Front Cover - Electronics - The Hong Kong Polytechnic University

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Front Cover - Electronics - The Hong Kong Polytechnic University

IC LEARNING SERIES

Electronics


The Hong Kong Polytechnic University

Industrial Centre

IC LEARNING SERIES

Electronics

Suitable for the following learning modules offered by the Industrial Centre:

TM1101 Basic Electronic Practice for Electronic and Information Engineering

TM1102 Advanced Electronic Practice for Electronic and Information Engineering

TM1131 Electronic Practice for Engineering Students

TM1133 Electronic Manufacturing Practice

TM1134 Electronic Testing Practice

TM1135 SMT Assembly Design and Manufacturing

Last updated: April 2011

Copyright reserved by Industrial Centre, The Hong Kong Polytechnic University


Electronics

Electronics

Objectives:





To recognize the background knowledge for electronic training modules

To understand the basic electronic components

To understand the interconnection techniques.

To recognize the reliability and maintainability of equipment.

1. Introduction

This literature provides supplementary reading material to students prior to their

trainings in the Electronics Workshop, Industrial Centre. In this literature, selected

basic electronic components and interconnection techniques especially printed

wiring board are discussed. A brief introduction to soldering and current capacity

of copper wire is included with a brief notes in the reliability and servicing of

electronic product and equipment. A flowchart for manufacturing project is

included as a simple guide for students working in Electronic Manufacturing

Project.

2. Basic Electronic Components

In electronics, there are many different types of components; we shall briefly

discuss some of them, particularly on their physical appearance, construction and

identification. In electronic components, normally some rules or marking are

used to identify the value, tolerance, rating and/or classes of components.

Different type of components or different manufacturer has different ways to

identify a component. Always refer to an applicable specification or industrial

standard if in doubt.

2.1 Color Coding

In electronic component identification, it is common to use color to identify

essential parameters of components. This color coding system is universal and

ten colors are used to represent ten digits in the decimal system, additional

colors; gold and silver are used to identify the percentage tolerance and less than

unity multiplier. Color code identification can be easily found on small resistors.

Color identification is also being used to indicate the value and tolerance of small

passive components such as small choke coils, capacitors and even some small

signal diode especially where alphanumeric marking on component case is

inconvenient.

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This color coding system consists of a value of the component, a multiplication

factor and tolerance. For resistor marking, the basic unit is expressed in ohms.

For small capacitor marking, the basic unit is expressed in pF; and for choke coil

marking, the basic unit is expressed in H. A color code table is given in the

Appendix A.

2.2 Fixed Resistor

The behaviour of resistor follows Ohm's Law,

where

v(t) = i(t) * R

v(t)

i(t)

R

= instantaneous voltage

= instantaneous current

= resistance in ohms

Commercial available resistors are classified by their basic material and

construction into metal film, metal-oxide film, cermet (metal glaze), carbon film,

carbon composition and wire wound. The cermet is a resistor made by high

temperature firing of material which composed of conductive metal particles in a

ceramic matrix, with an organic resin as a filler. Cermet is named because of the

ceramic and metal base. For general purpose 5% resistor, 4 color bands are

used to identify its value and tolerance. Due to the number of significant digits is

higher for precision resistors, 5 color bands are required to properly identify

tolerance 1% and 2% resistors. The power rating for common axial type film

resistors for signal control purposes are available in 1/8W, 1/4W, 1/2W, 1W and

2W. For higher wattage rating, wire-wound resistor is more commonly available.

For reference, a table of standard resistor is provided in Appendix B. The table

gives all standard resistor value from 2% 5% tolerance to 0.5% tolerance.

The following figures (Figure 1 – 3) illustrate the construction of some resistors.

