Aramadhan

The world of science and technology is changing exponentially and this is the main reason why an engineer should keep enhancing his skills and learn new ones so that he can keep up with this ever changing technology. Electronic engineering is also not speared form this rapid evolution. Moore’s Law (1965) for example has been the driving force behind innovation in IC manufacturing, and now according to professional engineer it has completed it’s life span only after 51 years. New technologies like graphene based transistors, quantum computing and Carbon Nanotubes and being developed for survival in electronics beyond this law. So for electronics engineers here are 10 ways to increase their practical knowledge and to keep up with modernized technology.

1) Hands-on Experience on Tools and gadgets

Tools and gadgets are of outmost importance in any form of creativity and it mandatory that one

should be proficient in using them. Multi-meter is the lifeline for electronics engineer. Every

electronics engineer should have a personal millimeter which is reliable and accurate not

necessarily an expensive one. Spend time with it and learn its functions and settings. The second

most important tool for EE engineers is an oscilloscope now this is an expensive tool and it is not

recommended to buy a personal. However having and easy access to such device in some lab is

very helpful.

2) Get an understanding of technical documents

All electronics engineer must understand electrical drawings and other technical documents.

Read different books and surf the internet to gain an understanding of symbols. Also try to grasp

the standards associated with these documents. Find such documents from your home appliances

like washing machines and microwaves, and try understand them. Another type of document is

the datasheet which provide very useful information about the component for example about

internal registers in case of microprocessor and controller. Download a few and read to get a basic

knowhow. This will help you a lot in professional job as well as when you start designing you own

product.

PCB or Printed Circuit Board is the physical implementation of an electronic circuit. PCB design is a very specialized task, an art which can only be mastered through training or attained with experience. For a novice electronic hobbyist, laying out a PCB design might turn out to be a pretty daunting task, especially if the circuit consists of a few hundred components and if there are lot of constraints, both mechanical and electrical. No matter how efficient the circuit design is, if the PCB design is not done efficiently the product may not even work.

In this article, you will know about:

Standards

CAD Software used for Design

PCB Design Flow

Footprint Creation

Constraint Definition

Component Placement

Routing

Design Rules Checking (DRC)

Gerber file generation

PCB design for EMC compliance – Best practices

PCB Thermal management

Single layer PCB design

Conclusion

In the early days, PCB design was manually implemented by drawing out the layout using pens or sticking adhesive tapes on a transparent film. But nowadays, it is a fully automated process which makes use of complex Computer Aided Design (CAD)software. This article is meant to serve as a guide to get through the nittygritties of PCB design fundamentals.

The primary building block of any PCB is the substrate, which in most cases in made up of FR4 glass epoxy. FR4 is a composite material made of woven fiberglass cloth with an epoxy resin binder that is fire resistant. FR4 stands for Fire retardant grade 4. The substrate mechanically supports the electronic components which are mounted on it. The components are connected to each other using conductive copper traces, which are etched out on the substrate, which is an insulator. Printed Circuit Board design involves the efficient layout of components on the board area and the layout of the pattern of interconnecting traces.

1. Standards

Standards by the Association Connecting Electronics Industries or IPC is the most widely followed and complied with, in connection with PCB design. Some of the IPC PCB design standards are listed below:
IPC-2221B: Generic Standard on Printed Circuit Board Design
IPC-7351: Generic requirements for Surface Mount Land Pattern and design

By complying to the above two standards, you can make sure that your PCB complies to a global standard and speaks the same language as any other PCB designed anywhere in the world which comply to the same standard.

2. CAD Software

Numerous CAD Software packages are available for PCB design. Mostly schematics capture and PCB layout are integrated in a single software package. Some of the popular freeware PCB CAD software packages are DipTrace, EagleCAD, KiCAD, ExpressPCB, gEDA, Fritzing etc. Some of these freeware packages have design limitations and one would have to buy the full version to use all the features.

The best among these is without doubt KiCAD, which is an open source software, available for a wide range of operating systems and completely free. DipTrace and EagleCAD are pretty capable PCB design packages too, but their free version have limitations on either the number of pins or the number of layers or both. To use all the advanced features, one would have to buy the full version.

Among the high end PCB design software, Altium Designer (Formerly Protel PCB), Cadence Allegro, Mentor Graphics PADS PCB and Xpedition. Among them, my vote goes to Altium Designer, for tight integration between schematics and PCB, ease of use, 3-Dimensional capabilities, integrated EMI analysis etc.

