Printed Circuit Board

Hot Printed Circuit Board Deals
2 layers, 100 inch square total - $79.99. 4 layers, 75 inch square total - $205. We provide price in China market and North America local service.
www.goldphoenixpcb.biz

Printed Circuit Board Manufacturer
Mfr of Printed Circuit Test Points, Boards & Card Edge Connectors.
www.ComponentsCorp.com

PCB Assemblies
EMS Services: SMT, Thru Hole, Mixed Techonology, Lead-Free, Turnkey.
www.MicronCorp.com

Buy AC Parts Online
On time shipping guaranteed. Quality AC parts for less.
www.bestbuyheatingandairconditioning.com

Printed Circuit Board
We are a PCB supplier with office in Hong Kong and factories in China. We supply high quality double-sided and multilayer PCBs which are complied with Rohs directive.
www.parason.com.hk

Warning: mkdir() [function.mkdir]: Permission denied in /home/webs/affiliatelib2/CacheManager.php on line 12

Warning: mkdir() [function.mkdir]: No such file or directory in /home/webs/affiliatelib2/CacheManager.php on line 12

Warning: fopen(/home/templatecore2cache//*cluesnet.com/8a/8ac340af6a6b3c6a4e4da4e55c62fab1a2ec17a8.tc2cache) [function.fopen]: failed to open stream: No such file or directory in /home/webs/affiliatelib2/CacheManager.php on line 130

Warning: fwrite(): supplied argument is not a valid stream resource in /home/webs/affiliatelib2/CacheManager.php on line 131

Warning: fclose(): supplied argument is not a valid stream resource in /home/webs/affiliatelib2/CacheManager.php on line 132

ZX Spectrum computer board. Populated PCB, showing conductive traces, through-hole paths onto the other surface, with some mounted electrical componentsIn electronics, printed circuit boards, or PCBs, are used to mechanically support and electrically connect electronic components using Conductor (material) pathways, or signal traces, industrial etchinged from copper sheets laminated onto a non-conductive substrate. Alternative names are printed wiring board (PWB),and etched wiring board. Populating the board with electronic components forms a printed circuit assembly (PCA), also known as a printed circuit board assembly (PCBA).

PCBs are rugged, inexpensive, and can be highly reliable. They require much more layout effort and higher initial cost than either wire wrap or point-to-point construction circuits, but are much cheaper, faster, and consistent in high volume production. Much of the electronics industry's PCB design, assembly, and quality control needs are set by standards that are published by the IPC (electronics) organization.

Manufacturing Patterning (etching) The vast majority of printed circuit boards are made by adhering a layer of copper over the entire substrate, sometimes on both sides, (creating a "blank PCB") then removing unwanted copper after applying a temporary mask (eg. by etching), leaving only the desired copper traces. A few PCBs are made by adding traces to the bare substrate (or a substrate with a very thin layer of copper) usually by a complex process of multiple electroplating steps.

There are three common "subtractive" methods (methods that remove copper) used for the production of printed circuit boards:

Silk screen 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.

Photoengraving uses a photomask and chemical etching to remove the copper foil from the substrate. 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.

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 or Gerber File file format.

"Additive" processes also exist. The most common is the "semi-additive" process. In this version, 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 original copper laminate from the board, isolating the individual traces.

The additive process is commonly used for multi-layer boards as it facilitates the plating-through of the holes (vias) in the circuit board.

Lamination Some PCBs have trace layers inside the PCB and are called multi-layer PCBs. These are formed by bonding together separately etched thin boards.

Drilling Holes, or vias, through a PCB are typically drilled with tiny drill bits made of solid tungsten carbide. The drilling is performed by Automation 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.

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 walls of the holes, for boards with 2 or more layers, are plated with copper to form plated-through holes that electrically connect the conducting layers of the PCB. For multilayer boards, those with 4 layers or more, drilling typically produces a smear comprised of the 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.

Exposed conductor plating and coating The pads and lands to which components will be mounted are typically plated, because bare copper oxidizes quickly, and therefore is not readily solderable. Traditionally, any exposed copper was plated with solder. This solder was a tin-lead alloy, however new solder compounds are now used to achieve compliance with the RoHS directive in the EU, which restricts the use of lead. Other platings used are OSP (organic surface protectant), immersion silver, electroless nickel with immersion gold coating (ENIG), and direct gold. Edge connectors, placed along one edge of some boards, are often gold plated.

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.IPC (electronics) Publication IPC-TR-476A, “Electrochemical Migration: Electrically Induced Failures in Printed Wiring Assemblies,” Northbrook, IL, May 1997.S.Zhan, M. H. Azarian and M. Pecht, "Reliability Issues of No-Clean Flux Technology with Lead-free Solder Alloy for High Density Printed Circuit Boards", 38th International Symposium on Microelectronics, pp. 367-375, Philadelphia, PA, September 25-29, 2005.

Solder resist Areas that should not be soldered to may be covered with a polymer solder resist (solder mask) coating. The solder resist prevents solder from bridging between conductors and thereby creating short circuits. Solder resist also provides some protection from the environment.

