PCBA - Printed Circuit Board Assembly

Printed Circuit Board Assembly Technology

2010-12-22T22:38:00.000-08:00

Right from their inception, assembly services have gained momentum and are considered as one of the most renowned services. Many companies are always on the look out for best assembling technology and services and manufacturers give the best of their services.

But before proceeding, let us first know about a PCB Assembly-
When electronic components are attached to a PCB, it is referred to as Printed Circuit Assembly. It is done only after a Circuit Board Assembly has been created completely. Various kinds of techniques are available to attach electronic components to printed circuit boards. Surface mount and through-the-hole technology are mostly combined on a single Printed Circuit Assembly. This is because of the availability of very few electronic components in surface mount packages.

Though, high volume production is executed by machine placement. Printed Circuit Assembly is used to connect and support electronic components mechanically. This is done by using conductive pathways or traces, engraved from the laminated copper sheers onto a non-conductive substrate.

There are three ways to create PCB assembly. Those are:

• Surface mount assembly – This technology emerged in 60s and evolved in 1980s. And now, it is widely used. In surface mount technology, components have metal tabs, and can be soldered easily to the board. Higher circuit densities can be achieved if components are attached on both the sides of the circuit.

• Conventional PTH Assembly – Plated through-hole technology includes components with leads attached. Thee components are inserted with the provision of drilled holes in a circuit board. This is an expensive technique; however it leads to the most efficient boards.

• Box-build, Electro-Mechanical Assembly – This technology involves the use of custom metalwork, wire harnesses and looms, cable assembly, and moulded plastics. All this is done to create Circuit Board Assembly.

But, no matter how robust your PCB Assembly design is, it is still prone to wear and tear. And the damaged or outdated parts of the PCB Assembly are not available easily in the market. In this case, it becomes necessary to avail Circuit Board Assembly services.

Hence, manufacturers should provide effective and efficient Printed Circuit Assembly service to their customer. This will not only keep the customers happy, but will also help the manufacturer to gain trust and goodwill in the market.

FPGA board for avionics applications designed by MEN Micro

2010-09-23T00:33:00.001-07:00

AMBLER, Pa., 4 Sept. 2010. MEN Micro Inc. now offers the 6U field programmable gate array (FPGA) -based, triple-redundant A602 64-bit VMEbus single board computer (SBC) that uses a lock-step architecture keeping software development at a minimum for avionics applications.

The A602 runs the same set of operations in parallel to ensure that the programming only views the hardware components once, Men Micro officials say.

The single-slot, commercial-off-the-shelf (COTS) A602 developed according to RTCA DO-254 offers reliability and economical implementation with high reliability up to Design Assurance Level (DAL) A (catastrophic) in avionics and up to Safety Integrity Level (SIL) 4 in trains -- the most stringent level in each class.

The 900 MHz PowerPC 750, the 512-megabyte main memory and the internal structure of the FPGA are triple-redundant. Critical functions, such as voters implemented as IP cores in the FPGA, monitor at least two of the three redundant components to provide the same result to guarantee system reliability. In the event one of the three redundant components fails, the system remains completely operational providing the required availability for highly critical systems.

Other redundant components in the SBC include local PSUs, Flash memory and clock oscillators. In an effort to increase safety and availability, additional diagnosis mechanisms (BITE, e.g. extensive self tests) help detect latent errors before they lead to a system error. The design is oriented towards strictly deterministic operation for the same purpose -- to avoid interrupts and DMA.

Standard I/O contained in the FPGA is accessible via the rear and this includes a sextuple UART, an I2C bus and an RS232 interface that can also be led to the front. The A602 also provides two PMC slots, one accessed via the front or rear I/O that can be used with all standard PMC modules and the other for an AFDX PMC connection via rear I/O.

Operating temperature is -40 to 50 degrees Celsius with qualified components. Pricing for the A602 is $12,994.

For more information visit http://www.menmicro.com/products/01A602-.html.

Dawn of a New Age in Serial Switch Fabrics

2010-09-20T05:21:00.000-07:00

By John Keller
Editor in Chief

We stand on the doorstep of the next generation in serial data switch fabric networking, which will see vast speed increases from today's data processing. The dominant switch fabrics of today–Gigabit Ethernet, PCI Express, and Serial RapidIO–all are ready to move to even faster versions, which promise fundamental leaps in embedded computing power.

Systems engineers, meanwhile, are finding innovative uses for point-to-point communications links called Aurora and SerialLite for field-programmable gate arrays (FPGAs) from Xilinx and Altera, and are even finding new value in old standbys.

Switch fabric technology is a godsend for embedded computing designers who increasingly realize that parallel databuses like VME 64 simply are no longer adequate for today's high-end aerospace and defense applications in electro-optical sensor processing, software-defined radio, signals intelligence, and radar signal processing.

Switch fabrics represent the next step in intra- and inter-system data communications in high-end and complex systems. Switch fabrics blend hardware and software to move data into a network that joins sensors, single-board computers, and central processing units to move data coming into a network node out by the correct path to the next node in the network. Without this kind of technology in today's world of high-speed central processors, data bottlenecks and roadblocks likely would proliferate through complex signal processing and cause crippling delays by a failure to move information quickly enough to keep up with processor capacity.

While switch fabrics have enabled systems designers to take the next steps in signal processing capability, the next generations will help move data and signal processing ahead even more. Gigabit Ethernet technology is enabling high-speed control and monitoring of complex data processing. While 1-gigabit and 10-gigabit Ethernet implementations are commonplace in switch fabric networks, 40- and 100-gigabit Ethernet implementations wait in the wings not only to speed control, monitoring, and predictive maintenance forward, but also to provide more options and standardization for designers of high-speed systems.

Several years ago, the PowerPC microprocessor architecture helped revolutionize digital signal processing (DSP) applications. Prior to that, designers had to use separate dedicated DSP chips and general-purpose microprocessors. The PowerPC enabled them to perform separate tasks with the same kind of chip to simplify programming, acquisition, maintenance, and technology insertion.

