SOLDERING
 SOLDERING
• Soldering is the process of joining two wires together by the use of a solder alloy
• Non-solder connections
• Bolts
• Rivets
• Staples
• Disadvantages
 Loose connections due to vibration or shock
 Oxidation
• Advantages of solder connections
• No loose connections when subjected to movement and vibration
• No oxidation (No contact surface exposed to oxidize)
• Continuous connective path
• Wetting action: It is when (by a chemical reaction, like a solvent) molecules of solder and
copper blend together to form a new alloy
 SOLDER (A METAL ALLOY)
• Solder used for electronics is a metal alloy made by combining tin, lead and silver in specific
proportions
• The range where solder begins to melt, but is not fully melted, until it reaches melting
temperature (Semi-liquid state of solder, between a solid an a liquid state)
• Solder identification
• Sn - tin. (Melting point = 480° F)
• Pb - lead (Melting point = 620° F)
• 1st number - percentage of tin (Sn)
• 2nd number - percentage of lead (Pb)
• Examples:
 60/40 - 60% Sn + 40 % Pb
 Sn63-63%Sn+37%Pb
• Types of solder
• 50/50
 Common in plumbing and automotive work
 More flexible than other solders
 Not suitable for electronics
• 60/40
 Most often used in electronics
 Preferred for most work because of longer plastic range
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63/37
 Known as lead free solder
 Has no plastic range (more difficult to master use)
 Used in high density, high reliability circuitry (missies, satellites, computers, with
conformal coatings)
Flux
• Flux removes oxides and keeps them removed during soldering
• Melts at a lower temperature than solder
• Types of flux
 Acid flux - not used in electronics
 Rob Rosin flux - only one used in electronics
 Flux cored solder - controlled amount of flux used at a solder joint
 SOLDERING IRONS
• Basic elements
• Resistance heating unit
• Heater block 3
• Types of solder irons
• Fixed heater
• Temperature controlled by operator
• Temperature controlled by built in magnetic switch
• Operator controlled temperature sensor
• Controlling heat at the solder joint
• Relative thermal mass vs. heat cycle
 Single pad - little mass
 Double sided pad with plate through holes
 Multi-layer boards
 Lead mass - Temperature rise is relative to tip mass vs. work mass (Not tip
temperature)
 Terminal mass
 Reservoir size
 Recovery rate (Ability to sustain heat - like a reservoir)
o Block size (Heating reservoir)
o Wattage - heating element
 If more heat is needed at the joint, use a larger tip and/or increase the core
capacity
 For the practical exercise, adjust heat control to a normal range of "7" to "8" for
soldering iron
• Surface condition of pads or leads
 Oxides and contaminants
 Cannot create good solder joint on dirty surface
 Clean surface before soldering
 Use abrasive stick (eraser)
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Thermal linkage
• Area of contact between iron tip and work
• Apply solder between tip and work piece to create a and increase thermal linkage and
speed up heat transfer
(The secret of craftsmanship)
• The reaction of the work piece to the work actions being performed on it (in soldering heat rate recognition)
• It is in the sensing of the change by sight, sound, smell and touch
• In soldering the primary indicator is heat rate recognition
• If tip is too large and too hot - heat rate too fast
• If tip is small - heat rate too slow (mush melt)
• Get in and out as fast as you can
• Using the hottest iron available you should spend no more than 1-2 seconds on a
particular joint being soldered, to prevent damage
• The key work piece indicator for soldering, therefore, is sight.
Selecting and handling the soldering iron
• 30 watt pencil type with changeable tips is a good general purpose iron for electronic
soldering
• Unplated tips - copper type
• Plated tips - iron type
• Fully insert the and tighten the tip
• Tin unplated tip when not using
• Before using soldering iron, wipe tip off on a damp sponge to "shock off' (remove) any
oxides
• Always store iron in holder (Pace "cubby") when not in use
WIRE STRIPPERS
• Mechanical stripper
 Clean strip without deforming or nicking wire
 Must use correct stripper notches
V-notch stripper
• Blades do not conform to wire
• Easy to nick wire
Stripper
• Best method
• Heat tips to melt or soften insulation and rotate lead, then pull off insulation prevents
nicking of wire
• Can be used for PVC (low temp) or Teflon (high temp) insulation
• For the practical exercise, adjust heat control to a normal range of "7" to "8" for the
thermal stripper
 SOLDER JOINTS
• Acceptable straight through lead
• Length of wire above pad = radius of pad
• .Smooth surface
• Well feathered out smoothly to the edge
• No pits or holes
• No evidence of flux or flux pockets
• Surface bright and shiny, free of any lumps
• Slightly concave, with minimum amount of solder needed to make the connection
• Acceptable clinched lead
• Length of wire = diameter of pad
• Shape. of wire apparent beneath solder
• Smooth surface
• Well feathered out to the edge
• No pits or holes
• No evidence of flux
• Surface bright and shiny
• Slightly concave
• Unacceptable solder joints
• joint
 Too little heat applied
 There is still a quantity of solidified flux between wire and terminal
• joint
 Heat withdrawn too soon, solder does not become liquid
 Solder beaded up and may also show peaks
• joint
 Movement of wire during solidification, ,before solder cools
 Looks frosty, dull, rough, granulated and may show cracks
• joint
 Repeated effort to reheat joint that will not properly wet due to contamination or
lack of sufficient flux
 It is chalky, dull or crystalline in appearance, and may show pitting on the surface
 TERMINALS
• Terminal
• Wrap of wire can be 180°, 270° or 360°
• We will use 270 degree wrap in practical exercise
• Entry location
 If only one wire, it is placed in the lower section, flat down against base
 Two wires come in from same direction and are stacked
• Insulation gap - one to two times wire diameter is permissible
• Terminal
• Used to attach wire to circuit board
• Resistance soldering tool
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 Useful in close quarters / limited lateral space
 Electrodes can be positioned when cold
• No danger of heating wrong area
• Turn off power to tool to avoid arcing
Terminal
• Entry of wire from side, top and bottom
• Wrap may be 90° or 180°
• Terminals
• Hook Terminal
 Found on hermetically sealed relays
 Wire wrap normally 90°, for repair work 270° recommended
• Pierced Terminal
 Has hole or eye
 Wrap of wire 90° to 270°
 COMPONENT SOLDERING - AXIAL LEAD (RESISTORS)
• Clean component leads and solder pads
• With abrasive stick
• Then with solvent (alcohol)
• Bend component leads
• Use Conform tool
• Clean again with solvent (alcohol)
• Insertion - clenched lead
• Cut lead one pad diameter exposed beyond insertion hole
• Press (bend) exposed end of lead flat against circuit board (with component fully inserted
and flat against other side of board).
• Soldering: (after flux application)
• Touch the joint first (position so as to make solder bridge between component lead and
pad).
• Soldering tip contacts the lead
• Paint the solder onto the joint, while moving the tip
• Sweep the end of the lead last
• Inspect your work