Screen printing Line art and text may be printed onto the outer surfaces of a PCB by Screen-printing. When space permits, the screen print text can indicate component designators, switch setting requirements, test points, and other features helpful in assembling, testing, and servicing the circuit board.

Screen print is also known as the silk screen, or, in one sided PCBs, the red print.

Lately some digital printing solutions have been developed to substitute the traditional screen printing process. This technology allows printing variable data onto the PCB, including serialization and barcode information for traceability purposes.

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 send a small amount of current through each contact point on the bed-of-nails as required, and verify that such current can be seen on the other appropriate contact points. A "short" on a board would be a solid connection where there should be no connection. An "open" is between two points that should be connected and are not. For small- or medium-volume boards, flying-probe testers use moving test heads to make contact with the copper lands or holes to verify the electrical connectivity of the board under test.

Populating After the 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 machine placement 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" by 0.01") by hand under a microscope tweezers and a fine tip soldering iron for small volume prototypes. Some parts are impossible to solder by hand, such as Ball Grid Array (BGA) packages.

Often, through-hole and surface-mount construction must be combined in a single PCA 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.

JEDEC guidelines for PCB component placement, soldering, and inspection are commonly used to maintain quality control in this stage of PCB manufacturing.

After the board is populated, the populated board may be tested with an in circuit test system. To facilitate this test, 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 nonvolatile 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.

When boards fail the test, technicians may desoldering and replace failed components.

Protection and packaging PCBs intended for extreme environments often have a conformal coat, 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. Some are engineering plastics sputtered onto the PCB in a vacuum chamber.

Many assembled PCBs are Electrostatic discharge sensitive, and therefore must be placed in antistatic bags during transport. When handling these boards, the user must be Ground (electricity); failure to do this might transmit an accumulated static charge through the board, damaging or destroying it. Even bare boards are sometimes static sensitive. Traces have gotten 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 Multi-Chip Module and microwave PCBs.

Safety Certification (US) Safety Standard UL 796 covers component safety requirements for printed wiring boards for use as components in devices or appliances. Testing analyzes characteristics such as flammability, maximum operating temperature, electrical tracking, heat deflection, and direct support of live electrical parts.

The boards may use organic or inorganic base materials in a single or multilayer, rigid or flexible form. Circuitry construction may include etched, die stamped, precut, flush press, additive, and plated conductor techniques. Printed-component parts may be used.

The suitability of the pattern parameters, temperature and maximum solder limits shall be determined in accordance with the applicable end-product construction and requirements.

"Cordwood" construction Cordwood construction can give large space-saving advantages and was often used with Through-hole technology in applications where space was at a premium (such as missile guidance and telemetry systems). In 'cordwood' construction, two leaded components are mounted axially between two parallel planes. Instead of soldering the components, they were connected to other components by thin nickel tapes welded at right angles onto the component leads. To avoid shorting together of different interconnection layers, thin insulating cards were placed between them. Perforations or holes in the cards would allow component leads to project through to the next interconnection layer. One disadvantage of this system was that special nickel leaded components had to be used to allow the interconnecting welds to be made.Some versions of cordwood construction used single sided PCBs as the interconnection method (as pictured). This meant that normal leaded components could be used.

Before the advent of integrated circuits, this method allowed the highest possible component packing density; because of this, it was used by a number of computer vendors including Control Data Corporation. The cordwood method of construction now appears to have fallen into disuse, probably because high packing densities can be more easily achieved using surface mount techniques and integrated circuits.

Multiwire boards Multiwire is a patented technique of interconnection which uses machine-routed insulated wires embedded in a non-conducting matrix (often plastic resin). It was used during the 1980s and 1990s. (Augat Inc., U.S. Patent 4,648,180)

Since it was quite easy to stack interconnections (wires) inside the embedding matrix, the approach allowed to forget completely about the routing of wires (usually a time-consuming operation of PCB design): Anywhere the designer needs a connection, the machine will draw a wire in straight line from one location/pin to another. This led to very short design times (no complex algorithms to use even for high density designs), reduced cross talk (an electrical phenomenon appearing where a current in one wire generates another current in another conductor, that is highly amplified when wires are parallel - this nearly never happens in Multiwire), but the cost is too high to compete with cheaper PCB technologies when large quantities are needed.

Surface-mount technology s, transistors and an integrated circuit.Surface-mount technology was developed in the 1960s, gained momentum in Japan in the early 1980s and became widely used globally by the mid 1990s.Components were mechanically redesigned to have small metal tabs or end caps that could be directly soldered to the surface of the PCB. Components became much smaller and component placement on both sides of the board became far more common with surface-mounting than through-hole mounting, allowing much higher circuit densities.Surface mounting lends itself well to a high degree of automation, reducing labour cost and greatly increasing production and quality rates. SMDs can be one-quarter to one-tenth the size and weight, and passive components can be one-half to one-quarter the cost of through-hole parts. Integrated circuits (where the chip itself is the most expensive part) are often priced the same regardless of package type however. As of 2006, some wire-ended components, such as small signal switch diodes (philips 1N4148 for instance), are actually significantly cheaper than corresponding SMD versions.