3. PCB Design Flow

The process flow for a generic Printed Circuit Board design is shown above. It is assumed that the component selection and Schematic capture is complete and the PCB layout design is all set to begin.Setting up the workspace area is the first task a PCB designer performs. It begins with setting a Grid and the measurement units. This is generally called a “snap grid” since the cursor snaps to the grid while moving around the workspace. Using a grid is important because it makes symmetrical placement of components easier and also simplifies layout of traces without uniform clearances.

The choice of units is between imperial and metric units. Imperial units have been traditionally followed by PCB designers around the world. Also a lot of electronic components are manufactured with imperial pin spacing.

This is followed by defining the board outline. Many CAD software allows importing a CAD drawing file as the board outline. If this is not available, the outline has to be created manually.

4. Footprint Creation

Once Schematic capture is complete, an output of the process is the Bill of Materials (BOM) document. Using the BOM, the PCB designer can begin creation of footprints. Footprints of standard packages will already be available in the PCB design software libraries. Those which are not available will have to be created by the designer using the corresponding datasheets as reference. Assigning PCB footprints to components at the schematic capture stage itself will make the job of the PCB layout designer much easier. Ensuring that the footprints created comply with IPC-7351, will make sure that there are no assembly issues at least as far as footprints are concerned.

5. Constraint Definition

PCB design constraints can be classified into Mechanical constraints, Electrical constraints, Design for Manufacturability (DFM) constraints and Design for Testability (DFT) constraints. The PCB constraint editor available in Altium designer is shown above.

Mechanical constraints generally involves restrictions such as positions of connectors, LEDs, LCD display, mounting holes etc., component height restrictions, Board shape and size etc.

Electrical constraints are related to the actual circuit that is being layout on the PCB. These constraints can be pre-set in the CAD software so that while designing the layout, the software will indicate whenever there is a violation of the rules set. Limits such as trace width, trace to trace clearance, trace to pad clearance, pad to pad clearance, pad/trace clearance to board edge etc., can be set using the constraints editor. Additionally specific constraints such as impedance control for high speed lines, differential trace routing, bus routing etc., can also be set. Presetting such constraints will reduce the design cycle time by reducing the number of iterations.

Design for Fabrication (DFF) and Design for Assembly (DFA) together make up Design for Manufacturability (DFM). Complying with DFM constraints will mean that the PCB layout design will be manufacturable. The objective of DFM is to minimize assembly failures and also reduce cost. Some of the critical DFM guidelines for PCB design are listed below:

Components selected verified for obsolescence and guaranteed availability for atleast the next five years
Distance between surface mount and plated through hole (PTH) components are adequate
Components are placed with a minimum clearance of 1.5mm (IPC 2221) from the edge of the board
Orientation symbols for components to be provided, for example pin no.1 indication for connectors and ICS, Anode/Cathode indication for diodes, Positive/negative indication for polar components like electrolytic capacitors
Connections to internal plane layers are made through thermal pads
Avoid acid traps and slivers



Fix minimum trace width and clearance after confirming with the fabrication house
Proper solder mask definition for component pads
Layer stack design should be symmetrical to minimize the risk of warpage of the board
Balance copper area distribution if possible
Use panelization to minimize wastage of the base material
Aspect ratio for a PCB is defined as the ratio of the board thickness to the drill size. Ensuring that the aspect ratio is < 10:1, makes sure that the PCB is manufacturable. It would also do well to confirm with the intended Fab house. Smaller ratios result in more uniform plating in hole.
Use standard copper thickness of 0.5 oz unless otherwise specified.
Check with Fab house for minimum thickness of legend text
Use a minimum of 3 board fiducials and if there are components with pad pitch ≤ 10 mils, use component fiducials as well. Board fiducials are placed at the corners and component fiducials are placed near pin no.1 of the component.
Check for oversized or overlapping solder mask
As far as possible component placement should be restricted to a single side and orientation of components should be in the same direction.
Select the optimum PCB surface finish for the corresponding application



Design for Testability constraints intend to make the PCB capable of being tested, both functional testing and In-Circuit Testing (ICT). Ideally, a 100% test point coverage is desirable. But space constraints on the PCB not allowing, it is then the discretion of the designer to decide which electrical nodes require assignment of test points. Functional testing is intended to validate the electrical design functionality and ICT is intended to detect any manufacturing defects. Both functional testers and ICT access the PCB under test through a Bed-of-nails fixture and connectors. The test points provided on the PCB serve as access points for the testers and hence the test points –

Should be on a grid of not less than 100 mils (1 mil = 0.001”)
Should be accessible from the bottom side of the PCB

6. Component Placement

Component placement is one of the most critical stages of PCB layout design. Depending on how efficiently the component placement is done, the trace routing will be that much easier. In general the component placement is based on electrical function, thermal management and electrical noise considerations.