Gigabit Ethernet technology could offer similar advantages. While complex switch-fabric based computer systems use Gigabit Ethernet, PCI Express, and Serial RapidIO separately for different tasks within the system, Gigabit Ethernet as it moves into the 40- and 100-gigabit realm may enable designers to implement several different high-speed data paths with the same networking technology. Depending on the application, Ethernet used on several layers of the OpenVPX Multiplane Architecture or similar design approaches could help simplify designs and reduce life cycle costs. Where Ethernet technology is not appropriate, the next generations of PCI Express, RapidIO, and even InfiniBand are ready to become available.

Where switch fabric architectures are concerned, systems designers are looking forward to more speed, less cost and complexity, and easier upgrades and technology insertion. Couple that with new generations of tools like POET from Mercury Computer Systems, and the future of switch fabric architectures looks bright indeed.

PCB |PCB Design Software |PCB Electronics |Printed Circuit Board |

Automated inspection in printed circuit board assembly (PCBA) manufacturing

2010-09-13T01:55:00.000-07:00

Visual inspection has long been a necessary method of quality control in Printed Circuit Board Assemblies (PCBA) manufacturing. The characteristics of electronic assemblies have changed substantially over the last decade. Todays high lead count, fine pitch SMT components are becoming even more difficult for humans to inspect at the same time automated inspection systems have become reliable than manual inspection and are now accepted as valuable tools for producing high quality PCBA products. The basic requirements of an automated inspection system remain same in all PCBA manufacturing but the type of the automated system (off- line/on-line), where applied in the production flow, entire boards or only on a sample basis, inspection coverage (100% or partial) vary between different PCBA manufacturers. In PCBA manufacturing the emphasis is more in the electrical functionality of the PCBA than in it's appearance. It is nearly impossible to impose stringent specifications in the appearance of the components and other materials used in PCBA manufacturing. Due to the large number of component/PCB supplier and wide variations in materials and processes the challenge in successfully automating the inspection process is the variability in the appearance of components on PCBA. But in a high volume PCBA manufacturing where fewer board types are running in large volumes for long periods of time, the variability in component appearance can be controlled much better than a low volume PCBA manufacturing where more types are running in low volumes for short period of time. This paper discusses the development and implementation of a low cost flexible automated inspection system for PCBAs. The system can detect over ninety percent of visual defects on PCBAs. The key features of the system are quick and easy set-up, capability to inspect different types of board and quick change over between different boards and low cost.

PCB Circuit Boards
PCB Electronics

Which Laptop battery is right for you?

2010-09-03T00:18:00.000-07:00

The short answer is: “Whichever type fits your laptop.”

Laptop batteries vary according to the model and type of laptop computer for which they’ve been designed. All laptop batteries do, however, share some common characteristics that differentiate them from regular household batteries:

• Laptop batteries are rechargeable
• They are composed of multiple internal cells
• Within each laptop battery is a small printed circuit board
• Shape and location of terminals differ from model to model.

As is the case with all batteries, laptop batteries create an electrochemical reaction, forcing a stream of electrons from one position to another. Also like other batteries, laptop batteries have positive and negative terminals that receive and send electrons.

Rechargeable batteries are more complex, however, than standard batteries. This is because the electrochemical reaction that provides power must be reversible. Care has to be taken when recharging them to ensure they perform at their best.

Frank McLarnon, Lawrence Berkley lab’s staff scientist explains it this way to Scientific American.com:

“When a battery is discharged, an electrochemical oxidation reaction proceeds at the negative electrode, and an electrochemical reduction reaction occurs at the positive electrode. When one attempts to recharge a battery by reversing the direction of electric current flow, the opposite takes place: a reduction reaction proceeds at the negative electrode, and an oxidation reaction takes place at the positive electrode.

In the case of the rechargeable battery, the electrochemical oxidation-reduction reactions are reversible at both electrodes. In the case of the non-rechargeable battery, when one attempts to recharge the battery by reversing the direction of electron current flow, at least one of the electrochemical oxidation-reduction reactions is not reversible. When the battery is charged, the overall reduction reaction that proceeds at the negative electrode may not be the true reverse of the oxidation reaction that proceeded when the battery was discharged.

If the laptop battery process isn’t exact, then unwanted build up can take place on either terminal over time, which can cause a dangerous short-circuit.”

It is so important to ensure that your laptop battery or notebook battery is the one designed for your particular model and type. Only buy Dell laptop batteries for a Dell laptop computer, Gateway aren’t compatible with Compaq laptop batteries and Toshiba laptop batteries won’t sit well in a Sony.

It is also wise to remember that old adage: “You get what you pay for.”
Some companies offer used “cheap laptop batteries” for sale, saying that they have refurbished each battery and restored most of its useful life. The fallacy of this is that, although possible to refurbish a second-hand laptop battery, the cost to do so would be more than the price of a new battery. So, “Buyer beware,” and if you must buy discount laptop batteries, buy new discounted batteries.

Laptop computers are a boon to business, large and small. As a wise person is just about to say: “Look after your laptop and it will look after you.”

Printed Circuit Board

Is Your Solder Mask Process Ready for the Fine Pitches?

2010-08-30T02:35:00.000-07:00

Component Technology and Miniaturization

Component technology and assembly have historically been driving new material developments to meet requirements for solder mask materials and application processes. The requirements for smaller component pitches with advanced functionalities have rapidly increased in the past few years. There is a continuous request for miniaturization of electronic designs, especially in consumer handheld electronics, where the component pitches are reduced to the minimum. The solder mask material has to be able to form smaller features on the surface combined with high registration and imaging accuracy on large production panels.

Fine pitch designs from 0.4 mm are in volume production while 0.3 mm has been tested and will be introduced in the next few years. The PCB producer needs to be able to process large production panels with fine pitch designs in both outer layer and solder mask HDI production processes.
So far this has been possible with standard contact printing equipment using optical registration technology. For the next-generation components this will be extremely challenging and it will be difficult to achieve acceptable production yields. Depending on pad size designs, solder mask clearances are down to 20 µm, with small features of 50 µm between pads (see Figure 1).

