Page 133 - CITS - Electronic Mechanic - TT - 2024

ELECTRONICS MECHANIC - CITS

14 lead plastic dual -In-line package
Advantages of SMDs

Advantages of SMDs are given below
1 PCBs area much smaller than by conventional through - hole components
2 Since the both layers of the PCB could be used for assembling, the final PCBs area for the same circuits could
be decreased by 50%.

3 Simple assembling-no bending and cutting of the wires.
4 Automatic assembling very easy. Low cost of the assembling.
5 Small size of components makes very high packingdensity possible. For the same circuits a volume of a module
assembled with SMD could be reduced to 30% of the device assembled with the conventional technique.
Therefore a size of the whole instrument decreases, too.
6 Very high resistance to mechanical shock and vibration.
7 Low store and transport cost. Low store area and volume.

8 Lack of hole’s drilling and metallization.
9 Thin pads.
10 For larger volumes, low manufacturing cost.
Reflow soldering and working principle

Reflow soldering is a process in which a solder paste (a sticky mixture of powdered solder and flux) is used to
temporarily attach one or several electrical components to their contact pads, after which the entire assembly
is subjected to controlled heat, which melts the solder, permanently connecting the joint. Heating may be
accomplished by passing the assembly through a reflow oven or under an infrared lamp or by soldering individual
joints with a hot air pencil as shown in fig. 1 reflow soldering process.
Reflow soldering is the most common method of attaching surface mount components to a circuit board, although
it can also be used for through-hole components by filling the holes with solder paste and inserting the component
leads through the paste. Because wave soldering can be simpler and cheaper, reflow is not generally used on
pure through-hole boards. When used on boards containing a mix of SMT and THT components, through-hole
reflow allows the wave soldering step to be eliminated from the assembly process, potentially reducing assembly
costs.

Tips and types
Most soldering irons for electronics have interchangeable tips, also known as bits that vary in size and shape
for different types of work. Pyramid tips with a triangular flat face and chisel tips with a wide flat face are useful
for soldering sheet metal. Fine conical or tapered chisel tips are typically used for electronics work. Tips may
be straight or have a bend. Concave or wicking tips with a chisel face with a concave well in the flat face to
hold a small amount of solder are available. Tip selection depends upon the type of work and access to the
joint; soldering of 0.5mm pitch surface-mount ICs, for example, is quite different from soldering a through-hole

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CITS : E & H - Electronics Mechanic - Lesson 69 - 72