There are two units generally used for PCB design – Imperial and Metric. The Imperial units are more popular among the PCB designers but currently the metric units are becoming the defacto standard in the PCB industry. Begin by making a PCB floor plan and decide which group of components will occupy which areas of the board. Following are the generic guidelines for effective and efficient component placement:

Begin by placing the critical components like Microprocessor/Microcontroller, clock circuit, DDR memory etc., and the fixed position components like connectors, LEDs, LCD display etc.
Use a grid of 100 or 50 mils for placing the critical components and a 25 mil grid for placing the other components
Segregate the Analog, Digital and Power supply circuit components and isolate them from each other
Place the clock and other high speed circuitry as far away from the I/O circuit as possible.
As far as possible, place all components on a single side. If absolutely unavoidable, place the low profile passive components on the bottom side
Place the following in close proximity
Decoupling capacitors to the power pins.
Series termination resistors to the source pins
EMI filters to signal entry point
Orient the components in a similar fashion during placement for ease of assembly
Do not place component legends on pads

7. Routing

With the component placement complete, it is now time to route the traces. Traces on a PCB can be power/ground traces or signal traces. Further, signal traces can be analog or digital.



We begin by designing the layer stack. For the current high speed designs, the minimum number of layers is 4. Two signal layers, a power plane and ground plane. Having a power plane and ground plane not only ensures efficient routing of the signal traces, but also good EMI-EMC compliance. Having an unbroken return path underneath every high speed trace ensures that there are no ground loops, which are one of the major reasons for emissions. As a rule of thumb, a 4 layer board will produce 15dB less emissions than a two layer board.

Quoting from “EMC and Printed Circuit Board” by Mark I Montrose – “When clock speeds are in excess of 5MHz or rise times are faster than 5ns, a multilayer board should be used”.

Traces on a multilayer board with at least one power and ground plane can be routed in a micro strip or a stripline configuration.





While designing a layer stackup, the following factors are to be considered:
A signal layer should be adjacent to an internal plane layer
The signal layer and the adjacent plane layer should be tightly coupled: use minimum thickness of dielectric between these layers
The power plane and ground plane should be closely coupled. The thickness of the dielectric between the planes should be minimum. Thus the two planes combined with the dielectric will act as a large embedded capacitance.
The layer stackup is symmetrical
Multiple ground planes will reduce the ground impedance of the PCB and hence reduce common mode radiation.

Generic guidelines for track routing is given below:
Minimum track width and clearance can be arrived upon after confirmation with the fab house. It is recommended to have a minimum track width and clearance of 8 mils for low to medium complexity PCBs. High current trace width needs to be calculated based on the maximum current and expected temperature rise.
Route the high speed signals and power and ground connections first, followed by the remaining connections.
Route the clock circuit with as short traces as possible.
Avoid running high speed traces in parallel as this will introduce crosstalk
On a multilayer board, the power and ground connections are to be made to the planes using short traces from the pins of the components. Thermal reliefs are to be used to make the connection to the plane. Follow the 20H rule for power and ground planes wherein the power plane is recessed from the edge of the board by a distance equal to 20 times the thickness of the dielectric between the two planes.
The 3W rule states that in order to avoid cross-talk between signals, the distance between the traces should be equal to or greater than 3 times the width of the trace.
Avoid creating discontinuities in the ground plane. This would increase the loop area.
In a mixed signal board, split the ground plane into analog and digital grounds and route the corresponding signals over the respective planes.
Track bends should be made at 45° and never at 90°.
If traces are to cross each other, they should do so at 90°, so as to minimize mutual capacitance and inductance.
Use impedance controlled traces wherever necessary
Minimize the use of vias, since vias add inductance to the traces.
All high speed traces whose propagation time is greater than or equal to the signal rise/fall times should be terminated using series resistance

To make the critical calculations such as trace width, differential routing parameters, cross-talk etc., there are many free PCB design tools available which could be used. Some of the freely available tools are Saturn PCB design toolkit and AppCAD.

8. Design Rules Checking (DRC)

Design Rules Checking (DRC) is a powerful automated feature than is available in most PCB design software that checks the design against any or all of the design rules set during the constraint definition stage. Running the DRC results in the generation of a report which is used as reference to clear the violations of the constraints.



Shown above is the DRC window in Altium Designer. Click on image for a larger view.

9. Gerber file generation

Once all errors listed in the DRC report are corrected and other review comments are updated in the PCB design, the designer can move towards generating Gerber file for PCB fabrication. Gerber format is a standard format used by the electronics industry for communicating the PCB design information to fabrication. It is an open ASCII vector format for 2D binary images. The set of documents for fabrication consists of a gerber file for each image layer of the PCB design. A standard set of files consist of a gerber file for :

Assorted discrete transistors. Packages in order from top to bottom: TO-3, TO-126, TO-92, SOT-23.