LDI Imaging Technology
LDI imaging technology was introduced in PCB manufacturing some years ago. PCB producers started to introduce the LDI imaging process to improve the registration accuracy in the production of inner and outer layers. There are a number of compatible resists available for LDI primary imaging where dry films are the most common materials in use for inner and outer layer imaging.
Digitalization, through elimination of artwork, will help producers to complete the whole PCB process, with high imaging accuracy and yield. The solder mask process has to follow at the end of the PCB production cycle without creation of a single artwork.
LDI equipment manufacturers are using single wavelength light sources of 355 or 405 nm. Recent developments increased the effective output energies, shortening the exposure time, but mechanical and registration cycle time has also been reduced for a faster total cycle time and higher productivity. Other market drivers are fast prototyping to eliminate artwork and reduce total lead times through production (see Figure 2).

Can Standard Solder Mask Material Be Used for LDI?
Not in an optimized way. The main reason is the absorption during imaging is different from LDI. The polymer/photo system of the solder mask material has to be able to absorb at a specific single wavelength of 355 or 405 nm, while a traditional standard exposure is emitting energy at a wider UV spectra (see Figure 3, Fe-doped lamp [blue] and Ga-doped lamp [orange]). The photo package can then absorb at various wavelengths, which is at an optimum for each photo initiator component.
The standard solder mask material will not absorb enough UV energy at LDI wave lengths to perform acceptably with fast and complete photo reaction. For high performance, a high cross linking density is needed to complete the layer thickness. If the cross linking density is too low, then undercut and low resolution will result, which in turn will not form small solder mask features such as 50 µm solder dams, on the surface. With decreased undercut, the risk of penetration or entrapment of chemicals in post-solder mask processes is reduced (see Figure 4).

LDI Imaging at 355 nm
An LDI solder mask applied in various thicknesses results in a solder dam thickness of 30 to 50 µm. To achieve a 50 µm (2 mil) dam in 30 µm film thickness, a thickness commonly applied for HDI outer layers, the exposure energy needs to be 50 to 60 mJ but requires 80 to 90 mJ at approximately a 40 µm thickness.

The exposure values for this process will be strongly influenced by the developing process, which has to be optimized for the aspect ratio of the panels, minimum hole diameters, and buried vias to be cleaned out from solder mask material. This also means that the wet solder mask application process will influence the exposure values and how much solder mask material is present in the plated holes or vias, which need to be cleaned out. The optimal application process is electrostatic spray or spray application in general as less volume of material is present in the plated holes (see Figure 5).

LDI Solder Mask
The excellent imaging properties of an LDI solder mask are demonstrated in Figure 6 to 8. The 50 µm (2 mil) dam in 30 µm thickness is processed on a UV 355 LDI (50 mJ exposure energy). The dam feature shows excellent shape and sidewall with a very low undercut. The demonstrated LDI products are formulated from IP-protected high-performance polymer binders, and they are modern state-of-the-art solder mask formulations that are halogen-free, RoHS-conforming, and UL-listed. LDI solder mask ranges are used for all conventional solder mask application technologies like screen print, spray, or curtain coating.

Split Imaging Process
PCB producers, in some cases, do not need to use LDI imaging for all panels they produce. The required registration accuracy could be handled in a standard contact exposure process while some panels do require LDI imaging due to tight tolerances. An LDI solder mask could be applied and processed on the same wet application line. After coating and drying, the processing of panels could be either imaged in LDI or in common used standard exposure using good vacuum.

PCB producers can benefit from high production flexibility where the difficult designs could be done with LDI imaging and conventional designs with standard exposure, using only one product applied in one wet solder mask application line.

Printed Circuit Boards

MAJOR DOMESTIC MARKETS AND TRENDS

2010-08-27T06:04:00.000-07:00

The seven basic markets for printed circuit boards are described below.

• Automotive: engine and drive performance, convenience and safety, entertainment (radios), and other applications for diagnostics display and security.

• Communication: mobile radio, touch tone phones, portable communication, pagers, data transmissions, microwave relay, telecommunications and telephone switching equipment, and navigation instruments

• Consumer Electronics: watches, clocks, portable calculators, musical instruments, electronic games, large appliances, microwave ovens, pinball/arcade games, television, home entertainment, video recorders, and smoke and intrusion detection systems.

• Computer/Business Equipment: mainframe computers, mini computers, broad level processors, add-on memory, input/output devices, terminals, printers, copy machines, facsimile machines, word processors, cash registers, teaching machines, gas pumps, and taxi meters.

• Government/Military/Aerospace: radar, guidance and control systems, communication and navigation, electronic warfare, ground support, sonar ordinance, missiles, and satellite and related systems.

• Industrial Electronics: machine and process control, production test and measurement, material handling, machining equipment, pollution, energy, and safety equipment, numerical controls, power controls, sensors, and weighing equipment.

• Instrumentation: test and measurement equipment, medical instruments and medical testers, analytical, nuclear, lasers, scientific instruments, and implant devices.

Computers are the major U.S. market for PCBs, with communications being the second largest application market. The Institute for Interconnecting and Packaging Electronic Circuits (IPC) indicates that nearly 39 percent of printed circuit boards produced in 1993 were used by the computer market, while 22 percent were used by the communication industry.

Outer Layer Circuit Formation

2010-08-25T01:17:00.000-07:00

This section describes the processes used to create the printed circuit design on the two outer layers of the panel.

1 RESIST APPLICATION OPERATIONS
The types of resist and application methods used by the PCB industry for Outer Layer Circuit Formation are the same as the Inner Layer Circuit Formation.

2 EXPOSURE UNITS
The resist that has been applied to the outer layers of a circuit board panel is selectively exposed to UV light using photo design tools and electric Exposure Units similar to those for inner layer circuit formation. However, the outer layer circuits are normally produced using a negative photoresist process. In a negative photoresist process, the resist covering the desired circuit traces remains soft because it is not exposed to the UV light, while the resist covering the undesired copper areas is exposed to the UV light and polymerized.

