SMT and Through-hole technology and their assembly line, different types of Soldering, ESD protection, Conformal coating, etc, all about PCB Production

1. Submitted By-
Name- Lakshya
Bhardwaj
Branch- ECE

2.  Autometers Alliance Ltd, an ISO 9001
certified company ranks amongst the
premier Railway Equipment and UPS
Manufacturer in the country. Ever since its
inception in 1959, Autometers Alliance
Ltd has been constantly striving to adapt
the best international technologies and
manufacturing practices, keeping in mind
the segment needs and application area.
 The Company has a well organized
production setup and state of the art
manufacturing capabilities in the field of
Switchgear, Power Electronics, Data
Acquisition, Display System and
Surveillance System at Noida and Baddi
having a manufacturing area of 200,000
square feet. The quality standards and
manufacturing facilities employed are at
par with the existing global standards. The
Company has its own in-house R&D
Centre recognized by Ministry of Science
and Technology , Government of India.

3.  Surface-MountTechnology (SMT) is
a method for producing electronic
circuits in which the components
are mounted or placed directly
onto the surface of printed circuit
boards (PCBs). An electronic
device so made is called a surface-
mount device (SMD).
 Through-Hole Technology (THT) is
the process in which the
components have pins that are
inserted into holes drilled in the
PCB and soldered on the reverse
side of the board.

4. Hand
Soldering
Reflow
Soldering
Wave
Soldering
Selective
Soldering

5.  Hand soldering uses an
iron, solder, soldering
wick, and sometimes flux
to attach surface mount
components to a circuit
board.
 A good solder joint is an
electrical and mechanical
connection which in the
best condition is made in
one shot with a
temperature as low as
possible, and as quick as
possible.
 Soldering quality and
performance vary
depending on tip
geometry, board thickness,
temperature, flux type,

6.  Reflow soldering is less
demanding on pad shape,
shadowing, board
orientation, temperature
profiles and more. For
surface mount
components, it is often a
very good choice.
 Solder and flux mix are
preapplied with a stencil or
other automated process,
components are placed in
position and are often
adequately retained by the
solder paste. Adhesive
may be used in
demanding cases.
 Use with through hole
parts is problematic or
worse. Hence, it is used
for SMD components only.

7.  Wave soldering is a bulk
soldering process used in
the manufacture of printed
circuit boards. The circuit
board is passed over a
pan of molten solder in
which a pump produces
an upwelling of solder that
looks like a standing wave.
As the circuit board makes
contact with this wave, the
components become
soldered to the board.
 Wave soldering is used for
both through-hole printed
and surface mount boards.
In the latter case, the
components are glued
onto the surface of PCB
by placement equipment,
before being run through
the molten solder wave.

8.  Selective soldering is
used
for soldering components
to PCBs that could be
damaged by the heat of
a reflow oven in a
traditional SMT assembly
process. This usually
follows an SMT oven
reflow process; parts to be
selectively soldered are
usually surrounded by
parts that have been
previously soldered in a
surface-mount reflow
process.
 Selective soldering allows
a manufacturer to solder
through-hole pins and
work around delicate SMT
packages by targeting
specific areas on the
board. This promotes
repeatability – and

9. Panoramic View
Magazine
Loader
Screen
Printer
Link
Conveyor
Solder
Paste
Inspection
Link
Conveyor
Pick & Place Machine
Inspection
Conveyor
Reflow Oven
Inspection
Conveyor
Automatic
Optical
Inspection
Reject /
Inspection
Conveyor
Magazine
Un-loader

10.  AUTOMATIC SCREEN PRINTER
•This is a much simpler and fast process.
Here we insert the PCB through a slot given
on the sideways of the machine. The
conveyer takes the PCB inside the machine.
The machine scans two marks placed on the
PCB.
•Then the machine automatically arranges the
PCB under the stencil and pore the solder
paste over the stencil. The paste is a semi
liquid paste. Then this paste is wiped on to
the stencil. The stencil contains slots where
the paste need to be deposited. The paste
passes through these slots and get deposited
on to the PCB. Then the PCB comes out of
the machine with solder paste deposited on
the PCB.

