World War II, the development of the anti-aircraft proximity fuse required an electronic circuit that could withstand being fired from a gun, and could be produced in quantity. The Centralab Division of Globe Union submitted a proposal which met the requirements: a ceramic plate would bescreenprinted with metallic paint for conductors and carbon material for resistors, with ceramic disc capacitors and subminiature vacuum tubes soldered in place. The technique proved viable, and the resulting patent on the process, which was classified by the U.S. Army, was assigned to Globe Union. It was not until 1984 that the Institute of Electrical and Electronics Engineers (IEEE) awarded Mr. Harry W. Rubinstein, the former head of Globe Union’s Centralab Division, its coveted Cledo Brunetti Award for early key contributions to the development of printed components and conductors on a common insulating substrate. As well, Mr. Rubinstein was honored in 1984 by his alma mater, the University of Wisconsin-Madison, for his innovations in the technology of printed electronic circuits and the fabrication of capacitors.
Originally, every electronic component had wire leads, and the PCB had holes drilled for each wire of each component. The components' leads were then passed through the holes and soldered to the PCB trace. This method of assembly is called through-hole construction. In 1949, Moe Abramson and Stanislaus F. Danko of the United States Army Signal Corps developed the Auto-Sembly process in which component leads were inserted into a copper foil interconnection pattern and dip soldered. The patent they obtained in 1956 was assigned to the U.S. Army. With the development of board lamination and etching techniques, this concept evolved into the standard printed circuit board fabrication process in use today. Soldering could be done automatically by passing the board over a ripple, or wave, of molten solder in a wave-soldering machine. However, the wires and holes are wasteful since drilling holes is expensive and the protruding wires are merely cut off.
From the 1980s small surface mount parts have been used increasingly instead of through-hole components; this has led to smaller boards for a given functionality and lower production costs, but with some additional difficulty in servicing faulty boards.

Types of PCBs 1. Single Sided PCB 2. Double sided PCB 3. Multilayer without Blind or Buried vias 4. Multilayer With Blind and or Buried vias 5. Multilayer Metal Core board without blind and or buried vias 6. Multilayer Metal Core board with blind and or buried vias
1. Single-sided board: Adequate for simple games and other non-complex electronics, a single-sided board is compromised of just one substrate with a fairly straight-forward set of components. An extremely thin layer of conducting material is applied to the board and electronic components are soldered to a set of interconnecting circuits. A series of contact fingers along the edges of the board serve to either connect this PCB to another or to a power source.
2. Double-sided board: As its name implies, an increase in application complexity may make it necessary for additional electronic components to be soldered to the other side of the substrate. Now that there are circuits on each side of the board, the components are connected via a series of strategically placed through-holes which allow for an unimpeded electrical connection between the two. The holes must therefore be coated with a conductive material to allow the PCB to work correctly.
3. Multi-layered board: With these printed circuit boards, the substrate is actually compromised of multiple layers of printed circuits. Separated by layers of specialized insulation, these printed circuit sheets are also connected via plated holes and allow for more complex applications.

Advantages of PCBs

1. The circuit board fabrication cost (pcb cost) is lower with mass quantity production.

2. Electronic circuit characteristics will be maintained without introducing parasite capacitance with a proper circuit board design. 3. Component wiring and assembly can be mechanized in a circuit board manufacturing facility. 4. PCB’s offer uniformity of electrical characteristics from assembly to assembly. 5. The location of electronic parts is fixed and so it simplifies components identification and maintanace of equipments.

6. Inspection time is reduced because printed circuitry eliminates the probability of error. 7.Chances of miswiring or short-circuited wiring are minimized.

Dis-Advantages

1. Re designing is required for the new type of circuit operation.

2. Very hard to get repaired if it gets damaged.

3. We can not update it , once printed.

4. Etching of this PCB generates chemicals which are the harmfull for the environment.

Top 12 PCB Manufacturers in India Rank Company 1. AT & S India Pvt Ltd. 2. Ascent Circuits Pvt Ltd. 3. Shogini Technoarts Pvt Ltd. 4. Epitome Components Ltd. 5. Circuit System India Ltd. 6. Akasaka Electronics Ltd. 7. Meena Cirtuits Pvt Ltd. 8. Fine-Lime Circuits Ltd. 9. Micropack Ltd. 10. Ace circuit Pvt Ltd. 11. BLG Electronics Ltd. 12. Sulakshana Circuits Ltd.

