Brazing and Soldering


Reading Assignment

  • 33.1 Introduction
  • 33.4 Brazing
  • 33.5 Soldering

Recommended Reading


Comparing Brazing and Soldering

  • Both use heat, filler metal and usually flux.
  • Primary difference is melting temperature of filler metal.
    • Brazing filler metals melt above 840°F (liquidus).
  • Filler metal in both cases melts below melting temperature of base metal.
  • Sometimes (especialy with brazing) the difference in melting temperaures is small (small process window).
  • Process window for soldering usually dictated by electronic components
  • Both rely on capillary action to create a strong joint.
    • Joint clearance is critical
    • Typical range is .001 to .005 for brazing, .003 to .006  for soldering (inches)
    • Joint design may need to compensate for thermal expansion



  • Prevents, dissolves and/or facilitates removal of oxides and other surface contaminants.
  • Fluxes are not designed to be cleaners.  Joint should be clean before brazing begins.

Six Categories

  • Type 1, 2, 3A, 3B, 4, 5
  • Selection is based on base metals.
  • Contain combinations of fluorides, chlorides, borates (including borax) and wetting agents
  • Each type has a different working temperature
  • Available as liquid, paste, powder.  Sometimes compounded with filler metal. Braze rod with flux covering or core is available.

Filler Metals

Filler metals are available as

  • wire
  • foil
  • paste
  • powder
  • preforms
  • braze sheet

Brazing Advantages

  • The joining of dissimilar metals, and materials
  • Very thin material can be brazed which would otherwise be damaged by welding
  • Inaccessible joints can more easily be brazed
  • Brazing is easily and more economically automated than many welding processes
  • Leaktight joints are easily attained
  • Multiple joints can be made simultaneously
  • Less-skilled operators are required
  • Braze joints are ductile
  • Braze process is readily automated

Brazable Materials

  • Most ferrous and non-ferrous metals.
    Many carbides and cermet

Brazing Processes

  • Torch Brazing
  • Dip Brazing
  • Induction Brazing
  • Furnace Brazing


Soldering is one of the oldest methods of joining metals. Because filler metals melt at low temperatures there is minimum part distortion and heat damage to sensitive parts.

Soldering Fluxes

  • Organic
    • Contain carbon, corrosive at elevated temperature, noncorrosive at room temp.
      Water soluble
  • Inorganic
    • Very Corrosive, provide better cleaning, do not char or burn easily. Parts must be cleaned after brazing.
  • Rosin Flux
    • Noncorrosive, used for electronics least effective cleaning ability

Solder Filler Metals

  • Filler materials include combinations of tin-lead, tin-silver-lead, tin-zinc, silver-copper-zinc and zinc-aluminum alloys.
  • As with brazing filler metals, solders are supplied as wires, foil, sheets, pastes, preforms, or as bars and ingots.

Solderable Materials

  • Many combinations of metal to metal, ceramic to metal, and glass to metal may be joined.
  • Soldering is used extensively in the electronics industry where it’s limited mechanical strength is not a major factor.

Soldering Processes

  • Iron Soldering
  • Wave Soldering
  • Reflow Soldering
  • Torch Soldering
  • Soldering Sheet (Soldering coppers/irons)




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