Resist ive elem ent - a

compressed slug of a

finely ground mixture

of carbon and silica

Leads

imbedded in

both slug and

molded case

Molded

Case

Figure 1 Carbon Composition Resistor

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Leads

Welded to

End Cap

Resistance Wire

Wound on

Ceramic Rod

Molded or

Conformal

Coated Case

Figure 2 Wire-wound Resistor

Glass or

Ceramic Rod

Carbon, metal or

metal oxide film

Leads

Welded to

End Cap

Spiral incised

through film into

substrate to increase

and adjust resistance

Molded or

Conformal

Coated Case

Figure 3 Film Resistor

2.3 Variable Resistor

Similar to fixed resistor, most popular commercial variable resistor is available

with carbon film or metal film on phenolic or paper-glass composite board.

Other technologies like wire wound, conductive plastic, cermet are also available

for more precise, stability and power application. The resistance of a variable

resistor is obtained by varying the position of a contact arm or slider on surface

of resistive material. The relationship between the mechanical position of the

slider and the change in resistance is known as the taper characteristics. Table 1

gives a few common taper characteristics. Taper B is normally used for general

application while Taper A is used for volume control in audio application. The

power rating of film variable resistor is very small; in the order of hundreds mW.

For power application, wire-wound resistor or rheostat should be used.

Table 1 Some Common Potentiometer Taper

Taper

A

B

C

D

Characteristics

15% Logarithm

Linear

15% Reverse Logarithm

10% Logarithm

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2.4 Capacitor

The impedance of a theoretical capacitor is given by,

X c = 1 / C

()

where

= 2f = angular frequency

ESR

C = capacitance in Farad

j


Z

Energy stored in the capacitor is given by

C

E = ½ CV 2

(J)

Figure 4 Phasor Diagram of a

Capacitor

where

the capacitor

V = potential difference across

Taken the loss of a real capacitor into consideration, the capacitor can be

described as a simple series resonance circuit. Its impedance is given by,

Z = R 2 + (X L - X C ) 2

where R

X L

X C

is the loss of the capacitor normally given as ESR

is the impedance of the lead inductance and

is the capacitive reactance

In mid frequency, X L is very small and usually can be ignored. The ESR(Equivalent

Series Resistance) is the equivalent ac resistance of a capacitor reflecting both

the series resistance which resulted from the electrodes attachment and the loss

of the dielectric material which made the capacitor.

Capacitor comes in many different size, material and types. The construction of a

capacitor is essentially layers of metallic or conductive material with the

electrode attached between layers of insulating or dielectric material. The

frequency response characteristics of a capacitor is having high impedance at DC

(almost non-conducting except some leakage current depending on dielectric) or

low frequency and low impedance at high frequency. Common dielectric

materials for capacitor are ceramic, barium titanate(high dielectric constant

ceramic), titanium oxide(temperature compensation ceramic), oil impregnated

paper, polyester, polystyrene, polycarbonate, tantalum oxide and wet aluminum

oxide electrolytic.

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The identification of capacitor depends on the size of the capacitor. For large

size capacitor, such as electrolytic type capacitor, parameters of the capacitor are

printed on the insulating plastic sleeve. For some capacitors, such as ceramic disk

capacitor or small polymeric capacitor, a 3 digits or 4 alphanumeric digits

printing or color code are used to identify the value of the capacitor. Appendix C

gives the marking convention of using alphanumeric digits.

2.5 Inductor

The impedance of an inductor is given by

X L = L ()

where

= 2f = angular frequency

L = inductance in Henry

Energy stored in the inductor is given by

E = ½ LI 2

(J)

where

I = current flow in the inductor in Amp.

Inductor is constructed by wiring enamel wire on air or magnetic material. The

frequency response characteristics of inductor is to provide low impedance at DC

and high impedance at high frequency. Ideal inductor is lossless. For real

inductor, the loss and the characteristics is modified by its interwinding

capacitance and the resistance of wire. Standard inductor is available

commercially in axial form and radial form, depending on inductance and current

rating. Inductor is commonly used in filtering and oscillator application.

Common axial type inductors are identified with the color code method. Typical

tolerances for fixed standard inductor are 10% and 20% with inductance

ranging from 0.1H to 40mH. The higher the inductance is, the lower the selfresonance

frequency is.

