PCB PLC

*PCB PLC*
Multilayer PCB fab - A quickturn pcb 123 How to Get Express PCB Prototypes - Prototype Printed Circuit Board.

PCB Printed Circuit Boards

A Printed Circuit Board, or PCB for short, is used to mechanically support and electrically connect electronic components using conductive pathways, or traces, etched from copper sheets laminated onto a non-conductive substrate. Alternative names are PWB printed wiring board, and etched wiring board. A PCB Printed circuit board populated with electronic components is a PCA printed circuit assembly, also known as a PCBA printed circuit board assembly.

PCBs are rugged, inexpensive, and can be highly reliable. They require much more layout effort and higher initial cost than either wire-wrapped or point-to-point constructed 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 organization.

Major PLC/ PCB brands and terms:

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PCB Manufacturing Processes

Patterning (etching)

The vast majority of printed circuit boards are made by bonding 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.

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 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.

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.

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[1], 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.

Test - Testing a PCB Printed Circuit Board

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 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.

Populating PCBs

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.

Protection and Packaging of a PCB

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.

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.

Surface-mount Technology SMT / SMD

In Surface-mount technology SMD components are 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.

PCB Do It Yourself (DIY) guides

Making PCBs with a laser printer and photo paper, no UV machine needed anymore. - http://max8888.orcon.net.nz/pcbs.htm
More detailed PCB DIY making with laser printer - http://homepage.tinet.ie/~ei9gq/pcb.html
Making PCBs by hand using an etch-resist pen (no printer or special paper needed) - http://www.stefanv.com/electronics/etching.htm

PCB Software

Some major PCB Software and companies are:

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 by Cadsoft
Expedition PCB by Mentor Graphics
ExpressPCB
Proteus PCB Design by Labcenter Electronics

Source Forge PCB is an interactive printed circuit board editor for the X11 window system. PCB includes a rats nest feature, design rule checking, and can provide industry standard RS-274-X (Gerber), NC drill, and centroid data (X-Y data) output for use in the board fabrication and assembly process. PCB offers high end features such as an autorouter and trace optimizer which can tremendously reduce layout time.

Printed Circuit Board Trace Calculators

PCB Printed Circuit Board Trace Calculators are just like softwares to speed up the process of calculating, designing and fab/producing from prototype to express final product.

Multilayer Circuit Board PCB differential impedance
http://www.icd.com.au/rego_form5.html - http://www.icd.com.au/board.html
Trace width calculator - For external and internal layers
http://circuitcalculator.com/wordpress/2006/01/31/pcb-trace-width-calculator/
Collection of calculators and PCB design tools
http://www.ultracad.com/calc.htm
Trace characteristic impedance - calculator
http://168.144.193.113/emc/emccalc.htm
IPC-7351 land pattern viewer, plus tools (replaced IPC-SM-782)
http://landpatterns.ipc.org/default.asp
PWB conduction heat transfer - calculator
http://www.coolingzone.com/Guest/News/NL_APR_2001/Tutorial/ECM_Article.html
Clearance and cree-page calculator
http://www.creepage.com/
IPC-7351A SMT Surface-Mounted Technology land pattern calculator
http://www.pcblibraries.com/IPC-7351/LPCalcLE.asp

PCB Power Circuit Breaker

A PCB Power Circuit Breaker, or simply circuit breaker, is an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city.

Surface-mount Technology SMT

Surface mount technology (SMT) is a method for constructing electronic circuits in which the components (SMC, or Surface Mounted Components) are mounted directly onto the surface of printed circuit boards (PCBs). Electronic devices so made are called surface-mount devices or SMDs. In the industry it has largely replaced the through-hole technology construction method of fitting components with wire leads into holes in the circuit board.

An SMT component is usually smaller than its leaded counterpart because it has either smaller leads or no leads at all. It may have short pins or leads of various styles, flat contacts, a matrix of balls (BGAs), or terminations on the body of the component.

Surface-mounted Devices SMDs

SMDs Surface-mounted devices are used in SMT Surface mount technology and usually made physically small and lightweight for this reason. Surface mounting lends itself well to a high degree of automation, reducing labor cost and greatly increasing production rates. SMDs can be one-quarter to one-tenth the size and weight, and one-half to one-quarter the cost of equivalent through-hole parts.

Prototype Printed Circuit Board - A Great Hobby! To Start!

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