3 DEVELOPER
The unexposed resist is removed by a Developer to reveal the copper foil circuit pattern. this developer normally contains potassium carbonate to dissolve the soft unpolymerized resist.

4 ELECTROLYTIC COPPER PLATING LINES
Additional copper is added to the copper foil circuit pattern by electrolytic copper plating. The electrolytic copper plating line includes several cleaning or etching baths, rinses, and a copper sulfate plating bath.

5 TIN AND TIN/LEAD PLATING LINES
The new copper circuit design is protected from subsequent processing steps by adding a second layer of metal. Most PCB facilities use tin or tin/lead alloy for this step. The tin or tin/lead alloy is added to the plating line which may include cleaning baths, etching baths, rinses, and electrolytic plating baths.

6 RESIST STRIPPERS
Resist Strippers are used to dissolve and remove the polymerized resist to reveal the unwanted copper foil.

7 ETCHERS
unwanted copper foil is removed by ammoniacal etchers.

8 TIN AND TIN/LEAD STRIPPERS
The protective layer of tin (or tin/lead) is removed from the copper circuits using either a chemical stripping process or an electrolytic stripping process. Both processes normally use inorganic solutions. Occasionally this step is skipped per customer requirements, and the tin/lead plate is left on the panel for reflow.

Printed Circuit Board

Printed Circuit Board Manufacturing

2010-08-23T01:45:00.000-07:00

Printed Circuit Board Manufacture

2010-08-19T00:33:00.000-07:00

The manufacture of a multi-layer circuit board typically starts with preparing the board laminates. Each laminate has a core of fiberglass-reinforced polymer resin, with both sides of the core laminated over with copper foil surfaces. The resulting laminate is then baked, to cure and stabilize the polymer core. Subsequent processing etches the copper surfaces, so that the copper circuit patterns are formed on each surface. After additional processing, the laminates are layered onto each other using isolation sheets, and fabricated into the multi-layer printed circuit board. Holes are then drilled through the board, according to the intended circuit design. After etching and deburring the drillholes, the board is electroless-plated with copper to deposit a conductive copper coating onto the wall of each drillhole. This conductive surface is then electroplated with copper, to strengthen and build up the copper surfaces on the drillhole walls. The purpose of the copper-coated drillhole walls is to connect the circuit pattern on each board laminate into a continuous circuit design among the laminated layers of the completed printed circuit board.

The copper-coated, multi-layered board then undergoes additional processing to complete the circuitry. Initially in this process, a dry film mask is applied onto the exposed copper surfaces on both sides of the board. The mask is applied as a pattern so that a circuit design is traced onto the copper surface. Subsequent processing exposes the copper tracings by removing the dry film mask according to the circuit design. The exposed copper tracings are plated with solder to protect the copper circuit. The mask is then stripped from the unplatted copper areas, which are then etched to remove any unsoldered copper strips. The ammoniacal etchant removes the unmasked copper, but does not remove the tin/lead solder plating that protects the copper circuit tracings. Then the panel is rinsed, and processed in 10% sulfuric acid as an oxidation inhibitor.

Wastestreams
For Circuit Board Manufacturers, the most prevalent hazardous wastestreams are spent aqueous process solutions, spent rinsewater, other metal-laden wastewaters, and the metalladen sludge that is precipitated by the treatment of the spent solutions, rinsewater, and other wastewaters. Many of the innovative source reduction measures listed here would reduce or eliminate sludge generation. Some of the measures would reduce the volume of aqueous wastestreams.

Source Reduction
Hazardous waste source reduction reduces or eliminates the quantity of hazardous waste generated at the source generating the waste. Source reduction can simplify and economize hazardous waste management.
Source reduction of process solutions includes several process substitution measures that reduce or eliminate the use of some process baths that generate hazardous waste. Some of the substitutions still do generate spent process solutions, but often at reduced volume, or as spent solutions that can be easily regenerated for reuse.

Recycling
Onsite and offsite recycling are a complement to source reduction. While source reduction avoids generation of waste at the source, recycling manages the waste to derive further benefit. Like source reduction, recycling is a preferable alternative to treatment or disposal of the waste. Recycling can recover spent process chemicals or rinsewaters. Recycling can also recover contaminants like copper and other etched metals. Like source reduction, recycling can reduce the risk and impact to human health and the environment. Recycling can reduce or delay the need for storage, handling, transport, and disposal of spent process chemicals.

Intel Makes a Digital Coin Tosser for Future Processors

2010-08-16T01:58:00.000-07:00

An all-digital random-number generator will help keep encryption strong and data safe for chips with features 45 nanometers and smaller 29 June 2010—Random-number generators make cryptography possible, thereby making safe digital communication possible, but because the generators rely on analog components, they are notoriously difficult to reduce in size. Engineers at Intel’s Circuit Research Lab, in Hillsboro, Ore., bet they could build one without the analog parts using the complementary metal-oxide-semiconductor (CMOS) processes that will soon be turning out chips with feature sizes as small as 32 nanometers (and eventually 22 nm).

At the VLSI Symposium earlier this month in Honolulu, the Intel researchers revealed they were close to winning that bet. They reported that they had made an all-digital version of a random-number generator using the 45-nm CMOS process that has been used to build Intel processors since 2007. ”Historically, RNGs have been analog,” says Greg Taylor, director of the Circuit Research Lab. ”But porting to smaller technology nodes [with analog devices] requires a lot of fine-tuning that is unnecessary with digital versions.”

Analog circuits require extra design work to manage things such as the signal-to-noise ratio, Taylor explains. “Supply voltages scale down as we move to more advanced technologies. This supply voltage reduction reduces signal power without changing device noise, consequently reducing the signal to noise ratio.”

The benefits of going digital were immediately obvious. ”The device generates billions of random bits per second and can run at very low voltage,” says Taylor. What’s more, making the generator all digital made it more random. The circuit takes advantage of a phenomenon that is a bugaboo for designers of logic that uses more than one clock. The Intel team engineered the number generator so that in each string of numbers turned out by the machine, every bit is the result of ”metastability.”

