Transcript Soldering - TeacherWeb

Electronics
Electrical Soldering
Alton G. Dunn
Laurens Central School
Abc’s of Electrical Soldering, by Louis M. Dezettel
Published by Howard W. Sams & Co., 1973.
Objectives
• Define what soldering is and
explain what it does
• Describe the solder alloy
• Distinguish between organic and
inorganic fluxes
• Identify types of soldering irons
and take proper care of tips
• Use a soldering iron properly
• Observe safety precautions
Objectives
• Define what soldering is and
explain what it does
• Describe the solder alloy
• Distinguish between organic and
inorganic fluxes
• Identify types of soldering irons
and take proper care of tips
• Use a soldering iron properly
• Observe safety precautions
What Soldering Is and Does
• Ancient soldering
– 4,000 year old vases
– Roman water pipes made of lead
– “Plumbing” comes from Latin word
for lead (plumbum)
• Recent uses
– Tin can
• Precise alloy of tin and lead
– Solder alloys and fluxes for plumbing
and electronics
Electronic Soldering
What Soldering Is and Does
• Soldering
– Joining of metals by heat for the
purpose of making something
structural or producing a continuous
and permanent path for the flow of
electricity
• Joining metals
– Soldering
– Brazing
– Welding
Joining Metals
• Soldering
–
–
–
–
Low melting point alloy (<800°F)
Heated to a liquid state
Flows onto the base metal
Alloys with it at the surface
• Brazing
– Higher temperature
– Different alloys and fluxes
• Welding
– Base metals are fused
– No separate alloy
What is a Metal?
• Free electrons in outer shell
• Interchange easily with free
electrons of adjacent atoms
– Makes good electrical conductors as
well as heat conductors
What is a Metal?
• Electrical attraction between
negative electrons and positive
ions makes metals solid
• Voids in crystal lattice structure
• Alloys are combinations (mixtures) of
different metals
Soldering
• Solder is an alloy of lead and tin
– Melts at a low temperature
– Transfers thermal activity by
conduction to the surface of other
metals (called the base metal)
• Combines with the base metal at
the interface
– Edges of the crystal lattice structure
overlap each other and join to form a
solid that is mechanically and
electrically continuous
What Can Be Soldered?
• Only certain metals are atomically
structured to accept wetting with
tin-lead alloy solder
– Copper
– Silver
– Iron and steel
– Zinc
– Nickel
– Gold
– Platinum
– Palladium
What Can Be Soldered?
• Other metals need special alloys
and fluxes
– Aluminum
– Stainless steel
– Magnesium
• Some are almost impossible to
solder
– Chromium
– Cobalt
– Silicon
Solder Alloy
• Solder
– Alloy of two or more metals which, in
various combinations, is used to join
base metals together by the
application of heat
• “Soft solder” for electrical
connections
• Tin (Sn, Stannum)
• Lead (Pb, Plumbum)
• Melting point depends on ratio
Solder Alloy
• Tin
– Is not attacked by air and water
– Reacts and alloys with the joining
metals well
– But has too high a melting point by
itself
– Also, too expensive
Solder Alloy
• Lead
– Soft and dense
– Reduces melting temperature
– Adds to overall strength although it
moderates the action of alloying
– Surface corrodes quickly
Tin-Lead Ratio
• 70/30
– Good for pre-tinning; expensive
• 63/37 (best solder)
– Eutectic solder; no pasty state
• 60/40
– Good general purpose solder
• 50/50
– Lower cost general purpose solder
• 40/60
– Lowest cost common solder
ASTM* Specifications
• First two digits represent the
percent of tin
• Letter suffix shows amount of
antimony (used for hardening)
– A = 0.12 to 0.25 percent
– B = 0.5 percent
– C = 2.0 percent
*American Society for Testing and Materials
Solder Additives
• Small amounts of one or more
other metals that have special