2.6 Identification of Polarized Component

Some components, especially radial type components such as electrolytic

capacitor, tantalum capacitor and light emitting diode (LED) are polarized. That

is, for proper function, the anode and cathode of component must be identified.

A straight forward method to identify the polarity of component is to mark the

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component with a "+" or "-" symbol near their respective terminals on the

component body. In some cases, where marking on the component body is not

practical, like small LED, manufacturer can use different length of component

leads to identify terminal polarity. Normally, a shorter lead is attached to the

cathode and the longer lead is attached to the anode. For axial type diode, a

band is normally printed on one end of diode to identify the cathode of the

device.

2.7 Semiconductor Material

Semiconductor is a form of matter situated between metals and insulators in

considering electric conductivity. The resistivity of semiconductor is in the order

of 10 to 10 4 cm while that of the insulator is below 10 -5 cm and that of the

conductor is above 10 12 cm. Common semiconductor materials are

germanium and silicon. Others like gallium arsenide are used increasingly in the

application for high frequency and optical electronics. Diode and transistor are

examples of devices that fabricate on semiconductor.

2.8 Diode

A diode is a 2-terminal device which ideally allow current to pass through the

device in one direction only, under forward biasing (fig. 5). Diodes are normally

used in signal rectification and switching. A typical VI Characteristic of diode is

given in fig 7. Depending on the characteristics of the semiconductor and

individual construction, diodes are

generally used for power rectification,

voltage regulation, signal detection, laser

or light generation and other special

application such as utilizing the reverse

biased (fig. 6) capacitance in signal tracking

and frequency modulation generation.

The packaging of diode depends on its

power rating, frequency of operation and

assembly technique. There are no

worldwide standard in the naming and

packaging of diode. The most common

conversion is the using of the 1N.... type

number which adopted by Electronic

+ -

Figure 5 Forward Biased

Diode

Industry Association (EIA) of the United State. The prefix 1N... means that the

semiconductor device has one junction. A sequential number follows the prefix

identified the device.

-

+

Figure 6 Reverse Biased

Diode

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2.9 Transistor

Common transistor is 3-terminals

semiconductor device. The graphical

symbol for both pnp and npn

transistors are shown at fig. 8. The

operation of transistor depends on

individual characteristics of the device

and the load line of the circuit.

Transistors are normally used for

signal amplification or switching. In

linear circuit, transistor is actually a

current controlled current source

(CCCS). For switching, transistor

operates between the cut-off region

and the saturate region of its

characteristic curve. For amplification,

transistor operates in the active region

of its characteristics. Fig 9 and fig. 10

described the operation of a transistor

amplifier and a transistor switch.

base

Reverse

Bias

I

Forward Bias

Figure 7 Diode VI Characteristics

NPN Transistor

collector

emitter

base

PNP Transistor

ure 8 Transistor Symbols

V

collector

emitter

Fig

Transistor can be broadly classified into

Power Transistor and Small Signal

Transistor. Transistors are sealed in

different type of packages. Similar to

other semiconductor devices, there are no

worldwide unified standard in the naming

and packaging of transistor.

I C

I CQ

Load Line

slope 1

R L

Operating Point

Electronic Industry Association (EIA) of the

V CE Q V CC

United State and Japan Industry

Association (JIS) are two major Figure 9 Operating Curve of a Transistor

organizations providing national

Amplifier

standardization on packaging and type

convention. EIA semiconductor device I C

On

starts with N... where N... represents the

I B = I B(ON)

number of junction within the device.

Since transistor has 2 junctions, the

industry type number starts with 2N...

(diode is 1N....) For Japanese transistor,

Off

State

the type numbering convention follows

V

V CE

V CE(sat)

CC

JIS-C-7012 Type Designation System for

Discrete Semiconductor Devices. The type Figure 10 Operating Curve of a

number pattern is jStxxxx; where digit j

represents the number of junction(s), S means semiconductor device, t is an

V CE

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alphabet representing the type of the device and xxxx is a sequential registered

number. For example, 2SC945 means a high frequency type NPN transistor.