Usually, you sample a digital device’s output when it has settled on a definite value, either a one or a zero. Metastability is what occurs when the voltage is sampled during a transition and the bit is caught between a zero and a one. Eventually, the bit drops down to one state or the other, but there is no way to tell on which side it will land. The Intel researchers deliberately sample during transitions; they enhanced the randomness even further by tuning the metastability so that the bit falls to one or zero with fairly equal probability, ”making it essentially a coin flip,” says Taylor.

Taylor says his research group is trying to help make the Internet a secure place, and the all-digital random-number generator is just one piece of the puzzle.

Resource: Printed Circuit Board

Build a Custom-Printed Circuit Board

2010-08-11T23:51:00.000-07:00

Breadboarding a new circuit is a key skill and an important step in many projects—especially early on, when you need to move wires around and substitute components. But that very flexibility also makes it easy to knock wires out. Eventually, if your project is a keeper, you’re going to want something with a bit more permanence.

Printed circuit boards (PCBs) solve all those shortcomings. But most people don’t even consider translating a one-off project into a PCB design. For one thing, PCB fabrication has traditionally been expensive, viable only in commercial quantities. (One alternative is to do it yourself with etches and silk screens, a messy and time-consuming process.) Also, there are technical constraints involved with PCB designs that are daunting to the casual hobbyist. But it turns out that nowadays you can produce a professional PCB very inexpensively.
I only recently delved into the mysteries of PCB fabrication, for an upcoming IEEE Spectrum article on building a robotic digital microscope. Part of the project is a variable LED illumination system, and to dim LEDs you need to design a pulse-wide-modulation circuit. With a little research, I found a design based around a 555 timer chip, a power transistor, a couple of diodes, two resistors, and three capacitors. Not a huge number of components, but enough that I was dreading getting them all hooked up on a breadboard. Since I already had the design in hand, I was pretty confident it would work out of the box. That made it a perfect candidate for doing it as a PCB.

I had looked into custom PCBs a while back. I had even downloaded Eagle, a PCB design program from CadSoft Computer. I liked Eagle (and eventually returned to it for this project), but back then the cost of a single board—US $75 and up—stopped me. This time I discovered BatchPCB.

BatchPCB consolidates a bunch of individual projects onto a single large board and then cuts them apart when they come back from the factory. Small boards can be fabricated for under $20 this way. There’s a three-week turnaround, but I wasn’t in a hurry. I dove into designing my LED dimmer board.A basic review of PCBs is in order here. A PCB consists of a thick, rigid insulating layer with conductive traces on the top and bottom. Because the middle insulates, the traces on the top and bottom can run over each other. To get a signal from one side to the other, you drill a hole called a via, which is like a trace running through the board vertically. You also drill holes for ICs, resistors, diodes, and other discrete pieces. The traces lead to the holes, and the components have solder pads, allowing them to be soldered in place.

Some components may be connectors to bring signals to the board, and you can also leave larger holes with solder pad rings around them to solder external wires directly. You can even add layers with traces in between the top and the bottom, although this can get pricey. At BatchPCB, a two-layer board costs $2.50 per square inch (about $0.40 per square centimeter), while a four-layer board costs $8 for the same area (about $1.24/cm2).

The first step in creating a custom PCB is laying out the schematic view. Place your components (which usually come from a component library included with your design software) onto a canvas, and then connect the pins with lines representing electrical connections. You may find yourself faced with multiple choices for the same part number. That’s because many components come in different packages, such as a DIP (dual in-line package) chip or a surface-mount chip. For hobby PCBs, you almost always want to go with the big, clunky DIPs and SIPs (system-in-packages), because they’re easily found at hobby venues and are easier to solder than surface-mounted devices, which are meant for commercial applications. Although the various packaging options may look the same in the schematic view, they will appear very different when you go into the layout view to actually design the board.

Printed Circuit Board Manufacturing

2010-07-29T03:54:00.000-07:00

Printed circuit boards are electronic circuits created by mounting electronic components on a nonconductive board, and creating conductive connections between them. The creation of circuit patterns is accomplished using both additive and subtractive methods. The conductive circuit is generally copper, although aluminum, nickel, chrome, and other metals are sometimes used. There are three basic varieties of printed circuit boards: single-sided, double-sided, and multi-layered. The spatial and density requirement and the circuitry complexity determine the type of board produced. Printed circuit boards are employed in the manufacturing of business machines and computers, as well as communication, control, and home entertainment equipment.

Production of printed circuit boards involves the plating and selective etching of flat circuits of copper supported on a nonconductive sheet of plastic. Production begins with a sheet of plastic laminated with a thin layer of copper foil. Holes are drilled through the board using an automated drilling machine. The holes are used to mount electronic components on the board and to provide a conductive circuit from one layer of the board to another.

Following drilling, the board is scrubbed to remove fine copper particles left by the drill. The rinse water from a scrubber unit can be a significant source of copper waste. In the scrubber, the copper is in a particulate form and can be removed by filtration or centrifuge. Equipment is available to remove this copper particulate, allowing recycle of the rinse water to the scrubber. However, once mixed with other waste streams, the copper can dissolve and contribute to the dissolved copper load on the treatment plant.

After being scrubbed, the board is cleaned and etched to promote good adhesion and then is plated with an additional layer of copper. Since the holes are not conductive,
electroless copper plating is employed to provide a thin continuous conductive layer over the surface of the board and through the holes. Electroless copper plating involves using chelating agents to keep the copper in solution at an alkaline pH. Plating depletes the metal and alkalinity of the electroless bath. Copper sulfate and caustic are added (usually automatically) as solutions, resulting in a .growth. in volume of the plating solution. This growth is a significant source of copper-bearing wastewater in the circuit board industry.

Treatment of this stream (and the rinse water from electroless plating) is complicated by the presence of chelating agents, making simple hydroxide precipitation ineffective. Iron salts can be added to break the chelate, but only at the cost of producing a significant volume of sludge.
Ion exchange is used to strip the copper from the chelating agent, typically by using a chelating ion exchange resin. Regeneration of the ion exchange resin with sulfuric acid produces a concentrated copper sulfate solution without the chelate. This regenerant can then be either treated by hydroxide precipitation, producing a hazardous waste sludge, or else concentrated to produce a useful product.