See also

Breadboard
C.I.D.+
Hybrid Integrated Circuit
Multi-Chip Module
Electronic waste
Electrical conductor

PCB Materials

Laminate materials:

FR-4, the most common PCB material
FR-2
Polyimide
GETEK
BT-Epoxy
Cyanate Ester
Pyralux, a material for flexible printed circuits
PTFE, Polytetrafluoroethylene
Rogers Bendflex

Conductive ink
For a comparison see NetworkPCB's "Material Spec"

PCB software

PCB Artist - PCB Artist is a free, user friendly, integrated schematic capture & PCB layout tool. Free Gerber files available. Free Tech Support.
PCB123 from Sunstone Circuits
Edwinxp by Visionics
Altium Designer 6 by Altium (formerly Protel)
AutoTRAX EDA
Eagle (program) by Cadsoft
Expedition PCB by Mentor Graphics
ExpressPCB
Cadstar by Zuken
CR5000 by Zuken
Electronics Workbench (now owned by National Instruments)
PADS by Mentor Graphics
gEDA, open-source PCB software project
OrCAD
P-CAD (owned by Altium)
Allegro (Cadence Design Systems)
SPECCTRA (now part of OrCAD)
TARGET 3001!
Kicad, open-source suite
WinQcad by Microcad
Proteus PCB Design by Labcenter Electronics
Ivex Winboard

References

Coombs, Clyde F., Jr. (Ed.) (1995). Printed Circuits Handbook, Fourth Edition, McGraw-Hill ISBN 0-07-012754-9.
Coombs, Clyde F., Jr. (Ed.) (2001). Printed Circuits Handbook, Fifth Edition" ', McGraw-Hill Professional ISBN 0-07-135016-0.

Coombs, Clyde F., Jr. (Ed.) (2007). Printed Circuits Handbook, Sixth Edition" ', McGraw-Hill Professional ISBN 0-07-146734-3.

External links Design guidelines

Digital System Design Guidelines by Tony Goodloe
PWB/PCB Design – Analog, RF & EMC Considerations in Printed Wiring Board Design
High Frequency Laminate Information by Chet Guiles

Standards and Specifications

Association Connecting Electronics Industries (IPC)
MIL-PRF-31032, Performance Specification Printed Circuit Board/Printed Wiring Board
MIL-PRF-55110, Performance Specification for Rigid Printed Circuit Board/Printed Wiring Board
MIL-PRF-50884, Performance Specification for Flexible and Rigid-Flexible Printed Circuit Board/Printed Wiring Board

Do It Yourself (DIY) guides

Making PCBs with a laser printer and photo paper, no UV machine needed anymore.
More detailed PCB DIY making with laser printer

Others

First PCB Patent - Patent Nº 2,756,485 - Process of Assembling Electrical Circuits ( pdf)
PCB Artist - PCB Artist is a free, user friendly, integrated schematic capture & PCB layout tool. Free Gerber files available. Free Tech Support.
List of PCB trade shows
Heat development on PCBs depending on current, trackwidth and copper thickness
General Information on Printed Board Programs
SMT & Printed Board Electronics Manufacturing Industry Portal
Information on PCB Layout software - DIY PCB hints & tips

printed circuit board from FOLDOC
printed circuit board < hardware > (PCB) A thin board to which electronic components are fixed by solder. Component leads and integrated circuit pins may pass through holes ("vias ...

printed circuit board | pcb | pcb assembly | circuit board | prototype ...
A printed circuit board manufacturer specialising in PCB/PWB manufacture, PCB assembly and associated printed circuit board services.

UK Printed Circuit Board Manufacturers - Photomechanical Services ...
Photomechanical Services (Essex) Ltd Printed Circuit Board Manufacturers Photomechanical Services (Essex) Ltd is an independent and privately owned company, registered in England ...

UK Printed Circuit Board Manufacturers - Photomechanical Services ...
A fully operational and documented Quality Management System has been in place since 1994. Circuit boards are final inspected to IPC-A-600

Prototype PCB Design, Printed Circuit Board Assembly
Tour Garner Osborne's printed circuit board services - protoype pcb design and assembly ... Prototype PCB Design and Assembly: To find out more about prototype PCB design and ...

Dictionary of Computers - printed circuit board
Skip to page content | Tiscali Quicklinks. Please visit our Accessibility Page for a list of the Access Keys you can use to find your way around the site, skip directly to the main ...

Printed Circuit Board
Mercom's core expertise has been built upon printed circuit board fault diagnosis and repair. These capabilities are evidenced by the diverse variety of products covered ranging ...

SPQR Europe Limited | Printed Circuit Board Manufacture
SPQR specialise in Printed Circuit Boards, guaranteeing a complete PCB service, from pre-production to volume manufacture, offering a price advantage and continuity of supply.

Printed Circuit Board (PCB) Manufacturers UK
Details of the printed circuit board development and manufacturing services available.

Home for Hamilton PCB Design Printed Circuit Board Design company in ...
Designers of printed circuit boards for large and small companies for 22 years in the Raleigh Durham NC area using the PADS innoveda software.