Common JIS semiconductor device designation is given in Table 2.

There are no unified worldwide standard to locate the terminal location of a

transistor. With different manufacturer, device with similar type number and

package might not pin-to-pin compatible. One must always refer to the

manufacturer's data sheet of individual parts for pin identification and device

characteristics.

However, some guidelines can still be used if data sheet is not available. For

example, for American made small signal transistor; TO-92 package, pins are

normally arranged in the CBE format. For Japanese made package, pins are

normally arranged in BCE format. Some European transistors have pins arranged

in EBC format. The packaging of transistor depends on their power rating,

operating frequency and assembly methods. In the design of packaging, the

objective is to get the heat out from the solid state material for a minimal cost.

The following diagrams are showing some common packages for transistors.

Figure 11 TO-92

Plastic Package

Figure 12 TO-3 Package

Figure 13 TO-220

Package

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Table 2 Common JIS Semiconductor Designation

3rd Digit

Classification

A

B

C

D

J

K

R

S

V

X

Z

PNP transistor for High Frequency Application

PNP transistor for Low Frequency Application

NPN transistor for High Frequency Application

NPN transistor for Low Frequency Application

P Channel Field Effect Transistor

N Channel Field Effect Transistor

Diode Rectifier

Signal Diode

Varactor Diode, PIN diode

Hall Effect Device

Zener Diode

2.10 Integrated Circuit

Integrated circuit(IC) is multi-terminal device and can be broadly classified into

digital integrated circuit and analog linear integrated circuit. In digital electronics,

binary system is normally employed to identify the state of a circuit. Binary digital

circuits either assume a high state (logical '1') or low state (logical '0'). Figure 14

illustrates the voltage levels of TTL.

Digital integrated circuits can also be classified into saturated logic circuit and

non-saturated logic circuit for its switching characteristics. Saturated logic circuit

consumes less power. In addition, logic integrated circuits can also be classified

by their physical implementation technology or circuit characteristics into

different logic families for various applications. Popular saturated logic families

are transistor-transistor-logic (TTL) and its derivative such as low-power schottky

(LS-TTL). Complementary Metal-Oxide Semiconductor (CMOS) is another popular

logic family which offers very low power dissipation. IC is packaged in many

different technology and assembly. Majority of standard logic circuit package for

non-automated assembly are sealed in 14 and 16 pins Dual In Line (DIL) package.

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For all IC, Pin 1 of the package are normally identify with a dot marked on top of

the package. Pins are numbered from pin 1 in a counterclockwise fashion. Nearly

all integrated circuits needed DC power. Most digital IC locates their power pins

on the 2 opposite corners of the package. Fig. 16 give an example of a digital IC

74LS00. LS00 is a Quad 2-input NAND gate; this integrated circuit contains four

individual 2-input logical negated-AND operation.

Analog linear integrated circuit includes all circuits which are having linear

transfer characteristics. Common analog circuits are regulators, op-amp,

comparator, oscillator and data acquisition devices. Fig. 15 illustrates a popular 8

pins DIL IC package for analog IC. It is common for single op-amp to locate the

power pins at pin 4 and pin 7. For dual op-amp, power pin are located at pin 4

and pin 8.

Voltage

5V

3.8V

Logic 1

0.8V

Logic 0

Time

Figure 14 TTL Logic Level

Figure 15 8 Pins DIL Package

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8 Pin DIL

Figure 16 Package, Block Diagram and Truth Table of 7400

3. Common SMT Components

Circuit assembly using surface mounted technology provides higher component

density, reduced space requirement, better electrical performance and

controllable or less component insertion error. It is easier to integrate SMT into

computer aided manufacturing (CAD) or computer integrated manufacturing

(CIM). We shall discuss some of the common SMT components.