Growth from electroless copper plating is typically too concentrated in copper to treat directly by ion exchange. Different methods have been employed to reduce the concentration of copper sufficiently either to discharge the effluent directly to the sewer or to treat it with ion exchange. One method, reported by Hewlett-Packard, replenishes growth with formaldehyde and caustic soda to enhance its autocatalytic plating tendency, and then mixes it with carbon granules on which the copper plates out in a form suitable for reclaiming.

Following electroless plating a plating resist is applied to the panel and photo-imaged to create the circuit design. Copper is then electroplated on the board to its final thickness. A thin layer of tin lead solder or pure tin is plated over the copper as an etch resist. The plating resist is then removed to expose the copper not part of the final circuit pattern.

The exposed copper is then removed by etching to reveal the circuit pattern. Ammonia-based etching solutions are most widely used. Use of ammonia complicates waste treatment and makes recovery of copper difficult. An alternative to ammonia etching is sulfuric acid/hydrogen peroxide etching solutions. This latter etchant is continuously replenished by adding concentrated peroxide and acid as the copper concentration increases to about 80 g/L. At this concentration, the solution is cooled to precipitate out copper sulfate. After replenishing with peroxide and acid, the etchant is reused. Disadvantages of the sulfuric acid-peroxide etching solution are that it is relatively slow when compared with ammonia, and controlling temperature can be difficult.

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Printed Circuit Board Layout

2010-07-23T03:56:00.000-07:00

Printed circuit board (PCB) design effort keeps growing as additional constraints such as rising clock frequencies, reduced area, increasing number of layers, mixed signal devices, and the ever increase in component numbers and densities. All of these factors combined have led to a steady rate of increase in development costs for current systems. As we design ever larger, denser and more complex systems, it is becoming increasingly difficult to estimate how much time would be required to design and verify them. To compound this problem, PCB design effort estimation still does not have a quantitative approach. We present in this paper a first step toward creating a design effort metric that is highly correlated with design effort for PCB layout. We follow the same approach taken in [1] as the principles that are applicable to microprocessors are also applicable to PCBs. In this paper, design effort corresponds to the number of engineering-hours required for implementation (layout) of a PCB design.

This paper analyzes and proposes various statistics to estimate the layout effort required to develop PCBs. We investigate and quantify statistics such as area, component count, pin count and device types and sizes for many PCBs. We analyze several of these statistics, and propose a metric, obtained after applying non-linear regression over the different statistics, which we call μPCBComplexity. In addition, we provide insights on the correlation between several statistics and design effort for several known layout design times. Different designs have different constraints, leading to specific challenges; typical design constraints being area, frequency, and cost. For example, having area being a primary design constraint, may lead to a requirement for additional layers, more expensive package types, and more complex placement and routing. A design constrained by cost, on the other hand, may require a balance between number of layers, area, drill density, types of packages and possibly the number of different drill sizes. Having clear constraints is necessary in estimating layout effort as it can drastically affect complexity. We define design effort to be the layout time required by one engineer. Design effort is equivalent to layout time when the project has a single developer, which is frequent even for complex PCBs. Nevertheless, for a given effort requirement, it is possible to reduce the design time by increasing the number of workers. Nevertheless, increasing the number of workers decreases the productivity per worker. The relationship between these two elements has been widely studied in software metrics and business models. Since the conversion between design effort and design time can be approximated, the remainder of this paper focuses only on design effort. The rest of the paper is organized as follows. Section 2 covers other work in this area; Section 3 describes the statistical techniques that allow us to calibrate and evaluate the μPCBComplexity regression model; Section 4 describes the setup for our evaluation; Section 5 evaluates several statistics for the boards in our analysis; and Section 6 presents conclusions and future work.

OVERVIEW OF PCB TYPES

2010-07-20T03:53:00.000-07:00

A PCB consists of a nonconducting substrate (typically fiberglass with epoxy resin) upon which a conductive pattern or circuitry is formed. Copper is the most prevalent conductor, although nickel, silver, tin, tin-lead, and gold may also be used as etch-resists or top-level metal. There are three types of PCBs: single-sided, double-sided, and multilayer. Single-sided boards have a conductive pattern on one side only, double-sided boards have conductive patterns on both faces, and multilayer boards consist of alternating layers of conductor and insulating material bonded together. The conductive layers are connected by plated through-holes, which are also used to mount and electrically connect components. PCBs may also be either rigid, flexible, or a combination of the two (rigid-flex).

Three Types of PCBs

SINGLE-SIDED PCB

Several critical manufacturing steps are not included in the typical single-sided manufacturing sequence and no process is unique to single-sided production. Therefore, any manufacturer of double-sided or multilayer PCBs can produce single-sided ones as well. Few shops produce single-sided panels exclusively, but instead include single-sided panels as part of their overall product mix. The most common sequence of single-sided production is drill, print-and-etch, surface finish, and final fabrication (all of these production processes are explained in Section 203). No inner-layer processing is required, and desmear is also eliminated. Furthermore, only in rare cases are plated through-holes required; therefore, all of the processes required to make the holes conductive are not applicable to single-sided manufactures. The holes instead provide mechanical stability for through-hole panels. Drilling may be completely eliminated on single-sided PCBs if the components are all surface-mounted.

DOUBLE-SIDED PCB
Not unlike single-sided, double-sided PCB manufacturing is also a subset of the multilayer process. The inner layer image transfer, lamination, and hole cleaning process are not performed. Therefore, any multilayer manufacturer can easily produce double-sided panels. Double-sided PCBs require electroless copper or other methods of making holes conductive, since the top and bottom sides of the board require interconnection.

MULTILAYER PCB

Single- and double-sided manufacturing processes are
subsets of the multilayer process. Therefore the multilayer manufacturing process will be described in detail in Section 205. Multilayer boards represent two-thirds of the overall value of U.S. production dollars, even though they are produced in lower numbers
than single- or double-sided PCBs. The rigid multilayer process (rigid PCBs) represent about 95% of U.S. production.

