Training Contents

• Safety Precautions
• Soldering Basics
• Soldering and Desoldering Tools
• Defects and Remedies
Safety Precautions
Soldering

• Process of joining two metal surfaces together using a filler metal called solder.
• Involves heating the surfaces to be joined and melting the solder, which is then allowed to cool and
solidify, creating a strong and durable joint.
• It is different to welding in that the parts being joined are not melted and are usually not the same
material as the solder
Applications

• Commonly used in the electronics industry for the manufacture and repair of printed circuit boards
(PCBs) and other electronic components.
• Also used in plumbing and metalwork, as well as in the manufacture of jewellery and other
decorative items.
• Solder used in the process can vary in composition, with different alloys used for different
applications. Common solder alloys include tin-lead, tin-silver, and tin-copper, among others.
• Lead-free solder has also become more widely used in recent years due to health and
environmental concerns associated with the use of lead.
Solderability

• A substrate is a measure of the ease with which a soldered joint can be made to that material.
• Some metals are easier to solder than others. Copper, zinc, brass, silver and gold are easy.
• Iron, mild steel and nickel are next in difficulty.
• Because of their thin, strong oxide films, stainless steel and some aluminium alloys are even more
difficult to solder.
• Titanium, magnesium, cast irons, some high-carbon steels, ceramics, and graphite can be soldered
but it involves a process similar to joining carbides: they are first plated with a suitable metallic
element that induces interfacial bonding.
Tools for Soldering and Desoldering

Soldering Station

Brass or Conventional Sponge

Solders

• Soldering filler materials are available in many different alloys for differing applications.
• In electronics assembly, the eutectic alloy with 63% tin and 37% lead (or 60/40, which is almost
identical in melting point) has been the alloy of choice.
• A eutectic formulation : the liquidus and solidus temperatures are the same, so there is no plastic
phase, and it has the lowest possible melting point.
• Having the lowest possible melting point minimizes heat stress on electronic components during
soldering. And, having no plastic phase allows for quicker wetting as the solder heats up, and
quicker setup as the solder cools.
• A non-eutectic formulation must remain still as the temperature drops through the liquidus and
solidus temperatures. Any movement during the plastic phase may result in cracks, resulting in an
unreliable joint.
Solders cont’d

• Common solder formulations based on tin and lead are:

• 63/37: melts at 183 °C (361 °F)
• 60/40: melts between 183–190 °C (361–374 °F)
• 50/50: melts between 183–215 °C (361–419 °F)
Flux

• This helps to clean the surfaces being soldered and prevent oxidization of the hot solder.
• The composition of the flux will vary depending on whether it is in a paste or wire, leaded or
unleaded solder.
• Solder wire usually contains a flux called “rosin”. Most fluxes will produce fumes when the solder is
heated and these fumes are likely harmful to health.
• Many fluxes also act as a wetting agent in the soldering process, reducing the surface tension of
the molten solder and causing it to flow and wet the work pieces more easily.
Flux cont’d

Fluxes for soft solder are currently available in three basic formulations:
• Water-soluble fluxes – higher activity fluxes which can be removed with water after soldering.
• No-clean fluxes – mild enough to not "require" removal due to their non-conductive and non-
corrosive residues. These fluxes are called "no-clean" because the residue left after the solder
operation is non-conductive and will not cause electrical shorts; nevertheless they leave a plainly
visible white residue
• Traditional rosin fluxes – available in non-activated (R), mildly activated (RMA) and activated (RA)
formulations.
• RA and RMA fluxes contain rosin combined with an activating agent, typically an acid, which
increases the wettability of metals to which it is applied by removing existing oxides.
• The residue resulting from the use of RA flux is corrosive and must be cleaned.
• RMA flux is formulated to result in a residue which is less corrosive, so that cleaning becomes
optional, though usually preferred.
• R flux is still less active and even less corrosive.
Soldering Methods

• Hand Soldering: manually using solder iron. Small joints are made by this way in very short
duration approximately in one second.
• Wave Soldering: mechanical and technique that allows multiple lead wires to be soldered to a
Printed Circuit Board (PCB) as it passes over a wave of molten solder.
• Reflow Soldering: solder paste consisting of solder powders in a flux binder is applied to spots on
the board where electrical contacts are to be made between surface mount components and the
copper circuit.
Soldering Procedure

• Good solder joint • Heat both ends to be soldered evenly

• “inside” wires • Both wires
• Strip wires • Wire and the PCB
• Join wires – • Heat your components, THEN add
the solder
• Apply flux
• Side of the iron, NOT the tip
• Apply iron
• “Sweet spot”
• 1 second count
• Apply solder
• Wait
• Remove solder
• Remove iron
Soldering Procedure cont’d
Tinning the Iron’s Tip

• Hot tips oxidize

• Tinned tips are easier to use
• Brass sponge/damp sponge
• “Buttering bread” motion
• Place solder on tip, let it melt
• Coat the tip in solder, let sit
• Brush off extra solder
Joining Wires

• Laying on top
• “Mash up”
• Twist
• Western Union Pigtail
• Best- NASA

• “Wrong” is doesn’t conduct

• Bulky is inconvenient
ESD

• When the tip of a soldering iron comes into direct electrical contact with the pins of a sensitive
component, there is a danger of voltage and/or current signal transfer between:
• the grounded iron tip and the grounded PC board,
• the ungrounded iron tip and the grounded PC board,
• the grounded iron tip and the ungrounded PC board.
This can cause Electrical Overstress (EOS) and Electrostatic Discharge (ESD).
• EOS: The exposure of a component or PCB board to a current and/or voltage outside its
operational range.
• ESD: The transfer of electric charge, which takes place when two objects which have been charged
to different electric potentials are brought in contact with one another or when two objects which
have different electric potentials due to static induction are brought in contact with one another.
Once electrostatic potential between the two materials is balanced, the ESD event will stop.
ESD Control Procedures
Soldering onto PCBs
Soldering Defects and Their Remedies

• Granular formation at the surface of the joint of solder is one of the common soldering defects.
• Formation of spheroids at the surface of soldering joint is also similar defect. This happen due to
under heating or over heating of solder iron, insufficient use of flux. Formation of spheroids make
the joint ugly and week in strength.
• Improper or uneven application of flux may make the joint of weaker strength.
• Proper coordination between flux application and soldering makes the joint of good quality.