3.1 Chip Resistor

The most common thick film chip resistor package is EIA 0603(1/16W), 0805

(1/10W) and 1206 (1/8W). Normally, the resistance value are marked on the glass

overcoat in white ink using a 3 digits system(5% (J), 2%(K)) and 4 digits system

(1%(F)). In all cases, the last digit is the multiplier. In addition to standard

resistance, zero ohm (jumper) chip is available to bridge between PCB tracks.

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Example :

Marking "123" = 12k

Resistive Element

Protect iv e Glass

Overcoat

Marking "4753" =47.5k

Solder Plating

Nickel Plating

Palladium Silver

Alumina Substrate

(96% min)

Figure 17 SMT Resistor

*Source: NIC Components Corp.

3.2 Ceramic Chip Capacitor

The most common ceramic chip capacitor packages are EIA 0603, 0805 and

1206. Depending on the value of capacitance require, other size may be used.

Some manufacturer also supplies low profile package for 1206 and 1210

packages. The capacitor, which is small in size, bears no marking on individual

package. One must be more careful to avoid mixing up of components.

4. Printed Wiring Board & Circuit Interconnection Technique

4.1 General

Electronic or electric circuit can be connected using point-to-point wiring,

soldering or wire wrapping. For complicated circuit, point-to-point wiring

becomes inefficient and messy. Hence, a convenient way to build a circuit is to

use printed wiring board (PWB) or printed circuit board (PCB). The

interconnecting wire is then fabricated on a copper-clad laminate. The PCB is

said to be 'printed' because its conductive area is usually generated by means of

a printing like process; artwork preparation, film development, photo-chemical

etching, silk screen printing and surface finishing. Common thickness of rigid PCB

is 1.6mm, in some cases where space is critical, 0.8mm thick laminate is a popular

choice.

Typical glossary for double-sided PCB is shown in Fig. 18. Depending on the

number of layers of copper clad and processes, 3 basic types of PCB are listed

below in ascending order of interconnection wiring and component density.

1. Single sided PCB- conductors on only one surface of a dielectric base

2. Double sided PCB- conductors on both sides of a dielectric base; usually

interconnected the two layers with plated-through-holes (PTHs)

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3. Multi-layer PCB- conductors on 3 or more layers separated by dielectric

material and interconnected by PTH or pads

Legend

C - component

F - mounting hole

FC - component hole

FCI - component and interconnecting hole

FI - interconnecting hole

FM - plated-through hole

FNM - non-plated-through hole

LC - component side

LS - soldering side

Figure 18 Basic Elements of a Printed Circuit Board

(Source:- Handbook of Printed Circuit Design, Manufacture,

Components & Assembly, G. Leonida, PP 124)

P - pad

PI - conductor

PO - jumper

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4.2 PCB Material

Printed circuit boards are composite material which made from a reinforcement

material immersed in a temperature resistant polymer. Conducting material like

copper foil is bonded on top of the laminate. Foil thickness, regardless of the

manufacturing process, are specified for printed circuit boards in ounce of

copper foil per square foot. Some common materials for printed wiring boards

are:-

1. Phenolic-resin-impregnated Paper, (e.g. XXXP, XXXPC, FR-2)

2. Epoxy-resin-impregnated Paper, (e.g. FR-3)

3. Epoxy-resin-impregnated cloth surface cellulose paper core, (e.g.

CEM-1)

4. Epoxy-resin-impregnated cloth surface nonwoven fibre glass core,

(e.g. CEM-3)

5. Acrylic-polyester-impregnated random glass mat, (e.g. FR-6)

6. Epoxy-impregnated fiberglass cloth, (e.g. G-10, FR-4) and

7. Other resin system like polyimides (Kapton) and

polytetrafluoroethylene (PTFE).

Notes:-

1. Kapton is a registered trademark of E.I. du Pont.

2. The classification of material inside the bracket follows National

Electrical & Manufacturers Association, USA, (NEMA) grading.

3. The number of X represents the amount of resin present in the board;

the amount of resin increase with the number of X. P suffix indicate

punchable at elevated temperature and PC suffix indicates that the

board can be cold punched.

4. XXXPC, FR2 and CEM-1 is normally used for single sided consumer

electronics application.