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Printed Circuit Board Manufacturing Industry Profile

2010-07-16T03:04:00.000-07:00

Manufacturers of printed circuit boards (PC boards) are included as part of the electronic component manufacturing industry. As of 1984, the printed circuit board manufacturing industry consisted of a total of 585 plants with an employment of 435,100 (NCO 1984). Industry personnel indicate that the actual number of plants may be closer to 1,000 (USEPA 1986). The industry consists of large facilities totally dedicated to printed circuit boards, large and small captive facilities, small job shops doing contract work, and specialty shops doing low-volume and high-volume precision work. Approximately half of the printed circuit boards produced are by independent producers, while the rest are by captive producers. Over 65 percent of all printed circuit board manufacturing sites are located in the northeastern states and in California (NCO 1984). The printed circuit board manufacturers visited as a part of this study are all considered small. Generally, these small companies can be characterized as those that produce up to 3,000 to 5,000 square feet of processed board each month and require approximately 8,000 to 10,000 square feet of building space. Large companies can be characterized as those that produce or 30,000 to 50,000 square feet per month.

Products and Their Use
Printed circuit boards can be classified into three basic types: single-sided, double-sided, and multi-layered. The total board production in 1983 was 14 million square meters (PEI 1983). Double-sided boards accounted for about 55 percent of the printed circuit boards produced, while multi-layer board production made up 26 percent (PEI 1983). The type of board produced depends on the spatial and density requirement, and on the complexity of the circuitry. Printed circuit boards are used mainly in the production of business machines, computers, communication equipment, control equipment and home entertainment equipment.
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PCB Testing – Prevention Is Always Better

2010-07-12T00:05:00.000-07:00

PCB’s find their application in electronic appliances like DVD, Televisions, cell phones, computers, calculators, watches, but to name a few. These appliances would not function if the PCB is not functioning; hence it is very important to test the PCB’s to check their reliability and performance before they are applied in these multifarious industries.
The testing process includes the bare board tests in which the unpopulated circuit boards are required to undergo and every connection is checked on the finished circuit board as correct. In case of mass production of circuit boards , the testing is done using a bed of nails tests or fixture where they are connected with the copper holes or lands present on either one or both sides of the board, so that the testing process is managed easily. Then with the use of computer electric testing unit, current in a small quantity is send on the nail bed through every point of contact thus ensuring that current is detected on appropriate contact points.

Even after the board is populated it has to be tested by different methods that include manual inspection of the PCB, optical inspection, analog signature analysis, and power off testing which is done when the electric current is not passed. When the power is on, the tests that are carried out are the in-circuit test which is done to test the voltage and frequency & the functional test wherein the PCB is tested for functionality.

After the process of testing is complete, the PCB’s which fail to work are disordered by the technicians and the components of the PCB are replaced through a process known as rework.

The process of PCB testing is a very significant process and is always given equal amount of importance as the manufacturing process. Imagine a well known brand, a well established brand having problems with its electronic goods. The brands reputation would be put to risk; moreover the customer may also lodge a complaint through the consumer court which would hinder the brands reputation adversely.

PCB Testing is more like an investment wherein you are assured of quality at a little overhead. So, it is very important to manage the testing activity. If you are outsourcing this activity always ensure the credibility of the testing company through their past records. Always take care of the quality of PCB’s by avoiding companies that are inexpensive ones, consider the quality service.

Whether it is a PCB or some other product, testing is always a good policy.

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PCB Fabrication - Printed Circuit Board Fabrication Is Possible At Home Also

2010-07-07T00:15:00.000-07:00

PCB fabrication for multiple layered printed circuit boards is managed with an objective of providing an extra degree of freedom when it comes to selecting complicated or noise sensitive electronic circuits. The process includes the stacking of circuits on one another to establish predetermined interconnection set amongst them, with the help of reliable and techniques used for the sole purpose.

It is even possible to manage PCB fabrication at home and the benefit of making one at home is solving problems related to complex circuits. The method of PCB fabrication at home is as follows:

In the first stage the magazine schematic is transferred to the layout programs schematic part. This is followed by utilizing the PCB layout program to place the parts on board as well as to manage the routing of computer traces. After completion of some parts, clearance of rat’s nets begins. After the layout is done, a laser printer manages the printing of the board layers on a special toner transfer paper. The process of transferring the board image on the bare copper board is done with the help of a laminating machine or an iron that is used for hot cloth ironing.

Then the board is kept under water so that the paper that has stuck to can be removed and the toner remains behind. For the etching activity, an aquarium is used. Two aquarium pumps move over the copper boards while the job of the two aquarium heaters is to maintain the temperatures at 110 F. Depending upon the copper thickness as well as the quality of the solution, this activity can be managed in around 30 minutes on a higher end.

Once the etching work is completed, a solvent is utilized for removing the toner and the tinning process is managed using a soldering iron as well as a small tinned solder wick piece. Though, tinning is not mandatory, even though, it is advisable because it enhances the appearance of the board as well as prevents the oxidation process of copper until the process of soldering parts of board is done.
Then, the drilling of holes for leaded components and mounting holes is managed. Finally, the board is completely read to be populated.

The PCB fabrication process can be successfully managed if each and every step is carefully executed as well as the quality of the material used in the fabrication also plays an important role. So, if you are planning to create a durable PCB then it is important to keep the quality aspect in mind always.

Some of the points to be kept in mind while choosing a quality and etchant system, a good etchant system will result in a good quality fabrication. Etchants like FeCI3, Chromic acid, cupric chloride etc are some of the popularly used ones.

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PCB Design Software – The Easy Way Out

2010-07-02T05:48:00.000-07:00

When searching for a high end PCB designs software, there are various aspects to be kept in mind so that the product you get is loaded with the required facilities at a reasonable price. Though if the product is good there is no harm in paying a bit more bucks.