A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material usually with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals controls the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.

The transistor is the fundamental building block of modern electronic devices, and is ubiquitous in modern electronic systems. Julius Edgar Lilienfeld patented a field-effect transistor in 1926 but it was not possible to actually construct a working device at that time. The first practically implemented device was a point-contact transistor invented in 1947 by American physicists John Bardeen, Walter Brattain, and William Shockley. The transistor revolutionized the field of electronics, and paved the way for smaller and cheaper radios, calculators, and computers, among other things. The transistor is on the list of IEEE milestones in electronics, and Bardeen, Brattain, and Shockley shared the 1956 Nobel Prize in Physics for their achievement.

Simplified operation

The essential usefulness of a transistor comes from its ability to use a small signal applied between one pair of its terminals to control a much larger signal at another pair of terminals. This property is called gain. It can produce a stronger output signal, a voltage or current, which is proportional to a weaker input signal; that is, it can act as an amplifier. Alternatively, the transistor can be used to turn current on or off in a circuit as an electrically controlled switch, where the amount of current is determined by other circuit elements.

There are two types of transistors, which have slight differences in how they are used in a circuit. A bipolar transistor has terminals labeled base, collector, and emitter. A small current at the base terminal (that is, flowing between the base and the emitter) can control or switch a much larger current between the collector and emitter terminals. For a field-effect transistor, the terminals are labeled gate, source, and drain, and a voltage at the gate can control a current between source and drain.

The image represents a typical bipolar transistor in a circuit. Charge will flow between emitter and collector terminals depending on the current in the base. Because internally the base and emitter connections behave like a semiconductor diode, a voltage drop develops between base and emitter while the base current exists. The amount of this voltage depends on the material the transistor is made from, and is referred to as VBE.

Transistor as switch

Transistors are commonly used in digital circuits as electronic switches which can be either in an "on" or "off" state, both for high-power applications such as switched-mode power supplies and for low-power applications such as logic gates. Important parameters for this application include the current switched, the voltage handled, and the switching speed, characterised by the rise and fall times.

In a grounded-emitter transistor circuit, such as the light-switch circuit shown, as the base voltage rises, the emitter and collector currents rise exponentially. The collector voltage drops because of reduced resistance from collector to emitter. If the voltage difference between the collector and emitter were zero (or near zero), the collector current would be limited only by the load resistance (light bulb) and the supply voltage. This is called saturation because current is flowing from collector to emitter freely. When saturated, the switch is said to be on.

Providing sufficient base drive current is a key problem in the use of bipolar transistors as switches. The transistor provides current gain, allowing a relatively large current in the collector to be switched by a much smaller current into the base terminal. The ratio of these currents varies depending on the type of transistor, and even for a particular type, varies depending on the collector current. In the example light-switch circuit shown, the resistor is chosen to provide enough base current to ensure the transistor will be saturated.

In a switching circuit, the idea is to simulate, as near as possible, the ideal switch having the properties of open circuit when off, short circuit when on, and an instantaneous transition between the two states. Parameters are chosen such that the "off" output is limited to leakage currents too small to affect connected circuitry; the resistance of the transistor in the "on" state is too small to affect circuitry; and the transition between the two states is fast enough not to have a detrimental effect.

Transistor as amplifier

The common-emitter amplifier is designed so that a small change in voltage (Vin) changes the small current through the base of the transistor; the transistor's current amplification combined with the properties of the circuit means that small swings in Vin produce large changes in Vout.

Various configurations of single transistor amplifier are possible, with some providing current gain, some voltage gain, and some both.

From mobile phones to televisions, vast numbers of products include amplifiers for sound reproduction, radio transmission, and signal processing. The first discrete-transistor audio amplifiers barely supplied a few hundred milliwatts, but power and audio fidelity gradually increased as better transistors became available and amplifier architecture evolved.

Modern transistor audio amplifiers of up to a few hundred watts are common and relatively inexpensive.


source : wikipedia

A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active elements, and terminate transmission lines, among other uses. High-power resistors that can dissipate many watts of electrical power as heat may be used as part of motor controls, in power distribution systems, or as test loads for generators. Fixed resistors have resistances that only change slightly with temperature, time or operating voltage. Variable resistors can be used to adjust circuit elements (such as a volume control or a lamp dimmer), or as sensing devices for heat, light, humidity, force, or chemical activity.

