Basic Skills in

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Basic Skills in Electricity and
Electronics Sixth Edition
Charles A. Schuler
Soldering and Desoldering Including SMT Rework
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Acknowledgement Many of the photos and all of
the video clips used in this presentation are
courtesy of
The Electronic Industries Association 2001
Pennsylvania Avenue Washington, DC 20006
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Soldering safety tips

• Wear eye protection.
• Work in a well-ventilated area.
• Do not put wires or solder in your mouth.
• Wash your hands when you are finished.

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Basic requirements

• Clean metal surfaces
• Clean, tinned soldering iron
• Correct solder and flux
• Correct temperature and time

The actual methods used depend on the tools and
materials at hand, the physical nature of
the parts and boards, and the skill of the worker.
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Solder
62 tin, 36 lead, 2 silver is preferred for
some work
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Electrostatic discharge (ESD)
Potentials as low as 200 volts can cause damage.
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A workstation equipped to prevent ESD damage
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When ESD measures are not available
Touch a known earth ground before touching
circuits and components.
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Tools and materials
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Temperature controlled iron with grounded tip.
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A magnifier is helpful for inspection.
Circuit board holder
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Desoldering methods
Desoldering braid
Vacuum pump
Vacuum desoldering station
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Using desoldering braid
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Using a vacuum pump
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Using a vacuum desoldering station
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After device removal
Clean the pads with desoldering braid
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Soldering
Apply the iron, then the solder. Remove
the solder, then the iron. (About 3 seconds per
lead)
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Removing a solder bridge with braid
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Clean the area
Spray with flux cleaner and then brush to remove
flux residue.
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Surface-mount technology (SMT)

• Is driven by economics.
• Has largely replaced through-hole technology.
• Is repaired when cost-effective.
• Is repaired often enough that technicians should
  know about the general procedures.
• Is evolving.

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This dual-inline package (DIP) served well, but .
Board stuffing is the term applied to loading
circuit boards with their component parts.
Today, board stuffing is automated. Its done
by pick and place robots. The DIP and other
through-hole mounted components do not work well
with todays automated assembly techniques.
The leads go through holes in the printed circuit
board.
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Surface-mount technology (SMT)

• Does not require holes in the circuit board.
• Works well with robotic parts placement.
• Allows higher component density.
• Lowers the cost of manufacturing.
• Improves the reliability of products.
• Allows smaller and less expensive products.

These leads do not need holes and are soldered on
the component side of the circuit board.
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Discrete devices with leads do not lend
themselves to robotic placement.
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Unleaded discrete devices (also known as chip
components)
The end terminals are soldered on the component
side of the circuit board. Automated parts
placement works well!
Used for resistors, capacitors, inductors,
diodes, fuses, etc.
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Small-outline transistor (SOT)
Gull-wing leads
Used for BJTs, FETs and diodes
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Small-outline integrated circuit (SOIC)
Gull-wing leads
Used for ICs analog, digital and digital memory
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The preferred removal method for chip
components, SOTs and some SOICs is thermal
tweezers.
(A.P.E. South)
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Quad flatpack (QFP)
Gull-wing leads
Used for ICs mixed signal, digital and
microprocessors
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This QFP is less than 1 inch by 1 inch and has
144 pins!
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Plastic leaded chip carrier (PLCC)
J-leads
Can be socketed or directly soldered to PC board
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The preferred removal method for most SMT ICs is
hot air.
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Hot air rework station
Nozzle shape, size and distance are important
factors.
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Portable hot air devices
Electric gun
Butane pen
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Custom tip for quad flat pack removal with
suction and hot air
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Use braid to clean pads after device removal.
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Apply liquid flux to the pads
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Tin the pads with a clean, freshly tinned iron.
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Apply flux again.
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Tin a corner pad with solder.
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Position the new device.
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Clean the board with flux remover and a brush.
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Solder paste consists of powdered solder, solvent
and flux.
Solder paste dispenser
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How do you solder a device when the
spacing between the pins is only 0.013 to 0.009
inches?
0.007 to 0.011 inches (pin width)
Pitch 0.02 inches (center to center spacing)
The space between pins can be as small as 9/1000
of an inch!
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After soldering two corner pins, solder paste is
applied and then hot air is used to melt and flow
the solder.
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The pitch keeps getting finer!
196 pins!
Pitch center to center lead spacing
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Ball Grid Array (BGA)
Bottom view
Side view
The connections are underneath the chip. These
devices are removed with hot air. The new part is
installed with hot air. Accurate positioning is
required.
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Fine pitch devices and BGA devices require a
rework station.
Rework stations offer hot air, vacuum pickup and
precision positioning of the replacement IC.
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Chipmaster SMT rework station (A.P.E. South)
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Hot air is used for device removal and reflow
device replacement.
Vacuum pickup
(A.P.E. South)
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Using desoldering braid to level the pads
After removal of a BGA, the pads must be prepared