Before buying a PCB design software it’s necessary to review your requisites. The software should provide facilities like easy to use interface, manual routing or auto rooting tools and automatic placers. The software should have the facility of creating new parts and footprints, a standard library wherein you can share designs, multi-level hierarchy with schematic capture as well as export the Spice, Net list or PCB layout. The most important of all is an easy to grasp tutorial which will simplify your PCB manufacturing activity.

There are a variety of software’s available in the market that provides most of the above mentioned facilities and features like

User Friendly Interface - This feature supports multispeed and schematic software’s and makes schematic design in a very simple and speedy process which can be managed simply by selecting and placing components on your documents and interconnecting them with the help of wire and bus tools. There is a tutorial which takes you through each and every step of PCB designing.

Automatic Routing Facility – This feature allows the routing of complicated layouts SMD components and single layer boards too. There are software’s that have two different routers, shape based router and grid based router which can be used for making single layer boards with jumper wires. These software’s support curved tracing and editing the traces to any degree.

Advance Testing Facility – This feature allows the testing of the schematic and PCB modules thus controlling the quality of the project at each and every phase. Functions like DRC and ERC provide a check on the inter-clearance of design objects as well as checks for errors in schematic pin connections. The facility includes the presentation of these errors in a graphical format so that the fixation of the errors can also be carried out flawlessly at every step. Features like net connective test the PCB’s or electrical connectivity.

Sharing Facility – With the help of this feature it is possible to exchange layouts, schematics and the libraries with other EDA and CAD packages

Many other features like spice support, support for manufacture of output formats etc have to be present with the design software you are purchasing. If the PCB design software is good the product would be of best quality so always compare the features of the shortlisted companies from where you are willing to buy the software and then purchase it.

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PCB Circuit Manufacture – The Methodology followed By Pcb Manufacturers

2010-06-29T05:03:00.000-07:00

Acronym for Printed circuit board, PCB finds its application in electronics and is highly cost effective and offer more reliability as compared to other circuits like point to point circuits or wire wrapped circuits. Though the manufacturing process of a PCB is a complicated one as it involves high initial investments, the results are highly rewarding.

PCB support electronic components mechanically and connects them electrically via copper etched traces, conductive pathways on a non conductive substrate and is also known as etched wiring or printed wiring board.

The process
There are three methods that are commonly used by the manufacturers of PCB’s & these differ in the subtractive methods. The process involves the bonding of a copper layer on either or both the sides of a full substrate. After this process the excess copper or undesired copper is removed completely whilst the necessary copper is retained with the help of a temporary mask.

The most common methods used by the PCB manufacturers in the subtractive process of PCBS are as follows:

Photo Engraving - This process makes use of a photo mask as well as chemical etching for removing the unwanted copper from the substrate. This photo mask is created with the help of a photo plotter that is again created by a technician through computer based manufacturing software.

Silk Screen Printing – This subtractive method employs etch resistant ink on the important parts and protects the requisite copper foils, while at the same time the etching process removes the unwanted or undesirable copper.

Pcb Milling – A PCB prototype is used for milling away the undesirable copper foil from the substrate. This system is also referred to as two or three axis mechanical milling system and works the same way as the plotter and the commands are transmitted via the host software that control the positions of all the three axis.

Lamination – The lamination process involves the bonding of multiple thin trace layers or etched boards, also referred to as multi layer printed circuits.

Drilling – Drilling is done to connect every single layer of the PCB with the other layer by drilling holes called VIAS with the help of an automated drilling machine. These drills are driven by the computer and are also known as numerically controlled drills or excellon files. Every wall of a multi layered board is copper plated forming plate through holes connecting the conductive layers of PCB.

The manufacturing process managed by the various PCB manufacturers also includes solder plating, silk screening and Testing before utilizing the boards. A complex process, though, finds its application in vast genres of electronics.

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PCBA Manufacturer – Populated Printed Circuit board Assembly :

2010-06-24T23:56:00.000-07:00

A PCBA is a printed circuit boards which is populated with electronic components and is known as printed circuit board assembly. PCB assembly has a significant role to play in the electronic industry. PCBA is deployed at different levels in the industry including rapid prototype products up to complicated, multi-technology assemblies also.

The services associated with PCBA manufacturing are as follows:

PCBA Types – Various manufacturers with the help of their R & D team have been successful in presenting PCBA for surface mounting that include the Rapid Turnaround PCBA’s and prototypes as well. Thus, offering conventional PCBA’s as well as mixed technology based ones.

Surface Mount Ability – The surface mount PCBA’s manufacturing has various aptitudes like BGA, UBFA and flip chip assemblies. The manufacturing process includes proper utilization of the automated assembly processes so as to make sure that quality is consistent and sustainable and the manufacturing expenses are optimum.

Full Capacity Assembling - Numerous PCBA manufacturers have the facility of both through hole and mixed technology assembling, as well as associated services like potting, conformal coating etc. Additionally, services like device programming and PCBA configuration are also provided before system integration or dispatch.

Design Of Text Fixtures – You can order custom designed functional text fixture for specific PCB assembly testing requisites. Herein, complex functional testing is managed prior to integration of the system or dispatch.

Most of the manufacturers do manage Lead free PCBA manufacturing and their peripheral services on offer include

Choice Of Grades – All the required assistance is provided whilst choosing different grades of laminates [FR4] as well as other material options so as to cope up with the high soldering temperatures and thermal cycles increased numbers.

Scrubbing Service – The services include the selection of lead free components after ensuring the quality of the same as well as alternatives wherever required.

Combination Trials – Under this aptitude trial of any combination PCB finish, materials as well as solder is managed with the help of conventional & SMD assembly methodologies.

Due to the competition between manufacturers, the customers get the advantage as these manufacturers take all the care to create PCBA’s with top notch quality as well as significant reduction in the prices of the same. So, we you are outsourcing the PCBA’s always shortlist a few of the good quality and reputed PCBA manufacturers, make a comparative of the quality , cost and services provided by them and finally choose one that is the most suitable as well as reliable. Cost factor is a secondary one, while quality should be the main criteria.

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