characteristics
– Antimony
• Hardens the solder
– Copper
• Reduces pitting of copper tips
– Silver or gold
• Retards reduction of precious metals
from plated connections
– Cadmium
• Lowers solder temperature
Tin-Lead Temperature Graph
• Pasty range
• Eutectic ratio
• Solidus (361°F)
– Horizontal line representing
temperature below which solder will
solidify as it cools
– Same for all ratios
• Liquidus
– Minimum temperature for melting
– Not the same for all ratios
Tin-Lead Temperature Graph
Solder Qualities
• Wetting
– Good capillary action in flowing over
the base metal, bonding or alloying
with its surface
• Temperature
– Able to reach the liquid state and wet
the base metal at a low temperature
• Strength
– As hard as possible consistent with
other qualities
Soldering
• Wetting
– Solution action between the solder
and the base metal
– Capillary action that breaks the
surface tension and flows solder
along the surface of a metal
– Metal must be clean
• Molten solder dropped on a nonmetallic
or unclean metal will form a ball (“bead”)
• Flux
– Used with solder to remove surface
oxides
Wetting
Forms of Solder
• Rosin-core solders
– Continuous inner core of flux
– Some multi-cored
• As many as five cores of flux
• Available without flux core for use
with liquid flux
Flux
• Oxygen in the air attacks copper,
and forms a thin layer of copper
oxide
• Flux acts on the oxides that form
on the surfaces of metals
– Thin tarnishes become soluble in the
flux, and evaporate when the flux is
heated to its boiling point
• No new air can reach the metal,
so it stays untarnished
Flux
• Organic “rosin” or “resin” fluxes
– Noncorrosive
– Used in electrical soldering
– Charring at high temperatures
• Inorganic fluxes
– Corrosive
– More active than organic fluxes
– Used in mechanical soldering
• Activated flux
– Amine hydrochloride or other
ingredients added to organic flux
Flux
• Flux removes thin tarnish resulting
form exposure of a base metal to
air for a short period
• Flux will not clean
– Greasy or oily surfaces
– Scales of other corrosive
atmospheres
– Oils and acids of human perspiration
Flux
Flux
• Dip and wave soldering of printed
circuit boards (PCBs)
– Flux applied in advance
– Entire board goes into a molten bath
of solder
– Rapid soldering system
– Post-cleaning necessary if activated
flux is used
Cleanliness
• Do not touch component leads
– Handle parts by their bodies
– Handle printed circuit boards by the
edges, like you should a photograph
or a DVD
• Clean old leads with emery cloth
or fine sandpaper
– NASA recommends a scraper tool
Forms of Solder
• Size
– 1 lb. spools (also 5 and 20 lbs.)
– Diameter depends on size of
soldering connection to be made
Wire Size
1/16 inch
1/32 inch
No. 16
No. 18
No. 20
Diameter
0.062 in.
0.031 in.
0.064 in.
0.048 in.
0.036 in.
Length of 1 lb. of Solder Wire
Gauge
Dia.
(in.)
Tin-Lead Ratio
60/40 50/50 40/60
18
20
22
24
26
28
30
32
34
0.048
0.036
0.028
0.022
0.018
0.015
0.012
0.011
0.009
182 ft.
324 ft.
536 ft.
865 ft.
1290 ft.
1910 ft.
2730 ft.
3590 ft.
4950 ft.
174 ft.
319 ft.
529 ft.
167 ft.
299 ft.
493 ft.
Soldering Irons
• Pencil-style soldering iron
Soldering Irons
• Pencil-style soldering iron
• Resistance soldering
– Electrodes pass current through the
connection
Soldering Irons
• Soldering gun
– Fast heating, trigger-pull
– Specially treated, low-voltage copper
coil near the tip
Soldering Irons
• Heat control
– Fixed wattage (W = E2÷R)
• Resistance increases with temperature
• Dissipation of heat to the surrounding
air
– Self-regulating
• Bimetallic strip or magnetic switch
– Transformer isolated
• Dial adjusts voltage supplied to heating
element
Soldering Irons
• Transformer isolated
– Dial adjusts voltage supplied to
heating element
How Much Heat Do You Need?
