Soldering and Assembling Electronics Circuit Boards

Provider: Parmida Amngostar

What is soldering?

• Soldering of a PCB is the process of joining electronic components to the board by melting solder to create strong electrical and mechanical connections.
• In soldering, there are four key elements:

Iron

Solder

Flux

Circuit Components

• Flux cored solder wire is used for hand soldering

Printed Circuit Board (PCB)

• Components are attached to a printed circuit board.
• The ‘front’ side of the board will have printed component information, such as resistor # and resistance, diode type and polarity, etc.
• Holes go all the way through the board from one side to the other. Through- hole soldering is needed to connect components to the board.

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Back of a Circuit Board

• The ‘back’ side of the board will have lines indicating connections between components.
• Thicker lines allow larger current (electrons) moving through.
• Components connect the lines.

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Required Tools for Assembly Work: �1. Soldering Iron: A heating tool needed for soldering work. ��2. Components: Handle, element, element casing, and tip. ��3. Proper tip selection based on power rating is recommended.

Types of Soldering Tips:

Safety Precautions: �1. The soldering iron is a very hot electronic device, keep it away from flammable materials. �2. Do not touch the soldering iron to check the temperature of it while working. �3. Be cautious of the fumes released while soldering as they can be harmful over time. �4. Ensure proper ventilation while working.

Soldering Station:

Flux and Solder Paste: �Helps remove oxidation and improves solderability. �Available in liquid and solid forms. �Avoid direct hand contact with the soldering tip as it may reduce its lifespan.�Useful for soldering small components.

Flux removes oxidation from metal surfaces, enhances solder flow, and improves the adhesion of solder to the joint by preventing re-oxidation during the soldering process.

A soldering iron should be cleaned regularly using a damp sponge or brass wire cleaner to remove oxidation and excess solder.

Desoldering Tool

Solder Wick

Tweezers

Tweezers are useful for holding small components.

Heat Gun

For assembling very small components.

SOLDERING

Solder Wire

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Solder is a fusible metal alloy used to create a permanent bond between metal and workpieces.

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You should be aware of following while choosing solder wire –

Lead (Pb) Content

Flux Content

Wire Size

Manual Soldering Process

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Inspection and Handling

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Supplemental slides

Electronics Components

Resistors

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• A resistor impedes the flow of electricity through a circuit.
• Resistors have a set value.
• Since voltage, current and resistance are related through Ohm’s law, resistors are a good way to control voltage and current in your circuit.

More on resistors

 Resistor color codes

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1^st band = 2^nd band =

3^rd band = 4^th band =

1^st number 2^nd number

# of zeros / multiplier tolerance

Color code

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Units

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• Knowing your units is important!
• Kilo and Mega are common in resistors
• Milli, micro, nano and pico can be used in other components

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K (kilo) = 1,000

M (mega) = 1,000,000

M (milli) = 1/1,000

u (micro) = 1/1,000,000

n (nano) = 1/1,000,000,000 (one trillionth)

p (pico) = 1 / 1,000,000,000,000 (one quadrillionth)

Capacitors

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 A capacitor stores electrical energy.

Capacitance is measured in Farads. The small capacitors usually used in

electronics are often measured in microfarads and nanofarads.

Some capacitors are polarized. Note the

different length terminals on one of the capacitors.

Polarity of capacitors

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• The shorter terminal goes on the negative side (cathode).

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Diode

 A diode is a one-way valve (or gate) for electricity. It is a component with an asymmetrical transfer characteristic. A diode has low (ideally zero) resistance in one direction and high (ideally infinite) resistance in the other direction.

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 Diodes will protect your electronics.

Diode circuit protection

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• In an electronic circuit, if the polarity is wrong, you can fry your components.

Diodes have a bar on the cathode (negative) side.

Light emitting diode (LED)

 A light emitting diode (LED) is a semiconductor light source. When electricity is passing through the diode, it emits light.

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Variable resistor / Potentiometer

 A potentiometer is a variable resistor. As you manually turn a dial, the resistance changes.

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Transistors

 A transistor is a semiconductor device used to amplify and switch electronic signals and electrical power.

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 This is our electronic switch!

Integrated circuit

 An integrated circuit (IC) is a set of transistors that is the controller or ‘brain’ of an electronic circuit.

 An input is received, an output is sent out.

Modern microprocessor ICs can have billions of transistors per square inch!

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SMD Components

Flux Function

What does it do?

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During soldering chemical reaction takes place. The flux removes all the surface tarnish leaving clean metal underneath.

Construction of Cored Solder

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Variables in Cored Solder Wire

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• Solder Alloy
• Most use Sn60/Pb40 or Sn62/Pb36/Ag2 or LEAD FREE
• Flux Type
• No-Clean RMA (Rosin Mildly Activated)

o Flux residue are safe to leave on PCB. They will not cause corrosion or electrical breakdown of ckt during its lifetime.

• Flux %
• 1, 2 or 3. Higher flux % makes soldering easier but can leave more flux residue which can make solder joint look cosmetically ‘dirty’
• Wire Diameter
• Select the right one for the required job
• Reel Size
• Generally 500gm.

Type of Solder wire

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There are two main types of solder:

• Lead-based solder
• Lead-free solder

*The main practical difference between the two is the melting temp.

Lead-based solder: It was made of a mixture of tin and lead. Usually a 60/40 (tin/lead) mix, that melts at around 180-190 degree C.

Because lead has some damaging effects to our health. The industry is moving away from lead and towards lead-free solder.

Lead-free solder: It is solder without lead. Now it is recommended to use lead-free solder (RoHS) because of the health hazards of lead.

It has a higher melting point, so it is bit harder to work with, but usually

not a problem.

Wire Size

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For basic electronics work, a solder wire between 0.711 mm to 1.63 mm diameter is good enough. However, solder diameter is determined by the gauge number.

• For restoring antique computers for the museum, and repairing vintage circuits that have huge solder tags, normally gauge 16 used.
• For PDIP and through-hole packages that have a standard pin spacing of 0.1-inch, gauges 18, 20, and 21 is preferred.
• For SMD components such as SOIC packages where the pin spacing is much closer, then a fine tipped soldering iron with a 22 gauge solder wire works well.

Construction of Tip

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A tip is mainly made up of Copper

core, to ensure good heat transfer.

• Iron plating is done on copper core to make it thermally insulative (Heat should be transferred in proper way)

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• Nickel layer is plated after iron to make non-wetting to keep solder wicking away from the tip.

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• Chrome plating is done at last as a protective layer.

Solder Wetting

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Melting and Diffusion

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• Alloy is formed by melting and diffusion of metals
• Tin and Copper together makes alloy formation

It takes certain amount of time to create the perfect solder joint. Too slow process can damage PCB/Component and too fast will not create a ‘sound’ joint

Manual Soldering Process

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Soldering Iron & Fume Extractor & PCB