Resistors are common elements of electrical networks and electronic circuits and are ubiquitous in electronic equipment. Practical resistors as discrete components can be composed of various compounds and forms. Resistors are also implemented within integrated circuits.

The electrical function of a resistor is specified by its resistance: common commercial resistors are manufactured over a range of more than nine orders of magnitude. The nominal value of the resistance falls within the manufacturing tolerance, indicated on the component.

A Zener diode allows current to flow from its anode to its cathode like a normal semiconductor diode, but it also permits current to flow in the reverse direction when its "Zener voltage" is reached. Zener diodes have a highly doped p-n junction. Normal diodes will also break down with a reverse voltage but the voltage and sharpness of the knee are not as well defined as for a Zener diode. Also normal diodes are not designed to operate in the breakdown region, but Zener diodes can reliably operate in this region.

The device was named after Clarence Melvin Zener, who discovered the Zener effect. Zener reverse breakdown is due to electron quantum tunnelling caused by a high strength electric field. However, many diodes described as "Zener" diodes rely instead on avalanche breakdown. Both breakdown types are used in Zener diodes with the Zener effect predominating under 5.6 V and avalanche breakdown above.

Zener diodes are widely used in electronic equipment of all kinds and are one of the basic building blocks of electronic circuits. They are used to generate low power stabilized supply rails from a higher voltage and to provide reference voltages for circuits, especially stabilized power supplies. They are also used to protect circuits from over-voltage, especially electrostatic discharge (ESD).

Operation

A conventional solid-state diode allows significant current if it is reverse-biased above its reverse breakdown voltage. When the reverse bias breakdown voltage is exceeded, a conventional diode is subject to high current due to avalanche breakdown. Unless this current is limited by circuitry, the diode may be permanently damaged due to overheating. A Zener diode exhibits almost the same properties, except the device is specially designed so as to have a reduced breakdown voltage, the so-called Zener voltage. By contrast with the conventional device, a reverse-biased Zener diode exhibits a controlled breakdown and allows the current to keep the voltage across the Zener diode close to the Zener breakdown voltage. For example, a diode with a Zener breakdown voltage of 3.2 V exhibits a voltage drop of very nearly 3.2 V across a wide range of reverse currents. The Zener diode is therefore ideal for applications such as the generation of a reference voltage (e.g. for an amplifier stage), or as a voltage stabilizer for low-current applications.[1]

Another mechanism that produces a similar effect is the avalanche effect as in the avalanche diode.[1] The two types of diode are in fact constructed the same way and both effects are present in diodes of this type. In silicon diodes up to about 5.6 volts, the Zener effect is the predominant effect and shows a marked negative temperature coefficient. Above 5.6 volts, the avalanche effect becomes predominant and exhibits a positive temperature coefficient.[2]

In a 5.6 V diode, the two effects occur together, and their temperature coefficients nearly cancel each other out, thus the 5.6 V diode is useful in temperature-critical applications. An alternative, which is used for voltage references that need to be highly stable over long periods of time, is to use a Zener diode with a temperature coefficient (TC) of +2 mV/°C (breakdown voltage 6.2–6.3 V) connected in series with a forward-biased silicon diode (or a transistor B-E junction) manufactured on the same chip.[3] The forward-biased diode has a temperature coefficient of −2 mV/°C, causing the TCs to cancel out.

Modern manufacturing techniques have produced devices with voltages lower than 5.6 V with negligible temperature coefficients,[citation needed] but as higher-voltage devices are encountered, the temperature coefficient rises dramatically. A 75 V diode has 10 times the coefficient of a 12 V diode.

Zener and avalanche diodes, regardless of breakdown voltage, are usually marketed under the umbrella term of "Zener diode".

Under 5.6 V, where the Zener effect dominates, the IV curve near breakdown is much more rounded, which calls for more care in targeting its biasing conditions. The IV curve for Zeners above 5.6 V (being dominated by Avalanche), is much sharper at breakdown.

Waveform clipper

Two Zener diodes facing each other in series will act to clip both halves of an input signal. Waveform clippers can be used to not only reshape a signal, but also to prevent voltage spikes from affecting circuits that are connected to the power supply.[4]

Voltage shifter

A Zener diode can be applied to a circuit with a resistor to act as a voltage shifter. This circuit lowers the output voltage by a quantity that is equal to the Zener diode's breakdown voltage.

Voltage regulator

A Zener diode can be applied in a voltage regulator circuit to regulate the voltage applied to a load, such as in a linear regulator.

Hi selamat datang, namaku Agung Ramadhan. Saya adalah seorang siswa dari SMPN 3 CILEGON . Silahkan Melihat-lihat isi blog ini.