5. CEM-3, G10 and FR4 are normally used for double sided

computer/industrial electronics application.

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4.3 Soldering

Soldering is the process of joining metal parts with a metal alloy that has a lower

melting temperature than that of the metal parts being joined. Common solder

alloys for electronic interconnection are soft solder. They are basically composed

of tin and lead in varies composition. Due to melting temperature and other

requirements, solders with different composition are having different melting

point and hence different characteristics which may be fabricate for a particular

application. In electronic circuit fabrication, it is desirable to choose the tin/lead

alloy that with composition near the eutectic point (63/37 solder). In general,

solder with higher tin content is more expensive; 60/40 solder gives a low cost

and acceptable solder joint for consumer electronics application. Table 2 gives

the melting point of some commercially available solder. The solder with higher

tin contain or bearing metal other than tin/lead is generally more expensive.

Effective from July 2006, the RoHS (Restriction of Hazardous Substances )

directive restricts the use of six hazardous materials in the manufacture of

various types of electronic and electrical equipment. In all electronic

manufacturing processes, lead free soldering is mandatory, lead soldering should

NOT be used. Typical composition for lead free solder will be Tin/Silver/Copper

(e.g. 96.5%Sn/3.0%Ag/ 0.5%Cu for SAC305 solder paste)

Composition of

Approx. Melting Temperature C

Solder Alloy Solidus Liquidus

100Sn 232 232

63Sn/37Pb 183 183

60Sn/40Pb 183 191

50Sn/50Pb 183 216

3Sn/97Pb 312 318

1Sn/97.5Pb/1.5Ag 309 309

62Sn/36Pb/2Ag 179 179

5Sn/92.5Pb/2.5Ag 280 280

37.5Sn/37.5Pb/25In 138 138

Table 3 Melting Point of Common Solder Alloy

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4.3.1 Wetting & Cleaning

Solder adheres to a work piece because the metals in the solder, tin, reacts with

the metals of the work piece, copper to form an intermetallic bond. When this

bonding action takes place, the solder surface forms a shallow angle (diehedral

angle) with the work piece surface. Diehedral angle is the angle between the

drop and the surface at the point of contact. Solder will only 'wet' clean metals. It

will not 'wet' metals which are badly oxidized or have grease or dirt on the

surface.

For good wetting, flux is used to help in removing minor contamination on the

metal surface. There are many different kinds of flux depending on their

application. They can be divided into 2 basic categories; rosin-based and watersoluble

flux. The most popular flux is rosin based. Rosin is a natural substance

extracted from pine trees. It is a mixture of many organic acid. There are 4

activity levels of rosin-based flux; rosin (R), rosin mildly activated (RMA) and rosin

activated (RA) and rosin superactivated(RSA). The solder wire used are commonly

made with RMA or RA core. Water soluble flux contains organic or inorganic

acids and is generally more active than rosin flux and the board assembly must

be cleaned after soldering to avoid corrosion problem. Soldering with RMA type

flux is generally quite reliable and may not require cleaning. In electronic grade

solder wires are normally made with flux in a single-core construction. Common

core solder flux percentages are 1.2%, 2.2% and 3%.

Good Wetting

Non-Wetting

Figure 19 Wetting and Non-wetting

4.3.2 Soldering Process

Soldering process can be broadly divided into hand soldering and machine

soldering. Hand soldering is done with soldering iron or solder-pot. Machine

soldering uses dip or wave soldering machines to perform the soldering. Wave

soldering can be used to solder SMT and leaded component. This soldering

process consists of moving assembly boards sequentially on conveyor of hooks.

The boards pass over different pots or regions which are constructed to apply

flux to the PCB assembly, preheating and soldering on turbulent of solder

wave(s). Another method to solder, in particular for SMT is called reflow

soldering. Solder cream is applied to the PCB by stainless-steel silk screening or

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syringe. The solder joint is done by the reflow of solder paste using basic heating

methods such as induction heating, infrared lamps, conveyorized hot plate and

Figure 20 Preferred and Faulty Solder Joints

hot air guns. Figure 20 gives some ideal on the inspection of solder joints.