AT & S India Pvt Ltd
Annual Revenue (2010-11); Rs 2506 million
AT&S India Pvt Ltd is a wholly owned subsidiary of Austria Technologie & Systemtechnik AG, Austria, one of the leading manufacturers of PCB in Europe. AT&S AG acquired India’s largest PCB manufacturer in 1999 and significantly expanded its capacity in the years that followed.
Year it was established: 1988
Location of manufacturing facility: Nanjangud, Karnataka
Manufactures: Double sided plated through multilayer PCBs

Materials used in manufacturing PCBs
Excluding exotic products using special materials or processes, all printed circuit boards manufactured today can be built using the following four items which are usually purchased from manufacturers: 1. Laminates 2. Copper-clad laminates 3. Resin impregnated B-stage cloth (Pre-preg) 4. Copper foil
Laminates

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 feet by 8 feet in width and length. Varying cloth weaves (threads per inch), cloth thickness, and resin percentage are used to achieve the desired final thickness and dielectric characteristics.

Patterning (etching)
The majority of printed circuit boards today are made from purchased laminate material with copper already applied to both sides. The unwanted copper is removed by various methods leaving only the desired copper traces, this is called subtractive. PCB's can also be produced using an additive method where traces are adding to the bare substrate this is a complex process of multiple electroplating steps. The advantage of the additive method is less pollution of the environment. The PCB manufacturing method primarily depends on whether it is for production volume or sample/prototype quantities. Double-sided boards or multi-layer boards use plated-through holes, called vias, to connect traces on different layers of the PWB.
Large volume * Silk screen printing–the main commercial method. * Photographic methods–used when fine linewidths are required.
Small volume * Print onto transparent film and use as photomask along with photo-sensitized boards. (i.e., pre-sensitized boards), then etch. (Alternatively, use a film photoplotter). * Laser resist ablation: Spray black paint onto copper clad laminate, place into CNC laser plotter. The laser raster-scans the PCB and ablates (vaporizes) the paint where no resist is wanted. Etch. (Note: laser copper ablation is rarely used and is considered experimental. * Use a CNC-mill with a spade-shaped (i.e., a flat-ended cone) cutter or miniature end-mill to rout away the undesired copper, leaving only the traces.
Hobbyist
* Laser-printed resist: Laser-print onto transparency film, heat-transfer with an iron or modified laminator onto bare laminate, touch up with a marker, then etch. * Vinyl film and resist, non-washable marker, some other methods. Labor-intensive, only suitable for single boards.
Subtractive processes