• Too high a temperature
– Can damage semiconductor
components
– Lift copper from a PCB
– Melt insulation on a wire
– Char the flux
• Too low a temperature
– Take too long to transfer heat from
the terminal to the solder and melt it
– Heat may affect attached parts
How Much Heat Do You Need?
• Wattage ratings of small pencil irons
with approximate temperature
reached at the tip
Wattage
(W)
Temperature
(°F)
25
650 – 700
40
750 – 800
50
850 – 1,000
Heat Recovery
Heating Elements
• Handles have sockets for
interchangeable heating elements
and/or tips
Tips
Care of Irons
• Tinning
– Always keep a thin layer of bright
solder on the tip
– Wipe excess solder on a damp
sponge
– When idle, the tip should have extra
solder on it, or the normally thin layer
will oxidize off
• Never leave idle without the tip
installed
• Never hit iron against work bench
Care of Irons
• Retinning
– Never retin a tip while it is hot
– File the surface smooth
• Copper only, not iron or nickel clad
– Get burrs off with fine sandpaper or
emery cloth
– Plug in for 60 to 90 seconds, then
apply solder at the coolest tip
temperature possible
– Discard tip if the end becomes too
short from filing or if iron is pitted
How to Solder
• The main purpose of soldering is
NOT to make a mechanical
connection, but to make a strong
electrical connection
• The purpose of the soldering iron
is NOT to melt the solder!
– It heats the connection
– The base metal then melts the
solder
How to Hold the Soldering Iron
• Large soldering iron
– Grip with your four fingers around
the handle, and thumb at the cord
end, with the iron pointing down
• Small soldering iron
– Hold a miniature style soldering iron
as you would a pen or pencil
Steps of Soldering
1. Apply the tip of the iron to the
wire and terminal
– Don’t be afraid to apply a little
pressure
– Object is to transfer heat from the
iron to the connection
– Hold the iron there for two or three
seconds
Steps of Soldering
2. Touch the end of the solder to
the terminal right at the point
where the iron is in contact with
the terminal
– Solder should begin to melt in less
than one second
– Feed about one inch of solder into
the connection
– Let it flow into all the crevices
between the wire and the terminal
– This takes about two seconds
Steps of Soldering
3. Remove the solder, then the iron*
– Don’t disturb the connection until it
has cooled
– Should be a strong connection with
a bright appearance
– All crevices filled, but with the
contour of the wire showing under
the solder
– Should feather out, without
rounded edges
*NASA says remove both at the same time
“Five America”
• Apply the soldering iron and count
out loud, “One America, two
America, Three America”
• Then while holding the iron to the
connection, apply the solder and
count on, “four America, five
America.”
“Cold” Solder Joints
Wire Stripping
• Tools for stripping insulation
– Production
– Manual
• Remove about 1/8 inch more than
the length to be soldered
– If the insulation ends too near the
connection, some of the plastic could
melt into the connection and prevent
good wetting by the solder
– If it is too far away, it may short
against other wires nearby
Wire Stripping
Pretinning Leads
• Working with pretinned leads,
especially stranded wire
• Easier to solder if already tinned
Wiring a Terminal
Soldering a Terminal
Printed Circuit Boards
• Traces
– Copper surface is etched away
leaving paths of copper equivalent to
wired connections
• Lands
– Places where leads of mounted
components come through the board
– Holes that are drilled or punched
• Pads
– Circles of copper around the lands
for soldering component leads
Printed Circuit Boards
Printed Circuit Boards
• Very little solder is needed for
printed circuit board connectors
Switch Terminals
• Do not allow solder to run down
onto the switch contact itself
– Contacts are usually silver plated
• Solder to the terminals of a switch
with the terminals hanging down
– Gravity will keep the solder out of the
contacts
– If this is not possible, use solder
sparingly and make the connection
quickly, but with enough heat for
good wetting action
Soldering to a Chassis
• Do not solder to aluminum chassis
• Cadmium plated steel chassis
– Scrape away cadmium plating with a
knife or screwdriver
