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Unit 34, Assignment 4 - Surface Mounting Technology (P5, P6 & M3)
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- PEARSON (PEARSON)
BTEC Engineering Level 3
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Unit 34 Surface Mounting Technology Assignment 4For this new assignment I will explain the use of SMT in the manufacture of an electronic
circuit & give 2 examples of the outlines & packages used for surface mounted devices.
SMT essentially stand for Surface Mount Technology & it is a method for producing huge
amounts of electronic circuits where the components are mount or are placed onto the surface
of a PCB.
There are many SMT components, such as:
- Passive SMDs have a large variety of different packages used; however, most of the
SMDs are capacitors or resistors for which the package sizes are rationally identical.
- Transistors & Diodes are components that are enclosed
in a plastic package, & the links are created via leads that
originate from the package & are twisted so that they
make contact with the board. Also, 3 leads are
continuously used for these packages, so this way, it’s
easier to recognise which way round the device should
go.
- Integrated Circuit,
there is a diversity of packages that are used, which
depends on the level of interconnectivity that is
needed.
There are many other packages that are available for use like
a BGA (Ball Grid Array), which is used underneath the
package. The connection pads have balls of alloys that melt
during the welding process, thus giving an acceptable
connection with board.
SMTs are smaller & generally offer a better level of performance as well as be used with
automated pick & place machines where in some cases eradicate the ned for manual
intervention in an assembly process. Wired components are known to be hard to place
automatically due to the wires as they need to be pre-formed to fit correctly in the right hole
spacing. Despite a lot of the connectors & a few other components still requiring supported
placement, PCBs are typically developed to reduce this to the bare minimum. Likewise,
component manufacturers have established some particular surface mount versions of
components that allow virtually complete automated assembly for the majority of the boards.
P5 Fahim Mohammed
, Unit 34 Surface Mounting Technology Assignment 4
Moving onwards to the next criteria, I will describe methods used for the manufacture of an
electronic circuit using SMT.
Firstly, electronics manufacturing using SMT is essentially electronic components that are
assembled with automated machines & are positioned on the surface of a PCB. In comparison
to ‘through-hole technology’ (THT) processes, SMT components are sited right on the surface
of a PCB rather than being fused to a wire lead.
SMT in essence took the idea of through-hole manufacturing & modernised it; so PCBs didn’t
need to have holes punctured through them, & in its place, components had the chance to be
applied using a solder paste that much stronger than glue.
Now, applying soldering paste is one of the earliest stages in the SMT assembly process;
soldering paste is somewhat printed on the boards using a method known as silk-screening.
But, depending on the design of the board, diverse stainless-steel templates for silk-screening
the paste onto the board & numerous product specific pastes are used. After, a laser cutter is
used on the stainless steel template, the paste is then to be applied to the sections where the
components will be fused. Subsequently, the soldering paste is on the boards, a 2D-soldering
paste review is executed to make sure that the paste is equally & properly smeared; & when
the precision of the paste application has been established, the boards are transported to the
SMT Assembly Line in where the parts will be joined.
Onto the Component Placement & Assembly, the electronic components that are going to be
gathered come in trays that are loaded into the SMT machine. So, during this loading process,
software systems are put in place to ensure that the parts are not accidentally switched or
misloaded. The SMT assembly machine then automatically eliminates singular component
with a vacuum tube from its tray & lays it on its right position on the board using extremely
accurate pre-programmed X-Y coordinates. Later, the SMT assembly is accomplished, the
boards are transported on to the Reflow Ovens for soldering, which attaches the parts to the
board.
Component Soldering is the next stage & to solder
electronic components, two different methods needs
to be used; each of which have their own pros
depending on the order quantity, but, for series
production orders, the Reflow-soldering procedure is
used. During this procedure though, the boards are
placed in a nitrogen atmosphere & are progressively
heated up with heated air until the soldering paste
lubricates & the flux evaporates, which combines the
components to the PCB. Afterwards, the boards are chilled off & as the tin in the soldering
paste toughens, the parts become everlastingly attached to the board & the SMT assembly
process is done.
Moving onto the next stage, which is essentially a Vapour Phase Procedure for samples or
sensitive components. So, during this process the boards are heated until a certain melting
point for the soldering paste is touched as this lets the worker/s to weld at lower temperatures
or solder different SMT components at diverse temperatures that are dependent on their own
soldering temperature sketches.
The last step is known as the AOI & Visual Check & in order to make sure the quality of the
assembled boards, or to latch & correct a mistake, AOI visual inspections are operated for the
majority of the series production orders. For this to be accomplished, numerous cameras
routinely checks each board & associates the form of each board with the correct, pre-defined
reference image. For e.g. If there are any aberrations, the worker of the machine is informed
P6 Fahim Mohammed
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