The two processing methods used to produce a double-sided PWB with plated through holes.
Subtractive methods, that remove copper from an entirely copper-coated board, used for the production of printed circuit boards: 1. Silk screen printing uses etch-resistant inks to protect the copper foil. Subsequent etching removes the unwanted copper. Alternatively, the ink may be conductive, printed on a blank (non-conductive) board. The latter technique is also used in the manufacture of hybrid circuits. 2. Photoengraving uses a photomask and developer to selectively remove a photoresist coating. The remaining photoresist protects the copper foil. Subsequent etching removes the unwanted copper. The photomask is usually prepared with a photoplotter from data produced by a technician using CAM, or computer-aided manufacturing software. Laser-printed transparencies are typically employed for phototools ; however, direct laser imaging techniques are being employed to replace phototools for high-resolution requirements. 3. PCB milling uses a two or three-axis mechanical milling system to mill away the copper foil from the substrate. A PCB milling machine (referred to as a 'PCB Prototyper') operates in a similar way to a plotter, receiving commands from the host software that control the position of the milling head in the x, y, and (if relevant) z axis. Data to drive the Prototyper is extracted from files generated in PCB design software and stored in HPGL orGerber file format.
Additive processes
Additive processes adds desired copper traces to an insulating substrate. In the full additive process the bare laminate is covered with a photosensitive film which is imaged (exposed to light though a mask and then developed which removes the unexposed film). The exposed areas are sensitized in a chemical bath, usually containing palladium and similar to that used for through hole plating which makes the exposed area capable of bonding metal ions. The laminate is then plated with copper in the sensitized areas. When the mask is stripped, you have a finished PCB.
The most common is the "semi-additive" process: the unpatterned board has a thin layer of copper already on it. A reverse mask is then applied. (Unlike a subtractive process mask, this mask exposes those parts of the substrate that will eventually become the traces.) Additional copper is then plated onto the board in the unmasked areas; copper may be plated to any desired weight. Tin-lead or other surface platings are then applied. The mask is stripped away and a brief etching step removes the now-exposed bare original copper laminate from the board, isolating the individual traces. Some single-sided boards which have plated-through holes are made in this way. General Electric made consumer radio sets in the late 1960s using additive boards. In 1977 Dr.J.F.Mansfeld (N.V. Philips Gloeilampenfabrieken) presented the PD-R process (Physical Development by Reduction) in a speech at the Hotel International Zurich.
The additive process is commonly used for multi-layer boards as it facilitates the plating-through of the holes to produce conductive vias in the circuit board. PCB copper electroplating line in the process of pattern plating copper. | PCBs in process of having copper pattern plated, notice the blue dry film resist. |
Circuit properties of the PCB
Each trace consists of a flat, narrow part of the copper foil that remains after etching. The resistance, determined by width and thickness, of the traces 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 the form of stripline and 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; but they can be used as a deliberate part of the circuit design, obviating the need for additional discrete components.
Chemical etching
Chemical etching is usually done with ammonium persulfate or ferric chloride. For PTH (plated-through holes), additional steps of electroless deposition are done after the holes are drilled, then copper is electroplated to build up the thickness, the boards are screened, and plated with tin/lead. The tin/lead becomes the resist leaving the bare copper to be etched away.
The simplest method, used for small-scale production and often by hobbyists, is immersion etching, in which the board is submerged in etching solution such as ferric chloride. Compared with methods used for mass production, the etching time is long. Heat and agitation can be applied to the bath to speed the etching rate. In bubble etching, air is passed through the etchant bath to agitate the solution and speed up etching. Splash etching uses a motor-driven paddle to splash boards with etchant; the process has become commercially obsolete since it is not as fast as spray etching. In spray etching, the etchant solution is distributed over the boards by nozzles, and recirculated by pumps. Adjustment of the nozzle pattern, flow rate, temperature, and etchant composition gives predictable control of etching rates and high production rates.
As more copper is consumed from the boards, the etchant becomes saturated and less effective; different etchants have different capacities for copper, with some as high as 150 grams of copper per litre of solution. In commercial use, etchants can be regenerated to restore their activity, and the dissolved copper recovered and sold. Small-scale etching requires attention to disposal of used etchant, which is corrosive and toxic due to its metal content.
The etchant removes copper on all surfaces exposed by the resist. "Undercut" occurs when etchant attacks the thin edge of copper under the resist; this can reduce conductor widths and cause open-circuits. Careful control of etch time is required to prevent undercut. Where metallic plating is used as a resist, it can "overhang" which can cause short-circuits between adjacent traces when closely spaced. Overhang can be removed by wire-brushing the board after etching.
Lamination
"Multi layer" printed circuit boards have trace layers inside the board. One way to make a 4-layer PCB is to use a two-sided copper-clad laminate, etch the circuitry on both sides, then laminate to the top and bottom prepreg and copper foil. Lamination is done by placing the stack of materials in a press and applying pressure and heat for a period of time. This results in an inseparable one piece product. It is then drilled, plated, and etched again to get traces on top and bottom layers. Finally the PCB is covered with solder mask, marking legend, and a surface finish may be applied. Multi-layer PCB's allow for much higher component density.
Drilling
Holes through a PCB are typically drilled with small-diameter drill bits made of solid coated tungsten carbide. Coated tungsten carbide is recommended since many board materials are very abrasive and drilling must be high RPM and high feed to be cost effective. Drill bits must also remain sharp so as not to mar or tear the traces. Drilling with high-speed-steel is simply not feasible since the drill bits will dull quickly and thus tear the copper and ruin the boards. The drilling is performed by automated drilling machines with placement controlled by a drill tape or drill file. These computer-generated files are also called numerically controlled drill (NCD) files or "Excellon files". The drill file describes the location and size of each drilled hole. These holes are often filled with annular rings (hollow rivets) to create vias. Vias allow the electrical and thermal connection of conductors on opposite sides of the PCB.
