Surface Mount Technology INTRODUCTION Compact size of electronic equipment is due to surface mount technology. Surface mount technology allow packaging of electronic components so that the overall assembly is compact. In SMT both components and conductive tracer (i.e. connections) are installed on the same side of substrate or surface. Substrate can be ceramic, paper plastic, rigid and flexible PCB’s. Govt. Poly. Washim 1
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Surface Mount Technology
INTRODUCTION
Compact size of electronic equipment is due to surface mount
technology. Surface mount technology allow packaging of electronic components so
that the overall assembly is compact.
In SMT both components and conductive tracer (i.e. connections) are
installed on the same side of substrate or surface. Substrate can be ceramic, paper
plastic, rigid and flexible PCB’s.
Govt. Poly. Washim 1
Surface Mount Technology
SURFACE MOUNT COMPONENTS
Many but not all through whole components have a surface mountable
counter part. Due to some physical limitations so conventional components cannot
be manufactured as SMC (Surface Mount Components).
e.g.
High capacity capacitor and power transformers, still most circuit can
be assembled, using SMT, even though some conventional through hole components
are required.
It is important for SMT surface designer and service technician to
know the general physical configuration and operating parameters of various SMC’s.
All SMC’s in familiar are available separately SMC’s used for
automatic assemblies are supplied in rills of paper or in magazine.
DETAILS ABOUT SOME (SMC’S)
1. Chip resister :
These are most widely produced of all SMC’s. They are originally
developed for used in hybrid micro circuit. The chip registers are leadless registers.
Constructionally deice is similar to thick film resister.
The typical size of resisters are 1.6 3.2 mm., 1.4 2 mm, 2.6 3.3
mm. The resistance range of most chip resistor is 10 to 2.2 M some companies
manufacture up to the value of 10 M or higher than this.
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Surface Mount Technology
2. Chip Capacitor :
There are originally developed from use in hybrid micro circuits.
There are basically three types of surface mountable chip capacitor.
a) Multi layer Ceramic
b) Electrolytic
c) Tantalum
Ceramic multi layer chip capacitors are commonly used. They are
stable and highly reliable. The capacitance value available are from 1 PF to 1 F.
Package style is identical to chip resister. The size of chip capacitor depends on the
value of capacitor.
For high capacity electrolytic and tantalum capacitor are used.
Tantalum capacitors are available for the values of 0.1 F to 100 F. Aluminium
electrolytic capacitors are larger than that of tantalum. Tantalum capacitors are
available in the values of 1.5 F to 47 F.
3. Potentiometer :
Both single and multiterm trimming potentiometers are available in
surface mountable configuration. They are made from ceramic or high temperature
plastic so as to protect than from emertion soldering. The dimension of smallest
single term trimmer is 4 x 4 mm. Multi terms trimmers are not designed for repeated
adjustments. They can be adjusted mostly 10 times. The trimmers are designed to
be adjusted by means of miniature screw driver or special tools.
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Surface Mount Technology
4. Inductors :
Many kind of surface mountable lead and leadless inductors and even
transformers are available. Inductance’s value ranges from few 10’s of nano henry
to 1 milli Henry ( 10’s of nano h to mh )
5. Descript Semiconductors :
Many diodes, transistors and descript semiconductors are available in
miniature surface mountable packages.
The S O D ( Small outline Diode ) package is leadless cylinder used
for diodes. The SOT ( Small outline transistor ) packages are used for transistors,
diodes various up opto electronic components.
Package configuration determines power dessipation of any
semiconductor.
6. Integrated Circuits (IC’s) :
Surface mountable IC’s are developed by Texal Instruments. The
most popular surface mountable IC packages is small – outlet (SO) configuration
developed by Philips. It resembles, a miniature ( Dual In Line Package ) DIP. An 50
i.e. small outlet device occupies 1/4th board space of an equipment ( Dual In Line
Package ) DIP.
7. Other Surface Mountable Components :
There are many other surface mountable devices available like photo
transistor opto isolators/couplers, infrared LED’s, ceramic filters, switches and
relays.
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Surface Mount Technology
SMT ASSEMBLY METHODS
Surface mountable components like conventional through hole
components can be placed an a board or soldier in place either by hand or by
machine.
Hand assembly is used by home experimental and electronic
companies for the production of prototype SMT circuit boards.
AUTOMATIC SMT ASSEMBLY
Automatic placement equipment can select the position on circuit
board from 1000 to 5 lakhs components per hour. There are three other categories of