11.  PICK AND PLACE MACHINE
•The PCB prepared out of the screen printer
acts as an input to this machine. A program is
stored in the machine so that it could work
accordingly. Different components are fed into
the machine using a feeder frame. The PCB is
scanned by the machine and arranged
accordingly in the machine.
•There is a nozzle in the machine which could
pick up 5 components at a time and can place
it on the PCB at once. If the components gets
empty in the feeder frame, the machine stops
and indicates an alarm onto the screen saying
that there is no component in the respective
feeder. Once all the components are placed on
the PCB, the PCB comes out of the machine
on the conveyer belt.
•If there are some components missing in the
store, then there is an option of skipping that
component. We go in the settings option and
skip the respective step that we want. And
once the component is available then we could
again resume the step following the same
steps.

12.  REFLOW OVEN
•This machine is used to heat up the PCB
gradually so that the solder paste could melt and
then harden as it moves forward in the oven. The
oven has 7 zones. 5 zones for heating and 2 for
cooling. Once the PCB enters the oven its
temperature gradually changes so that the
components and the PCB does not get
damaged.
•In the first 5 zones the temperature increases
gradually so that the solder paste melts and the
components could stick on to it easily, then in the
last 2 zones the temperature is lowered so that
the PCB cools down and the solder paste harden
and the components hold on to the PCB.
•In order to set the temperature of the 5 heating
zones, a device known as Profiler is used. It is a
slick hard covered device. The components used
in the PCB are connected with wires and these
wires are connected to the Profiler. Then the
whole apparatus is sent into the oven on
conveyer belt. Once the profiler comes out of the
oven from the other end, it is connected to a
computer using a USB cable and a profile is
generated. That profile lets us know what
temperatures need to be set for different heating
zones.
Thermal Profiler

13.  Automatic Optical Inspection
•AOI, automatic optical inspection systems
use visual methods to monitor printed
circuit boards for defects. They are able to
detect a variety of surface feature defects
such as nodules, scratches and stains as
well as the more familiar dimensional
defects such as open circuits, shorts and
thinning of the solder. They can also detect
incorrect components, missing components
and incorrectly placed components.
•They achieve this by visually scanning the
surface of the board. The board is lit by
several light sources and one or more high
definition cameras are used. In this way the
AOI machine is able to build up a picture of
the board.
•The automated optical inspection, AOI
system uses the captured image which is
processed and then compared with the
knowledge the machine has of what the
board should look like. Using this
comparison the AOI system is able to
detect and highlight any defects or suspect
areas.

14.  ADVANTAGES of SMT
 The components are much smaller than
through hole components.
 Much higher component density and
many more connections per component.
 Higher density of connections because
holes do not block routing space on inner or
back-side layers.
 Components can be placed on both sides
of the circuit board.
 Small errors in component placement are
corrected automatically as the surface
tension of molten solder pulls components
into alignment with solder pads.
 Better mechanical performance under
shake and vibration conditions.
 Lower resistance and inductance at the
connection; consequently, fewer unwanted
RF signal effects and better and more
predictable high-frequency performance.
 Fewer holes need to be drilled.
 Lower initial cost and time of setting up
for production.
 Simpler and faster automated assembly.
Some placement machines are capable of
placing more than 136,000 components per
hour.
 DISADVANTAGES of SMT
 Manual prototype assembly or component-
level repair is more difficult and requires
skilled operators and more expensive tools,
due to the small sizes and lead spacing of
many SMDs.
 SMDs cannot be used directly with plug-
in breadboards, requiring either a custom
PCB for every prototype or the mounting of
the SMD upon a pin-leaded carrier.
 SMDs' solder connections may be
damaged by potting compounds going
through thermal cycling.
 Solder joint dimensions in SMT quickly
become much smaller as advances are
made toward ultra-fine pitch technology. The
reliability of solder joints becomes more of a
concern, as less and less solder is allowed
for each joint.
 SMT is unsuitable for large, high-power, or
high-voltage parts, for example in power
circuitry. It is common to combine SMT and
through-hole construction, with transformers,
physically large capacitors, fuses, connectors,
and so on mounted on one side of the PCB
through holes.