When very small vias are required, drilling with mechanical bits is costly because of high rates of wear and breakage. In this case, the vias may be evaporated by lasers. Laser-drilled vias typically have an inferior surface finish inside the hole. These holes are called micro vias.
It is also possible with controlled-depth drilling, laser drilling, or by pre-drilling the individual sheets of the PCB before lamination, to produce holes that connect only some of the copper layers, rather than passing through the entire board. These holes are called blind vias when they connect an internal copper layer to an outer layer, or buried vias when they connect two or more internal copper layers and no outer layers.
The hole walls for boards with 2 or more layers can be made conductive and then electroplated with copper to form plated-through holes. These holes electrically connect the conducting layers of the PCB. For multilayer boards, those with 3 layers or more, drilling typically produces a smear of the high temperature decomposition products of bonding agent in the laminate system. Before the holes can be plated through, this smear must be removed by a chemical de-smear process, or by plasma-etch. The de-smear process ensures that a good connection is made to the copper layers when the hole is plated through. On high reliability boards a process called etch-back is performed chemically with a potassium permanganate based etchant or plasma.The etch-back removes resin and the glass fibers so that the copper layers extend into the hole and as the hole is plated become integral with the deposited copper.
Exposed conductor plating and coating
PCBs are plated with solder, tin, or gold over nickel as a resist for etching away the unneeded underlying copper.
After PCBs are etched and then rinsed with water, the soldermask is applied, and then any exposed copper is coated with solder, nickel/gold, or some other anti-corrosion coating.
Matte solder is usually fused to provide a better bonding surface or stripped to bare copper. Treatments, such as benzimidazolethiol, prevent surface oxidation of bare copper. The places to which components will be mounted are typically plated, because untreated bare copper oxidizes quickly, and therefore is not readily solderable. Traditionally, any exposed copper was coated with solder by hot air solder levelling (HASL). The HASL finish prevents oxidation from the underlying copper, thereby guaranteeing a solderable surface. This solder was a tin-lead alloy, however new solder compounds are now used to achieve compliance with the RoHS directive in the EU and US, which restricts the use of lead. One of these lead-free compounds is SN100CL, made up of 99.3% tin, 0.7% copper, 0.05% nickel, and a nominal of 60ppm germanium.
It is important to use solder compatible with both the PCB and the parts used. An example is Ball Grid Array (BGA) using tin-lead solder balls for connections losing their balls on bare copper traces or using lead-free solder paste.
Other platings used are OSP (organic surface protectant), immersion silver (IAg), immersion tin, electroless nickel with immersion gold coating (ENIG), and direct gold plating (over nickel). Edge connectors, placed along one edge of some boards, are often nickel plated then gold plated. Another coating consideration is rapid diffusion of coating metal into Tin solder. Tin forms intermetallics such as Cu5Sn6 and Ag3Cu that dissolve into the Tin liquidus or solidus(@50C), stripping surface coating or leaving voids.
Electrochemical migration (ECM) is the growth of conductive metal filaments on or in a printed circuit board (PCB) under the influence of a DC voltage bias. Silver, zinc, and aluminum are known to grow whiskers under the influence of an electric field. Silver also grows conducting surface paths in the presence of halide and other ions, making it a poor choice for electronics use. Tin will grow "whiskers" due to tension in the plated surface. Tin-Lead or Solder plating also grows whiskers, only reduced by the percentage Tin replaced. Reflow to melt solder or tin plate to relieve surface stress lowers whisker incidence. Another coating issue is tin pest, the transformation of tin to a powdery allotrope at low temperature.
Solder resist
Areas that should not be soldered may be covered with "solder resist" (solder mask). One of the most common solder resists used today is called LPI (liquid photoimageable). A photo sensitive coating is applied to the surface of the PWB, then exposed to light through the solder mask image film, and finally developed where the unexposed areas are washed away. Dry film solder mask is similar to the dry film used to image the PWB for plating or etching. After being laminated to the PWB surface it is imaged and develop as LPI. Once common but no longer commonly used because of its low accuracy and resolution is to screen print epoxy ink. Solder resist also provides protection from the environment.
Silkscreen
Line art and text may be printed onto the outer surfaces of a PCB usually by screen printing epoxy ink in a contrasting color , but can also be done with LPI or dry film like the solder resist. When space permits, the legend can indicate component designators, switch setting requirements, test points, and other features helpful in assembling, testing, and servicing the circuit board.
Some digital printing solutions are used instead of screen printing. This technology allows printing variable data onto the PCB, including individual serial numbers as text and bar code.
Test
Unpopulated boards may be subjected to a bare-board test where each circuit connection (as defined in a netlist) is verified as correct on the finished board. For high-volume production, a bed of nails tester, a fixture or a rigid needle adapter is used to make contact with copper lands or holes on one or both sides of the board to facilitate testing. A computer will instruct the electrical test unit to apply a small voltage to each contact point on the bed-of-nails as required, and verify that such voltage appears at other appropriate contact points. A "short" on a board would be a connection where there should not be one; an "open" is between two points that should be connected but are not. For small- or medium-volume boards, flying probe and flying-grid testers use moving test heads to make contact with the copper/silver/gold/solder lands or holes to verify the electrical connectivity of the board under test. Another method for testing is industrial CT scanning, which can generate a 3D rendering of the board along with 2D image slices and can show details such a soldered paths and connections.
Printed circuit assembly