4.4 Solderless Connections and Terminations

Crimping is one of many popular methods for permanently attaching wire to

wire, wire to terminal or wire to PCB. In crimping mechanical force is used to

connect two pieces of similar ductile metal. For good and reliable joint, one

must consider the mechanical strength of the joint and the impact on electrical

performance. Tooling design is critical because insufficient force can cause poor

contact and excessive force can reduce the overall cross-sectional area of the

crimped joint and resulted in poor mechanical strength or even the failure of the

joint.

A crimped joint is made by first striped off the wire insulation, then place the

wire and terminal/splice over a crimping machine (fig. 21), the crimp is formed

from the action of the die. The following diagram shown common crimping

connectors for connecting wire to a terminal block..

Figure 21 Making a Crimp

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Figure 22 Common Solderless Terminals

(Source: AMP Corp., U.S.A.)

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5. Wire

Wire is used to distribute electrical energy. Common wire materials are copper,

aluminum and gold. Wire normally consists of a conductor enclosed by

insulation. In the design of wiring, increasing current capacity increases the

heating of the wire. Poor design can result insulation break down and causing

circuit malfunction or fire. In electronics, a good rule of thumb for current density

is 500 cmil. per Ampere.

A wire table commonly used in electronics is AWG (American Wire Gage). This

wire gage divides the range from 0.005 inch diameter wire (AWG36) to 0.46 inch

diameter wire (AWG0000) into 39 intervals. Sizes progress in geometrical fashion

with a ratio of 1.1229322 between adjacent gages. Wires are classified with their

cross-sectional areas into gage numbers. Larger gage number implies smaller

wire. In addition, the cross sectional area and current carrying capacity roughly

doubles or halves for each decrease or increase of three gage numbers. For

example, the maximum current density of AWG-19 wire is roughly doubles that

of AWG-22 wire.

Size

AWG

Diameter

(mm)

500 cmil/A

Current

Capacity (A)

16 1.291 5.16

18 1.024 3.24

22 0.6438 1.28

24 0.5106 0.81

26 0.4049 0.51

28 0.3211 0.32

Table 4 Current Capacity of Selected Copper Wire

cmil. -- A unit of area that equals the cross-sectional area of 1 mil diameter (0.001 inch) wire.

1 cmil. = 0.7854 mil 2

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6. Reliability and Maintainability of Equipment

6.1 Reliability

Reliability , is the ability of an item to perform a required function under stated

conditions for a stated period of time.

Reliability is the probability of no failure in a period of time.

6.2 Maintainability

Maintainability is the ability of an item, under stated conditions of use, to be

retained in, or restored to, a state in which it can perform its required functions,

when maintenance is performed under stated conditions and using prescribed

procedures and resources.

Maintainability is the probability of repair in a period of time. It is often

expressed in terms of mean time to repair (MTTR).

6.3 The Bath-tub curve

The failure rate of a system can be described by the bath-tub curve which named

after its shape. The operating life of a system can be divided into three parts,

namely early failure period, useful life period and wearout failure period. In the

useful life period, a nearly constant failure rate can be identified.

Early

Failure

Useful Life

Wearout

Failure

Failure Rate

(FITS)

Operation Time

(Power On Hours)

Figure 23 Bath Tub Curve

BS4778 : Glossary of Terms used in Quality Assurance, BSI, U.K.