15. Bare PCB
Paste
Printer
Pick &
Place
Reflow
Oven
Visual
Testing
Through
hole
component
insertion
Soldering
Testing
(Stage 1)
Lacquering
Testing
(Stage 2)
Heat Run
Testing
Final
Dispatched
for
assembly

16. Panoramic View
Manual Assembly
Line
Wave
Soldering
Selective
Soldering
Ultrasonic Cleaning
Conformal Coating

17.  The wave soldering machine consists of a heated
tank of solder. This is maintained at the required
temperature for the soldering process. Within the
tank, a wave of solder is set up and the printed
circuit boards are passed over this so that the
underside of the board just contacts the solder
wave. Care must be taken in adjusting the height
of the wave so that it does not flow over the top
side of the board where it would cause solder to
enter places where it is not required.
 The boards are held firmly in place on a conveyor
using metal fingers. These are typically made of
titanium because it is able to withstand the
temperatures and it is not affected by the solder.
 To ensure that the areas to be soldered are clean
and free from oxidation, etc, flux is required. Flux
is applied to the side of the board to be soldered,
i.e. the underside. Careful control of the
quantities of flux are needed. Too little flux and
there is a high risk of poor joints, and too much
flux and there will be residual flux on the board.
There is also the risk of long term degradation
because of the acidic nature of the flux. There are
two main methods of applying the flux : Spray
Flux and Foam Flux.
 The thermal shock gives rise to a considerably
increased level of failure if it were not addressed.
To overcome this, the board is preheated so that
it can be steadily brought up to the required
temperature to prevent any thermal shock. Pre-
heating is also necessary to activate the flux.

18.  Ultrasonic cleaning
uses cavitation bubbles induced by
high frequency pressure (sound)
waves to agitate a liquid.
 The agitation produces high forces on
contaminants adhering to substrates
like metals, plastics, glass, rubber, and
ceramics. This action also
penetrates blind holes, cracks, and
recesses. The intention is to
thoroughly remove all traces of
contamination tightly adhering or
embeddedontosolid surfaces.
 Water or solvents can be used,
depending on the type of
contamination and the work piece.
Contaminants can include dust, dirt,
oil, pigments, rust, grease, algae,
fungus, bacteria, polishing
compounds, flux agents, fingerprints
and so on.
 Ultrasonic cleaning can be used for a

19.  Conformal coating material is a thin
polymeric film which ‘conforms’ to the
contours of a printed circuit board to
protect the board's components. Typically
applied at 25-250 μm, it is applied
to electronic circuitry to act as protection
against moisture, dust, chemicals, and
temperature extremes that, if uncoated,
could result in damage or failure of the
electronics to function. When electronics
must withstand harsh environments and
added protection is necessary, most
circuit board assembly houses coat
assemblies with a layer of transparent
conformal coating rather than potting.
 Conformal coating provides insulation to
PCBs, allowing reduction in conductor
spacing.
 It eliminates the need for complex,
sophisticated enclosures.
 It has minimal effect on component
weight.
 It protects the assembly against chemical
and corrosive attack.
 It also eliminates potential performance

20. Advantages of THT
 THT provides stronger mechanical
bonds than SMT, making through-
hole ideal for components
that might undergo mechanical
stress, such as connectors or
transformers.
 SMT components are secured
only by solder on the surface of
the board, whereas through-hole
component leads run through the
board, allowing the components to
withstand more environmental
stress.
 This is why through-hole
technology is commonly used in
military and aerospace products
that may experience extreme
accelerations, collisions, or high
temperatures.
 Through-hole technology is also
useful in test and prototyping
applications that sometimes
require manual adjustments and
replacements.
Disadvantages of THT
 THT also limits the available
routing area on any multilayer
boards, because the drilled holes
must pass through all the PCB’s
layers.
 On the assembly side, component
placement rates for THT are a
fraction of surface mount placement
rates, making THT expensive.
 On the bare PCB side, THT
requires the drilling holes, which
is expensive and time consuming.
 Further, THM requires the use of
wave, selective, or hand-soldering
techniques, which are much less
reliable and repeatable than reflow
ovens used for surface mount.
 Most of all, through-hole
technology requires soldering on
both sides of the board, as opposed
to surface-mounts, which only
require attention to one side of the
board.

21. Panoramic View
X-Ray Inspection In Circuit Tester Flying Probe Tester BGA Rework Station
(for Rework)