Transcript Document

Basic Skills in
Electricity and Electronics
Sixth Edition
Charles A. Schuler
Soldering and Desoldering
Including SMT Rework
©2003
Glencoe/McGraw-Hill
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
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.
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.
Cleaning with wire brush
Tinning the iron
Cleaning by wiping tip
on a damp sponge
A diameter of 0.025
inches is common for
most electronic work.
Solder
Eutectic alloy
(lowest melting point)
63% tin, 37% lead
62% tin, 36% lead, 2% silver is preferred for some work
Electrostatic discharge (ESD)
Potentials as low as 200 volts can
cause damage.
Wrist strap
Conductive
work surface
A workstation equipped
to prevent ESD damage
Wrist strap connection point
When ESD measures are not available
Touch a known earth ground before
touching circuits and components.
Tools and materials
Temperature controlled iron with grounded tip.
A magnifier is
helpful for
inspection.
Circuit board holder
Solder bridge
Desoldering methods
Desoldering braid
Vacuum pump
Vacuum desoldering
station
Using desoldering braid
Click the center of the photo to start the video.
Using a vacuum pump
Click the center of the photo to start the video.
Using a vacuum desoldering station
Click the center of the photo to start the video.
After device removal
Clean the pads with desoldering braid
Soldering
Apply the iron, then the solder. Remove the
solder, then the iron. (About 3 seconds per lead)
Click the center of the photo to start the video.
Removing a solder bridge with braid
Clean the area
Spray with flux cleaner and then brush to remove flux residue.
Click the center of the photo to start the video.
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.
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. It’s done by
pick and place robots. The
DIP and other through-hole
mounted components do not
work well with today’s
automated assembly techniques.
The leads go through holes in the printed circuit board.
Surface-mount technology (SMT)
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•
•
•
•
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.
Discrete devices with leads do not
lend themselves to robotic placement.
These leads can be preformed (bent)
to go through the appropriate holes
in a printed circuit board but
automated board stuffing is a problem.
These devices
are readily
placed with
robots.
Unleaded discrete devices
(also known as chip components)
No leads (tinned ends)
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.
Small-outline transistor (SOT)
Gull-wing leads
Used for BJTs, FETs and diodes
Small-outline integrated circuit (SOIC)
Gull-wing leads
Used for ICs … analog, digital and digital memory
The preferred removal method for chip components,
SOTs and some SOICs is thermal tweezers.
(A.P.E. South)
Quad flatpack (QFP)
Gull-wing leads
Used for ICs … mixed signal, digital and microprocessors
This QFP is less than
1 inch by 1 inch and
has 144 pins!
Plastic leaded chip carrier (PLCC)
J-leads
Can be socketed or directly soldered to PC board
The preferred removal method for
most SMT ICs is hot air.
Click the center of the photo to start the video.
Hot air rework station
1000° F
750° F
Nozzle
800° F
Accepts various nozzles
Nozzle shape, size and distance
are important factors.
Portable hot air devices
Electric gun
Butane pen
Custom tip for quad flat pack
removal with suction and hot air
Click the center of the photo to start the video.
Use braid to clean pads after device removal.
Apply liquid flux to the pads
Tin the pads with a clean, freshly tinned iron.
Apply flux again.
Tin a corner pad with solder.
Position the new device.
Click the center of the photo to start the video.
Clean the board with flux remover and a brush.
Solder paste consists of powdered
solder, solvent and flux.
Solder paste dispenser
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!
After soldering two corner pins, solder
paste is applied and then hot air
is used to melt and flow the solder.
Click the center of the photo to start the video.
The pitch keeps getting finer!
196 pins!
Pitch = center to center lead spacing
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.
Fine pitch devices and BGA devices
require a rework station.
Rework stations offer hot air, vacuum
pickup and precision positioning
of the replacement IC.
Chipmaster SMT rework station (A.P.E. South)
Hot air is used for device removal
and reflow device replacement.
Vacuum
pickup
(A.P.E. South)
Using desoldering braid to level the pads
After removal of a BGA,
the pads must be prepared