– Pretin both the chassis and the braid
– Use a 100 watt iron because the
chassis metal carries the applied
heat away so fast, and it must be
replaced quickly
Semiconductors
• Excessive heat can destroy diodes
and transistors, as well as IC’s
– Developed internally by exceeding
their ratings
– Applied externally by soldering
• Use a heat sink
– Clamp type
– Copper alligator clip
– Long-nose pliers with a rubber band
Wire Splices
• Splices should be avoided if
possible
– Should be enough terminal tie-points
on the chassis to accommodate all
components by their own leads
• If splicing is necessary
– Use heat shrink tubing to insulate
the wire splice to prevent shorts to
other bare metal
Wire Splices
• Clean wires with
emery cloth
• Twist wires
together tightly
• Move hot iron
along splice, as
solder melts
• Solder will tend
to go towards
the heat
Inspection
• When you are finished, always
inspect your own work for
– Cold solder connections
– Bridges (icicles)
– Frosty looking connections
• Use a jeweler’s loupe or magnifier
Inspection
• Cross-section of a wire hooked
through a terminal hole
Tacking
• Temporary solder connection
– Components soldered to terminals
without shortening the leads and
without hooking them into the
terminal holes and bending them
around
– Easy to unsolder a resistor, for
example, and replace it with one of
another value
– Easier if the leads and the terminals
are pre-tinned
Repairs/Replacement
Soldering Aids
Soldering Aids
• Double- ended pick
– One end pointed
– Other end forked (bifurcated)
Soldering Aids
• Vacuum desoldering iron
– Depress the bulb
– Apply the heated iron to the
connection
– Release the bulb
Soldering Aids
• Special desoldering tips
Soldering Aids
• Special double-edged bar for
desoldering all 16 terminals of an
integrated circuit chip at one time
Safety
• Wear proper eye protection
• If you leave the soldering station,
turn the soldering iron off
• Precautions against burns
– Always lay the iron down in the
same place between connections
– Place your iron in a stand during
standby
– Avoid placing flammable objects
near the hot iron
– Be aware of people near you
Safety
• Inexpensive stand guards hot iron
from accidental contact
Safety
• Protect wall by using metal sheet
Classification of Burns
• Causes of burns
– Radiation
– Electrical
– Chemical
– Thermal
• Area of body
– Shock is possible with 15 to 25% of
the body burned
– Entire palm of the hand and front of
all fingers is about 1%
Classification of Burns
• Depth of burn
– First degree
• Skin is reddened, sore, and tender, but
not blistered
• Damage is to outer layer of skin only
– Second degree
• Outer and adjacent layers of skin
• Skin will appear red and swollen and
there will be blisters
– Third degree
• Skin tissues and underlying flesh
• Nerve damage
Treatment of Burns
• First aid
– Reduce pain
– Prevent infection
• Light burns
– Cover with clean cloth or bandage
– May use ointment or baking soda
• Heavy burns
– Cover with a clean cloth and see a
doctor
– Do not open blisters
– Treat for shock
Summary
• Soldering is a chemical process
that uses heat to alloy two other
metals together with it
• Solder wire has a flux core that
cleans oxidation from the metals
• Temperature and amount of time
are crucial to the operation
• Accessories make soldering and
repairs easier
• Always practice safe soldering
Review
• Methods for joining metals
– Soldering
– Brazing
– Welding
• Electrical soldering
– Joining of metals by heat for the
purpose of producing a continuous
and permanent path for the flow of
electricity
– Chemical process called, alloying
Review
• Solder
– Combination of tin and lead in
varying proportions
• Flux
– Used for cleaning surfaces prior to
making the solder joint
– Can be brushed on or contained in
the core of the solder wire
Proper Soldering
• Steps
– Apply heat to the connection
– Apply solder
– Remove solder
– Remove iron
• Solder joint
– Shiny (silver, not grey)
– Smooth surface (not cracked)
– Good wetting (flowing edges)
– No unintentional bridging
Proper Soldering
• Controlled temperature
– Too high
• Flux chars
• Components damaged
– Too low
• Solder does not flow; poor joint
• Components damaged
Burns
Abc’s of Electrical Soldering, by Louis M. Dezettel
Published by Howard W. Sams & Co., 1973.