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6.4 Failure Rate Expression

Failure rate of any system in a given period of time is given by

Number of Observed Failure

Failure Rate ( ) =

Number of Power On Hours

The following are common units for expressing the reliability of component or

system,

FIT - Failure In Time (expresses the number of failure per billion hours)

MTBF - Mean Time Between Failure (expresses the time to failure)

Percent Failure - expresses the number of failure in %/1000Hours or failure per

million hours

e.g. The demonstrated reliability of an integrated circuit is 520 FITs. That means the

following,

a) 520 failure per 10 9 hours (520 FITS)

b) 0.52 failure per 10 6 hours (failure in million hours)

c) 0.052% per 1000 hours

d) 0.0046 failure per year

e) MTBF is 520 billion hours

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Within the useful life of a system (constant failure rate), the Mean Time Between

Failure (MTBF) is given as

1

MBTF =


Failure Rate ( )

Up Time

MTBF

Availability (A) = =

Total Time

MTBF+MTTR

and 1

Repair Rate ()

=

MTTR

For constant failure rate the reliability function is given by

R(t) = e -t

= e -t/MTBF

and the unreliability is given by,

Q(t)

= 1 - R = 1 - e -t/MTBF

Hence the probability of survival for a system with the constant failure rate after

operating for a period of time equals to one MTBF is 37%.

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7. Logical Troubleshooting Procedure

1. Study the symptoms or perform necessary prescribed in available test

procedure.

2. Identify the mode and nature of the failure in the context of circuit behavior.

3. Thinking about possible causes segregate the functional block of the circuit

that can cause the failure.

4. Check all power supply sources; e.g. ac input, biasing for transistors and

integrated circuits.

5. Looking for damaged components and any abnormality. Measure the

behavior of circuit with relevant instrument.

6. Trace the signals of the circuit in a logical input to output manner.

7. Before replacing the faulty component, check if the malfunction of this

component can be caused by the malfunction in other parts of the circuit or

vice versa.

8. Replace the faulty component and test the system.

8. Electronic Equipment Manufacturing Project

The purpose of training in manufacturing project is to provide an opportunity for

students to develop logical thinking and decision for solving problem, in the

course of design and fabrication of the electronic equipment with a simplified

industrial type approach. On receiving assignment, student should be able to

design the equipment, produce necessary drawings and specifications, fabricate

a prototype, review necessary manufacturing process and to introduce and

explain the project in a presentation. A typical flowchart for the manufacturing

project is given in Appendix D.

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Appendix

Appendix A Resistor Colour Code

COLOUR DIGIT MULTIPLIER

BLACK 0 10 0 1

BROWN 1 10 1 10

RED 2 10 2 100

ORANGE 3 10 3 1000

YELLOW 4 10 4 10000

GREEN 5 10 5 100000

BLUE 6 10 6 1000000

VIOLET 7 10 7 10000000

GRAY 8 10 8 100000000

WHITE 9 10 9 1000000000

GOLD 10 -1 0.1

SILVER 10 -2 0.01

ORANGE 3

WHITE 9

BLACK 0

1st Digit

2nd Digit

3rd Digit

Multiplier

Tolerence

RED 10 2

BROWN 1%

Resistance 39.0k

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Appendix B Table of Nominal Standard Resistor

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Appendix C Identification of Common Ceramic/Polymeric Capacitor

Electronics

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Appendix D Electronic Manufacturing Project Flowchart

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References




G. Leonida, “Handbook of Printed Circuit Design, Manufacture,

Components & Assembly”, PP 124

SMT Resistor, NIC Components Corp

Standard tongue styles, AMP Corp, U.S.A.

Bibliography



Charles A. Harper, Electronic Assembly Fabrication: chips, circuit boards,

packages and components, McGraw-Hill ,2002.

Harper, Charles A., Electronic Packaging and Interconnection Handbook, 4 th

ed., McGraw-Hill, 2005.

Clyde F. Coombs, Printed Circuit Handbook, 6 th Ed., McGraw-Hill, 2007.

Recommended Readings

Witte, Robert A., Electronic Test Instruments, 2 nd Ed., Prentice Hall, 2002.

Stadtmiller, D. Joseph, Applied Electronic Design, Prentice-Hall, N.J., 2003.

Tooley, Michael H., Electronic Circuits: Fundamentals and Applications, 3rd ed.,

Newnes, Oxford, Boston, 2006.

Code of Practice for the Electricity (wiring) Regulations, EMSD, The

Government of the HKSAR.

Last Updated: April 2011

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