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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