PCB with test connection pads
After the printed circuit board (PCB) is completed, electronic components must be attached to form a functional printed circuit assembly, or PCA (sometimes called a "printed circuit board assembly" PCBA). In through-hole construction, component leads are inserted in holes. In surface-mount construction, the components are placed on pads or lands on the outer surfaces of the PCB. In both kinds of construction, component leads are electrically and mechanically fixed to the board with a molten metal solder.
There are a variety of soldering techniques used to attach components to a PCB. High volume production is usually done with SMT placement machine and bulk wave soldering or reflow ovens, but skilled technicians are able to solder very tiny parts (for instance 0201 packages which are 0.02 in. by 0.01 in.) by hand under a microscope, using tweezers and a fine tip soldering iron for small volume prototypes. Some parts may be extremely difficult to solder by hand, such as BGA packages.
Often, through-hole and surface-mount construction must be combined in a single assembly because some required components are available only in surface-mount packages, while others are available only in through-hole packages. Another reason to use both methods is that through-hole mounting can provide needed strength for components likely to endure physical stress, while components that are expected to go untouched will take up less space using surface-mount techniques.
After the board has been populated it may be tested in a variety of ways: * While the power is off, visual inspection, automated optical inspection. JEDEC guidelines for PCB component placement, soldering, and inspection are commonly used to maintain quality control in this stage of PCB manufacturing. * While the power is off, analog signature analysis, power-off testing. * While the power is on, in-circuit test, where physical measurements (i.e. voltage, frequency) can be done. * While the power is on, functional test, just checking if the PCB does what it had been designed to do.
To facilitate these tests, PCBs may be designed with extra pads to make temporary connections. Sometimes these pads must be isolated with resistors. The in-circuit test may also exercise boundary scan test features of some components. In-circuit test systems may also be used to program non volatile memory components on the board.
In boundary scan testing, test circuits integrated into various ICs on the board form temporary connections between the PCB traces to test that the ICs are mounted correctly. Boundary scan testing requires that all the ICs to be tested use a standard test configuration procedure, the most common one being the Joint Test Action Group (JTAG) standard. The JTAG test architecture provides a means to test interconnects between integrated circuits on a board without using physical test probes. JTAG tool vendors provide various types of stimulus and sophisticated algorithms, not only to detect the failing nets, but also to isolate the faults to specific nets, devices, and pins.
When boards fail the test, technicians may desolder and replace failed components, a task known as rework.
Protection and packaging
PCBs intended for extreme environments often have a conformal coating, which is applied by dipping or spraying after the components have been soldered. The coat prevents corrosion and leakage currents or shorting due to condensation. The earliest conformal coats were wax; modern conformal coats are usually dips of dilute solutions of silicone rubber, polyurethane, acrylic, or epoxy. Another technique for applying a conformal coating is for plastic to be sputtered onto the PCB in a vacuum chamber. The chief disadvantage of conformal coatings is that servicing of the board is rendered extremely difficult.
Many assembled PCBs are static sensitive, and therefore must be placed in antistati bags during transport. When handling these boards, the user must be grounded (earthed). Improper handling techniques might transmit an accumulated static charge through the board, damaging or destroying components. Even bare boards are sometimes static sensitive. Traces have become so fine that it's quite possible to blow an etch off the board (or change its characteristics) with a static charge. This is especially true on non-traditional PCBs such as MCMs and microwave PCBs.

ACKNOWLEDGEMENT I bestow my hearted appreciation and great fullness to the effort made by our instructor in charge Mr. Harnek singh in terms of the project idea, instruction and opportunity without which my force would have remained astray.

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